HomeMy WebLinkAboutReports - Drainage - 08/15/2025
Project No. 892-002
Date: August 2025
EPS Group
Arizona | Greeley
970.221.4158
epsgroupinc.com
Final Drainage Report:
Gateway at Prospect
Developer:
Fort Collins/ I-25 Interchange, LLC
2 North Cascade Avenue Suite 1490
Colorado Springs, CO 80903
(719)-540-5800
Engineer:
EPS Group
301 N. Howes Street, Suite 100
Fort Collins, Colorado 80521
(970) 221-4158
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TABLE OF CONTENTS
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August 15, 2025
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, CO 80521
RE: FINAL DRAINAGE REPORT FOR
GATEWAY TO PROSPECT
Dear Staff:
EPS Group is pleased to submit this Preliminary Drainage Report for your review. This report accompanies the Final
Development Review submittal for the proposed Gateway at Prospect project.
This report has been prepared in accordance with the Fort Collins Stormwater Criteria Manual (FCSCM) in conjunction
with Mile High Flood Control District Stormwater Criteria and serves to document the stormwater impacts associated
with the proposed Gateway at Prospect project. We understand review by the City is to assure general compliance with
standardized criteria contained in the FCSCM and Mile High Flood Control District Stormwater Criteria Manual.
If you should have any questions as you review this report, please feel free to contact us.
Sincerely,
EPS Group, Inc.
Stephanie Thomas, PE
Project Manager
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TABLE OF CONTENTS
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TABLE OF CONTENTS
1.0 GENERAL LOCATION AND DESCRIPTION .......................................................................5
1.1 LOCATION ...................................................................................................................................................................................... 5
1.2 DESCRIPTION OF PROPERTY ................................................................................................................................................... 6
1.3 FLOODPLAIN ................................................................................................................................................................................. 6
2.0 DRAIN BASINS AND SUB-BASINS ...................................................................................8
2.1 MAJOR BASIN DESCRIPTION ................................................................................................................................................... 8
2.2 SUBBASIN DESCRIPTION........................................................................................................................................................... 8
3.0 DRAINAGE DESIGN CRITERIA ....................................................................................... 10
3.1 REGULATIONS ........................................................................................................................................................................... 10
3.2 FOUR STEP PROCESS ............................................................................................................................................................... 10
3.3 DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS ..................................................................................... 11
3.4 HYDROLOGICAL CRITERIA .................................................................................................................................................... 11
3.5 HYDRAULIC CRITERIA ............................................................................................................................................................. 11
3.6 FLOODPLAIN REGULATIONS COMPLIANCE ................................................................................................................... 12
3.7 MODIFICATIONS OF CRITERIA ............................................................................................................................................. 12
4.0 DRAINAGE FACILITY DESIGN ....................................................................................... 12
4.1 GENERAL CONCEPT ................................................................................................................................................................. 12
4.2 FULL SPECTRUM DETENTION, EURV, AND WQCV ....................................................................................................... 16
4.3 DETENTION POND CALCULATIONS .................................................................................................................................. 17
4.4 SPECIFIC DETAILS ..................................................................................................................................................................... 19
5.0 CONCLUSIONS .............................................................................................................. 21
5.1 COMPLIANCE WITH STANDARDS ...................................................................................................................................... 21
5.2 DRAINAGE CONCEPT .............................................................................................................................................................. 21
6.0 REFERENCES .................................................................................................................. 22
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APPENDICES
APPENDIX A – Hydrologic Computations
APPENDIX B – Low Impact Development Responsibility Exhibit
APPENDIX C – Hydraulic Computations
APPENDIX D – Cooper Slough HEC-RAS Model
APPENDIX E – FEMA Firmette
APPENDIX F – Erosion Control Report
MAP POCKET
DR1 –Drainage Exhibit
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FIGURES AND TABLES
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TABLE OF FIGURES
Figure 1 - Vicinity Map ............................................................................................................................................................... 5
Figure 3 - Existing FEMA Floodplains .................................................................................................................................. 7
Figure 2 - Existing City Floodplains ...................................................................................................................................... 7
Figure 4 - Snapshot of Existing Fort Collins SWMM Model ......................................................................................... 9
TABLE OF TABLES
Table 1 - Land Use - Percent impervious (Per Table 4.1.2 FCSCM) ........................................................................... 6
Table 2 - Flowrates for Project Specific Nodes ................................................................................................................. 9
Table 3 - Pond Summaries .................................................................................................................................................... 19
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1.0 GENERAL LOCATION AND DESCRIPTION
1.1 LOCATION
1. Gateway at Prospect is in Section 16, Township 7 North, Range 68 West of the 6th Principal Meridian, City of Fort
Collins, County of Larimer, State of Colorado.
2. The project site is located near the northwest corner of the Prospect Road and I-25 interchange. The site is
situated along the existing I-25 west frontage road, just south of the existing Crossroads East Business Center
and east of the existing Boxelder Estates 1st Replat.
3. Zoning across the site includes Low-Density Mixed Use (LMN), Medium-Density Mixed Use (MMN), Employment
District (E), Commercial District (C), and Urban Estate (UE). The existing lot does not have any stormwater or
water quality facilities.
4. The Boxelder Creek runs north to south through the middle of Gateway at Prospect project. Near the northern
property line, the Cache La Poudre Inlet Canal runs west to east; the canal siphons under the Boxelder Creek and
continues east of I-25. The Lake Canal runs northwest to southeast along the northern boundary of the site; this
canal also siphons under the Boxelder Creek and continues east of I-25.
Figure 1 - Vicinity Map
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1.2 DESCRIPTION OF PROPERTY
1. Gateway at Prospect is approximately 182.30 net acres, including the existing frontage road.
2. Gateway at Prospect proposes realigning the I-25 West Frontage Road and installing two connector streets with
utilities using master planning concepts. A span bridge will also be installed with Gateway at Prospect, which will
cross the Boxelder Creek. In the future, this area will consist of low-density and medium-density mixed-use
districts and a small urban estate district, commercial districts, and an employment district.
3. The proposed development site is in the City of Fort Collins Boxelder Creek/Cooper Slough Basin. Detention and
water quality requirements for each future development will be laid out within this report. Future developments
will still be responsible for calculating and implementing LID requirements set forth in the City of Fort Collins
Stormwater Criteria Manual.
4. Currently, Gateway at Prospect is proposing to detain and treat interim conditions. Therefore, the proposed
connector roads will be detained, and water quality will also be provided via extended detention. LID will be
provided for connector roadways that do not drain through a future development. Additionally, Gateway at
Prospect will install storm lines sized for future developments to utilize.
5. According to the United States Department of Agriculture (USDA) Natural Resources Conservation Service
(NRCS) Soil Survey, a majority of the project site consists of Nunn clay loam and Satanta Variant clay loam which
fall into Hydrologic Soil Groups C-D.
1.3 FLOODPLAIN
1. The FEMA regulated Boxelder Floodplain and Floodway is located within the eastern half of the project. This
floodplain is found on panel 984 of 1420 of Map Number 08069C0984H revised February 21, 2019.
2. The FEMA regulated Cooper Slough Floodplain and Floodway exists in the northwest corner of the project. This
floodplain is found on panel 984 of 1420 of Map Number 08069C0984H revised February 21, 2019.
3. The Gateway at Prospect project will be pursuing a CLOMR/LOMR with this project. This CLOMR/LOMR will revise
the floodplain and floodway along the Boxelder Creek within the limits of this project. This CLOMR/LOMR will
Table 1 - Land Use - Percent impervious (Per Table 4.1.2 FCSCM)
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effectively limit the extent of the floodplain within the development parcels and allow for the installation of a
bridge over Boxelder Creek.
The CLOMR will be pursued with FEMA concurrently with this proposal. The CLOMR will not be detailed in this
report but will instead be a separate report and model. Please see the “Boxelder Creek at Gateway at Prospect
Conditional Letter of Map Revision Request” by Jacobs Engineering originally submitted August 2022, revised
July 2025. A LOMR process through FEMA will be required after construction of this project.
A floodplain use permit will be required for any construction within the floodplains of this project.
Figure 2 - Existing FEMA Floodplains
Figure 3 - Existing City Floodplains
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An Erosion Buffer runs along the Boxelder Creek on the east side of the project site. The erosion buffer is regulated by the
Fort Collins Municipal Code, Chapter 10 Flood Prevention and Protection, Division 7 Erosion Buffer Zones. Sec. 10-202 2J
and 2K. This code section prohibits the grading, excavation and construction traffic within the erosion buffer.
This portion of the Boxelder Creek was studied for erosion susceptibility in the report “Assessments and Rehabilitation
Decision-Making Framework for the Streams of Fort Collins” (January 2012) and the subsequent “Boxelder Creek/Cooper
Slough Basin Water Quality Master Plan” (March 30, 2012).
As a part of this project, this section of the Boxelder Creek was studied in the Jacobs’ report “Boxelder Creek at Gateway
at Prospect: Stream Stability Study”. The report concluded that there will need to be grading and excavation done on the
Boxelder Creek to reduce velocities and shear stresses to match either existing conditions or the MHFD criteria during the
100-year event.
2.0 DRAIN BASINS AND SUB-BASINS
2.1 MAJOR BASIN DESCRIPTION
1. Gateway at Prospect is located within the Boxelder Creek/Cooper Slough Basin. Boxelder Creek/Cooper Slough
Basin encompasses 265 square miles beginning north of the Colorado/Wyoming border and extending
southward into east Fort Collins, ending at the Cache La Poudre River.
2. Improvements along the Boxelder Creek were recently constructed and detailed in the LOMR case number 17-
08-1354P. A 100-year overflow channel and box culverts under Prospect Road were constructed as a part of that
project.
2.2 SUBBASIN DESCRIPTION
1. Historically the property generally drains south and towards the center of the property where the Boxelder
Creek sits. The 100-year overflow channel is situated within the Gateway at Prospect site. In normal flowing
conditions, the Boxelder Creek flows within its typical channel and heads south through a newly constructed
box culvert under Prospect Road. Boxelder Creek continues south until it discharges into the Poudre River.
During the 100-year event, an emergency overflow weir will reroute runoff to the west of the typical creek and
into the overflow channel. Once runoff is routed to the overflow channel, it is conveyed south through a
separate box culvert under Prospect Road. From there, the runoff will remain in the overflow channel until it
enters the Poudre River.
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In 2018 Ayers Associates, as a part of the previous LOMR effort, created a SWMM model that modeled existing flows for
the 2-year, 5-year, 10-year, 25-year, 50-year, and 100-year events of the Boxelder Creek/Cooper Slough Basin with the
proposed Boxelder Creek improvements. Gateway at Prospect property falls within this model. This model was used to
verify downstream infrastructure will not be impacted by future developments within the Gateway at Prospect property.
2. There are some important Nodes to take note of within this model. Node 884 is the closest upstream node
before Gateway at Prospect discharging into the Boxelder Creek. Divider 885 represents the previously
described emergency overflow weir. Nodes 886 and 887 are the downstream nodes in both the normal
conveyance path and the emergency overflow channel. A more in-depth explanation can be found later in the
report.
3. Gateway at Prospect is located toward the lower end of the Boxelder Creek/Cooper Slough Basin. Traditionally
new developments within Fort Collins must detain the difference between the 100-year developed inflow rate
and the historic 2-year release rate. However, this location is optimal for the use of full spectrum detention. The
City of Fort Collins has approved the use of full spectrum detention for this project with the caveat that it can be
shown there are no “substantial” increases in flow to Boxelder Creek.
4. During the interim condition - when only connector streets, utilities, and the span bridge are installed, a portion
of the ponds will be interim ponds with interim release rates. As stated previously, future developments must
adhere to the recommendation made in this report when it comes to pond sizing and, more importantly, total
full spectrum release rates. However, the ultimate storm line sizing will be installed with Gateway at Prospect to
minimize future demolition and disturbance within the Boxelder Creek and 100-year overflow channel.
5. The detention ponds adjacent to Boxelder Creek have been sized for the ultimate condition. This is an attempt
to limit and disturbance within the floodplain and natural habitat buffer zone in the future.
6. All future developments must follow Fort Collins Stormwater Criteria Manual for LID sizing and implementation.
7. A full-size copy of the Proposed Drainage Exhibit can be found in the Map Pocket at the end of this report. This
Proposed Drainage Exhibit represents the interim condition.
SWMM ID
Ayers Associate Boxelder Basin
Model 100-YR Flow Rates (cfs)
Node 884 3377.99
Divider 885 3377.89
Node 886 950.98
Node 887 2426.9
Figure 4 - Snapshot of Existing Fort Collins SWMM Model
Table 2 - Flowrates for Project Specific Nodes
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3.0 DRAINAGE DESIGN CRITERIA
3.1 REGULATIONS
Gateway at Prospect proposes utilizing full spectrum for detention and traditional 40-hour water quality treatment for
this site. By utilizing full spectrum, Gateway at Prospect will be able to “beat the peak” of the existing condition within the
Boxelder Creek/Cooper Slough Basin. Therefore, it is expected the Gateway at Prospect project will not cause damage to
downstream infrastructure and/or cause more maintenance than historical conditions. Full Spectrum design should
improve stream stability by mimicking the historic conditions. Full spectrum guidelines laid out by Mile High Flood
Control District were followed.
3.2 FOUR STEP PROCESS
The overall stormwater management strategy employed with the Gateway at Prospect project utilizes the “Four Step
Process” to minimize adverse impacts of urbanization on receiving waters. The following describes how the proposed
development has incorporated each step.
Step 1 – Employ Runoff Reduction Practices
Gateway at Prospect will be reducing peak flow rates by 10% of the historic value via full spectrum. Full spectrum
detention is designed to address two limitations of traditional detention. First, it is focused on controlling peak
discharges over the full spectrum of runoff events from small, frequent storms up to the 100-year storm event. Second,
full spectrum detention facilities produce outflow hydrographs that, other than a small release rate of the excess urban
runoff volume (EURV), replicate the shape of predevelopment hydrographs. Full spectrum detention modeling shows a
reduction of urban runoff peaks to levels similar to predevelopment conditions over an entire watershed, even with
multiple independent detention facilities. For a thorough, in-depth explanation of full spectrum, please refer to Volume
2, Chapter 12 of the Urban Drainage Stormwater Criteria Manual published by the Mile High Flood Control District.
At the time of future development tracts within the Gateway at Prospect, each development will be responsible for
implementing Low Impact Development (LID) measures. These measures can include rain gardens, grass buffers,
underground infiltration and detention basins, permeable pavers, etc. These measures effectively work to reduce runoff
from developed areas.
Step 2 – Implement BMPs that Provide a Water Quality Capture Volume (WQCV) with Slow Release
Water quality will be provided via extended detention per Mile High Flood Control District standards for full spectrum
detention. Full spectrum water quality capture volume (WQCV) utilizes the same criteria the Fort Collins Stormwater
Criteria Manual uses. Additionally, the lower portion of volume in a full spectrum detention facility is designed to capture
and slowly release the excess urban runoff volume (EURV). The EURV is the difference between the developed condition
runoff volume and the predevelopment volume. The EURV is typically two to three times the WQCV. However, no LID
measures will be installed with Gateway at Prospect. Future developments will be responsible for sizing and
implementing their own LID measures per the Fort Collins Stormwater Criteria Manual. However, there will be large
swaths of greenspace during the interim condition, which will still absorb a large amount of interim runoff.
Step 3 – Stabilize Drainageways
The Gateway at Prospect proposes to limit the amount of disturbance to Boxelder Creek. By limiting disturbance to the
creek banks, the project will effectively maintain the existing vegetation. In areas of disturbance, the banks will be
stabilized via methods that include riprap pads, erosion control blankets, and scour pads.
The Gateway at Prospect project aims to protect the existing Boxelder Creek by limiting any increases beyond the
historical flow rates within the creek to a negligible amount. By utilizing a combination of full spectrum detention and
the resulting “beat the peak” model, the peak discharge from the Gateway at Prospect project will be passed before the
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peak of the creek. As such, the peak discharge from the Gateway at Prospect project will not be compounded with peak
flow in the creek. Furthermore, this project will pay a one-time stormwater development fee, as well as ongoing monthly
stormwater utility fees, both of which help achieve citywide drainageway stability.
Step 4 – Implement Site Specific and Other Source Control BMPs
This step typically applies to industrial and commercial developments.
3.3 DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS
1. There are no known drainage studies for this specific property. However, it has been mentioned that Ayers
Associates produced a SWMM model showing the 2-year, 5-year, 10-year, 25-year, 50-year, and 100-year events
for the Boxelder Creek/Cooper Slough Basin. Gateway at Prospect is only analyzing the 100-year event for both
the interim condition and future condition.
2. Gateway at Prospect is proposing to only install interim ponds via full spectrum criteria. Because full spectrum
detention is based on predevelopment conditions, both the interim and future developments will have
approximately the same release rates. Therefore, future developments will not be hindered by the storm line
sizes that are installed by Gateway at Prospect.
3. Future developments are responsible for their own LID calculations and implementation.
3.4 HYDROLOGICAL CRITERIA
1. The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as depicted in Figure RA-16 of the FCSCM,
serve as the source for all hydrologic computations associated with this development. Tabulated data contained
in Table RA-7 has been utilized for Rational Method runoff calculations.
2. The Rational Method has been employed to compute stormwater runoff utilizing coefficients contained in
Tables 4.1-2 and 4.1-3 of the FCSCM.
3. Full spectrum detention has been utilized for detention storage calculations.
4. Three separate design storms have been utilized to address distinct drainage scenarios. The first event analyzed
is the “Minor,” or “Initial” Storm, which has a 2-year recurrence interval. The second event considered is the
“Major Storm,” which has a 100-year recurrence interval. The third storm computed, for comparison purposes
only, is the 10-year event.
5. No other assumptions or calculation methods have been used with this development that are not referenced by
current City of Fort Collins criteria.
3.5 HYDRAULIC CRITERIA
1. As previously noted, the subject property historically drains towards its center, where the Boxelder Creek runs
north to south through the site. Currently, a majority of the site drains stormwater via overland flow. It will
continue to be mostly overland flow during the interim condition, but as the ultimate conditions come online,
this will most likely change to concentrated flows within curb and gutter as well as storm line conveyance.
2. All drainage facilities proposed with Gateway at Prospect project are designed in accordance with criteria
outlined in the Mile High Flood Control District’s “Urban Storm Drainage Criteria Manual.”
3. As stated in Section 1.3, above, the subject property is subject to regulatory floodplain restrictions and
development code.
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4. HEC-RAS has been used to model the future Cooper Slough drainageway planned by Fort Collins along between
Lake Canal and Timnath Reservoir Inlet Canal.
5. Gateway at Prospect design is intended to maintain the downstream integrity of the Boxelder Creek to fullest
extent possible.
3.6 FLOODPLAIN REGULATIONS COMPLIANCE
The project site is encroached by the FEMA designated 100- Year Floodway and Floodplain according to FIRM Panel
08069C098H for Larimer County. This map has been revised to reflect LOMR effective February 21, 2019.
No occupied structures are being proposed with the Gateway Prospect project.
This project is pursuing a CLOMR/LOMR to remove portions of the site from the 100-year floodplain, to provide for stream
stabilization grading and to build a bridge spanning the floodplain/floodway.
As per Section 10-103 (9), Critical Facilities are prohibited in the floodplain. The definition of Critical Facilities includes
facilities for at-risk populations (daycares, schools, nursing homes, et.), facilities utilizing hazardous materials (gas
stations, auto repair, laboratories), emergency services facilities (urgent care, hospitals, fire, police) and government
services (municipal offices, library). A floodplain use permit is required prior to building permit issuance. Future
developments proposed within the floodplain are subject to all floodplain regulations.
Development within the floodplain must comply with Chapter 10 of the Municipal Code.
Please see appendix for a Floodplain Exhibit and all regulatory notes regarding development within the floodplain.
3.7 MODIFICATIONS OF CRITERIA
Gateway at Prospect requests full spectrum detention as laid out by the Mile High Flood Control District be substituted
for the Fort Collins Stormwater Criteria detention requirements. A variance request has been provided for the use of Full
Spectrum Detention.
4.0 DRAINAGE FACILITY DESIGN
4.1 GENERAL CONCEPT
1. The main objectives of Gateway at Prospect are to provide detention and water quality for the interim
conditions further from Boxelder Creek and ultimate conditions near Boxelder Creek as well as layout a
comprehensive master plan for future developments to utilize. Additionally, maintaining Boxelder Creek
stabilization is of the utmost importance.
2. The Cooper Slough currently drains from north to south along the project’s western boundary. This flow
impacts the northwestern and southwestern corners of the propety. Much of this flow is intercepted by the
Timnath Reservoir Inlet Canal, but a portion may spill onto the Gateway project. Any development near this area
will need to provide ample grade separation and conveyance for this potential spillage.
3. The Boxelder Creek, Timnath Reservoir Inlet Canal, and Lake Canal also drain through the project.
4. A list of tables and figures used within this report can be found in the Table of Contents at the front of the
document. The tables and figures are located within the sections to which the content best applies.
5. Gateway at Prospect project comprises ten major drainage basins, designated as Basins A, B, C, D, E, F, G, H, I,
BOX, and PUD. The drainage patterns for each major basin are described below.
Basin A
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Basin A is encumbered by multiple easements and is challenged for access. As such, future development of this
basin will be limited. If, in the future, this basin develops, it will need to be studied for full spectrum detention and
water quality.
If this basin is maintained as an undeveloped greenbelt or open space, it will not be subject to detention or water
quality treatment.
Basin A currently captures and conveys the existing and future Cooper Slough overflow.
Basin B
Basin B is composed of three subbasins, Basin B1, B2 and B3. Runoff from Basin B is conveyed to Pond B.
Basin B1
During the interim condition, Basin B1 will be undeveloped. Ultimately, Basin B1 is zoned to have low-density
residential and urban estate districts. Basin B1 will be detained and treated within Pond B and will discharge into
the Boxelder Creek via pipe sized to the ultimate release rate of Pond B.
Basin B2 and B3
Basins B2 and B3 include a small portion of the new connector street. Basin B2 will drain to a proposed rain
garden prior to being detained and treated for additional water quality in Pond B. B3 will be detained and
treated within Pond B and will discharge into the Boxelder Creek via an RCP pipe sized to the ultimate release
rate of Pond B.
Basin C
Basin C is composed of two subbasins, Basin C1 and Basin C2. Runoff from Basin C is conveyed to Pond C.
Basin C1
During the interim condition, Basin C1 be undeveloped. Basin C1 will overland flow from northwest to the
southeast to Pond C. During the ultimate condition, Basin C1 is zoned to have an employment district. Basin C1
will be detained and treated within Basin C1 and will discharge via pipe to Boxelder Creek.
Basin C2
Basin C2 encompasses half of the right of way for the new connector road and half of the span bridge. Basin C2
has the same condition in the interim and ultimate conditions. Basin C2 will convey runoff to Pond C via inlet
and pipe culvert into a rain garden. Basin C2 will drain to a proposed rain garden prior to being detained and
treated for additional water quality in Pond C.
Basin D
Basin D is composed of two subbasins, Basin D1 and Basin D2. Basin D does not have an interim condition. Runoff
from Basin D is conveyed to Pond D.
Basin D1
Basin D1 is composed of open space and Pond D. Basin D1 sheet flows towards Pond D, which discharges to the
Boxelder Creek via pipe.
Basin D2
Basin D2 encompasses a portion of the entire right-of-way (ROW) associated with the I-25 frontage road
realignment. Runoff generated in Basin D2 is captured by inlets within the ROW and conveyed to a proposed
rain garden prior to being detained and treated for additional water quality in Pond D.
Basin E
Basin E is composed of two subbasins, Basin E1 and E2.
Basin E1
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During the interim condition, Basin E1 will remain undeveloped except for Pond E. In the ultimate condition,
Basin E1 will be built out per its zoning designation of medium density mixed-use.
Basin E2
Basin E2 is comprised of the connector road and Prospect Road as well as a small portion of open space adjacent
to the southwest corner of the project site. Basin E2 has the same condition in the interim and ultimate
condition. Runoff from Basin E2 is captured by inlets within the connector road and conveyed to a rain garden
prior to being detained and treated for additional water quality in Pond E. Pond E discharges via pipe to the
Boxelder Overflow Channel. This pipe is sized for the ultimate release of Pond E.
Basin F
Basin F is composed of five subbasins, Basin F1-F5. Runoff from Basin F is conveyed to Pond F.
Basin F1
Basin F1 will remain undeveloped during the interim condition except for Pond F. In the ultimate condition,
Basin F1 will be built out per its zoning designation of medium density residential. Basin F1 will be detained and
treated within Basin F1 and will discharge via pipe to Boxelder Creek. This pipeline is sized for the ultimate
release of Pond F.
Basin F2
Basin F2 is comprised of half the right of way for the new connector road internal to the project site. Runoff is
captured by an inlet and conveyed via temporary swale in Basin F1 to Pond F. Basin F2 does not have an interim
condition. Basin F2 is detained and treated for water quality in Pond F. It is anticipated that LID treatment may
be provided for this basin by the future development due to the available travel path through the parcel. Please
see the LID exhibit for more information.
Basin F3
Basin F3 is comprised of half the right of way for the new connector roads internal to the project site as well as
half the span bridge. Runoff is captured by an inlet and conveyed via pipeline in Basin F1 to Pond F. Basin F3
does not have an interim condition. Basin F3 is detained and treated for water quality in Pond F. It is anticipated
that LID treatment may be provided for this basin by the future development due to the available travel path
through the parcel. Please see the LID exhibit for more information.
Basin F4
Basin F4 is comprised of half the right of way for the new connector roads internal to the project site. Runoff is
captured by an inlet and conveyed via pipeline in Basin F1 to Pond F. Basin F4 does not have an interim
condition. Basin F4 is detained and treated for water quality in Pond F. It is anticipated that LID treatment may
be provided for this basin by the future development due to the available travel path through the parcel. Please
see the LID exhibit for more information.
Basin F5
Basin F5 is comprised of half the right of way for the new connector roads internal to the project site as well as
the open space along the western boundary of the it. Runoff is captured by an inlet and conveyed via pipeline in
Basin F1 to Pond F. Basin F5 does not have an interim condition. Basin F5 is detained and treated for water
quality in Pond F. It is anticipated that LID treatment may be provided for this basin by the future development
due to the available travel path through the parcel. Please see the LID exhibit for more information.
Basin G
Basin G is composed of three subbasins, Basin G1, G2 and G3. Runoff from Basin G is conveyed to Pond G.
Basin G1
Basin G1 will remain undeveloped during the interim condition except for Pond G. In the ultimate condition,
Basin G will be used for commercial land uses. Runoff in Basin G1 flows via sheet flow to Pond G. Pond G
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discharges to Boxelder Creek via pipeline sized for the ultimate release rate for all of Basin G. Basin G1 is detained
and treated for water quality in Pond G.
Basin G2
Basin G2 is comprised of half of the right of way of the I-25 Frontage Road and a small portion of the
roundabout. Runoff in Basin G2 is captured via sidewalk culvert and conveyed to Pond G via swale. Basin G2 is
detained and treated for water quality in Pond G. It is anticipated that LID treatment may be provided for this
basin by the future development due to the available travel path through the parcel. Please see the LID exhibit
for more information.
Basin G3
Basin G3 is comprised of a small portion of the roundabout. Runoff from Basin G3 is captured via inlet and
conveyed to a rain garden prior to being detained and treated for additional water quality in Pond G.
Basin G4
Basin G4 is comprised of half of the right of way of Prospect Road. Runoff in Basin G4 is captured via sidewalk
culvert and conveyed to Pond G via swale. Basin G4 is detained and treated for water quality in Pond G. It is
anticipated that LID treatment may be provided for this basin by the future development due to the available
travel path through the parcel. Please see the LID exhibit for more information.
Basin H
Basin H is comprised of two subbasins, Basin H1 and Basin H2. Runoff from Basin H is conveyed to Pond I in the
interim but will be directly to Pond H in the future.
A storm pipe is proposed to serve as the release for Future Pond H to Boxelder Creek. This pipeline has been sized
for the ultimate release rate for all of Basin H and I. In the interim a small culvert will convey the runoff from Basin H
to Interim Pond I.
Basin H1
Basin H1 will remain undeveloped during the interim condition except for a portion of Interim Pond I and a small
portion of the roundabout. Interim Basin H1 will be detained and treated within Interim Pond I, located within
Basin I1.
Future Pond H will be located within Basin H1.
Basin H2
Basin H2 encompasses a portion of the ROW associated with the I-25 frontage road realignment. Basin H2 does
not have an interim condition. Runoff from Basin H2 will be captured by an inlet and conveyed to Interim Pond I
via temporary swale. Basin H2 will be detained and treated during the interim condition within Interim Pond I. It
is anticipated that LID treatment may be provided for this basin by the future development due to the available
travel path through the parcel. Please see the LID exhibit for more information.
Basin I
Basin I is comprised of two subbasins, Basin I1 and Basin I2. Runoff from Basin I is conveyed to Pond I in the interim
and ultimate conditions.
A storm pipe is proposed to serve as the release for Future Pond I. This pipeline has been sized for the ultimate
release rate for all of Basin I and Basin H.
Basin I1
Basin I1 will remain undeveloped during the interim condition except for Pond I. Runoff from Basin I1 will be
conveyed via surface flow to Interim Pond I. Interim Basin I1 will be detained and treated within Interim Pond I.
Basin I2
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Basin I2 encompasses a portion of the ROW associated with the I-25 frontage road realignment. Basin I2 does not
have an interim condition. Runoff from Basin I2 will be captured by an sidewalk culvert and conveyed to a rain
garden prior to being detained and treated for additional water quality in Interim Pond I.
Basin BOX
Basin BOX is associated with the Boxelder Creek and is comprised of two subbasins, Basin BOX1 and Basin BOX2. As
mentioned earlier, it is especially important to Gateway at Prospect to maintain stabilization within this
drainageway. Jacobs has prepared a CLOMR Report and Stability Study which addresses Boxelder Creek stream
stability impacts from the proposed improvements.
Basin BOX1
Basin BOX1 is associated with Boxelder Creek downstream of the proposed span bridge that will be installed
with Gateway at Prospect
As mentioned earlier, there is an emergency overflow weir within Boxelder Creek on this site. This overflow weir
has been included in the CLOMR Report and Boxelder Creek Stability Report by Jacobs, and is found within Basin
BOX1.
Basin BOX2
Basin BOX2 is associated with Boxelder Creek upstream of the proposed span bridge that will be installed with
Gateway at Prospect.
Basin PUD1
Basin PUD1 is associated with the Timnath Reservoir Inlet Canal. Basin PUD1 runs west to east and conveys off-site
flows through the Gateway at Prospect site. These flows are siphoned under the Boxelder Creek and continue east
of I-25. Gateway at Prospect does not propose to alter this drainageway/Irrigation ditch during the interim or
ultimate condition.
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of this report.
4.2 FULL SPECTRUM DETENTION, EURV, AND WQCV
1. Gateway at Prospect is located near the downstream end of the Boxelder Creek/Cooper Slough Basin and will be
discharging into Boxelder Creek. To maintain stream stability, full spectrum detention was utilized to size interim
ponds and future release rates. The rationale behind this is to “beat the peak” and have the site drained before
the peak flowrates within Boxelder Creek occur. In beating the peak, Gateway at Prospect can further avoid
adversely impacting downstream infrastructure.
2. Gateway at Prospect proposes providing 100-year detention, detaining the EURV, and utilizing extended
detention for water quality. However, storm lines have been sized for ultimate conditions unless otherwise
stated. In the ultimate condition, all future parcels will be held to the ultimate release rates, WQCV, and EURV, as
stated below. Additionally, future developments are responsible for sizing and implementing LID measures per
the Fort Collins Stormwater Criteria Manual.
3. There will be two interim ponds (Interim Pond B and Interim Pond I) and five final Ponds (Pond C, Pond D, Pond
E, Pond F and Pond G) installed with Gateway at Prospect. Pond H is a future Pond, not proposed to be built
with the Gateway at Prospect project.
4. Information regarding future ponds for the ultimate condition for Pond B and Pond I are detailed below and in
Appendix B.
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4.3 DETENTION POND CALCULATIONS
Detention pond calculations were done via full spectrum method as described in Volume 2, Chapter 12, Section 3 in the
Urban Strom Drainage Criteria Manual. Two ponds (Pond B and Pond I) will have interim ponds. Ponds C, D, E, F and G will
be built out to its ultimate condition utilizing master planning assumptions. The Ultimate condition Ponds are designed
to accommodate the future full buildout of their associated basins including water quality and detention volume without
further modification. However, if future plans propose to modify these ultimate ponds, they may be subject to further
floodplain review. Lastly, Pond D will not have an interim pond condition because Basin D during the interim condition
remains unchanged from the existing condition.
For interim ponds that will be fully constructed in the future and not with Gateway at Prospect (i.e., Pond B, Pond H and
Pond I), the release rates stated in the proceeding paragraphs are the ultimate release rates. The corresponding ultimate
detention volumes are only for conceptual purposes. Future developments might find it advantageous to have several
ponds per basin instead of one large Pond. However, the summation of these pond volumes should be very close to the
overall volumes as described below. Future Developments must provide for the WQCV and EURV as well. Please refer to
Appendix B for additional information not captured in this narrative.
Interim Pond B
Pond B will provide detention and water quality for the interim condition of Basin B. Pond B has been sized for the
interim condition to allow for more flexibility of the future development. LID treatment is proposed with this project to
treat the adjacent connector roadway. The future development of basin B will need to reanalyze the detention
requirements based on the proposed use and provide 100-year detention, detained EURV and WQCV per revised Full
Spectrum Detention calculations along with LID measures as laid forth in the Fort Collins Stormwater Criteria Manual.
Future LID facilities should be located upstream and outside of the detention pond. The ultimate release rate should
closely match the Ultimate Condition as stated below; however, it may vary slightly due to outlet geometry.
Pond C
Pond C will provide detention and water quality for the interim condition of Basin C. Pond C has been sized for the
ultimate condition in order to limit work in the floodplain and natural habitat buffer zone in the future. LID treatment is
proposed with this project to treat the adjacent connector roadway. The future development of basin C will need to
maintain Pond C in its proposed form or provide an equivalent level of Full Spectrum Detention along with LID measures
as laid forth in the Fort Collins Stormwater Criteria Manual. Future LID facilities should be located upstream and outside
of the detention pond.
Pond D
Pond D provides detention and water quality treatment for Basin D. Pond D has been sized for the ultimate condition. LID
treatment is proposed with this project to treat the I-25 Frontage Road Improvements. The Metropolitan District will be
responsible to maintain Pond D.
Pond E
Pond E provides detention and water quality treatment for Basin E. Pond E has been sized for the ultimate condition. LID
treatment is proposed with this project to treat the adjacent connector roadway and a portion of Prospect Road. The
future development of basin E will need to maintain Pond E in its proposed form or provide an equivalent level of Full
Spectrum Detention along with LID measures as laid forth in the Fort Collins Stormwater Criteria Manual. Future LID
facilities should be located upstream and outside of the detention pond.
Pond F
Pond F has been sized for the ultimate condition in order to limit work in the floodplain and natural habitat buffer zone in
the future. The future development of basin F will need to maintain Pond F in its proposed form or provide an equivalent
level of Full Spectrum Detention along with LID measures as laid forth in the Fort Collins Stormwater Criteria Manual.
Future LID facilities should be located upstream and outside of the detention pond.
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Pond G
Pond G provides detention and water quality treatment for Basin G. Pond G has been sized for the ultimate condition in
order to limit work in the floodplain and natural habitat buffer zone in the future. The future development of basin G will
need to maintain Pond G in its proposed form or provide an equivalent level of Full Spectrum Detention along with LID
measures as laid forth in the Fort Collins Stormwater Criteria Manual. Future LID facilities should be located upstream
and outside of the detention pond.
Future Pond H
Future Pond H provides detention and water quality treatment for the future condition of Basin H. Future Pond H is being
deferred until the time of development to allow for more flexibility of the future development. The future development
of basin H will need to analyze the detention requirements based on the proposed use and provide 100-year detention,
detained EURV and WQCV per revised Full Spectrum Detention calculations along with LID measures as laid forth in the
Fort Collins Stormwater Criteria Manual. The development will be required to build an outlet structure to direct runoff
from basin H around Pond I; thereby creating a separate Pond H. The ultimate release rate and volumes should closely
match the Ultimate Condition as stated below; however, it may vary slightly due to outlet geometry. Future LID facilities
should be located upstream and outside of the detention pond.
Interim Pond I
Interim Pond I will provide detention and water quality for the interim condition of Basins H and I. Pond I has been sized
for the interim condition where Basin H is also draining to Pond I. LID treatment is proposed with this project to treat the
adjacent I-25 Frontage Road improvements and a portion of Prospect Road. The future development of basin H and I will
need to reanalyze the detention requirements of Pond I based on the proposed use and provide 100-year detention,
detained EURV and WQCV per revised Full Spectrum Detention calculations along with LID measures as laid forth in the
Fort Collins Stormwater Criteria Manual. The interim grading of Pond I was designed to accommodate the future volume
needs of Pond I once Pond H discharge is bypassed. Future LID facilities should be located upstream and outside of the
detention pond.
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Pond Summary
Pond sizing and associated release rates were calculated via full spectrum detention methods. All interim and final ponds
will be released to Boxelder Creek. By utilizing full spectrum detention, it allows Gateway at Prospect and future
developments to maintain downstream infrastructure within Boxelder Creek by beating the peak flows in the creek.
Table 3 - Pond Summaries
Pond Summaries
Pond ID Tributary
Area
Interim
Impervious
Final
Impervious
Interim
100-yr
Storage
Interim
WQCV +
EURV
Interim
Release
Rate
Final 100-yr
Storage
Final
WQCV +
EURV
Final
Release
Rate
(acre) (%) (%) ac-ft
(elev.)
ac-ft
(elev.) (cfs) ac-ft (elev.) ac-ft (elev.) (cfs)
Pond B 67.23 3% 46% 1.726
(4908.38)
0.152
(4904.54) 96.00 7.07 (TBD)* 2.907
(TBD)* 103.7*
Pond C 21.13 n/a 79% n/a n/a n/a 3.323
(4907.89)
1.638
(4906.47) 26.90
Pond D 2.94 n/a 27% n/a n/a n/a 0.222
(4904.69)
0.072
(4903.97) 4.50
Pond E 4.92 n/a 66% n/a n/a n/a 0.669
(4901.84)
0.314
(4900.70) 9.30
Pond F 12.20 n/a 77% n/a n/a n/a 1.878
(4905.02)
0.92
(4903.84) 14.00
Pond G 7.05 n/a 70% n/a n/a n/a 1.004
(4901.72)
0.48
(4901.04) 11.40
Pond H 16.72
13%
80% 1.067
(4902.80)
0.232
(4901.25) 25.70
2.658
(TBD)*
1.313
(TBD)* 20.9*
Pond I 4.26 76% 0.648
(4903.13)
0.316
(4901.91) 3.30
* Future required pond volumes and WSELs to be determined at time of development and once pond layout and grading is
known.
It is evident that the final release rates between the interim condition and ultimate condition are slightly different. Due to
how the full spectrum spreadsheet by Mile High Flood Control district is put together, it iterates the 100-year release rate
to 0.90 of the predevelopment flows. The predevelopment flows are the same between the interim and final ponds on a
per basin comparison. However, the WQCV, EURV, and total volume are different between interim and ultimate
conditions. These differences in volumes impact the head pressure generated at the outfall structure. Because of this
difference in head pressure the outlet structures are constructed differently, and thus, the ultimate release rate is slightly
adjusted. It is also important to note that the full spectrum spreadsheet rounds the ratio peak outflow to
predevelopment to 0.90 for the 100-year event. However, in most situations, the ratio peak outflow to predevelopment is
rarely exactly 0.90 but somewhere within the range of 0.86 to 0.94.
4.4 SPECIFIC DETAILS
1. Stormline J was sized to convey the bypass from the Timnath Reservoir Inlet Canal. This bypass was estimated at
approximately 203 cfs. This flow was provided in the City of Fort Collins 10-year SWMM model for the Boxelder
Creek basin. The intent would be that the 10-year flow would be conveyed under the future Fort Collins trail and
flow greater than 10-year would overtop the trail.
2. The Reservoir Company has confirmed that they do not discharge irrigation water from the Timnath Reservoir
Inlet Canal at this location. When they are not filling the Timnath Reservoir, they keep the gate open to
discharge any stormwater that gets intercepted by the ditch into Boxelder Creek.
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3. A future Cooper Slough drainage channel was modeled with this study. The Cooper Slough drainage channel is
expected to be built by the City of Fort Collins in order to alleviate flooding upstream of this site. The future
Cooper Slough channel is anticipated to be built within Basin A. The Cooper Slough channel was estimated by
Fort Collins to divert a total flow of 1050 cfs in the 100-year event with an additional 224 cfs added just upstream
of the confluence with Boxelder Creek. This project modeled both the 100-year and 10-year event. The 100-year
event exceeded the banks of the formalized channel, but was still contained within the drainage tract. The 10-
year event was well contained within the channel.
4. Due to concerns regarding shallow groundwater with higher hydraulic conductive potential, each detention
pond has been outfitted with an underdrain to reduce the risk of groundwater exposure within the ponds. This
underdrain section is generally located 2’ below the bottom flowline of each pond. The underdrain is designed
to be encased in a gravel bedding. Please see the report by Miller Groundwater for additional information and
modeling of the subsurface water.
5. To meet the City’s desires to limit the amount concrete pans within detention ponds, especially adjacent to
environmentally sensitive areas, this project proposes a soft pan to be installed within the flowline of each
detention pond. This soft pan is integrated with the underdrain network described above. The soft pan will
allow the ponds to release any ponded water through the soil to the proposed underdrain system.
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5.0 CONCLUSIONS
The outfall for most of the site south of the Welch Lateral will be Dry Creek. The outfall for the site north of the Welch
Lateral will be the Town’s major drainageway at the intersection of Berthoud Parkway and Welch Avenue.
5.1 COMPLIANCE WITH STANDARDS
1. The drainage design proposed with the Gateway at Prospect project does not comply with the City of Fort
Collins’ Stormwater Criteria Manual but does meet the Mile High Flood Control District Criteria Manual. However,
the City of Fort Collins has approved this divergence from the detention standards set in the FCSCM. A variance
request has been provided to the City.
2. The drainage design proposed with the Gateway at Prospect project complies with the City of Fort Collins’
Master Drainage Plan for the Boxelder and Cooper Slough Basin.
3. There are regulatory floodplains associated with the Gateway at Prospect development.
4. The drainage plan and stormwater management measures proposed with Gateway at Prospect development
are compliant with all applicable State and Federal regulations governing stormwater discharge.
5.2 DRAINAGE CONCEPT
1. Gateway at Prospect project’s drainage infrastructure is designed based on the future the ultimate condition of
the site, with the exception of two interim detention ponds.
2. The drainage design proposed with this project will effectively limit potential damage associated with its
stormwater runoff.
3. This drainage study has set out guidelines for future development to ensure the downstream integrity of
Boxelder Creek. Gateway at Prospect utilized full spectrum detention as a mechanism to “beat the peak” of
Boxelder Creek.
4. The proposed Gateway at Prospect development will not impact the Master Drainage Plan recommendations for
the Boxelder and Cooper Slough major drainage basin.
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6.0 REFERENCES
1. City of Fort Collins Landscape Design Guidelines for Stormwater and Detention Facilities, November 5,
2009, BHA Design, Inc. with City of Fort Collins Utility Services.
2. Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, as adopted by Ordinance No. 174,
2011, and referenced in Section 26-500 (c) of the City of Fort Collins Municipal Code.
3. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and Reenacted,
Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007.
4. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation Service,
United States Department of Agriculture.
5. Urban Storm Drainage Criteria Manual, Volumes 1-3, Mile High Flood District, Wright-McLaughlin
Engineers, Denver, Colorado, Revised September 2017.
6. SWMM Analysis for the Boxelder and Cooper Slough Major Basin, Ayers Associates, Fort Collins,
Colorado, 2018.
7. Overall Drainage Report for Gateway at Prospect Overall Development Plan, by Northern Engineering,
May 3, 2016.
GATEWAY AT PROSPECT
APPENDIX
epsgroupinc.com Arizona | Colorado
APPENDIX A
Hydrologic Computations
Hydrologic Soil Group—Larimer County Area, Colorado
(Gateway at Prospect)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
8/14/2025
Page 1 of 4
44
9
0
6
0
0
44
9
0
7
0
0
44
9
0
8
0
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9
0
9
0
0
44
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1
0
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44
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1
1
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44
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0
498900 499000 499100 499200 499300 499400 499500 499600 499700 499800 499900
498900 499000 499100 499200 499300 499400 499500 499600 499700 499800 499900
40° 34' 45'' N
10
5
°
0
'
5
0
'
'
W
40° 34' 45'' N
10
5
°
0
'
0
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'
W
40° 33' 56'' N
10
5
°
0
'
5
0
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'
W
40° 33' 56'' N
10
5
°
0
'
0
'
'
W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 350 700 1400 2100
Feet
0 100 200 400 600
Meters
Map Scale: 1:7,490 if printed on A portrait (8.5" x 11") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Lines
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Points
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Survey Area Data: Version 19, Aug 29, 2024
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Jul 2, 2021—Aug 25,
2021
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Hydrologic Soil Group—Larimer County Area, Colorado
(Gateway at Prospect)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
8/14/2025
Page 2 of 4
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
22 Caruso clay loam, 0 to 1
percent slope
D 22.6 11.9%
24 Connerton-Barnum
complex, 0 to 3
percent slopes
C 5.0 2.6%
33 Fluvaquents, nearly
level
B 7.1 3.7%
35 Fort Collins loam, 0 to 3
percent slopes
C 1.1 0.6%
54 Kim loam, 3 to 5 percent
slopes
B 3.8 2.0%
73 Nunn clay loam, 0 to 1
percent slopes
C 4.2 2.2%
74 Nunn clay loam, 1 to 3
percent slopes
C 2.5 1.3%
76 Nunn clay loam, wet, 1
to 3 percent slopes
C 92.6 48.7%
98 Satanta Variant clay
loam, 0 to 3 percent
slopes
D 51.1 26.9%
Totals for Area of Interest 190.2 100.0%
Hydrologic Soil Group—Larimer County Area, Colorado Gateway at Prospect
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
8/14/2025
Page 3 of 4
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive
precipitation from long-duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three dual classes (A/D, B/D, and C/D). The groups are defined as follows:
Group A. Soils having a high infiltration rate (low runoff potential) when
thoroughly wet. These consist mainly of deep, well drained to excessively
drained sands or gravelly sands. These soils have a high rate of water
transmission.
Group B. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well
drained soils that have moderately fine texture to moderately coarse texture.
These soils have a moderate rate of water transmission.
Group C. Soils having a slow infiltration rate when thoroughly wet. These consist
chiefly of soils having a layer that impedes the downward movement of water or
soils of moderately fine texture or fine texture. These soils have a slow rate of
water transmission.
Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink-swell
potential, soils that have a high water table, soils that have a claypan or clay
layer at or near the surface, and soils that are shallow over nearly impervious
material. These soils have a very slow rate of water transmission.
If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is
for drained areas and the second is for undrained areas. Only the soils that in
their natural condition are in group D are assigned to dual classes.
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—Larimer County Area, Colorado Gateway at Prospect
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
8/14/2025
Page 4 of 4
Gateway at Prospect
CHARACTER OF SURFACE1:
Percentage
Impervious Runoff Coefficient
Developed
Asphalt .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………100%0.95
Concrete .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………100%0.95
Gravel .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………40%0.50
Unimproved Areas
Undeveloped, Greenbelts, agricultural .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………2%0.20
Lawns Sandy Soil .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………2%0.20
Notes:
Basin ID Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Gravel
(ac)
Area of
Undeveloped,
Greenbelts,
Agricultural
(ac)
Composite
% Imperv.
2-year
Composite Runoff
Coefficient
5-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
CxCf
Cf=1.00
100-year
Composite
Runoff
Coefficient CxCf
Cf=1.25
EX1 29.57 0.00 0.00 1.34 28.23 4% 0.21 0.21 0.21 0.26
EX2 3.13 0.00 0.00 0.00 3.13 2% 0.20 0.20 0.20 0.25
EX3 21.62 0.00 0.00 0.42 21.19 3% 0.21 0.21 0.21 0.26
EX4A 43.42 0.00 0.00 0.88 42.55 3% 0.21 0.21 0.21 0.26
EX4B 4.21 0.00 0.00 0.09 4.13 3% 0.21 0.21 0.21 0.26
EX5 57.56 0.64 0.00 0.42 56.50 3% 0.21 0.21 0.21 0.26
EX6 17.31 0.42 0.00 0.00 16.89 4% 0.22 0.22 0.22 0.28
EXISTING BASIN % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
2) Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Chapter 3. Table 3.2-1 and 3.2-2
1) Percentage impervious taken from the Fort Collins Stormwater Criteria Manual, Chapter 5, Table 4.1-2 and Table 4.1-3
Gateway at Prospect
Overland Flow, Time of Concentration:
Channelized Flow, Time of Concentration:
Total Time of Concentration :
T c is the lesser of the values of Tc calculated using T c = T i + T t
C2,10 C100
Length,
L
(ft)
Slope,
S
(%)
Ti2 Ti100
Length,
L
(ft)
Slope,
S
(%)
Roughness
Coefficient
Assumed
Hydraulic
Radius
Velocity,
V
(ft/s)
Tt
(min)Tc (Eq. 3.3-5) Tc2 = Ti +Tt Tc100 = Ti +Tt Tc2,10 Tc100
EX1 EX1 NO 0.21 0.26 500 0.40%50.5 47.5 1700 0.29%0.025 0.59 2.26 12.5 N/A 63.0 60.0 63.0 60.0
EX2 EX2 NO 0.20 0.25 15 33.33%2.0 1.9 2561 0.08%0.025 0.59 1.17 36.6 N/A 38.6 38.5 38.6 38.5
EX3 EX3 NO 0.21 0.26 500 1.30%34.1 32.1 1050 0.62%0.025 0.59 3.28 5.3 N/A 39.4 37.4 39.4 37.4
EX4 EX4A NO 0.21 0.26 500 0.80%40.1 37.7 1800 0.40%0.025 0.59 2.64 11.4 N/A 51.5 49.1 51.5 49.1
EX4 EX4B NO 0.21 0.26 424 0.71%38.5 36.2 212 3.30%0.025 0.59 7.58 0.5 N/A 38.9 36.7 38.9 36.7
EX5 EX5 NO 0.21 0.26 500 0.64%43.2 40.6 1250 0.38%0.025 0.59 2.59 8.1 N/A 51.2 48.7 51.2 48.7
EX6 EX6 NO 0.22 0.28 500 1.40%32.9 30.8 152 0.66%0.025 0.59 3.38 0.7 N/A 33.6 31.6 33.6 31.6
EXISTING DEVELOPED DIRECT TIME OF CONCENTRATION
Channelized Flow
Design
Point Basin
Overland Flow Time of Concentration
Urban?
(Equation 3.3-2 FCSCM)
(Equation 5-5 FCSCM)
(Equation 5-4 FCSCM)
(Equation 3.3-5 FCSCM)
Gateway at Prospect
Rational Method Equation:
Rainfall Intensity:
EX1 29.57 63.0 60.0 0.21 0.21 0.26 0.79 1.35 2.78 4.91 8.40 21.55
EX2 3.13 38.6 38.5 0.20 0.20 0.25 1.10 1.88 3.84 0.69 1.17 3.00
EX3 21.62 39.4 37.4 0.21 0.21 0.26 1.09 1.86 3.80 4.95 8.44 21.56
EX4A 43.42 51.5 49.1 0.21 0.21 0.26 0.91 1.56 3.18 8.30 14.22 36.25
EX4B 4.21 38.9 36.7 0.21 0.21 0.26 1.10 1.88 3.84 0.97 1.66 4.24
EX5 57.56 51.2 48.7 0.21 0.21 0.26 0.91 1.56 3.18 11.00 18.86 48.05
EX6 17.31 33.6 31.6 0.22 0.22 0.28 1.21 2.06 4.20 4.59 7.84 19.99
EXISTING DEVELOPED RUNOFF COMPUTATIONS
Design
Point
Area, A
(acres)
Tc2,10
(min)
Flow,
Q2
(cfs)
Flow,
Q100
(cfs)
C2 C100
IDF Table for Rational Method - Table 3.4-1 FCSCM
Flow,
Q10
(cfs)
Intensity,
i10
(in/hr)
C10
Tc100
(min)
Intensity,
i2
(in/hr)
Intensity,
i100
(in/hr)
()()()AiCCQf=
Gateway at Prospect
CHARACTER OF SURFACE1: Percentage
Impervious
2-yr Runoff
Coefficient
5-yr Runoff
Coefficient
Developed
ROW (Connector 63' ROW).…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………75%0.77 0.77
ROW (Connector 69' ROW).…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………77%0.79 0.79
ROW (Collector 92' ROW).…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………86%0.85 0.85
Urban Estate .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………30%0.30 0.30
Low Density Residential .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………50%0.55 0.55
Medium Density Residential .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………70%0.65 0.65
Commercial .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………80%0.85 0.85
Park .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………25%0.35 0.35
Unimproved Areas
Undeveloped, Greenbelts, agricultural .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………2%0.20 0.20
Lawns Sandy Soil .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………2%0.20 0.20
Notes:
Basin ID Basin Area
(ac)
Area of
Connector
63' R.O.W
(ac)
Area of
Connector
69' R.O.W
(ac)
Area of
Collector 92'
R.O.W
(ac)
Area of
Urban
Estate
(ac)
Area of
Low Density
Residential
(ac)
Area of
Medium Density
Residential
(ac)
Area of
Commercia
l
(ac)
Area of
Park
(ac)
Area of
Undeveloped,
Greenbelts,
Agricultural
(ac)
Composite
% Imperv.
2-year
Composite Runoff
Coefficient
5-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
CxCf
Cf=1.00
100-year
Composite
Runoff
Coefficient
CxCf
Cf=1.25
A1 29.57 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 29.57 2%0.20 0.20 0.20 0.25
B1 66.71 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 66.71 2%0.20 0.20 0.20 0.25
B2 0.35 0.35 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 75%0.77 0.77 0.77 0.97
B3 0.17 0.17 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 75%0.77 0.77 0.77 0.97
C1 20.77 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 20.77 2%0.20 0.20 0.20 0.25
C2 0.36 0.00 0.36 0.00 0.00 0.00 0.00 0.00 0.00 0.00 77%0.79 0.79 0.79 0.98
D1 2.07 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2.07 2%0.20 0.20 0.20 0.25
D2 0.86 0.00 0.00 0.86 0.00 0.00 0.00 0.00 0.00 0.00 86%0.85 0.85 0.85 1.00
E1 3.08 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.08 2%0.20 0.20 0.20 0.25
E2 1.85 0.62 0.00 0.73 0.00 0.00 0.00 0.00 0.00 0.50 60%0.65 0.65 0.65 0.81
F1 9.43 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 9.43 2%0.20 0.20 0.20 0.25
F2 0.36 0.36 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 75%0.77 0.77 0.77 0.97
F3 0.42 0.00 0.42 0.00 0.00 0.00 0.00 0.00 0.00 0.00 77%0.79 0.79 0.79 0.98
F4 0.79 0.79 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 75%0.77 0.77 0.77 0.97
F5 1.20 0.53 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.67 34%0.45 0.45 0.45 0.57
G1 5.28 0.00 0.00 0.32 0.00 0.00 0.00 0.00 0.00 4.96 7%0.24 0.24 0.24 0.30
G2 0.92 0.00 0.00 0.92 0.00 0.00 0.00 0.00 0.00 0.00 86%0.85 0.85 0.85 1.00
G3 0.35 0.00 0.00 0.35 0.00 0.00 0.00 0.00 0.00 0.00 86%0.85 0.85 0.85 1.00
G4 0.51 0.00 0.00 0.51 0.00 0.00 0.00 0.00 0.00 0.00 86%0.85 0.85 0.85 1.00
H1 15.97 0.00 0.00 0.37 0.00 0.00 0.00 0.00 0.00 15.60 4%0.22 0.22 0.22 0.27
H2 0.75 0.00 0.00 0.75 0.00 0.00 0.00 0.00 0.00 0.00 86%0.85 0.85 0.85 1.00
I1 2.54 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2.54 2%0.20 0.20 0.20 0.25
I2 1.72 0.00 0.00 1.72 0.00 0.00 0.00 0.00 0.00 0.00 86%0.85 0.85 0.85 1.00
BOX1 5.53 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5.53 2%0.20 0.20 0.20 0.25
BOX2 4.66 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4.66 2%0.20 0.20 0.20 0.25
PUD1 3.13 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.13 2%0.20 0.20 0.20 0.25
Basin B (B1, B2 and B3)67.23 0.53 0.00 0.00 0.00 0.00 0.00 0.00 0.00 66.71 3%0.20 0.20 0.20 0.26
Basin C (C1 and C2)21.13 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 21.13 2%0.20 0.20 0.20 0.25
Basin D (D1 and D2)2.94 0.00 0.00 0.86 0.00 0.00 0.00 0.00 0.00 2.07 27%0.39 0.39 0.39 0.49
Basin E (E1 and E2)4.92 0.62 0.00 0.73 0.00 0.00 0.00 0.00 0.00 3.57 24%0.37 0.37 0.37 0.46
Basin F (F1, F2, F3, F4 and F5)12.20 1.68 0.42 0.00 0.00 0.00 0.00 0.00 0.00 10.52 15%0.31 0.31 0.31 0.38
Basin G (G1, G2, G3, G4)7.05 0.00 0.00 2.09 0.00 0.00 0.00 0.00 0.00 4.96 27%0.39 0.39 0.39 0.49
Basin H (H1 and H2)16.72 0.00 0.00 1.13 0.00 0.00 0.00 0.00 0.00 15.60 8%0.24 0.24 0.24 0.30
Basin I (I1 and I2)4.26 0.00 0.00 1.72 0.00 0.00 0.00 0.00 0.00 2.54 36%0.46 0.46 0.46 0.58
Basin H & I 20.98 0.00 0.00 2.84 0.00 0.00 0.00 0.00 0.00 18.14 13%0.29 0.29 0.29 0.36
INTERIM BASIN % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
2) Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Chapter 3. Table 3.2-1 and 3.2-2
1) Percentage impervious taken from the Fort Collins Stormwater Criteria Manual, Chapter 5, Table 4.1-2 and Table 4.1-3
Combined Basins
Gateway at Prospect
Overland Flow, Time of Concentration:
Channelized Flow, Time of Concentration:
Total Time of Concentration :
T c is the lesser of the values of Tc calculated using T c = T i + T t
C2 C100
Length,
L
(ft)
Slope,
S
(%)
Ti2 Ti100
Length,
L
(ft)
Slope,
S
(%)
Roughness
Coefficient
Assumed
Hydraulic
Radius
Velocity,
V
(ft/s)
Tt
(min)Tc (Eq. 3.3-5) Tc2 = Ti +Tt Tc100 = Ti +Tt Tc2 Tc100
A1 0.20 0.25 489 0.40%50.6 47.8 200 2.00%0.025 0.55 5.66 0.6 13.8 51.2 48.3 13.8 13.8
Interim Pond B B1 0.20 0.25 100 3.00%11.7 11.0 1835 0.50%0.025 0.55 2.83 10.8 20.8 22.5 21.8 20.8 20.8
Interim Pond B B2 0.77 0.97 20 2.25%2.1 0.9 175 0.91%0.013 0.15 3.08 0.9 11.1 3.0 1.8 5.0 5.0
Interim Pond B B3 0.77 0.97 20 2.25%2.1 0.9 156 0.67%0.013 0.15 2.65 1.0 11.0 3.1 1.8 5.0 5.0
Pond C C1 0.20 0.25 100 2.50%12.4 11.7 700 0.50%0.025 0.55 2.83 4.1 14.4 16.5 15.8 14.4 14.4
Pond C C2 0.79 0.98 20 2.25%2.0 0.7 337 1.19%0.013 0.15 3.53 1.6 12.0 3.6 2.3 5.0 5.0
Pond D D1 0.20 0.25 110 1.60%15.1 14.3 50 0.50%0.025 0.55 2.83 0.3 10.9 15.4 14.5 10.9 10.9
Pond D D2 0.85 1.00 25 2.24%1.8 0.7 439 0.57%0.013 0.15 2.45 3.0 12.6 4.8 3.7 5.0 5.0
Pond E E1 0.20 0.25 100 2.00%13.4 12.6 400 0.50%0.025 0.55 2.83 2.4 12.8 15.7 15.0 12.8 12.8
Pond E E2 0.65 0.81 105 3.33%5.8 3.7 378 1.48%0.013 0.15 3.94 1.6 12.7 7.4 5.3 7.4 5.3
Pond F F1 0.20 0.25 100 2.00%13.4 12.6 600 0.50%0.025 0.55 2.83 3.5 13.9 16.9 16.2 13.9 13.9
Pond F F2 0.77 0.97 25 2.24%2.3 1.0 335 0.60%0.013 0.15 2.50 2.2 12.0 4.6 3.2 5.0 5.0
Pond F F3 0.79 0.98 20 2.25%2.0 0.7 337 1.19%0.013 0.15 3.53 1.6 12.0 3.6 2.3 5.0 5.0
Pond F F4 0.77 0.97 20 2.25%2.1 0.9 675 0.71%0.013 0.15 2.73 4.1 13.9 6.2 5.0 6.2 5.0
Pond F F5 0.45 0.57 20 2.25%4.1 3.4 564 0.71%0.013 0.15 2.72 3.5 13.2 7.6 6.9 7.6 6.9
Pond G G1 0.24 0.30 100 2.00%12.8 11.9 270 0.50%0.025 0.55 2.83 1.6 12.1 14.4 13.5 12.1 12.1
Pond G G2 0.85 1.00 25 3.00%1.6 0.6 560 1.87%0.013 0.15 4.42 2.1 13.3 3.7 2.8 5.0 5.0
Pond G G3 0.85 1.00 25 3.00%1.6 0.6 131 0.50%0.013 0.15 2.29 1.0 10.9 2.6 1.6 5.0 5.0
Pond G G4 0.85 1.00 96 1.56%3.9 1.6 132 0.53%0.013 0.15 2.36 0.9 11.3 4.9 2.5 5.0 5.0
Interim Pond I H1 0.22 0.27 100 2.00%13.1 12.3 750 0.50%0.025 0.55 2.83 4.4 14.7 17.6 16.8 14.7 14.7
Interim Pond I H2 0.85 1.00 35 2.25%2.1 0.8 334 0.95%0.013 0.15 3.15 1.8 12.1 3.9 2.6 5.0 5.0
Interim Pond I I1 0.20 0.25 35 2.25%7.6 7.2 250 0.58%0.025 0.55 3.06 1.4 11.6 9.0 8.5 9.0 8.5
Interim Pond I I2 0.85 1.00 25 3.14%1.6 0.6 593 1.81%0.013 0.15 4.35 2.3 13.4 3.9 2.9 5.0 5.0
BOX1 0.20 0.25 15 2.67%4.7 4.4 500 0.30%0.025 0.55 2.19 3.8 12.9 8.5 8.2 8.5 8.2
BOX2 0.20 0.25 15 2.67%4.7 4.4 500 0.30%0.025 0.55 2.19 3.8 12.9 8.5 8.2 8.5 8.2
PUD1 0.20 0.25 10 3.00%3.7 3.5 500 0.20%0.025 0.55 1.79 4.7 12.8 8.3 8.1 8.3 8.1
Interim Pond B Basin B (B1, B2 and B3)0.20 0.26 100 3.00%11.6 10.9 1835 0.50%0.025 0.55 0.28 108.1 20.8 119.7 119.1 20.8 20.8
Pond C Basin C (C1 and C2)0.20 0.25 100 2.50%12.4 11.7 700 0.50%0.025 0.55 0.28 41.2 14.4 53.6 53.0 14.4 14.4
Pond D Basin D (D1 and D2)0.39 0.49 110 1.60%11.9 10.2 50 0.50%0.025 0.55 0.28 2.9 10.9 14.8 13.2 10.9 10.9
Interim Pond E Basin E (E1 and E2)0.37 0.46 100 2.00%10.9 9.5 400 0.50%0.025 0.55 0.28 23.6 12.8 34.4 33.1 12.8 12.8
Pond F Basin F (F1, F2, F3, F4 and
F5)0.31 0.38 100 2.00% 11.8 10.7 600 0.50% 0.025 0.55 0.28 35.3 13.9 47.1 46.0 13.9 13.9
Pond G Basin G (G1, G2, G3, G4)0.39 0.49 100 2.00%10.5 9.0 270 0.50%0.025 0.55 0.28 15.9 12.1 26.4 24.9 12.1 12.1
Interim Pond I Basin H (H1 and H2)0.24 0.30 100 2.00%12.7 11.8 750 0.50%0.025 0.55 0.28 44.2 14.7 56.9 56.0 14.7 14.7
Combined Basins
INTERIM DEVELOPED DIRECT TIME OF CONCENTRATION
Channelized Flow
Design
Point Basin
Overland Flow Time of Concentration
(Equation 3.3-2 FCSCM)
(Equation 5-5 FCSCM)
(Equation 5-4 FCSCM)
(Equation 3.3-5 FCSCM)
Gateway at Prospect
Rational Method Equation:
Rainfall Intensity:
A1 29.57 13.8 13.8 0.20 0.25 1.95 6.82 11.53 50.39
Interim Pond B B1 66.71 20.8 20.8 0.20 0.25 1.59 5.53 21.15 92.22
B2 0.35 5.0 5.0 0.77 0.97 2.85 9.95 0.78 3.40
B3 0.17 5.0 5.0 0.77 0.97 2.85 9.95 0.38 1.67
Pond C C1 20.77 14.4 14.4 0.20 0.25 1.92 6.71 7.98 34.84
Pond C C2 0.36 5.0 5.0 0.79 0.98 2.85 9.95 0.82 3.57
Pond D D1 2.07 10.9 10.9 0.20 0.25 2.17 7.57 0.90 3.93
Pond D D2 0.86 5.0 5.0 0.85 1.00 2.85 9.95 2.09 8.59
Pond E E1 3.08 12.8 12.8 0.20 0.25 2.02 7.04 1.24 5.42
Pond E E2 1.85 5.3 5.3 0.65 0.81 2.85 9.95 3.42 14.92
Pond F F1 9.43 13.9 13.9 0.20 0.25 1.95 6.82 3.68 16.07
Pond F F2 0.36 5.0 5.0 0.77 0.97 2.85 9.95 0.80 3.47
Pond F F3 0.42 5.0 5.0 0.79 0.98 2.85 9.95 0.95 4.13
Pond F F4 0.79 5.0 5.0 0.77 0.97 2.85 9.95 1.73 7.57
Pond F F5 1.20 6.9 6.9 0.45 0.57 2.60 9.06 1.40 6.13
Pond G G1 5.28 12.1 12.1 0.24 0.30 2.05 7.16 2.59 11.30
Pond G G2 0.92 5.0 5.0 0.85 1.00 2.85 9.95 2.23 9.14
Pond G G3 0.35 5.0 5.0 0.85 1.00 2.85 9.95 0.84 3.45
Pond G G4 0.51 5.0 5.0 0.85 1.00 2.85 9.95 1.23 5.06
Interim Pond I H1 15.97 14.7 14.7 0.22 0.27 1.90 6.62 6.51 28.41
Interim Pond I H2 0.75 5.0 5.0 0.85 1.00 2.85 9.95 1.83 7.51
Interim Pond I I1 2.54 8.5 8.5 0.20 0.25 2.35 8.21 1.19 5.21
Interim Pond I I2 1.72 5.0 5.0 0.85 1.00 2.85 9.95 4.16 17.08
BOX1 5.53 8.2 8.2 0.20 0.25 2.40 8.38 2.65 11.58
BOX2 4.66 8.2 8.2 0.20 0.25 2.40 8.38 2.24 9.77
PUD1 3.13 8.1 8.1 0.20 0.25 2.40 8.38 1.50 6.55
Interim Pond B Basin B (B1, B2 and B3)67.23 20.8 20.8 0.20 0.26 1.59 5.53 21.79 95.04
Pond C Basin C (C1 and C2)21.13 14.4 14.4 0.20 0.25 1.92 6.71 8.12 35.45
Pond D Basin D (D1 and D2)2.94 10.9 10.9 0.39 0.49 2.17 7.57 2.50 10.88
Interim Pond E Basin E (E1 and E2)4.92 12.8 12.8 0.37 0.46 2.02 7.04 3.66 15.97
Pond F Basin F (F1, F2, F3, F4 and
F5)12.20 13.9 13.9 0.31 0.38 1.95 6.82 7.28 31.79
Pond G Basin G (G1, G2, G3, G4)7.05 12.1 12.1 0.39 0.49 2.05 7.16 5.68 24.80
Interim Pond I Basin H (H1 and H2)16.72 14.7 14.7 0.24 0.30 1.90 6.62 7.73 33.72
Interim Pond I Basin I (I1 and I2)4.26 11.6 11.6 0.46 0.58 2.09 7.29 4.12 17.94
Combined Basins
Tc100
(min)
Intensity,
i2
(in/hr)
Intensity,
i100
(in/hr)
INTERIM DEVELOPED RUNOFF COMPUTATIONS
Design
Point Basin(s)Area, A
(acres)
Tc2
(min)
Flow,
Q2
(cfs)
Flow,
Q100
(cfs)
C2 C100
IDF Table for Rational Method - Table 3.4-1 FCSCM
AiCCQf
Gateway at Prospect
CHARACTER OF SURFACE1: Percentage
Impervious
2-yr Runoff
Coefficient
5-yr Runoff
Coefficient
Developed
ROW (Connector 63' ROW).…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………75%0.77 0.77
ROW (Connector 69' ROW).…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………77%0.79 0.79
ROW (Collector 92' ROW).…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………86%0.85 0.85
Urban Estate .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………30%0.30 0.30
Low Density Residential .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………50%0.55 0.55
Medium Density Residential .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………70%0.65 0.65
Commercial .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………80%0.85 0.85
Park .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………25%0.35 0.35
Unimproved Areas
Undeveloped, Greenbelts, agricultural .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………2%0.20 0.20
Lawns Sandy Soil .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………2%0.20 0.20
Notes:
Basin ID Basin Area
(ac)
Area of
Connector
63' R.O.W
(ac)
Area of
Connector
69' R.O.W
(ac)
Area of
Collector 92'
R.O.W
(ac)
Area of
Urban
Estate
(ac)
Area of
Low Density
Residential
(ac)
Area of
Medium Density
Residential
(ac)
Area of
Commercia
l
(ac)
Area of
Park
(ac)
Area of
Undeveloped,
Greenbelts,
Agricultural
(ac)
Composite
% Imperv.
2-year
Composite Runoff
Coefficient
5-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
CxCf
Cf=1.00
100-year
Composite
Runoff
Coefficient
CxCf
Cf=1.25
A1 29.57 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 29.57 2%0.20 0.20 0.20 0.25
B1 66.71 0.00 0.00 0.00 13.56 53.14 0.00 0.00 0.00 13.56 46%0.54 0.54 0.54 0.67
B2 0.35 0.35 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 75%0.77 0.77 0.77 0.97
B3 0.17 0.17 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 75%0.77 0.77 0.77 0.97
C1 20.77 0.00 0.00 0.00 0.00 0.00 0.00 20.77 0.00 0.00 80%0.85 0.85 0.85 1.00
C2 0.36 0.00 0.36 0.00 0.00 0.00 0.00 0.00 0.00 0.00 77%0.79 0.79 0.79 0.98
D1 2.07 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2.07 2%0.20 0.20 0.20 0.25
D2 0.86 0.00 0.00 0.86 0.00 0.00 0.00 0.00 0.00 0.00 86%0.85 0.85 0.85 1.00
E1 3.08 0.00 0.00 0.00 0.00 0.00 3.08 0.00 0.00 0.00 70%0.65 0.65 0.65 0.81
E2 1.85 0.62 0.00 0.73 0.00 0.00 0.00 0.00 0.00 0.50 60%0.65 0.65 0.65 0.81
F1 9.43 0.00 0.00 0.00 0.00 0.00 0.00 9.43 0.00 0.00 80%0.85 0.85 0.85 1.00
F2 0.36 0.36 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 75%0.77 0.77 0.77 0.97
F3 0.42 0.00 0.42 0.00 0.00 0.00 0.00 0.00 0.00 0.00 77%0.79 0.79 0.79 0.98
F4 0.79 0.79 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 75%0.77 0.77 0.77 0.97
F5 1.20 0.53 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.67 34%0.45 0.45 0.45 0.57
G1 5.28 0.00 0.00 0.32 0.00 0.00 0.00 4.23 0.00 0.73 70%0.76 0.76 0.76 0.95
G2 0.92 0.00 0.00 0.92 0.00 0.00 0.00 0.00 0.00 0.00 86%0.85 0.85 0.85 1.00
G3 0.35 0.00 0.00 0.35 0.00 0.00 0.00 0.00 0.00 0.00 86%0.85 0.85 0.85 1.00
G4 0.51 0.00 0.00 0.51 0.00 0.00 0.00 0.00 0.00 0.00 86%0.85 0.85 0.85 1.00
H1 15.97 0.00 0.00 0.37 0.00 0.00 0.00 15.60 0.00 0.00 80%0.85 0.85 0.85 1.00
H2 0.75 0.00 0.00 0.75 0.00 0.00 0.00 0.00 0.00 0.00 86%0.85 0.85 0.85 1.00
I1 2.54 0.00 0.00 0.00 0.00 0.00 0.00 2.20 0.00 0.34 70%0.76 0.76 0.76 0.95
I2 1.72 0.00 0.00 1.72 0.00 0.00 0.00 0.00 0.00 0.00 86%0.85 0.85 0.85 1.00
BOX1 5.53 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5.53 2%0.20 0.20 0.20 0.25
BOX2 4.66 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4.66 2%0.20 0.20 0.20 0.25
PUD1 3.13 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.13 2%0.20 0.20 0.20 0.25
Basin B (B1, B2 and B3)67.23 0.53 0.00 0.00 13.56 53.14 0.00 0.00 0.00 0.00 46%0.50 0.50 0.50 0.63
Basin C (C1 and C2)21.13 0.00 0.00 0.00 0.00 0.00 0.00 20.77 0.00 0.36 79%0.84 0.84 0.84 1.00
Basin D (D1 and D2)2.94 0.00 0.00 0.86 0.00 0.00 0.00 0.00 0.00 2.07 27%0.39 0.39 0.39 0.49
Basin E (E1 and E2)4.92 0.62 0.00 0.73 0.00 0.00 3.08 0.00 0.00 0.50 66%0.65 0.65 0.65 0.81
Basin F (F1, F2, F3, F4 and F5)12.20 1.68 0.42 0.00 0.00 0.00 0.00 9.43 0.00 1.09 77%0.81 0.81 0.81 1.00
Basin G (G1, G2, G3, G4)7.05 0.00 0.00 2.09 0.00 0.00 0.00 4.23 0.00 0.73 70%0.78 0.78 0.78 0.98
Basin H (H1 and H2)16.72 0.00 0.00 1.13 0.00 0.00 0.00 15.60 0.00 0.00 80%0.85 0.85 0.85 1.00
Basin I (I1 and I2)4.26 0.00 0.00 1.72 0.00 0.00 0.00 2.20 0.00 0.34 76%0.80 0.80 0.80 1.00
FINAL BASIN % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
2) Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Chapter 3. Table 3.2-1 and 3.2-2
1) Percentage impervious taken from the Fort Collins Stormwater Criteria Manual, Chapter 5, Table 4.1-2 and Table 4.1-3
Combined Basins
Gateway at Prospect
Overland Flow, Time of Concentration:
Channelized Flow, Time of Concentration:
Total Time of Concentration :
T c is the lesser of the values of Tc calculated using T c = T i + T t
C2 C100
Length,
L
(ft)
Slope,
S
(%)
Ti2 Ti100
Length,
L
(ft)
Slope,
S
(%)
Roughness
Coefficient
Assumed
Hydraulic
Radius
Velocity,
V
(ft/s)
Tt
(min)Tc (Eq. 3.3-5) Tc2 = Ti +Tt Tc100 = Ti +Tt Tc2 Tc100
A1 0.20 0.25 489 0.40%50.6 47.8 200 2.00%0.025 0.55 5.66 0.6 13.8 51.2 48.3 13.8 13.8
Final Pond B B1 0.54 0.67 100 3.00%7.3 5.5 1835 0.50%0.013 0.15 2.29 13.4 20.8 20.6 18.9 20.6 18.9
Final Pond B B2 0.77 0.97 20 2.25%2.1 0.9 175 0.91%0.013 0.15 3.08 0.9 11.1 3.0 1.8 5.0 5.0
Final Pond B B3 0.77 0.97 20 2.25%2.1 0.9 156 0.67%0.013 0.15 2.65 1.0 11.0 3.1 1.8 5.0 5.0
Pond C C1 0.85 1.00 100 2.50%3.4 1.4 700 0.50%0.013 0.15 2.29 5.1 14.4 8.5 6.5 8.5 6.5
Pond C C2 0.79 0.98 20 2.25%2.0 0.7 337 1.19%0.013 0.15 3.53 1.6 12.0 3.6 2.3 5.0 5.0
Pond D D1 0.20 0.25 110 1.60%15.1 14.3 50 0.50%0.025 0.55 2.83 0.3 10.9 15.4 14.5 10.9 10.9
Pond D D2 0.85 1.00 25 2.24%1.8 0.7 439 0.57%0.013 0.15 2.45 3.0 12.6 4.8 3.7 5.0 5.0
Pond E E1 0.65 0.81 100 2.00%6.7 4.3 400 0.50%0.013 0.15 2.29 2.9 12.8 9.6 7.2 9.6 7.2
Pond E E2 0.65 0.81 105 3.33%5.8 3.7 378 1.48%0.013 0.15 3.94 1.6 12.7 7.4 5.3 7.4 5.3
Pond F F1 0.85 1.00 100 2.00%3.7 1.5 600 0.50%0.013 0.15 2.29 4.4 13.9 8.1 5.9 8.1 5.9
Pond F F2 0.77 0.97 25 2.24%2.3 1.0 335 0.60%0.013 0.15 2.50 2.2 12.0 4.6 3.2 5.0 5.0
Pond F F3 0.79 0.98 20 2.25%2.0 0.7 337 1.19%0.013 0.15 3.53 1.6 12.0 3.6 2.3 5.0 5.0
Pond F F4 0.77 0.97 20 2.25%2.1 0.9 675 0.71%0.013 0.15 2.73 4.1 13.9 6.2 5.0 6.2 5.0
Pond F F5 0.45 0.57 20 2.25%4.1 3.4 564 0.71%0.013 0.15 2.72 3.5 13.2 7.6 6.9 7.6 6.9
Pond G G1 0.76 0.95 100 2.00%5.0 2.2 270 0.50%0.025 0.55 2.83 1.6 12.1 6.6 3.8 6.6 5.0
Pond G G2 0.85 1.00 25 3.00%1.6 0.6 560 1.87%0.013 0.15 4.42 2.1 13.3 3.7 2.8 5.0 5.0
Pond G G3 0.85 1.00 25 3.00%1.6 0.6 131 0.50%0.013 0.15 2.29 1.0 10.9 2.6 1.6 5.0 5.0
Pond G G4 0.85 1.00 96 1.56%3.9 1.6 132 0.53%0.013 0.15 2.36 0.9 11.3 4.9 2.5 5.0 5.0
Final Pond H H1 0.85 1.00 100 2.00%3.7 1.5 750 0.50%0.013 0.15 2.29 5.5 14.7 9.2 6.9 9.2 6.9
Final Pond H H2 0.85 1.00 35 2.25%2.1 0.8 334 0.95%0.013 0.15 3.15 1.8 12.1 3.9 2.6 5.0 5.0
Final Pond I I1 0.76 0.95 35 2.25%2.8 1.2 250 0.58%0.013 0.55 5.88 0.7 11.6 3.6 1.9 5.0 5.0
Final Pond I I2 0.85 1.00 25 3.14%1.6 0.6 593 1.81%0.013 0.15 4.35 2.3 13.4 3.9 2.9 5.0 5.0
BOX1 0.20 0.25 15 2.67%4.7 4.4 500 0.30%0.025 0.55 2.19 3.8 12.9 8.5 8.2 8.5 8.2
BOX2 0.20 0.25 15 2.67%4.7 4.4 500 0.30%0.025 0.55 2.19 3.8 12.9 8.5 8.2 8.5 8.2
PUD1 0.20 0.25 10 3.00%3.7 3.5 500 0.20%0.025 0.55 1.79 4.7 12.8 8.3 8.1 8.3 8.1
Final Pond B Basin B (B1, B2 and B3)0.50 0.63 100 3.00%7.8 6.1 1835 0.50%0.013 0.15 0.23 133.7 20.8 141.5 139.8 20.8 20.8
Pond C Basin C (C1 and C2)0.84 1.00 100 2.50%3.6 1.4 700 0.50%0.013 0.15 0.23 51.0 14.4 54.6 52.4 14.4 14.4
Pond D Basin D (D1 and D2)0.39 0.49 110 1.60%11.9 10.2 50 0.50%0.013 0.15 0.23 3.6 10.9 15.5 13.9 10.9 10.9
Pond E Basin E (E1 and E2)0.65 0.81 100 2.00%6.7 4.3 400 0.50%0.013 0.15 0.23 29.1 12.8 35.8 33.4 12.8 12.8
Pond F Basin F (F1, F2, F3, F4 and
F5)0.81 1.00 100 2.00% 4.3 1.5 600 0.50% 0.013 0.15 0.23 43.7 13.9 48.0 45.2 13.9 13.9
Pond G Basin G (G1, G2, G3, G4)0.78 0.98 100 2.00%4.7 1.8 270 0.50%0.013 0.15 0.23 19.7 12.1 24.4 21.5 12.1 12.1
Final Pond H Basin H (H1 and H2)0.85 1.00 100 2.00%3.7 1.5 750 0.50%0.013 0.15 0.23 54.6 14.7 58.3 56.1 14.7 14.7
Combined Basins
FINAL DEVELOPED DIRECT TIME OF CONCENTRATION
Channelized Flow
Design
Point Basin
Overland Flow Time of Concentration
(Equation 3.3-2 FCSCM)
(Equation 5-5 FCSCM)
(Equation 5-4 FCSCM)
(Equation 3.3-5 FCSCM)
Gateway at Prospect
Rational Method Equation:
Rainfall Intensity:
A1 29.57 13.8 13.8 0.20 0.25 1.95 6.82 11.53 50.39
Final Pond B B1 66.71 18.9 18.9 0.54 0.67 1.68 5.84 60.32 262.65
B2 0.35 5.0 5.0 0.77 0.97 2.85 9.95 0.78 3.40
B3 0.17 5.0 5.0 0.77 0.97 2.85 9.95 0.38 1.67
Pond C C1 20.77 6.5 6.5 0.85 1.00 2.67 9.31 47.13 193.35
Pond C C2 0.36 5.0 5.0 0.79 0.98 2.85 9.95 0.82 3.57
Pond D D1 2.07 10.9 10.9 0.20 0.25 2.17 7.57 0.90 3.93
Pond D D2 0.86 5.0 5.0 0.85 1.00 2.85 9.95 2.09 8.59
Pond E E1 3.08 7.2 7.2 0.65 0.81 2.52 8.80 5.04 22.00
Pond E E2 1.85 5.3 5.3 0.65 0.81 2.85 9.95 3.42 14.92
Pond F F1 9.43 5.9 5.9 0.85 1.00 2.76 9.63 22.12 90.81
Pond F F2 0.36 5.0 5.0 0.77 0.97 2.85 9.95 0.80 3.47
Pond F F3 0.42 5.0 5.0 0.79 0.98 2.85 9.95 0.95 4.13
Pond F F4 0.79 5.0 5.0 0.77 0.97 2.85 9.95 1.73 7.57
Pond F F5 1.20 6.9 6.9 0.45 0.57 2.60 9.06 1.40 6.13
Pond G G1 5.28 5.0 5.0 0.76 0.95 2.85 9.95 11.43 49.89
Pond G G2 0.92 5.0 5.0 0.85 1.00 2.85 9.95 2.23 9.14
Pond G G3 0.35 5.0 5.0 0.85 1.00 2.85 9.95 0.84 3.45
Pond G G4 0.51 5.0 5.0 0.85 1.00 2.85 9.95 1.23 5.06
Final Pond H H1 15.97 6.9 6.9 0.85 1.00 2.60 9.06 35.22 144.59
Final Pond H H2 0.75 5.0 5.0 0.85 1.00 2.85 9.95 1.83 7.51
Final Pond I I1 2.54 5.0 5.0 0.76 0.95 2.85 9.95 5.52 24.11
Final Pond I I2 1.72 5.0 5.0 0.85 1.00 2.85 9.95 4.16 17.08
BOX1 5.53 8.2 8.2 0.20 0.25 2.40 8.38 2.65 11.58
BOX2 4.66 8.2 8.2 0.20 0.25 2.40 8.38 2.24 9.77
PUD1 3.13 8.1 8.1 0.20 0.25 2.40 8.38 1.50 6.55
Final Pond B Basin B (B1, B2 and B3)67.23 20.8 20.8 0.50 0.63 1.59 5.53 53.42 232.99
Pond C Basin C (C1 and C2)21.13 14.4 14.4 0.84 1.00 1.92 6.71 34.03 141.80
Pond D Basin D (D1 and D2)2.94 10.9 10.9 0.39 0.49 2.17 7.57 2.50 10.88
Pond E Basin E (E1 and E2)4.92 12.8 12.8 0.65 0.81 2.02 7.04 6.45 28.16
Pond F Basin F (F1, F2, F3, F4 and
F5)12.20 13.9 13.9 0.81 1.00 1.95 6.82 19.23 83.12
Pond G Basin G (G1, G2, G3, G4)7.05 12.1 12.1 0.78 0.98 2.05 7.16 11.32 49.41
Final Pond H Basin H (H1 and H2)16.72 14.7 14.7 0.85 1.00 1.90 6.62 26.94 110.62
Final Pond I Basin I (I1 and I2)4.26 11.6 11.6 0.80 1.00 2.09 7.29 7.10 30.98
FINAL DEVELOPED RUNOFF COMPUTATIONS
Design
Point Basin(s)Area, A
(acres)
Tc2
(min)
Flow,
Q2
(cfs)
Flow,
Q100
(cfs)
C2 C100
IDF Table for Rational Method - Table 3.4-1 FCSCM
Combined Basins
Tc100
(min)
Intensity,
i2
(in/hr)
Intensity,
i100
(in/hr)
AiCCQf
GATEWAY AT PROSPECT
APPENDIX
epsgroupinc.com Arizona | Colorado
APPENDIX B
Low Impact Development Responsibility Exhibit
X
X
X
X
X /
/
/
/
/
/
/
/
FO
/ / / / / / / /
/ /
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
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/
/
/
/
X
10
"
S
S
FO
FO
FO
T S
VAULTELECT
VAULT
ELEC
T S
V.P.
GASTESTSTA VAULT
ELEC T S TESTSTA
ELEC
VAULT
ELEC
MH
GAS
GAS
VAULT
ELEC
F.O.
F.O.
F.O.
ELEC
ELEC
VAULT
ELEC
VAULT
ELEC
VAULTELEC
VAULT
ELEC
VAULTELEC
AC
T
ELEC VAULTELECVAULTELECTRAFFICVAULTE
VAULTELECTRAFFICVAULT ELEC
T ST S
VAULTELEC
ELEC
VAULTELEC
VAULTELEC
E
V.P.
V.P.
V.P.
6" W
12
"
W
T ST S
BASIN D - ZONE GREENBELT AND OPEN SPACE
RESPONSIBLE FOR 2.94 ACRES
OF LID REQUIREMENTS PER CITY OF FORT
COLLINS STANDARDS.
BASIN G - ZONE CE
RESPONSIBLE FOR 7.05 ACRES
OF LID REQUIREMENTS
PER CITY OF FORT
COLLINS STANDARDS
BASIN E - ZONE MMN
RESPONSIBLE FOR 4.92 ACRES
OF LID REQUIREMENTS
PER CITY OF FORT
COLLINS STANDARDS
BASIN A - ZONE GREENBELT AND OPEN SPACE
RESPONSIBLE FOR 0 ACRES
OF LID REQUIREMENTS PER CITY OF FORT
COLLINS STANDARDS AS LONG AS IT REMAINS
UNDEVELOPED.
BASIN F - ZONE MMN
RESPONSIBLE FOR 12.20 ACRES
OF LID REQUIREMENTS
PER CITY OF FORT
COLLINS STANDARDS
BASIN B - ZONE LMN AND UE
RESPONSIBLE FOR 67.23 ACRES
OF LID REQUIREMENTS
PER CITY OF FORT
COLLINS STANDARDS
BASIN C - ZONE E
RESPONSIBLE FOR 21.13 ACRES
OF LID REQUIREMENTS
PER CITY OF FORT
COLLINS STANDARDS
PROSPECT ROAD
BASIN H - ZONE CE
RESPONSIBLE FOR 16.72 ACRES
OF LID REQUIREMENTS
PER CITY OF FORT
COLLINS STANDARDS
BASIN I - ZONE CE
RESPONSIBLE FOR 4.26 ACRES
OF LID REQUIREMENTS
PER CITY OF FORT
COLLINS STANDARDS
LID/WQCV REQUIREMENTS FOR EACH PARCEL
FORT COLLINS, CO
GATEWAY AT PROSPECT
07.07.2025
P:\892-002\DWG\DRNG\892-002_LID.DWG
NOTES:
1. EACH PARCEL IS RESPONSIBLE FOR THEIR LID AND WQCV SIZING BASED
ON ACREAGE SIZE DEPICTED ON THIS EXHIBIT. THIS INCLUDES PORTIONS
OF ADJACENT RIGHT-OF-WAYS.
2. LID AND WQCV REQUIREMENT AREAS ARE NOT EQUAL TO DETENTION
AREA REQUIREMENTS.
3. FOR ADDITIONAL INFORMATION ON THE BASIN DELINEATIONS REFER TO
THE DRAINAGE PLAN FROM GATEWAY AT PROSPECT UTILITY PLAN SET.
4. LID AND WQCV SIZING MUST FOLLOW CITY OF FORT COLLINS
STANDARDS.
5. AT THE TIME OF EACH PARCELS DEVELOPMENT THE DESIGN ENGINEER
SHALL CALCULATE THE PROPOSED PERCENT IMPERVIOUS AND NOT USE
THE IMPERVIOUS LISTED IN THE FINAL DRAINAGE REPORT FOR GATEWAY
AT PROSPECT BY EPS GROUP INC.
LEGEND:
BASIN B
BASIN C
BASIN D
BASIN E
BASIN F
BASIN G
BASIN H
BASIN I
TREATMENT PROPOSED AT INTERIM
SUMMARY:
Basin ID Area
Minimum % of Imperv. Area
Treated by LID
A 29.57 0%, if remains Open Space
B 67.23 75%
C 21.13 75%
D 2.94 75%
E 4.92 75%
F 12.20 75%
G 7.05 75%
H 16.72 75%
I 4.26 75%
Basin ID Area Land Use Impervious
Impervious
Area*
LID
Treatment?
Percent
Treatment
Treated
Area Land Use Impervious
Impervious
Area*
LID
Treatment?
Percent
Treatment
Treated
Area
acres %acres %acres %acres %acres
A1 29.57 Open Space/Undevel. 2% 0.00 No 0% 0.00 Open Space/Undevel. 2% 0.00 No 0% 0.00
B1 66.71 Open Space/Undevel. 2% 0.00 No 0% 0.00 Residential 46% 30.69 Yes 75% 23.01
B2 0.35 Roads 75% 0.27 Yes 100% 0.27 Roads 75% 0.27 Yes 100% 0.27
B3 0.17 Roads 75% 0.13 No 0% 0.00 Roads 75% 0.13 Yes 75% 0.10
C1 20.77 Open Space/Undevel. 2% 0.00 No 0% 0.00 Employment 80% 16.61 Yes 75% 12.46
C2 0.36 Roads 77% 0.28 Yes 100% 0.28 Roads 77% 0.28 Yes 100% 0.28
D1 2.07 Open Space/Undevel. 2% 0.00 No 0% 0.00 Open Space/Undevel. 2% 0.00 No 0% 0.00
D2 0.86 Roads 86% 0.74 Yes 100% 0.74 Roads 86% 0.74 Yes 100% 0.74
E1 3.08 Open Space/Undevel. 2% 0.00 No 0% 0.00 Residential 70% 2.15 Yes 75% 1.62
E2 1.85 Roads 60% 1.11 Yes 100% 1.11 Roads 60% 1.11 Yes 100% 1.11
F1 9.43 Open Space/Undevel. 2% 0.00 No 0% 0.00 Residential 80% 7.54 Yes 75% 5.66
F2 0.36 Roads 75% 0.27 No 0% 0.00 Roads 75% 0.27 Yes 75% 0.20
F3 0.42 Roads 77% 0.32 No 0% 0.00 Roads 77% 0.32 Yes 75% 0.24
F4 0.79 Roads 75% 0.59 No 0% 0.00 Roads 75% 0.59 Yes 75% 0.44
F5 1.20 Roads 34% 0.41 No 0% 0.00 Roads 34% 0.41 Yes 75% 0.30
G1 5.28 Open Space/Undevel. 7% 0.00 No 0% 0.00 Commercial 70% 3.69 Yes 75% 2.77
G2 0.92 Roads 86% 0.79 No 0% 0.00 Roads 86% 0.79 Yes 75% 0.59
G3 0.35 Roads 86% 0.30 Yes 100% 0.30 Roads 86% 0.30 Yes 100% 0.30
G4 0.51 Roads 86% 0.44 No 0% 0.00 Roads 86% 0.44 Yes 75% 0.33
H1 15.97 Open Space/Undevel. 4% 0.00 No 0% 0.00 Commercial 80% 12.77 Yes 75% 9.58
H2 0.75 Roads 86% 0.65 No 0% 0.00 Roads 86% 0.65 Yes 75% 0.49
I1 2.54 Open Space/Undevel. 2% 0.00 No 0% 0.00 Commercial 70% 1.78 Yes 75% 1.33
I2 1.72 Roads 86% 1.48 Yes 100% 1.48 Roads 86% 1.48 Yes 100% 1.48
Totals 166.03 7.77 4.17 83.01 63.30
Percent Treated Imperv.
*Open Space and Undeveloped areas are excluded from impervious area calculation
54% 76%
Interim Future
LOW IMPACT DEVELOPMENT (LID) COMPLIANCE
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia =75.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100)i =0.750
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.24 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 15,410 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =308 cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER =cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER =cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum)DWQCV =12 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin =231 sq ft
D) Actual Flat Surface Area AActual =286 sq ft
E) Area at Design Depth (Top Surface Area)ATop =618 sq ft
F) Rain Garden Total Volume VT=452 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
4. Underdrain System
A) Are underdrains provided?1
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y =ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 =cu ft
iii) Orifice Diameter, 3/8" Minimum DO = in
Design Procedure Form: Rain Garden (RG)
S. Thomas
EPS Group
June 30, 2025
Gateway at Prospect Basin B2
Fort Collins
UD-BMP (Version 3.07, March 2018)
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
892-002_basin B2-UD-BMP_v3.07.xlsm, RG 6/30/2025, 2:07 PM
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is an impermeable liner provided due to proximity
of structures or groundwater contamination?
6. Inlet / Outlet Control
A) Inlet Control
7. Vegetation
8. Irrigation
A) Will the rain garden be irrigated?
Notes:
Design Procedure Form: Rain Garden (RG)
S. Thomas
EPS Group
June 30, 2025
Gateway at Prospect Basin B2
Fort Collins
Choose One
Choose One
Choose One
Sheet Flow- No Energy Dissipation Required
Concentrated Flow- Energy Dissipation Provided
Plantings
Seed (Plan for frequent weed control)
Sand Grown or Other High Infiltration Sod
Choose One
YES
NO
YES
NO
892-002_basin B2-UD-BMP_v3.07.xlsm, RG 6/30/2025, 2:07 PM
Weir Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Monday, Jul 7 2025
Rain Garden B2 Spillway
Trapezoidal Weir
Crest = Sharp
Bottom Length (ft) = 4.00
Total Depth (ft) = 0.50
Side Slope (z:1) = 4.00
Calculations
Weir Coeff. Cw = 3.10
Compute by: Known Q
Known Q (cfs) = 3.40
Highlighted
Depth (ft) = 0.36
Q (cfs) = 3.400
Area (sqft) = 1.96
Velocity (ft/s) = 1.74
Top Width (ft) = 6.88
0 1 2 3 4 5 6 7 8 9 10
Depth (ft) Depth (ft)Rain Garden B2 Spillway
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
Length (ft)Weir W.S.
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia =77.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100)i =0.770
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.25 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 15,890 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =329 cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER =cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER =cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum)DWQCV =12 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin =245 sq ft
D) Actual Flat Surface Area AActual =248 sq ft
E) Area at Design Depth (Top Surface Area)ATop =677 sq ft
F) Rain Garden Total Volume VT=463 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
4. Underdrain System
A) Are underdrains provided?1
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y =ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 =cu ft
iii) Orifice Diameter, 3/8" Minimum DO = in
Design Procedure Form: Rain Garden (RG)
S. Thomas
EPS Group
June 30, 2025
Gateway at Prospect Basin C2
Fort Collins
UD-BMP (Version 3.07, March 2018)
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
892-002_basin C2-UD-BMP_v3.07.xlsm, RG 6/30/2025, 2:16 PM
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is an impermeable liner provided due to proximity
of structures or groundwater contamination?
6. Inlet / Outlet Control
A) Inlet Control
7. Vegetation
8. Irrigation
A) Will the rain garden be irrigated?
Notes:
Design Procedure Form: Rain Garden (RG)
S. Thomas
EPS Group
June 30, 2025
Gateway at Prospect Basin C2
Fort Collins
Choose One
Choose One
Choose One
Sheet Flow- No Energy Dissipation Required
Concentrated Flow- Energy Dissipation Provided
Plantings
Seed (Plan for frequent weed control)
Sand Grown or Other High Infiltration Sod
Choose One
YES
NO
YES
NO
892-002_basin C2-UD-BMP_v3.07.xlsm, RG 6/30/2025, 2:16 PM
Weir Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Monday, Jul 7 2025
Rain Garden C2 Spillway
Trapezoidal Weir
Crest = Sharp
Bottom Length (ft) = 4.00
Total Depth (ft) = 0.50
Side Slope (z:1) = 4.00
Calculations
Weir Coeff. Cw = 3.10
Compute by: Known Q
Known Q (cfs) = 3.57
Highlighted
Depth (ft) = 0.37
Q (cfs) = 3.570
Area (sqft) = 2.03
Velocity (ft/s) = 1.76
Top Width (ft) = 6.96
0 1 2 3 4 5 6 7 8 9 10
Depth (ft) Depth (ft)Rain Garden C2 Spillway
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
Length (ft)Weir W.S.
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia =86.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100)i =0.860
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.30 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 37,617 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =927 cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER =cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER =cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum)DWQCV =12 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin =647 sq ft
D) Actual Flat Surface Area AActual =726 sq ft
E) Area at Design Depth (Top Surface Area)ATop =1431 sq ft
F) Rain Garden Total Volume VT=1,079 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
4. Underdrain System
A) Are underdrains provided?1
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y =ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 =cu ft
iii) Orifice Diameter, 3/8" Minimum DO = in
Design Procedure Form: Rain Garden (RG)
S. Thomas
July 18, 2025
Gateway at Prospect Basin D2
Fort Collins
UD-BMP (Version 3.07, March 2018)
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
892-002_basin D2-UD-BMP_v3.07.xlsm, RG 7/18/2025, 4:07 PM
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is an impermeable liner provided due to proximity
of structures or groundwater contamination?
6. Inlet / Outlet Control
A) Inlet Control
7. Vegetation
8. Irrigation
A) Will the rain garden be irrigated?
Notes:
Design Procedure Form: Rain Garden (RG)
S. Thomas
July 18, 2025
Gateway at Prospect Basin D2
Fort Collins
Choose One
Choose One
Choose One
Sheet Flow- No Energy Dissipation Required
Concentrated Flow- Energy Dissipation Provided
Plantings
Seed (Plan for frequent weed control)
Sand Grown or Other High Infiltration Sod
Choose One
YES
NO
YES
NO
892-002_basin D2-UD-BMP_v3.07.xlsm, RG 7/18/2025, 4:07 PM
Weir Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Monday, Jul 7 2025
Rain Garden D2 Spillway
Trapezoidal Weir
Crest = Sharp
Bottom Length (ft) = 12.00
Total Depth (ft) = 0.50
Side Slope (z:1) = 4.00
Calculations
Weir Coeff. Cw = 3.10
Compute by: Known Q
Known Q (cfs) = 8.59
Highlighted
Depth (ft) = 0.36
Q (cfs) = 8.590
Area (sqft) = 4.84
Velocity (ft/s) = 1.78
Top Width (ft) = 14.88
0 2 4 6 8 10 12 14 16 18 20
Depth (ft) Depth (ft)Rain Garden D2 Spillway
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
Length (ft)Weir W.S.
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia =60.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100)i =0.600
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.19 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 80,407 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER =cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER =1,519 cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum)DWQCV =12 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin =965 sq ft
D) Actual Flat Surface Area AActual =1099 sq ft
E) Area at Design Depth (Top Surface Area)ATop =1976 sq ft
F) Rain Garden Total Volume VT=1,538 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
4. Underdrain System
A) Are underdrains provided?1
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y =ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 =cu ft
iii) Orifice Diameter, 3/8" Minimum DO = in
Design Procedure Form: Rain Garden (RG)
S. Thomas
EPS Group
June 25, 2025
Gateway at Prospect Basin E2
Fort Collins
UD-BMP (Version 3.07, March 2018)
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
892-002_basin E2-UD-BMP_v3.07.xlsm, RG 6/25/2025, 10:57 AM
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is an impermeable liner provided due to proximity
of structures or groundwater contamination?
6. Inlet / Outlet Control
A) Inlet Control
7. Vegetation
8. Irrigation
A) Will the rain garden be irrigated?
Notes:
Design Procedure Form: Rain Garden (RG)
S. Thomas
EPS Group
June 25, 2025
Gateway at Prospect Basin E2
Fort Collins
Choose One
Choose One
Choose One
Sheet Flow- No Energy Dissipation Required
Concentrated Flow- Energy Dissipation Provided
Plantings
Seed (Plan for frequent weed control)
Sand Grown or Other High Infiltration Sod
Choose One
YES
NO
YES
NO
892-002_basin E2-UD-BMP_v3.07.xlsm, RG 6/25/2025, 10:57 AM
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia =86.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100)i =0.860
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.30 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 15,085 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =372 cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER =cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER =cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum)DWQCV =12 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin =259 sq ft
D) Actual Flat Surface Area AActual =310 sq ft
E) Area at Design Depth (Top Surface Area)ATop =634 sq ft
F) Rain Garden Total Volume VT=472 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
4. Underdrain System
A) Are underdrains provided?1
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y =ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 =cu ft
iii) Orifice Diameter, 3/8" Minimum DO = in
Design Procedure Form: Rain Garden (RG)
S. Thomas
June 25, 2025
Gateway at Prospect Basin G3
Fort Collins
UD-BMP (Version 3.07, March 2018)
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
892-002_basin G3-UD-BMP_v3.07.xlsm, RG 6/25/2025, 1:36 PM
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is an impermeable liner provided due to proximity
of structures or groundwater contamination?
6. Inlet / Outlet Control
A) Inlet Control
7. Vegetation
8. Irrigation
A) Will the rain garden be irrigated?
Notes:
Design Procedure Form: Rain Garden (RG)
S. Thomas
June 25, 2025
Gateway at Prospect Basin G3
Fort Collins
Choose One
Choose One
Choose One
Sheet Flow- No Energy Dissipation Required
Concentrated Flow- Energy Dissipation Provided
Plantings
Seed (Plan for frequent weed control)
Sand Grown or Other High Infiltration Sod
Choose One
YES
NO
YES
NO
892-002_basin G3-UD-BMP_v3.07.xlsm, RG 6/25/2025, 1:36 PM
Weir Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Monday, Jul 7 2025
Rain Garden G3 Spillway
Trapezoidal Weir
Crest = Sharp
Bottom Length (ft) = 4.00
Total Depth (ft) = 0.50
Side Slope (z:1) = 4.00
Calculations
Weir Coeff. Cw = 3.10
Compute by: Known Q
Known Q (cfs) = 3.45
Highlighted
Depth (ft) = 0.37
Q (cfs) = 3.450
Area (sqft) = 2.03
Velocity (ft/s) = 1.70
Top Width (ft) = 6.96
0 1 2 3 4 5 6 7 8 9 10
Depth (ft) Depth (ft)Rain Garden G3 Spillway
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
Length (ft)Weir W.S.
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia =86.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100)i =0.860
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.30 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 74,778 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =1,842 cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER =cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER =cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum)DWQCV =12 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin =1286 sq ft
D) Actual Flat Surface Area AActual =1410 sq ft
E) Area at Design Depth (Top Surface Area)ATop =3131 sq ft
F) Rain Garden Total Volume VT=2,271 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
4. Underdrain System
A) Are underdrains provided?1
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y =ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 =cu ft
iii) Orifice Diameter, 3/8" Minimum DO = in
Design Procedure Form: Rain Garden (RG)
S. Thomas
June 25, 2025
Gateway at Prospect Basin I2
Fort Collins
UD-BMP (Version 3.07, March 2018)
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
892-002_basin I2_v3.07.xlsm, RG 6/25/2025, 2:16 PM
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is an impermeable liner provided due to proximity
of structures or groundwater contamination?
6. Inlet / Outlet Control
A) Inlet Control
7. Vegetation
8. Irrigation
A) Will the rain garden be irrigated?
Notes:
Design Procedure Form: Rain Garden (RG)
S. Thomas
June 25, 2025
Gateway at Prospect Basin I2
Fort Collins
Choose One
Choose One
Choose One
Sheet Flow- No Energy Dissipation Required
Concentrated Flow- Energy Dissipation Provided
Plantings
Seed (Plan for frequent weed control)
Sand Grown or Other High Infiltration Sod
Choose One
YES
NO
YES
NO
892-002_basin I2_v3.07.xlsm, RG 6/25/2025, 2:16 PM
Weir Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Monday, Jul 7 2025
Rain Garden I2 Spillway
Trapezoidal Weir
Crest = Sharp
Bottom Length (ft) = 15.00
Total Depth (ft) = 0.50
Side Slope (z:1) = 4.00
Calculations
Weir Coeff. Cw = 3.10
Compute by: Known Q
Known Q (cfs) = 17.08
Highlighted
Depth (ft) = 0.49
Q (cfs) = 17.08
Area (sqft) = 8.31
Velocity (ft/s) = 2.06
Top Width (ft) = 18.92
0 2 4 6 8 10 12 14 16 18 20 22 24
Depth (ft) Depth (ft)Rain Garden I2 Spillway
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
Length (ft)Weir W.S.
Gateway at Prospect
Project: 892-002
Date: 07/02/2025
By: S. Thomas t=240 seconds
Storm Line A E2 1.85 1,266 13 12 13 2.00 5 3 15 0.58 6.92 3.00 7.07
Storm Line D D2 0.86 927 10 12 10 1.25 3 4 12 0.46 5.54 3.00 7.07
Storm Line M C2 0.36 329 4 12 4 1.25 3 2 6 0.23 2.77 2.00 3.14
Storm Line N G3 0.35 372 4 12 4 1.25 3 2 6 0.23 2.77 2.00 3.14
Sidewalk Culvert B2 B2 0.35 308 4 12 4 2.00 4 2 8 0.31 3.69 2.00 3.14
Sidewalk Culvert I2 I2 1.72 1,842 19 12 19 4.00 6 4 24 0.92 11.08 4.00 12.57
Storm Line/Culvert
Label
Rain
Garden
WQCV
(ft3)
Depth, hmax
(inches)
Minimum
Area
(sf)
Culvert
Width
(ft)
Forebay
Width
(ft)
1% WQCV
CALCULATIONS FOR FOREBAY AT RAIN GARDENS
Forebay
Length
(ft)
Forebay
Volume
(cf)
Calc'd Notch
Width, w
(inches)
Notch Open
Area
(sq inches)
Pipe
Equivalent
(in. dia.)
Pipe Area
(sq. in.)
Tributary
Area
(acres)
𝑤= 9.23 𝐴
𝑡
1
ℎ
GATEWAY AT PROSPECT
APPENDIX
epsgroupinc.com Arizona | Colorado
APPENDIX C
Hydraulic Computations
C.1 – Storm Sewers (Future Use)
C.2 – Inlets (Future Use)
C.3 – Detention Facilities
C.4 – Weir Calculations
C.5 – Riprap Calculations
GATEWAY AT PROSPECT
APPENDIX
epsgroupinc.com Arizona | Colorado
C.1 Storm Sewers
GATEWAY AT PROSPECT
APPENDIX
epsgroupinc.com Arizona | Colorado
C.2 Inlets
Project:
Inlet ID:
Gutter Geometry (Enter data in the blue cells)
Maximum Allowable Width for Spread Behind Curb TBACK =11.5 ft
Side Slope Behind Curb (leave blank for no conveyance credit behind curb)SBACK =0.020 ft/ft
Manning's Roughness Behind Curb (typically between 0.012 and 0.020)nBACK =0.015
Height of Curb at Gutter Flow Line HCURB =6.00 inches
Distance from Curb Face to Street Crown TCROWN =18.0 ft
Gutter Width W =2.00 ft
Street Transverse Slope SX =0.025 ft/ft
Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft)SW =0.083 ft/ft
Street Longitudinal Slope - Enter 0 for sump condition SO =0.000 ft/ft
Manning's Roughness for Street Section (typically between 0.012 and 0.020)nSTREET =0.013
Minor Storm Major Storm
Max. Allowable Spread for Minor & Major Storm TMAX =18.0 18.0 ft
Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX =6.0 6.2 inches
Check boxes are not applicable in SUMP conditions
MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm
MAJOR STORM Allowable Capacity is based on Depth Criterion Qallow =SUMP SUMP cfs
Version 4.06 Released August 2018
ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm)
(Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread)
Gateway at Prospect
Inlet A2
1
Design Information (Input)MINOR MAJOR
Type of Inlet Type =
Local Depression (additional to continuous gutter depression 'a' from above)alocal =3.00 3.00 inches
Number of Unit Inlets (Grate or Curb Opening) No = 2 2
Water Depth at Flowline (outside of local depression) Ponding Depth = 6.0 6.2 inches
Grate Information MINOR MAJOR
Length of a Unit Grate Lo (G) =N/A N/A feet
Width of a Unit Grate Wo =N/A N/A feet
Area Opening Ratio for a Grate (typical values 0.15-0.90)Aratio =N/A N/A
Clogging Factor for a Single Grate (typical value 0.50 - 0.70)Cf (G) =N/A N/A
Grate Weir Coefficient (typical value 2.15 - 3.60)Cw (G) =N/A N/A
Grate Orifice Coefficient (typical value 0.60 - 0.80)Co (G) =N/A N/A
Curb Opening Information MINOR MAJOR
Length of a Unit Curb Opening Lo (C) =5.00 5.00 feet
Height of Vertical Curb Opening in Inches Hvert =6.00 6.00 inches
Height of Curb Orifice Throat in Inches Hthroat =6.00 6.00 inches
Angle of Throat (see USDCM Figure ST-5) Theta = 63.40 63.40 degrees
Side Width for Depression Pan (typically the gutter width of 2 feet)Wp =2.00 2.00 feet
Clogging Factor for a Single Curb Opening (typical value 0.10)Cf (C) =0.10 0.10
Curb Opening Weir Coefficient (typical value 2.3-3.7)Cw (C) =3.60 3.60
Curb Opening Orifice Coefficient (typical value 0.60 - 0.70)Co (C) =0.67 0.67
Low Head Performance Reduction (Calculated)MINOR MAJOR
Depth for Grate Midwidth dGrate =N/A N/A ft
Depth for Curb Opening Weir Equation dCurb =0.33 0.35 ft
Combination Inlet Performance Reduction Factor for Long Inlets RFCombination =0.57 0.58
Curb Opening Performance Reduction Factor for Long Inlets RFCurb =0.93 0.95
Grated Inlet Performance Reduction Factor for Long Inlets RFGrate =N/A N/A
MINOR MAJOR
Total Inlet Interception Capacity (assumes clogged condition)Qa =10.5 11.4 cfs
Inlet Capacity IS GOOD for Minor and Major Storms(>Q PEAK)Q PEAK REQUIRED =1.7 7.5 cfs
CDOT Type R Curb Opening
INLET IN A SUMP OR SAG LOCATION
Version 4.06 Released August 2018
H-VertH-Curb
W
Lo (C)
Lo (G)
Wo
WP
CDOT Type R Curb Opening
Override Depths
1
Project:
Inlet ID:
Gutter Geometry (Enter data in the blue cells)
Maximum Allowable Width for Spread Behind Curb TBACK =12.0 ft
Side Slope Behind Curb (leave blank for no conveyance credit behind curb)SBACK =0.020 ft/ft
Manning's Roughness Behind Curb (typically between 0.012 and 0.020)nBACK =0.015
Height of Curb at Gutter Flow Line HCURB =6.00 inches
Distance from Curb Face to Street Crown TCROWN =25.0 ft
Gutter Width W =2.00 ft
Street Transverse Slope SX =0.025 ft/ft
Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft)SW =0.083 ft/ft
Street Longitudinal Slope - Enter 0 for sump condition SO =0.000 ft/ft
Manning's Roughness for Street Section (typically between 0.012 and 0.020)nSTREET =0.013
Minor Storm Major Storm
Max. Allowable Spread for Minor & Major Storm TMAX =19.0 19.0 ft
Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX =6.0 6.0 inches
Check boxes are not applicable in SUMP conditions
MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm
MAJOR STORM Allowable Capacity is based on Depth Criterion Qallow =SUMP SUMP cfs
Version 4.06 Released August 2018
ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm)
(Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread)
Gateway at Prospect
Inlet D3
1
Design Information (Input)MINOR MAJOR
Type of Inlet Type =
Local Depression (additional to continuous gutter depression 'a' from above)alocal =3.00 3.00 inches
Number of Unit Inlets (Grate or Curb Opening) No = 2 2
Water Depth at Flowline (outside of local depression) Ponding Depth = 6.0 6.0 inches
Grate Information MINOR MAJOR
Length of a Unit Grate Lo (G) =N/A N/A feet
Width of a Unit Grate Wo =N/A N/A feet
Area Opening Ratio for a Grate (typical values 0.15-0.90)Aratio =N/A N/A
Clogging Factor for a Single Grate (typical value 0.50 - 0.70)Cf (G) =N/A N/A
Grate Weir Coefficient (typical value 2.15 - 3.60)Cw (G) =N/A N/A
Grate Orifice Coefficient (typical value 0.60 - 0.80)Co (G) =N/A N/A
Curb Opening Information MINOR MAJOR
Length of a Unit Curb Opening Lo (C) =5.00 5.00 feet
Height of Vertical Curb Opening in Inches Hvert =6.00 6.00 inches
Height of Curb Orifice Throat in Inches Hthroat =6.00 6.00 inches
Angle of Throat (see USDCM Figure ST-5) Theta = 63.40 63.40 degrees
Side Width for Depression Pan (typically the gutter width of 2 feet)Wp =2.00 2.00 feet
Clogging Factor for a Single Curb Opening (typical value 0.10)Cf (C) =0.10 0.10
Curb Opening Weir Coefficient (typical value 2.3-3.7)Cw (C) =3.60 3.60
Curb Opening Orifice Coefficient (typical value 0.60 - 0.70)Co (C) =0.67 0.67
Low Head Performance Reduction (Calculated)MINOR MAJOR
Depth for Grate Midwidth dGrate =N/A N/A ft
Depth for Curb Opening Weir Equation dCurb =0.33 0.33 ft
Combination Inlet Performance Reduction Factor for Long Inlets RFCombination =0.57 0.57
Curb Opening Performance Reduction Factor for Long Inlets RFCurb =0.93 0.93
Grated Inlet Performance Reduction Factor for Long Inlets RFGrate =N/A N/A
MINOR MAJOR
Total Inlet Interception Capacity (assumes clogged condition)Qa =10.5 10.5 cfs
Inlet Capacity IS GOOD for Minor and Major Storms(>Q PEAK)Q PEAK REQUIRED =2.1 8.6 cfs
CDOT Type R Curb Opening
INLET IN A SUMP OR SAG LOCATION
Version 4.06 Released August 2018
H-VertH-Curb
W
Lo (C)
Lo (G)
Wo
WP
CDOT Type R Curb Opening
Override Depths
1
Project:
Inlet ID:
Gutter Geometry (Enter data in the blue cells)
Maximum Allowable Width for Spread Behind Curb TBACK =11.5 ft
Side Slope Behind Curb (leave blank for no conveyance credit behind curb)SBACK =0.020 ft/ft
Manning's Roughness Behind Curb (typically between 0.012 and 0.020)nBACK =0.015
Height of Curb at Gutter Flow Line HCURB =6.00 inches
Distance from Curb Face to Street Crown TCROWN =18.0 ft
Gutter Width W =2.00 ft
Street Transverse Slope SX =0.025 ft/ft
Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft)SW =0.083 ft/ft
Street Longitudinal Slope - Enter 0 for sump condition SO =0.000 ft/ft
Manning's Roughness for Street Section (typically between 0.012 and 0.020)nSTREET =0.013
Minor Storm Major Storm
Max. Allowable Spread for Minor & Major Storm TMAX =18.0 18.0 ft
Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX =6.0 9.0 inches
Check boxes are not applicable in SUMP conditions
MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm
MAJOR STORM Allowable Capacity is based on Depth Criterion Qallow =SUMP SUMP cfs
Version 4.06 Released August 2018
ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm)
(Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread)
Gateway at Prospect
Inlet F7
1
Design Information (Input)MINOR MAJOR
Type of Inlet Type =
Local Depression (additional to continuous gutter depression 'a' from above)alocal =2.00 2.00 inches
Number of Unit Inlets (Grate or Curb Opening) No = 2 2
Water Depth at Flowline (outside of local depression) Ponding Depth = 6.0 6.8 inches
Grate Information MINOR MAJOR
Length of a Unit Grate Lo (G) =3.00 3.00 feet
Width of a Unit Grate Wo =1.73 1.73 feet
Area Opening Ratio for a Grate (typical values 0.15-0.90)Aratio =0.43 0.43
Clogging Factor for a Single Grate (typical value 0.50 - 0.70)Cf (G) =0.50 0.50
Grate Weir Coefficient (typical value 2.15 - 3.60)Cw (G) =3.30 3.30
Grate Orifice Coefficient (typical value 0.60 - 0.80)Co (G) =0.60 0.60
Curb Opening Information MINOR MAJOR
Length of a Unit Curb Opening Lo (C) =3.00 3.00 feet
Height of Vertical Curb Opening in Inches Hvert =6.50 6.50 inches
Height of Curb Orifice Throat in Inches Hthroat =5.25 5.25 inches
Angle of Throat (see USDCM Figure ST-5) Theta = 0.00 0.00 degrees
Side Width for Depression Pan (typically the gutter width of 2 feet)Wp =2.00 2.00 feet
Clogging Factor for a Single Curb Opening (typical value 0.10)Cf (C) =0.10 0.10
Curb Opening Weir Coefficient (typical value 2.3-3.7)Cw (C) =3.70 3.70
Curb Opening Orifice Coefficient (typical value 0.60 - 0.70)Co (C) =0.66 0.66
Low Head Performance Reduction (Calculated)MINOR MAJOR
Depth for Grate Midwidth dGrate =0.523 0.589 ft
Depth for Curb Opening Weir Equation dCurb =0.33 0.40 ft
Combination Inlet Performance Reduction Factor for Long Inlets RFCombination =0.71 0.80
Curb Opening Performance Reduction Factor for Long Inlets RFCurb =1.00 1.00
Grated Inlet Performance Reduction Factor for Long Inlets RFGrate =0.71 0.80
MINOR MAJOR
Total Inlet Interception Capacity (assumes clogged condition)Qa =5.3 7.5 cfs
WARNING: Inlet Capacity less than Q Peak for Major Storm Q PEAK REQUIRED =1.7 7.6 cfs
CDOT/Denver 13 Combination
INLET IN A SUMP OR SAG LOCATION
Version 4.06 Released August 2018
H-VertH-Curb
W
Lo (C)
Lo (G)
W o
WP
CDOT/Denver 13 Combination
Override Depths
1
Project:
Inlet ID:
Gutter Geometry (Enter data in the blue cells)
Maximum Allowable Width for Spread Behind Curb TBACK =11.5 ft
Side Slope Behind Curb (leave blank for no conveyance credit behind curb)SBACK =0.002 ft/ft
Manning's Roughness Behind Curb (typically between 0.012 and 0.020)nBACK =0.015
Height of Curb at Gutter Flow Line HCURB =6.00 inches
Distance from Curb Face to Street Crown TCROWN =18.0 ft
Gutter Width W =2.00 ft
Street Transverse Slope SX =0.025 ft/ft
Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft)SW =0.083 ft/ft
Street Longitudinal Slope - Enter 0 for sump condition SO =0.000 ft/ft
Manning's Roughness for Street Section (typically between 0.012 and 0.020)nSTREET =0.013
Minor Storm Major Storm
Max. Allowable Spread for Minor & Major Storm TMAX =18.0 18.0 ft
Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX =6.0 9.0 inches
Check boxes are not applicable in SUMP conditions
MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm
MAJOR STORM Allowable Capacity is based on Depth Criterion Qallow =SUMP SUMP cfs
Version 4.06 Released August 2018
ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm)
(Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread)
Gateway at Prospect
Inlet F8
1
Design Information (Input)MINOR MAJOR
Type of Inlet Type =
Local Depression (additional to continuous gutter depression 'a' from above)alocal =2.00 2.00 inches
Number of Unit Inlets (Grate or Curb Opening) No = 2 2
Water Depth at Flowline (outside of local depression) Ponding Depth = 6.0 6.8 inches
Grate Information MINOR MAJOR
Length of a Unit Grate Lo (G) =3.00 3.00 feet
Width of a Unit Grate Wo =1.73 1.73 feet
Area Opening Ratio for a Grate (typical values 0.15-0.90)Aratio =0.43 0.43
Clogging Factor for a Single Grate (typical value 0.50 - 0.70)Cf (G) =0.50 0.50
Grate Weir Coefficient (typical value 2.15 - 3.60)Cw (G) =3.30 3.30
Grate Orifice Coefficient (typical value 0.60 - 0.80)Co (G) =0.60 0.60
Curb Opening Information MINOR MAJOR
Length of a Unit Curb Opening Lo (C) =3.00 3.00 feet
Height of Vertical Curb Opening in Inches Hvert =6.50 6.50 inches
Height of Curb Orifice Throat in Inches Hthroat =5.25 5.25 inches
Angle of Throat (see USDCM Figure ST-5) Theta = 0.00 0.00 degrees
Side Width for Depression Pan (typically the gutter width of 2 feet)Wp =2.00 2.00 feet
Clogging Factor for a Single Curb Opening (typical value 0.10)Cf (C) =0.10 0.10
Curb Opening Weir Coefficient (typical value 2.3-3.7)Cw (C) =3.70 3.70
Curb Opening Orifice Coefficient (typical value 0.60 - 0.70)Co (C) =0.66 0.66
Low Head Performance Reduction (Calculated)MINOR MAJOR
Depth for Grate Midwidth dGrate =0.523 0.589 ft
Depth for Curb Opening Weir Equation dCurb =0.33 0.40 ft
Combination Inlet Performance Reduction Factor for Long Inlets RFCombination =0.71 0.80
Curb Opening Performance Reduction Factor for Long Inlets RFCurb =1.00 1.00
Grated Inlet Performance Reduction Factor for Long Inlets RFGrate =0.71 0.80
MINOR MAJOR
Total Inlet Interception Capacity (assumes clogged condition)Qa =5.3 7.5 cfs
Inlet Capacity IS GOOD for Minor and Major Storms(>Q PEAK)Q PEAK REQUIRED =1.4 6.1 cfs
CDOT/Denver 13 Combination
INLET IN A SUMP OR SAG LOCATION
Version 4.06 Released August 2018
H-VertH-Curb
W
Lo (C)
Lo (G)
W o
W P
CDOT/Denver 13 Combination
Override Depths
1
Project:
Inlet ID:
Gutter Geometry (Enter data in the blue cells)
Maximum Allowable Width for Spread Behind Curb TBACK =13.5 ft
Side Slope Behind Curb (leave blank for no conveyance credit behind curb)SBACK =0.020 ft/ft
Manning's Roughness Behind Curb (typically between 0.012 and 0.020)nBACK =0.015
Height of Curb at Gutter Flow Line HCURB =6.00 inches
Distance from Curb Face to Street Crown TCROWN =21.0 ft
Gutter Width W =2.00 ft
Street Transverse Slope SX =0.025 ft/ft
Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft)SW =0.083 ft/ft
Street Longitudinal Slope - Enter 0 for sump condition SO =0.000 ft/ft
Manning's Roughness for Street Section (typically between 0.012 and 0.020)nSTREET =0.013
Minor Storm Major Storm
Max. Allowable Spread for Minor & Major Storm TMAX =18.0 21.0 ft
Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX =6.0 12.0 inches
Check boxes are not applicable in SUMP conditions
MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm
MAJOR STORM Allowable Capacity is based on Depth Criterion Qallow =SUMP SUMP cfs
Version 4.06 Released August 2018
ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm)
(Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread)
Gateway at Prospect
Inlet K5
1
Design Information (Input)MINOR MAJOR
Type of Inlet Type =
Local Depression (additional to continuous gutter depression 'a' from above)alocal =2.00 2.00 inches
Number of Unit Inlets (Grate or Curb Opening) No = 1 1
Water Depth at Flowline (outside of local depression) Ponding Depth = 6.0 7.7 inches
Grate Information MINOR MAJOR
Length of a Unit Grate Lo (G) =3.00 3.00 feet
Width of a Unit Grate Wo =1.73 1.73 feet
Area Opening Ratio for a Grate (typical values 0.15-0.90)Aratio =0.43 0.43
Clogging Factor for a Single Grate (typical value 0.50 - 0.70)Cf (G) =0.50 0.50
Grate Weir Coefficient (typical value 2.15 - 3.60)Cw (G) =3.30 3.30
Grate Orifice Coefficient (typical value 0.60 - 0.80)Co (G) =0.60 0.60
Curb Opening Information MINOR MAJOR
Length of a Unit Curb Opening Lo (C) =3.00 3.00 feet
Height of Vertical Curb Opening in Inches Hvert =6.50 6.50 inches
Height of Curb Orifice Throat in Inches Hthroat =5.25 5.25 inches
Angle of Throat (see USDCM Figure ST-5) Theta = 0.00 0.00 degrees
Side Width for Depression Pan (typically the gutter width of 2 feet)Wp =2.00 2.00 feet
Clogging Factor for a Single Curb Opening (typical value 0.10)Cf (C) =0.10 0.10
Curb Opening Weir Coefficient (typical value 2.3-3.7)Cw (C) =3.70 3.70
Curb Opening Orifice Coefficient (typical value 0.60 - 0.70)Co (C) =0.66 0.66
Low Head Performance Reduction (Calculated)MINOR MAJOR
Depth for Grate Midwidth dGrate =0.523 0.664 ft
Depth for Curb Opening Weir Equation dCurb =0.33 0.48 ft
Combination Inlet Performance Reduction Factor for Long Inlets RFCombination =0.94 1.00
Curb Opening Performance Reduction Factor for Long Inlets RFCurb =1.00 1.00
Grated Inlet Performance Reduction Factor for Long Inlets RFGrate =0.94 1.00
MINOR MAJOR
Total Inlet Interception Capacity (assumes clogged condition)Qa =3.6 5.7 cfs
Inlet Capacity IS GOOD for Minor and Major Storms(>Q PEAK)Q PEAK REQUIRED =1.0 4.1 cfs
CDOT/Denver 13 Combination
INLET IN A SUMP OR SAG LOCATION
Version 4.06 Released August 2018
H-VertH-Curb
W
Lo (C)
Lo (G)
Wo
WP
CDOT/Denver 13 Combination
Override Depths
1
Project:
Inlet ID:
Gutter Geometry (Enter data in the blue cells)
Maximum Allowable Width for Spread Behind Curb TBACK =11.5 ft
Side Slope Behind Curb (leave blank for no conveyance credit behind curb)SBACK =0.020 ft/ft
Manning's Roughness Behind Curb (typically between 0.012 and 0.020)nBACK =0.015
Height of Curb at Gutter Flow Line HCURB =6.00 inches
Distance from Curb Face to Street Crown TCROWN =18.0 ft
Gutter Width W =2.00 ft
Street Transverse Slope SX =0.025 ft/ft
Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft)SW =0.083 ft/ft
Street Longitudinal Slope - Enter 0 for sump condition SO =0.000 ft/ft
Manning's Roughness for Street Section (typically between 0.012 and 0.020)nSTREET =0.013
Minor Storm Major Storm
Max. Allowable Spread for Minor & Major Storm TMAX =18.0 18.0 ft
Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX =6.0 6.2 inches
Check boxes are not applicable in SUMP conditions
MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm
MAJOR STORM Allowable Capacity is based on Depth Criterion Qallow =SUMP SUMP cfs
Version 4.06 Released August 2018
ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm)
(Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread)
Gateway at Prospect
Inlet O2
1
Design Information (Input)MINOR MAJOR
Type of Inlet Type =
Local Depression (additional to continuous gutter depression 'a' from above)alocal =2.00 2.00 inches
Number of Unit Inlets (Grate or Curb Opening) No = 1 1
Water Depth at Flowline (outside of local depression) Ponding Depth = 6.0 6.2 inches
Grate Information MINOR MAJOR
Length of a Unit Grate Lo (G) =3.00 3.00 feet
Width of a Unit Grate Wo =1.73 1.73 feet
Area Opening Ratio for a Grate (typical values 0.15-0.90)Aratio =0.43 0.43
Clogging Factor for a Single Grate (typical value 0.50 - 0.70)Cf (G) =0.50 0.50
Grate Weir Coefficient (typical value 2.15 - 3.60)Cw (G) =3.30 3.30
Grate Orifice Coefficient (typical value 0.60 - 0.80)Co (G) =0.60 0.60
Curb Opening Information MINOR MAJOR
Length of a Unit Curb Opening Lo (C) =3.00 3.00 feet
Height of Vertical Curb Opening in Inches Hvert =6.50 6.50 inches
Height of Curb Orifice Throat in Inches Hthroat =5.25 5.25 inches
Angle of Throat (see USDCM Figure ST-5) Theta = 0.00 0.00 degrees
Side Width for Depression Pan (typically the gutter width of 2 feet)Wp =2.00 2.00 feet
Clogging Factor for a Single Curb Opening (typical value 0.10)Cf (C) =0.10 0.10
Curb Opening Weir Coefficient (typical value 2.3-3.7)Cw (C) =3.70 3.70
Curb Opening Orifice Coefficient (typical value 0.60 - 0.70)Co (C) =0.66 0.66
Low Head Performance Reduction (Calculated)MINOR MAJOR
Depth for Grate Midwidth dGrate =0.523 0.539 ft
Depth for Curb Opening Weir Equation dCurb =0.33 0.35 ft
Combination Inlet Performance Reduction Factor for Long Inlets RFCombination =0.94 0.97
Curb Opening Performance Reduction Factor for Long Inlets RFCurb =1.00 1.00
Grated Inlet Performance Reduction Factor for Long Inlets RFGrate =0.94 0.97
MINOR MAJOR
Total Inlet Interception Capacity (assumes clogged condition)Qa =3.6 3.9 cfs
Inlet Capacity IS GOOD for Minor and Major Storms(>Q PEAK)Q PEAK REQUIRED =0.8 3.5 cfs
CDOT/Denver 13 Combination
INLET IN A SUMP OR SAG LOCATION
Version 4.06 Released August 2018
H-VertH-Curb
W
Lo (C)
Lo (G)
Wo
WP
CDOT/Denver 13 Combination
Override Depths
1
Project:
Inlet ID:
Gutter Geometry (Enter data in the blue cells)
Maximum Allowable Width for Spread Behind Curb TBACK =12.0 ft
Side Slope Behind Curb (leave blank for no conveyance credit behind curb)SBACK =0.020 ft/ft
Manning's Roughness Behind Curb (typically between 0.012 and 0.020)nBACK =0.015
Height of Curb at Gutter Flow Line HCURB =6.00 inches
Distance from Curb Face to Street Crown TCROWN =25.0 ft
Gutter Width W =2.00 ft
Street Transverse Slope SX =0.025 ft/ft
Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft)SW =0.083 ft/ft
Street Longitudinal Slope - Enter 0 for sump condition SO =0.000 ft/ft
Manning's Roughness for Street Section (typically between 0.012 and 0.020)nSTREET =0.013
Minor Storm Major Storm
Max. Allowable Spread for Minor & Major Storm TMAX =19.0 19.0 ft
Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX =6.0 6.0 inches
Check boxes are not applicable in SUMP conditions
MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm
MAJOR STORM Allowable Capacity is based on Depth Criterion Qallow =SUMP SUMP cfs
Version 4.06 Released August 2018
ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm)
(Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread)
Gateway at Prospect
Inlet L1
1
Design Information (Input)MINOR MAJOR
Type of Inlet Type =
Local Depression (additional to continuous gutter depression 'a' from above)alocal =3.00 3.00 inches
Number of Unit Inlets (Grate or Curb Opening) No = 2 2
Water Depth at Flowline (outside of local depression) Ponding Depth = 6.0 6.0 inches
Grate Information MINOR MAJOR
Length of a Unit Grate Lo (G) =N/A N/A feet
Width of a Unit Grate Wo =N/A N/A feet
Area Opening Ratio for a Grate (typical values 0.15-0.90)Aratio =N/A N/A
Clogging Factor for a Single Grate (typical value 0.50 - 0.70)Cf (G) =N/A N/A
Grate Weir Coefficient (typical value 2.15 - 3.60)Cw (G) =N/A N/A
Grate Orifice Coefficient (typical value 0.60 - 0.80)Co (G) =N/A N/A
Curb Opening Information MINOR MAJOR
Length of a Unit Curb Opening Lo (C) =5.00 5.00 feet
Height of Vertical Curb Opening in Inches Hvert =6.00 6.00 inches
Height of Curb Orifice Throat in Inches Hthroat =6.00 6.00 inches
Angle of Throat (see USDCM Figure ST-5) Theta = 63.40 63.40 degrees
Side Width for Depression Pan (typically the gutter width of 2 feet)Wp =2.00 2.00 feet
Clogging Factor for a Single Curb Opening (typical value 0.10)Cf (C) =0.10 0.10
Curb Opening Weir Coefficient (typical value 2.3-3.7)Cw (C) =3.60 3.60
Curb Opening Orifice Coefficient (typical value 0.60 - 0.70)Co (C) =0.67 0.67
Low Head Performance Reduction (Calculated)MINOR MAJOR
Depth for Grate Midwidth dGrate =N/A N/A ft
Depth for Curb Opening Weir Equation dCurb =0.33 0.33 ft
Combination Inlet Performance Reduction Factor for Long Inlets RFCombination =0.57 0.57
Curb Opening Performance Reduction Factor for Long Inlets RFCurb =0.93 0.93
Grated Inlet Performance Reduction Factor for Long Inlets RFGrate =N/A N/A
MINOR MAJOR
Total Inlet Interception Capacity (assumes clogged condition)Qa =10.5 10.5 cfs
Inlet Capacity IS GOOD for Minor and Major Storms(>Q PEAK)Q PEAK REQUIRED =1.8 7.5 cfs
CDOT Type R Curb Opening
INLET IN A SUMP OR SAG LOCATION
Version 4.06 Released August 2018
H-VertH-Curb
W
Lo (C)
Lo (G)
Wo
WP
CDOT Type R Curb Opening
Override Depths
1
Project:
Inlet ID:
Gutter Geometry (Enter data in the blue cells)
Maximum Allowable Width for Spread Behind Curb TBACK =13.5 ft
Side Slope Behind Curb (leave blank for no conveyance credit behind curb)SBACK =0.020 ft/ft
Manning's Roughness Behind Curb (typically between 0.012 and 0.020)nBACK =0.015
Height of Curb at Gutter Flow Line HCURB =6.00 inches
Distance from Curb Face to Street Crown TCROWN =21.0 ft
Gutter Width W =2.00 ft
Street Transverse Slope SX =0.025 ft/ft
Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft)SW =0.083 ft/ft
Street Longitudinal Slope - Enter 0 for sump condition SO =0.005 ft/ft
Manning's Roughness for Street Section (typically between 0.012 and 0.020)nSTREET =0.013
Minor Storm Major Storm
Max. Allowable Spread for Minor & Major Storm TMAX =18.0 21.0 ft
Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX =6.0 12.0 inches
Allow Flow Depth at Street Crown (leave blank for no) check = yes
MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm
MAJOR STORM Allowable Capacity is based on Spread Criterion Qallow =10.4 23.6 cfs
Version 4.06 Released August 2018
ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm)
(Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread)
Gateway at Prospect
Inlet N2 & N3
Minor storm max. allowable capacity GOOD - greater than the design flow given on sheet 'Inlet Management'
Major storm max. allowable capacity GOOD - greater than the design flow given on sheet 'Inlet Management'
1
Design Information (Input)MINOR MAJOR
Type of Inlet Type =
Local Depression (additional to continuous gutter depression 'a')aLOCAL =2.0 2.0 inches
Total Number of Units in the Inlet (Grate or Curb Opening) No = 2 2
Length of a Single Unit Inlet (Grate or Curb Opening)Lo =3.00 3.00 ft
Width of a Unit Grate (cannot be greater than W, Gutter Width) Wo =1.73 1.73 ft
Clogging Factor for a Single Unit Grate (typical min. value = 0.5)Cf-G =0.50 0.50
Clogging Factor for a Single Unit Curb Opening (typical min. value = 0.1)Cf-C =0.10 0.10
Street Hydraulics: OK - Q < Allowable Street Capacity'MINOR MAJOR
Total Inlet Interception Capacity Q =0.5 1.6 cfs
Total Inlet Carry-Over Flow (flow bypassing inlet) Qb = 0.0 0.1 cfs
Capture Percentage = Qa/Qo = C% = 100 92 %
INLET ON A CONTINUOUS GRADE
Version 4.06 Released August 2018
CDOT/Denver 13 CombinationCDOT/Denver 13 Combination
1
Project:
Inlet ID:
Gutter Geometry (Enter data in the blue cells)
Maximum Allowable Width for Spread Behind Curb TBACK =11.5 ft
Side Slope Behind Curb (leave blank for no conveyance credit behind curb)SBACK =0.020 ft/ft
Manning's Roughness Behind Curb (typically between 0.012 and 0.020)nBACK =0.015
Height of Curb at Gutter Flow Line HCURB =6.00 inches
Distance from Curb Face to Street Crown TCROWN =18.0 ft
Gutter Width W =2.00 ft
Street Transverse Slope SX =0.083 ft/ft
Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft)SW =0.083 ft/ft
Street Longitudinal Slope - Enter 0 for sump condition SO =0.000 ft/ft
Manning's Roughness for Street Section (typically between 0.012 and 0.020)nSTREET =0.012
Minor Storm Major Storm
Max. Allowable Spread for Minor & Major Storm TMAX =18.0 18.0 ft
Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX =6.0 6.2 inches
Check boxes are not applicable in SUMP conditions
MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm
MAJOR STORM Allowable Capacity is based on Depth Criterion Qallow =SUMP SUMP cfs
Version 4.06 Released August 2018
ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm)
(Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread)
Gateway at Prospect
Inlet A3
1
Design Information (Input)MINOR MAJOR
Type of Inlet Type =
Local Depression (additional to continuous gutter depression 'a' from above)alocal =3.00 3.00 inches
Number of Unit Inlets (Grate or Curb Opening) No = 2 2
Water Depth at Flowline (outside of local depression) Ponding Depth = 6.0 6.2 inches
Grate Information MINOR MAJOR
Length of a Unit Grate Lo (G) =N/A N/A feet
Width of a Unit Grate Wo =N/A N/A feet
Area Opening Ratio for a Grate (typical values 0.15-0.90)Aratio =N/A N/A
Clogging Factor for a Single Grate (typical value 0.50 - 0.70)Cf (G) =N/A N/A
Grate Weir Coefficient (typical value 2.15 - 3.60)Cw (G) =N/A N/A
Grate Orifice Coefficient (typical value 0.60 - 0.80)Co (G) =N/A N/A
Curb Opening Information MINOR MAJOR
Length of a Unit Curb Opening Lo (C) =5.00 5.00 feet
Height of Vertical Curb Opening in Inches Hvert =6.00 6.00 inches
Height of Curb Orifice Throat in Inches Hthroat =6.00 6.00 inches
Angle of Throat (see USDCM Figure ST-5) Theta = 63.40 63.40 degrees
Side Width for Depression Pan (typically the gutter width of 2 feet)Wp =2.00 2.00 feet
Clogging Factor for a Single Curb Opening (typical value 0.10)Cf (C) =0.10 0.10
Curb Opening Weir Coefficient (typical value 2.3-3.7)Cw (C) =3.60 3.60
Curb Opening Orifice Coefficient (typical value 0.60 - 0.70)Co (C) =0.67 0.67
Low Head Performance Reduction (Calculated)MINOR MAJOR
Depth for Grate Midwidth dGrate =N/A N/A ft
Depth for Curb Opening Weir Equation dCurb =0.33 0.35 ft
Combination Inlet Performance Reduction Factor for Long Inlets RFCombination =0.57 0.58
Curb Opening Performance Reduction Factor for Long Inlets RFCurb =0.93 0.95
Grated Inlet Performance Reduction Factor for Long Inlets RFGrate =N/A N/A
MINOR MAJOR
Total Inlet Interception Capacity (assumes clogged condition)Qa =10.5 11.4 cfs
Inlet Capacity IS GOOD for Minor and Major Storms(>Q PEAK)Q PEAK REQUIRED =1.7 7.5 cfs
CDOT Type R Curb Opening
INLET IN A SUMP OR SAG LOCATION
Version 4.06 Released August 2018
H-VertH-Curb
W
Lo (C)
Lo (G)
Wo
WP
CDOT Type R Curb Opening
Override Depths
1
GATEWAY AT PROSPECT
APPENDIX
epsgroupinc.com Arizona | Colorado
C.3 Detention Facilities
Gateway at Prospect
Pond ID Tributary Area Interim
Impervious
Final
Impervious
Interim 100-yr
Storage
Interim
WQCV + EURV
Interim Release
Rate
Final 100-yr
Storage
Final
WQCV + EURV
Final Release
Rate
(acre) (%) (%) ac-ft (elev.) ac-ft (elev.) (cfs) ac-ft (elev.) ac-ft (elev.) (cfs)
Pond B 67.23 3% 46% 1.726 (4908.38) 0.152 (4904.54) 96.00 7.07 (TBD)* 2.907 (TBD)* 103.7*
Pond C 21.13 n/a 79% n/a n/a n/a 3.323 (4907.89) 1.638 (4906.47) 26.90
Pond D 2.94 n/a 27% n/a n/a n/a 0.222 (4904.69) 0.072 (4903.97) 4.50
Pond E 4.92 n/a 66% n/a n/a n/a 0.669 (4901.84) 0.314 (4900.70) 9.30
Pond F 12.20 n/a 77% n/a n/a n/a 1.878 (4905.02) 0.92 (4903.84) 14.00
Pond G 7.05 n/a 70% n/a n/a n/a 1.004 (4901.72) 0.48 (4901.04) 11.40
Pond H 16.72 80% 2.658 (TBD)* 1.313 (TBD)* 20.9*
Pond I 4.26 76% 0.648 (4903.13) 0.316 (4901.91) 3.30
* Future required pond volumes and WSELs to be determined at time of development and once pond layout and grading is known.
Pond Summaries
13% 1.067 (4902.80) 0.232 (4901.25) 25.70
Project:
Basin ID:
Depth Increment = 0.20 ft
Watershed Information Top of Micropool -- 0.00 -- -- -- 15 0.000
Selected BMP Type =EDB -- 0.20 -- -- -- 758 0.017 77 0.002
Watershed Area = 67.23 acres -- 0.40 -- -- -- 1,288 0.030 282 0.006
Watershed Length = 2,370 ft -- 0.60 -- -- -- 1,755 0.040 586 0.013
Watershed Length to Centroid = 1,150 ft -- 0.80 -- -- -- 2,266 0.052 988 0.023
Watershed Slope = 0.010 ft/ft -- 1.00 -- -- -- 2,786 0.064 1,493 0.034
Watershed Imperviousness = 3.00% percent -- 1.20 -- -- -- 3,348 0.077 2,107 0.048
Percentage Hydrologic Soil Group A = 0.0% percent -- 1.40 -- -- -- 3,963 0.091 2,838 0.065
Percentage Hydrologic Soil Group B = 0.0% percent -- 1.60 -- -- -- 4,620 0.106 3,696 0.085
Percentage Hydrologic Soil Groups C/D = 100.0% percent -- 1.80 -- -- -- 5,306 0.122 4,689 0.108
Target WQCV Drain Time = 40.0 hours -- 2.00 -- -- -- 6,008 0.138 5,820 0.134
Location for 1-hr Rainfall Depths = User Input -- 2.20 -- -- -- 6,732 0.155 7,094 0.163
-- 2.40 -- -- -- 7,459 0.171 8,513 0.195
-- 2.60 -- -- -- 8,225 0.189 10,082 0.231
Optional User Overrides -- 2.80 -- -- -- 8,975 0.206 11,802 0.271
Water Quality Capture Volume (WQCV) = 0.125 acre-feet acre-feet -- 3.00 -- -- -- 9,812 0.225 13,680 0.314
Excess Urban Runoff Volume (EURV) = 0.152 acre-feet acre-feet -- 3.20 -- -- -- 10,758 0.247 15,737 0.361
2-yr Runoff Volume (P1 = 0.82 in.) = 0.079 acre-feet 0.82 inches -- 3.40 -- -- -- 11,816 0.271 17,995 0.413
5-yr Runoff Volume (P1 = 1.14 in.) = 0.675 acre-feet 1.14 inches -- 3.60 -- -- -- 12,983 0.298 20,475 0.470
10-yr Runoff Volume (P1 = 1.4 in.) = 1.730 acre-feet 1.40 inches -- 3.80 -- -- -- 14,262 0.327 23,199 0.533
25-yr Runoff Volume (P1 = 1.81 in.) = 4.340 acre-feet 1.81 inches -- 4.00 -- -- -- 15,652 0.359 26,191 0.601
50-yr Runoff Volume (P1 = 2.27 in.) = 6.831 acre-feet 2.27 inches -- 4.20 -- -- -- 17,156 0.394 29,471 0.677
100-yr Runoff Volume (P1 = 2.86 in.) = 10.591 acre-feet 2.86 inches -- 4.40 -- -- -- 18,777 0.431 33,065 0.759
500-yr Runoff Volume (P1 = 4.39 in.) = 19.805 acre-feet 4.39 inches -- 4.60 -- -- -- 20,519 0.471 36,994 0.849
Approximate 2-yr Detention Volume = 0.080 acre-feet -- 4.80 -- -- -- 22,395 0.514 41,286 0.948
Approximate 5-yr Detention Volume = 0.406 acre-feet -- 5.00 -- -- -- 24,383 0.560 45,963 1.055
Approximate 10-yr Detention Volume = 0.685 acre-feet -- 5.20 -- -- -- 26,481 0.608 51,050 1.172
Approximate 25-yr Detention Volume = 0.875 acre-feet -- 5.40 -- -- -- 28,701 0.659 56,568 1.299
Approximate 50-yr Detention Volume = 0.956 acre-feet -- 5.60 -- -- -- 31,040 0.713 62,542 1.436
Approximate 100-yr Detention Volume = 1.663 acre-feet -- 5.80 -- -- -- 33,490 0.769 68,995 1.584
-- 6.00 -- -- -- 36,031 0.827 75,947 1.744
Define Zones and Basin Geometry -- 6.20 -- -- -- 38,481 0.883 83,399 1.915
Zone 1 Volume (WQCV) = 0.125 acre-feet -- 6.40 -- -- -- 40,681 0.934 91,315 2.096
Zone 2 Volume (EURV - Zone 1) = 0.027 acre-feet -- 6.60 -- -- -- 42,578 0.977 99,641 2.287
Zone 3 (100yr + 1 / 2 WQCV - Zones 1 & 2) = 1.574 acre-feet -- 7.60 -- -- -- 50,000 1.148 145,929 3.350
Total Detention Basin Volume = 1.726 acre-feet -- -- -- --
Initial Surcharge Volume (ISV) = user ft 3 -- -- -- --
Initial Surcharge Depth (ISD) = user ft -- -- -- --
Total Available Detention Depth (Htotal) =user ft -- -- -- --
Depth of Trickle Channel (HTC) = user ft -- -- -- --
Slope of Trickle Channel (STC) =user ft/ft -- -- -- --
Slopes of Main Basin Sides (Smain) =user H:V -- -- -- --
Basin Length-to-Width Ratio (RL/W) =user -- -- -- --
-- -- -- --
Initial Surcharge Area (AISV) =user ft 2 -- -- -- --
Surcharge Volume Length (LISV) =user ft -- -- -- --
Surcharge Volume Width (WISV) =user ft -- -- -- --
Depth of Basin Floor (HFLOOR) =user ft -- -- -- --
Length of Basin Floor (LFLOOR) =user ft -- -- -- --
Width of Basin Floor (WFLOOR) =user ft -- -- -- --
Area of Basin Floor (AFLOOR) =user ft 2 -- -- -- --
Volume of Basin Floor (VFLOOR) =user ft 3 -- -- -- --
Depth of Main Basin (HMAIN) =user ft -- -- -- --
Length of Main Basin (LMAIN) =user ft -- -- -- --
Width of Main Basin (WMAIN) =user ft -- -- -- --
Area of Main Basin (AMAIN) =user ft 2 -- -- -- --
Volume of Main Basin (VMAIN) =user ft 3 -- -- -- --
Calculated Total Basin Volume (Vtotal) =user acre-feet -- -- -- --
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DETENTION BASIN STAGE-STORAGE TABLE BUILDER
Optional
Override
Area (ft 2)
Length
(ft)
Optional
Override
Stage (ft)
Stage
(ft)
Stage - Storage
Description
Area
(ft 2)
Width
(ft)
Gateway at Prospect
Pond B - Interim
MHFD-Detention, Version 4.06 (July 2022)
Volume
(ft 3)
Volume
(ac-ft)
Area
(acre)
After providing required inputs above including 1-hour rainfall
depths, click 'Run CUHP' to generate runoff hydrographs using
the embedded Colorado Urban Hydrograph Procedure.
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond B (Interim) - Full Spectrum Detention.xlsm, Basin 7/1/2025, 5:40 PM
1 User Defined Stage-Area Booleans for Message
1 Equal Stage-Area Inputs Watershed L:W
1 CountA Watershed Lc:L
Watershed Slope
0 Calc_S_TC Booleans for CUHP
1 CUHP Inputs Complete
H_FLOOR 1 CUHP Results Calculated
L_FLOOR_OTHER
0.00 ISV 0.00 ISV
0.00 Floor 0.00 Floor
1.94 Zone 1 (WQCV) 1.94 Zone 1 (WQCV)
2.14 Zone 2 (EURV) 2.14 Zone 2 (EURV)
5.98 Z3 (100+1/2WQCV)5.98 Z3 (100+1/2WQCV)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
MHFD-Detention, Version 4.06 (July 2022)
0.000
0.840
1.680
2.520
3.360
0.000
0.290
0.580
0.870
1.160
0.00 2.00 4.00 6.00 8.00
Vo
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u
m
e
(
a
c
-
f
t
)
Ar
e
a
(
a
c
r
e
s
)
Stage (ft.)
Area (acres)Volume (ac-ft)
0
12500
25000
37500
50000
0
5
10
15
20
0.00 2.00 4.00 6.00 8.00
Ar
e
a
(
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Le
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W
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Stage (ft)
Length (ft)Width (ft)Area (sq.ft.)
MHFD-Detention_v4-06 Pond B (Interim) - Full Spectrum Detention.xlsm, Basin 7/1/2025, 5:40 PM
Project:
Basin ID:
Estimated Estimated
Stage (ft) Volume (ac-ft) Outlet Type
Zone 1 (WQCV) 1.94 0.125 Orifice Plate
Zone 2 (EURV) 2.14 0.027 Orifice Plate
Z3 (100+1/2WQCV) 5.98 1.574 Weir&Pipe (Restrict)
Total (all zones) 1.726
User Input: Orifice at Underdrain Outlet (typically used to drain WQCV in a Filtration BMP)Calculated Parameters for Underdrain
Underdrain Orifice Invert Depth = N/A ft (distance below the filtration media surface) Underdrain Orifice Area = N/A ft2
Underdrain Orifice Diameter = N/A inches Underdrain Orifice Centroid = N/A feet
User Input: Orifice Plate with one or more orifices or Elliptical Slot Weir (typically used to drain WQCV and/or EURV in a sedimentation BMP)Calculated Parameters for Plate
Centroid of Lowest Orifice = 0.00 ft (relative to basin bottom at Stage = 0 ft) WQ Orifice Area per Row = 5.000E-03 ft2
Depth at top of Zone using Orifice Plate = 2.30 ft (relative to basin bottom at Stage = 0 ft) Elliptical Half-Width = N/A feet
Orifice Plate: Orifice Vertical Spacing = 9.00 inches Elliptical Slot Centroid = N/A feet
Orifice Plate: Orifice Area per Row = 0.72 sq. inches (diameter = 15/16 inch) Elliptical Slot Area = N/A ft2
User Input: Stage and Total Area of Each Orifice Row (numbered from lowest to highest)
Row 1 (required) Row 2 (optional) Row 3 (optional) Row 4 (optional) Row 5 (optional) Row 6 (optional) Row 7 (optional) Row 8 (optional)
Stage of Orifice Centroid (ft) 0.00 0.80 1.60
Orifice Area (sq. inches) 0.72 0.72 0.72
Row 9 (optional) Row 10 (optional) Row 11 (optional) Row 12 (optional) Row 13 (optional) Row 14 (optional) Row 15 (optional) Row 16 (optional)
Stage of Orifice Centroid (ft)
Orifice Area (sq. inches)
User Input: Vertical Orifice (Circular or Rectangular)Calculated Parameters for Vertical Orifice
Not Selected Not Selected Not Selected Not Selected
Invert of Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Area = N/A N/A ft2
Depth at top of Zone using Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Centroid = N/A N/A feet
Vertical Orifice Diameter = N/A N/A inches
User Input: Overflow Weir (Dropbox with Flat or Sloped Grate and Outlet Pipe OR Rectangular/Trapezoidal Weir and No Outlet Pipe) Calculated Parameters for Overflow Weir
grate Zone 3 Weir Not Selected Zone 3 Weir Not Selected
Overflow Weir Front Edge Height, Ho = 2.30 N/A ft (relative to basin bottom at Stage = 0 ft)Height of Grate Upper Edge, Ht =4.30 N/A feet
Overflow Weir Front Edge Length = 11.00 N/A feet Overflow Weir Slope Length = 6.32 N/A feet
Overflow Weir Grate Slope = 3.00 N/A H:V Grate Open Area / 100-yr Orifice Area = 4.24 N/A
Horiz. Length of Weir Sides = 6.00 N/A feet Overflow Grate Open Area w/o Debris = 48.42 N/A ft2
Overflow Grate Type = Type C Grate N/A Overflow Grate Open Area w/ Debris = 48.42 N/A ft2
Debris Clogging % = 0% N/A %
User Input: Outlet Pipe w/ Flow Restriction Plate (Circular Orifice, Restrictor Plate, or Rectangular Orifice)Calculated Parameters for Outlet Pipe w/ Flow Restriction Plate
Zone 3 Restrictor Not Selected Zone 3 Restrictor Not Selected
Depth to Invert of Outlet Pipe = 0.00 N/A ft (distance below basin bottom at Stage = 0 ft)Outlet Orifice Area = 11.43 N/A ft2
Outlet Pipe Diameter = 48.00 N/A inches Outlet Orifice Centroid = 1.84 N/A feet
Restrictor Plate Height Above Pipe Invert = 41.00 inches Half-Central Angle of Restrictor Plate on Pipe = 2.36 N/A radians
User Input: Emergency Spillway (Rectangular or Trapezoidal)Calculated Parameters for Spillway
Spillway Invert Stage= 6.00 ft (relative to basin bottom at Stage = 0 ft) Spillway Design Flow Depth= 0.39 feet
Spillway Crest Length = 130.00 feet Stage at Top of Freeboard = 6.89 feet
Spillway End Slopes = 30.00 H:V Basin Area at Top of Freeboard = 1.03 acres
Freeboard above Max Water Surface = 0.50 feet Basin Volume at Top of Freeboard = 2.58 acre-ft
Max Ponding Depth of Target Storage Volume =5.44 feet Discharge at Top of Freeboard = 505.00 cfs
Routed Hydrograph Results
Design Storm Return Period =WQCV EURV 2 Year 5 Year 10 Year 25 Year 50 Year 100 Year 500 Year
One-Hour Rainfall Depth (in) =N/A N/A 0.82 1.14 1.40 1.81 2.27 2.86 4.39
CUHP Runoff Volume (acre-ft) =0.125 0.152 0.079 0.675 1.730 4.340 6.831 10.591 19.805
Inflow Hydrograph Volume (acre-ft) =N/A N/A 0.079 0.675 1.730 4.340 6.831 10.591 19.805
CUHP Predevelopment Peak Q (cfs) =N/A N/A 0.6 7.6 18.5 45.9 69.4 103.5 183.2
OPTIONAL Override Predevelopment Peak Q (cfs) =N/A N/A
Predevelopment Unit Peak Flow, q (cfs/acre) =N/A N/A 0.01 0.11 0.27 0.68 1.03 1.54 2.72
Peak Inflow Q (cfs) =N/A N/A 0.9 8.0 18.9 46.3 69.8 103.9 183.5
Peak Outflow Q (cfs) =0.1 0.1 0.0 4.8 15.3 42.0 64.0 96.0 187.3
Ratio Peak Outflow to Predevelopment Q =N/A N/A N/A 0.6 0.8 0.9 0.9 0.9 1.0
Structure Controlling Flow =Plate Plate Plate Overflow Weir 1 Overflow Weir 1 Overflow Weir 1 Overflow Weir 1 Overflow Weir 1 Spillway
Max Velocity through Grate 1 (fps) =N/A N/A N/A 0.1 0.3 0.9 1.3 2.0 2.4
Max Velocity through Grate 2 (fps) =N/A N/A N/A N/A N/A N/A N/A N/A N/A
Time to Drain 97% of Inflow Volume (hours) =39 42 32 40 29 12 4 3 3
Time to Drain 99% of Inflow Volume (hours) =41 45 34 49 42 31 25 17 4
Maximum Ponding Depth (ft) =1.94 2.13 1.45 2.84 3.39 4.25 4.79 5.44 6.31
Area at Maximum Ponding Depth (acres) =0.13 0.15 0.09 0.21 0.27 0.40 0.51 0.67 0.91
Maximum Volume Stored (acre-ft) =0.125 0.152 0.070 0.277 0.410 0.696 0.943 1.325 2.004
The user can override the default CUHP hydrographs and runoff volumes by entering new values in the Inflow Hydrographs table (Columns W through AF).
DETENTION BASIN OUTLET STRUCTURE DESIGN
MHFD-Detention, Version 4.06 (July 2022)
Gateway at Prospect
Pond B - Interim
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond B (Interim) - Full Spectrum Detention.xlsm, Outlet Structure 7/1/2025, 5:39 PM
COUNTA for Basin Tab = 1 Ao Dia WQ Plate Type Vert Orifice 1Vert Orifice 2
Count_Underdrain = 0 0.11(diameter = 3/8 inch)2 1 1
Count_WQPlate = 1 0.14(diameter = 7/16 inch)
Count_VertOrifice1 = 0 0.18(diameter = 1/2 inch)Outlet Plate 1 Outlet Plate 2 Drain Time Message Boolean
Count_VertOrifice2 = 0 0.24(diameter = 9/16 inch)4 1 5yr, <72hr 0
Count_Weir1 = 1 0.29(diameter = 5/8 inch)>5yr, <120hr 0
Count_Weir2 = 0 0.36(diameter = 11/16 inch)Max Depth Row
Count_OutletPipe1 = 1 0.42(diameter = 3/4 inch)WQCV 195
Count_OutletPipe2 = 0 0.50(diameter = 13/16 inch)2 Year 146
COUNTA_2 (Standard FSD Setup)= 1 0.58(diameter = 7/8 inch)EURV 214
Hidden Parameters & Calculations 0.67(diameter = 15/16 inch)5 Year 285
MaxPondDepth_Error? FALSE 0.76 (diameter = 1 inch)10 Year 340 Spillway Depth
Cd_Broad-Crested Weir 3.00 0.86(diameter = 1-1/16 inches)25 Year 426 0.39
WQ Plate Flow at 100yr depth = 0.16 0.97(diameter = 1-1/8 inches)50 Year 480
CLOG #1= 100% 1.08(diameter = 1-3/16 inches)100 Year 545 1 Z1_Boolean
n*Cdw #1 = 0.18 1.20(diameter = 1-1/4 inches)500 Year 632 1 Z2_Boolean
n*Cdo #1 = 1.78 1.32(diameter = 1-5/16 inches)Zone3_Pulldown Message 1 Z3_Boolean
Overflow Weir #1 Angle = 0.322 1.45(diameter = 1-3/8 inches)1 Opening Message
CLOG #2= N/A 1.59(diameter = 1-7/16 inches)Draintime Running
n*Cdw #2 = N/A 1.73(diameter = 1-1/2 inches)Outlet Boolean Outlet Rank Total (1 to 4)
n*Cdo #2 = N/A 1.88(diameter = 1-9/16 inches)Vertical Orifice 1 0 0 1
Overflow Weir #2 Angle = N/A 2.03(diameter = 1-5/8 inches)Vertical Orifice 2 0 0 Boolean
Underdrain Q at 100yr depth = 0.00 2.20(diameter = 1-11/16 inches)Overflow Weir 1 1 1 0 Max Depth
VertOrifice1 Q at 100yr depth = 0.00 2.36(diameter = 1-3/4 inches)Overflow Weir 2 0 0 0 500yr Depth
VertOrifice2 Q at 100yr depth = 0.00 2.54(diameter = 1-13/16 inches)Outlet Pipe 1 1 1 0 Freeboard
2.72(diameter = 1-7/8 inches)Outlet Pipe 2 0 0 1 Spillway
Count_User_Hydrographs 0 2.90(diameter = 1-15/16 inches)0 Spillway Length
CountA_3 (EURV & 100yr) = 1 3.09(diameter = 2 inches)FALSE Time Interval
CountA_4 (100yr Only) = 1 3.29(use rectangular openings)Button Visibility Boolean
COUNTA_5 (FSD Weir Only)= 0 0 WQCV Underdrain
COUNTA_6 (EURV Weir Only)= 1 1 WQCV Plate
0 EURV-WQCV Plate
Outlet1_Pulldown_Boolean 0 EURV-WQCV VertOriice
Outlet2_Pulldown_Boolean 1 Outlet 90% Qpeak
Outlet3_Pulldown_Boolean 0 Outlet Undetained
0 Weir Only 90% Qpeak
0 Five Year Ratio Plate
0 Five Year Ratio VertOrifice
EURV_draintime_user
Spillway Options
Offset
Overlapping
S-A-V-D Chart Axis Default X-axis Left Y-Axis Right Y-Axis
minimum bound 0.00 0 0
maximum bound 8.00 120,000 510
S-A-V-D Chart Axis Override X-axis Left Y-Axis Right Y-Axis
minimum bound
maximum bound
MHFD-Detention, Version 4.06 (July 2022)
DETENTION BASIN OUTLET STRUCTURE DESIGN
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PONDING DEPTH [ft]
User Area [ft^2]
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Outflow [cfs]
Summary Outflow [cfs]
MHFD-Detention_v4-06 Pond B (Interim) - Full Spectrum Detention.xlsm, Outlet Structure 7/1/2025, 5:39 PM
Project:
Basin ID:
Depth Increment = 0.10 ft
Watershed Information Top of Micropool 0.00 17.8 17.8 318 0.007
Selected BMP Type =EDB ISV 0.45 17.8 17.8 318 0.007 143 0.003
Watershed Area = 67.23 acres 0.50 17.8 17.8 318 0.007 159 0.004
Watershed Length = 2,370 ft 0.60 17.8 17.8 318 0.007 191 0.004
Watershed Length to Centroid = 1,150 ft 0.70 17.8 17.8 318 0.007 223 0.005
Watershed Slope = 0.015 ft/ft 0.80 17.8 17.8 318 0.007 255 0.006
Watershed Imperviousness = 46.00% percent 0.90 17.8 17.8 318 0.007 286 0.007
Percentage Hydrologic Soil Group A = 0.0% percent 1.00 28.1 21.8 613 0.014 325 0.007
Percentage Hydrologic Soil Group B = 0.0% percent 1.10 48.6 29.8 1,450 0.033 426 0.010
Percentage Hydrologic Soil Groups C/D = 100.0% percent 1.20 69.1 37.8 2,614 0.060 626 0.014
Target WQCV Drain Time = 40.0 hours 1.30 89.6 45.8 4,107 0.094 959 0.022
Location for 1-hr Rainfall Depths = Thornton - Civic Center 1.40 110.1 53.8 5,927 0.136 1,458 0.033
1.50 130.6 61.8 8,075 0.185 2,156 0.049
1.60 151.1 69.8 10,552 0.242 3,084 0.071
Optional User Overrides 1.70 171.6 77.8 13,356 0.307 4,277 0.098
Water Quality Capture Volume (WQCV) = 1.096 acre-feet acre-feet 1.80 192.1 85.8 16,488 0.379 5,766 0.132
Excess Urban Runoff Volume (EURV) = 2.906 acre-feet acre-feet 1.90 212.6 93.8 19,949 0.458 7,586 0.174
2-yr Runoff Volume (P1 = 0.82 in.) = 1.881 acre-feet 0.82 inches 2.00 233.1 101.8 23,737 0.545 9,767 0.224
5-yr Runoff Volume (P1 = 1.14 in.) = 3.138 acre-feet 1.14 inches 2.10 253.6 109.8 27,854 0.639 12,344 0.283
10-yr Runoff Volume (P1 = 1.4 in.) = 4.449 acre-feet 1.40 inches 2.20 274.1 117.8 32,298 0.741 15,349 0.352
25-yr Runoff Volume (P1 = 1.81 in.) = 6.992 acre-feet 1.81 inches 2.30 294.6 125.8 37,070 0.851 18,814 0.432
50-yr Runoff Volume (P1 = 2.27 in.) = 9.650 acre-feet 2.27 inches 2.40 315.1 133.8 42,171 0.968 22,774 0.523
100-yr Runoff Volume (P1 = 2.86 in.) = 13.328 acre-feet 2.86 inches 2.50 335.6 141.8 47,599 1.093 27,260 0.626
500-yr Runoff Volume (P1 = 4.39 in.) = 22.605 acre-feet 4.39 inches 2.60 356.1 149.8 53,355 1.225 32,305 0.742
Approximate 2-yr Detention Volume = 1.760 acre-feet 2.70 376.6 157.8 59,440 1.365 37,942 0.871
Approximate 5-yr Detention Volume = 2.942 acre-feet 2.80 397.1 165.8 65,852 1.512 44,203 1.015
Approximate 10-yr Detention Volume = 3.534 acre-feet Zone 1 (WQCV)2.86 409.4 170.6 69,857 1.604 48,274 1.108
Approximate 25-yr Detention Volume = 4.349 acre-feet 2.90 417.6 173.8 72,593 1.666 51,123 1.174
Approximate 50-yr Detention Volume = 5.032 acre-feet Floor 2.91 419.6 174.6 73,285 1.682 51,852 1.190
Approximate 100-yr Detention Volume = 6.522 acre-feet 3.00 420.5 175.5 73,820 1.695 58,472 1.342
3.10 421.5 176.5 74,417 1.708 65,884 1.512
Define Zones and Basin Geometry 3.20 422.5 177.5 75,016 1.722 73,356 1.684
Zone 1 Volume (WQCV) = 1.096 acre-feet 3.30 423.5 178.5 75,618 1.736 80,887 1.857
Zone 2 Volume (EURV - Zone 1) = 1.811 acre-feet 3.40 424.5 179.5 76,221 1.750 88,479 2.031
Zone 3 (100yr + 1 / 2 WQCV - Zones 1 & 2) = 4.163 acre-feet 3.50 425.5 180.5 76,826 1.764 96,131 2.207
Total Detention Basin Volume = 7.070 acre-feet 3.60 426.5 181.5 77,433 1.778 103,844 2.384
Initial Surcharge Volume (ISV) = 143 ft 3 3.70 427.5 182.5 78,042 1.792 111,618 2.562
Initial Surcharge Depth (ISD) = 0.45 ft 3.80 428.5 183.5 78,653 1.806 119,453 2.742
Total Available Detention Depth (Htotal) =6.00 ft Zone 2 (EURV)3.90 429.5 184.5 79,266 1.820 127,349 2.924
Depth of Trickle Channel (HTC) = 0.50 ft 4.00 430.5 185.5 79,881 1.834 135,306 3.106
Slope of Trickle Channel (STC) =0.005 ft/ft 4.10 431.5 186.5 80,498 1.848 143,325 3.290
Slopes of Main Basin Sides (Smain) =5 H:V 4.20 432.5 187.5 81,117 1.862 151,406 3.476
Basin Length-to-Width Ratio (RL/W) =2.5 4.30 433.5 188.5 81,738 1.876 159,548 3.663
4.40 434.5 189.5 82,361 1.891 167,753 3.851
Initial Surcharge Area (AISV) =318 ft 2 4.50 435.5 190.5 82,986 1.905 176,021 4.041
Surcharge Volume Length (LISV) =17.8 ft 4.60 436.5 191.5 83,614 1.920 184,351 4.232
Surcharge Volume Width (WISV) =17.8 ft 4.70 437.5 192.5 84,243 1.934 192,744 4.425
Depth of Basin Floor (HFLOOR) =1.96 ft 4.80 438.5 193.5 84,874 1.948 201,199 4.619
Length of Basin Floor (LFLOOR) =419.6 ft 4.90 439.5 194.5 85,507 1.963 209,718 4.814
Width of Basin Floor (WFLOOR) =174.6 ft 5.00 440.5 195.5 86,142 1.978 218,301 5.011
Area of Basin Floor (AFLOOR) =73,285 ft 2 5.10 441.5 196.5 86,779 1.992 226,947 5.210
Volume of Basin Floor (VFLOOR) =51,242 ft 3 5.20 442.5 197.5 87,418 2.007 235,657 5.410
Depth of Main Basin (HMAIN) =3.09 ft 5.30 443.5 198.5 88,059 2.022 244,430 5.611
Length of Main Basin (LMAIN) =450.5 ft 5.40 444.5 199.5 88,702 2.036 253,269 5.814
Width of Main Basin (WMAIN) =205.5 ft 5.50 445.5 200.5 89,347 2.051 262,171 6.019
Area of Main Basin (AMAIN) =92,603 ft 2 5.60 446.5 201.5 89,994 2.066 271,138 6.224
Volume of Main Basin (VMAIN) =255,715 ft 3 5.70 447.5 202.5 90,643 2.081 280,170 6.432
Calculated Total Basin Volume (Vtotal) =7.054 acre-feet 5.80 448.5 203.5 91,294 2.096 289,267 6.641
5.90 449.5 204.5 91,948 2.111 298,429 6.851
6.00 450.5 205.5 92,603 2.126 307,656 7.063
Z3 (100+1/2WQCV)6.01 450.6 205.6 92,668 2.127 308,583 7.084
6.10 451.5 206.5 93,260 2.141 316,949 7.276
6.20 452.5 207.5 93,919 2.156 326,308 7.491
6.30 453.5 208.5 94,580 2.171 335,733 7.707
6.40 454.5 209.5 95,243 2.186 345,224 7.925
6.50 455.5 210.5 95,908 2.202 354,782 8.145
6.60 456.5 211.5 96,575 2.217 364,406 8.366
6.70 457.5 212.5 97,244 2.232 374,097 8.588
6.80 458.5 213.5 97,915 2.248 383,855 8.812
6.90 459.5 214.5 98,588 2.263 393,680 9.038
7.00 460.5 215.5 99,263 2.279 403,573 9.265
7.10 461.5 216.5 99,940 2.294 413,533 9.493
7.20 462.5 217.5 100,619 2.310 423,561 9.724
7.30 463.5 218.5 101,301 2.326 433,657 9.955
7.40 464.5 219.5 101,984 2.341 443,821 10.189
7.50 465.5 220.5 102,669 2.357 454,054 10.424
7.60 466.5 221.5 103,356 2.373 464,355 10.660
7.70 467.5 222.5 104,045 2.389 474,725 10.898
7.80 468.5 223.5 104,736 2.404 485,164 11.138
7.90 469.5 224.5 105,429 2.420 495,672 11.379
8.00 470.5 225.5 106,124 2.436 506,250 11.622
8.10 471.5 226.5 106,821 2.452 516,897 11.866
8.20 472.5 227.5 107,520 2.468 527,614 12.112
8.30 473.5 228.5 108,221 2.484 538,401 12.360
8.40 474.5 229.5 108,924 2.501 549,258 12.609
8.50 475.5 230.5 109,629 2.517 560,186 12.860
8.60 476.5 231.5 110,337 2.533 571,184 13.113
8.70 477.5 232.5 111,046 2.549 582,253 13.367
8.80 478.5 233.5 111,757 2.566 593,393 13.622
8.90 479.5 234.5 112,470 2.582 604,605 13.880
9.00 480.5 235.5 113,185 2.598 615,887 14.139
9.10 481.5 236.5 113,902 2.615 627,242 14.399
9.20 482.5 237.5 114,621 2.631 638,668 14.662
9.30 483.5 238.5 115,342 2.648 650,166 14.926
9.40 484.5 239.5 116,065 2.664 661,736 15.191
9.50 485.5 240.5 116,790 2.681 673,379 15.459
9.60 486.5 241.5 117,517 2.698 685,095 15.728
9.70 487.5 242.5 118,246 2.715 696,883 15.998
9.80 488.5 243.5 118,977 2.731 708,744 16.271
After providing required inputs above including 1-hour rainfall
depths, click 'Run CUHP' to generate runoff hydrographs using
the embedded Colorado Urban Hydrograph Procedure.
Volume
(ft 3)
Volume
(ac-ft)
Area
(acre)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
Optional
Override
Area (ft 2)
Length
(ft)
Optional
Override
Stage (ft)
Stage
(ft)
Stage - Storage
Description
Area
(ft 2)
Width
(ft)
Gateway at Prospect
Pond B - Future
MHFD-Detention, Version 4.06 (July 2022)
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond B (Future) - Full Spectrum Detention.xlsm, Basin 6/26/2025, 10:23 AM
0 User Defined Stage-Area Booleans for Message
0 Equal Stage-Area Inputs Watershed L:W
1 CountA Watershed Lc:L
Watershed Slope
0 Calc_S_TC Booleans for CUHP
1 CUHP Inputs Complete
1.96 H_FLOOR 1 CUHP Results Calculated
L_FLOOR_OTHER
0.45 ISV 0.45 ISV
2.91 Floor 2.86 Zone 1 (WQCV)
2.86 Zone 1 (WQCV) 2.91 Floor
3.90 Zone 2 (EURV) 3.90 Zone 2 (EURV)
6.01 Z3 (100+1/2WQCV)6.01 Z3 (100+1/2WQCV)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
MHFD-Detention, Version 4.06 (July 2022)
0.000
4.070
8.140
12.210
16.280
0.000
0.685
1.370
2.055
2.740
0.00 2.50 5.00 7.50 10.00
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MHFD-Detention_v4-06 Pond B (Future) - Full Spectrum Detention.xlsm, Basin 6/26/2025, 10:23 AM
Project:
Basin ID:
Estimated Estimated
Stage (ft) Volume (ac-ft) Outlet Type
Zone 1 (WQCV) 2.86 1.096 Orifice Plate
Zone 2 (EURV) 3.90 1.811 Orifice Plate
Z3 (100+1/2WQCV) 6.01 4.163 Weir&Pipe (Restrict)
Total (all zones) 7.070
User Input: Orifice at Underdrain Outlet (typically used to drain WQCV in a Filtration BMP)Calculated Parameters for Underdrain
Underdrain Orifice Invert Depth = N/A ft (distance below the filtration media surface) Underdrain Orifice Area = N/A ft2
Underdrain Orifice Diameter = N/A inches Underdrain Orifice Centroid = N/A feet
User Input: Orifice Plate with one or more orifices or Elliptical Slot Weir (typically used to drain WQCV and/or EURV in a sedimentation BMP)Calculated Parameters for Plate
Centroid of Lowest Orifice = 0.00 ft (relative to basin bottom at Stage = 0 ft) WQ Orifice Area per Row = N/A ft2
Depth at top of Zone using Orifice Plate = 3.90 ft (relative to basin bottom at Stage = 0 ft) Elliptical Half-Width = N/A feet
Orifice Plate: Orifice Vertical Spacing = 16.00 inches Elliptical Slot Centroid = N/A feet
Orifice Plate: Orifice Area per Row = N/A sq. inches Elliptical Slot Area = N/A ft2
User Input: Stage and Total Area of Each Orifice Row (numbered from lowest to highest)
Row 1 (required) Row 2 (optional) Row 3 (optional) Row 4 (optional) Row 5 (optional) Row 6 (optional) Row 7 (optional) Row 8 (optional)
Stage of Orifice Centroid (ft) 0.00 1.30 2.60
Orifice Area (sq. inches) 3.80 3.80 9.00
Row 9 (optional) Row 10 (optional) Row 11 (optional) Row 12 (optional) Row 13 (optional) Row 14 (optional) Row 15 (optional) Row 16 (optional)
Stage of Orifice Centroid (ft)
Orifice Area (sq. inches)
User Input: Vertical Orifice (Circular or Rectangular)Calculated Parameters for Vertical Orifice
Not Selected Not Selected Not Selected Not Selected
Invert of Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Area = N/A N/A ft2
Depth at top of Zone using Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Centroid = N/A N/A feet
Vertical Orifice Diameter = N/A N/A inches
User Input: Overflow Weir (Dropbox with Flat or Sloped Grate and Outlet Pipe OR Rectangular/Trapezoidal Weir and No Outlet Pipe) Calculated Parameters for Overflow Weir
grate Zone 3 Weir Not Selected Zone 3 Weir Not Selected
Overflow Weir Front Edge Height, Ho = 3.90 N/A ft (relative to basin bottom at Stage = 0 ft)Height of Grate Upper Edge, Ht =4.90 N/A feet
Overflow Weir Front Edge Length = 20.00 N/A feet Overflow Weir Slope Length = 6.08 N/A feet
Overflow Weir Grate Slope = 6.00 N/A H:V Grate Open Area / 100-yr Orifice Area = 7.74 N/A
Horiz. Length of Weir Sides = 6.00 N/A feet Overflow Grate Open Area w/o Debris = 84.67 N/A ft2
Overflow Grate Type = Type C Grate N/A Overflow Grate Open Area w/ Debris = 84.67 N/A ft2
Debris Clogging % = 0% N/A %
User Input: Outlet Pipe w/ Flow Restriction Plate (Circular Orifice, Restrictor Plate, or Rectangular Orifice)Calculated Parameters for Outlet Pipe w/ Flow Restriction Plate
Zone 3 Restrictor Not Selected Zone 3 Restrictor Not Selected
Depth to Invert of Outlet Pipe = 0.00 N/A ft (distance below basin bottom at Stage = 0 ft)Outlet Orifice Area = 10.94 N/A ft2
Outlet Pipe Diameter = 48.00 N/A inches Outlet Orifice Centroid = 1.77 N/A feet
Restrictor Plate Height Above Pipe Invert = 39.00 inches Half-Central Angle of Restrictor Plate on Pipe = 2.25 N/A radians
User Input: Emergency Spillway (Rectangular or Trapezoidal)Calculated Parameters for Spillway
Spillway Invert Stage= 7.00 ft (relative to basin bottom at Stage = 0 ft) Spillway Design Flow Depth= 0.58 feet
Spillway Crest Length = 130.00 feet Stage at Top of Freeboard = 8.08 feet
Spillway End Slopes = 30.00 H:V Basin Area at Top of Freeboard = 2.45 acres
Freeboard above Max Water Surface = 0.50 feet Basin Volume at Top of Freeboard = 11.82 acre-ft
Max Ponding Depth of Target Storage Volume =5.65 feet Discharge at Top of Freeboard = 657.28 cfs
Routed Hydrograph Results
Design Storm Return Period =WQCV EURV 2 Year 5 Year 10 Year 25 Year 50 Year 100 Year 500 Year
One-Hour Rainfall Depth (in) =N/A N/A 0.82 1.14 1.40 1.81 2.27 2.86 4.39
CUHP Runoff Volume (acre-ft) =1.096 2.906 1.881 3.138 4.449 6.992 9.650 13.328 22.605
Inflow Hydrograph Volume (acre-ft) =N/A N/A 1.881 3.138 4.449 6.992 9.650 13.328 22.605
CUHP Predevelopment Peak Q (cfs) =N/A N/A 0.6 8.3 20.2 49.3 74.8 110.9 196.9
OPTIONAL Override Predevelopment Peak Q (cfs) =N/A N/A
Predevelopment Unit Peak Flow, q (cfs/acre) =N/A N/A 0.01 0.12 0.30 0.73 1.11 1.65 2.93
Peak Inflow Q (cfs) =N/A N/A 25.6 44.2 63.2 104.7 143.0 195.5 325.0
Peak Outflow Q (cfs) =0.5 0.8 0.6 1.1 11.5 41.7 74.0 103.7 202.1
Ratio Peak Outflow to Predevelopment Q =N/A N/A N/A 0.1 0.6 0.8 1.0 0.9 1.0
Structure Controlling Flow =Plate Overflow Weir 1 Plate Overflow Weir 1 Overflow Weir 1 Overflow Weir 1 Overflow Weir 1 Outlet Plate 1 Spillway
Max Velocity through Grate 1 (fps) =N/A N/A N/A 0.0 0.1 0.5 0.9 1.2 1.5
Max Velocity through Grate 2 (fps) =N/A N/A N/A N/A N/A N/A N/A N/A N/A
Time to Drain 97% of Inflow Volume (hours) =38 68 53 71 71 68 64 60 50
Time to Drain 99% of Inflow Volume (hours) =40 71 56 75 75 74 73 71 68
Maximum Ponding Depth (ft) =2.86 3.90 3.25 3.93 4.25 4.71 5.05 5.65 7.33
Area at Maximum Ponding Depth (acres) =1.60 1.82 1.73 1.82 1.87 1.94 1.98 2.07 2.33
Maximum Volume Stored (acre-ft) =1.108 2.924 1.753 2.978 3.569 4.444 5.091 6.307 10.002
The user can override the default CUHP hydrographs and runoff volumes by entering new values in the Inflow Hydrographs table (Columns W through AF).
DETENTION BASIN OUTLET STRUCTURE DESIGN
MHFD-Detention, Version 4.06 (July 2022)
Gateway at Prospect
Pond B - Future
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond B (Future) - Full Spectrum Detention.xlsm, Outlet Structure 7/1/2025, 5:21 PM
COUNTA for Basin Tab = 1 Ao Dia WQ Plate Type Vert Orifice 1Vert Orifice 2
Count_Underdrain = 0 0.11(diameter = 3/8 inch)2 1 1
Count_WQPlate = 1 0.14(diameter = 7/16 inch)
Count_VertOrifice1 = 0 0.18(diameter = 1/2 inch)Outlet Plate 1 Outlet Plate 2 Drain Time Message Boolean
Count_VertOrifice2 = 0 0.24(diameter = 9/16 inch)4 1 5yr, <72hr 0
Count_Weir1 = 1 0.29(diameter = 5/8 inch)>5yr, <120hr 0
Count_Weir2 = 0 0.36(diameter = 11/16 inch)Max Depth Row
Count_OutletPipe1 = 1 0.42(diameter = 3/4 inch)WQCV 287
Count_OutletPipe2 = 0 0.50(diameter = 13/16 inch)2 Year 326
COUNTA_2 (Standard FSD Setup)= 1 0.58(diameter = 7/8 inch)EURV 391
Hidden Parameters & Calculations 0.67(diameter = 15/16 inch)5 Year 394
MaxPondDepth_Error? FALSE 0.76 (diameter = 1 inch)10 Year 426 Spillway Depth
Cd_Broad-Crested Weir 3.00 0.86(diameter = 1-1/16 inches)25 Year 472 0.58
WQ Plate Flow at 100yr depth = 1.09 0.97(diameter = 1-1/8 inches)50 Year 506
CLOG #1= 100% 1.08(diameter = 1-3/16 inches)100 Year 566 1 Z1_Boolean
n*Cdw #1 = 0.44 1.20(diameter = 1-1/4 inches)500 Year 734 1 Z2_Boolean
n*Cdo #1 = 1.17 1.32(diameter = 1-5/16 inches)Zone3_Pulldown Message 1 Z3_Boolean
Overflow Weir #1 Angle = 0.165 1.45(diameter = 1-3/8 inches)1 Opening Message
CLOG #2= N/A 1.59(diameter = 1-7/16 inches)Draintime Running
n*Cdw #2 = N/A 1.73(diameter = 1-1/2 inches)Outlet Boolean Outlet Rank Total (1 to 4)
n*Cdo #2 = N/A 1.88(diameter = 1-9/16 inches)Vertical Orifice 1 0 0 1
Overflow Weir #2 Angle = N/A 2.03(diameter = 1-5/8 inches)Vertical Orifice 2 0 0 Boolean
Underdrain Q at 100yr depth = 0.00 2.20(diameter = 1-11/16 inches)Overflow Weir 1 1 1 0 Max Depth
VertOrifice1 Q at 100yr depth = 0.00 2.36(diameter = 1-3/4 inches)Overflow Weir 2 0 0 0 500yr Depth
VertOrifice2 Q at 100yr depth = 0.00 2.54(diameter = 1-13/16 inches)Outlet Pipe 1 1 1 0 Freeboard
2.72(diameter = 1-7/8 inches)Outlet Pipe 2 0 0 1 Spillway
Count_User_Hydrographs 0 2.90(diameter = 1-15/16 inches)0 Spillway Length
CountA_3 (EURV & 100yr) = 1 3.09(diameter = 2 inches)FALSE Time Interval
CountA_4 (100yr Only) = 1 3.29(use rectangular openings)Button Visibility Boolean
COUNTA_5 (FSD Weir Only)= 0 0 WQCV Underdrain
COUNTA_6 (EURV Weir Only)= 1 1 WQCV Plate
0 EURV-WQCV Plate
Outlet1_Pulldown_Boolean 0 EURV-WQCV VertOriice
Outlet2_Pulldown_Boolean 1 Outlet 90% Qpeak
Outlet3_Pulldown_Boolean 0 Outlet Undetained
0 Weir Only 90% Qpeak
0 Five Year Ratio Plate
0 Five Year Ratio VertOrifice
EURV_draintime_user
Spillway Options
Offset
Overlapping
S-A-V-D Chart Axis Default X-axis Left Y-Axis Right Y-Axis
minimum bound 0.00 0 0
maximum bound 10.00 520,000 660
S-A-V-D Chart Axis Override X-axis Left Y-Axis Right Y-Axis
minimum bound
maximum bound
MHFD-Detention, Version 4.06 (July 2022)
DETENTION BASIN OUTLET STRUCTURE DESIGN
0
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Volume [ft^3]
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Outflow [cfs]
Summary Outflow [cfs]
MHFD-Detention_v4-06 Pond B (Future) - Full Spectrum Detention.xlsm, Outlet Structure 7/1/2025, 5:21 PM
Project:
Basin ID:
Depth Increment = 0.20 ft
Watershed Information Top of Micropool -- 0.00 -- -- -- 14 0.000
Selected BMP Type =EDB -- 0.20 -- -- -- 1,865 0.043 170 0.004
Watershed Area = 21.13 acres -- 0.40 -- -- -- 4,172 0.096 750 0.017
Watershed Length = 1,750 ft -- 0.60 -- -- -- 7,183 0.165 1,927 0.044
Watershed Length to Centroid = 850 ft -- 0.80 -- -- -- 9,767 0.224 3,622 0.083
Watershed Slope = 0.015 ft/ft -- 1.00 -- -- -- 12,333 0.283 5,832 0.134
Watershed Imperviousness = 79.00% percent -- 1.20 -- -- -- 15,138 0.348 8,428 0.193
Percentage Hydrologic Soil Group A = 0.0% percent -- 1.40 -- -- -- 17,964 0.412 11,710 0.269
Percentage Hydrologic Soil Group B = 0.0% percent -- 1.60 -- -- -- 19,986 0.459 15,684 0.360
Percentage Hydrologic Soil Groups C/D = 100.0% percent -- 1.80 -- -- -- 22,042 0.506 19,887 0.457
Target WQCV Drain Time = 40.0 hours -- 2.00 -- -- -- 24,117 0.554 24,503 0.563
Location for 1-hr Rainfall Depths = User Input -- 2.01 -- -- -- 24,224 0.556 24,745 0.568
-- 2.20 -- -- -- 26,255 0.603 29,278 0.672
-- 2.40 -- -- -- 28,496 0.654 34,731 0.797
Optional User Overrides -- 2.60 -- -- -- 30,484 0.700 40,913 0.939
Water Quality Capture Volume (WQCV) = 0.567 acre-feet acre-feet -- 2.80 -- -- -- 32,585 0.748 47,220 1.084
Excess Urban Runoff Volume (EURV) = 1.638 acre-feet acre-feet -- 3.00 -- -- -- 34,807 0.799 53,959 1.239
2-yr Runoff Volume (P1 = 0.82 in.) = 1.076 acre-feet 0.82 inches -- 3.20 -- -- -- 37,206 0.854 60,789 1.396
5-yr Runoff Volume (P1 = 1.14 in.) = 1.610 acre-feet 1.14 inches -- 3.40 -- -- -- 39,975 0.918 68,480 1.572
10-yr Runoff Volume (P1 = 1.4 in.) = 2.076 acre-feet 1.40 inches -- 3.60 -- -- -- 42,839 0.983 77,160 1.771
25-yr Runoff Volume (P1 = 1.81 in.) = 2.863 acre-feet 1.81 inches -- 3.80 -- -- -- 45,495 1.044 85,994 1.974
50-yr Runoff Volume (P1 = 2.27 in.) = 3.728 acre-feet 2.27 inches -- 4.00 -- -- -- 48,322 1.109 95,375 2.190
100-yr Runoff Volume (P1 = 2.86 in.) = 4.867 acre-feet 2.86 inches -- 4.20 -- -- -- 51,345 1.179 104,829 2.407
500-yr Runoff Volume (P1 = 4.39 in.) = 7.790 acre-feet 4.39 inches -- 4.40 -- -- -- 54,508 1.251 115,383 2.649
Approximate 2-yr Detention Volume = 1.021 acre-feet -- 4.60 -- -- -- 58,077 1.333 127,186 2.920
Approximate 5-yr Detention Volume = 1.537 acre-feet -- 4.80 -- -- -- 62,331 1.431 139,227 3.196
Approximate 10-yr Detention Volume = 1.863 acre-feet -- 5.00 -- -- -- 66,137 1.518 152,073 3.491
Approximate 25-yr Detention Volume = 2.234 acre-feet -- 5.20 -- -- -- 70,281 1.613 165,715 3.804
Approximate 50-yr Detention Volume = 2.551 acre-feet -- 6.40 -- -- -- 102,601 2.355 269,444 6.186
Approximate 100-yr Detention Volume = 3.039 acre-feet -- -- -- --
-- -- -- --
Define Zones and Basin Geometry -- -- -- --
Zone 1 Volume (WQCV) = 0.567 acre-feet -- -- -- --
Zone 2 Volume (EURV - Zone 1) = 1.071 acre-feet -- -- -- --
Zone 3 (100yr + 1 / 2 WQCV - Zones 1 & 2) = 1.685 acre-feet -- -- -- --
Total Detention Basin Volume = 3.323 acre-feet -- -- -- --
Initial Surcharge Volume (ISV) = user ft 3 -- -- -- --
Initial Surcharge Depth (ISD) = user ft -- -- -- --
Total Available Detention Depth (Htotal) =user ft -- -- -- --
Depth of Trickle Channel (HTC) = user ft -- -- -- --
Slope of Trickle Channel (STC) =user ft/ft -- -- -- --
Slopes of Main Basin Sides (Smain) =user H:V -- -- -- --
Basin Length-to-Width Ratio (RL/W) =user -- -- -- --
-- -- -- --
Initial Surcharge Area (AISV) =user ft 2 -- -- -- --
Surcharge Volume Length (LISV) =user ft -- -- -- --
Surcharge Volume Width (WISV) =user ft -- -- -- --
Depth of Basin Floor (HFLOOR) =user ft -- -- -- --
Length of Basin Floor (LFLOOR) =user ft -- -- -- --
Width of Basin Floor (WFLOOR) =user ft -- -- -- --
Area of Basin Floor (AFLOOR) =user ft 2 -- -- -- --
Volume of Basin Floor (VFLOOR) =user ft 3 -- -- -- --
Depth of Main Basin (HMAIN) =user ft -- -- -- --
Length of Main Basin (LMAIN) =user ft -- -- -- --
Width of Main Basin (WMAIN) =user ft -- -- -- --
Area of Main Basin (AMAIN) =user ft 2 -- -- -- --
Volume of Main Basin (VMAIN) =user ft 3 -- -- -- --
Calculated Total Basin Volume (Vtotal) =user acre-feet -- -- -- --
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After providing required inputs above including 1-hour rainfall
depths, click 'Run CUHP' to generate runoff hydrographs using
the embedded Colorado Urban Hydrograph Procedure.
Volume
(ft 3)
Volume
(ac-ft)
Area
(acre)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
Optional
Override
Area (ft 2)
Length
(ft)
Optional
Override
Stage (ft)
Stage
(ft)
Stage - Storage
Description
Area
(ft 2)
Width
(ft)
Gateway at Prospect
Pond C
MHFD-Detention, Version 4.06 (July 2022)
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond C - Full Spectrum Detention.xlsm, Basin 7/1/2025, 11:53 AM
1 User Defined Stage-Area Booleans for Message
1 Equal Stage-Area Inputs Watershed L:W
1 CountA Watershed Lc:L
Watershed Slope
0 Calc_S_TC Booleans for CUHP
1 CUHP Inputs Complete
H_FLOOR 1 CUHP Results Calculated
L_FLOOR_OTHER
0.00 ISV 0.00 ISV
0.00 Floor 0.00 Floor
2.01 Zone 1 (WQCV) 2.01 Zone 1 (WQCV)
3.47 Zone 2 (EURV) 3.47 Zone 2 (EURV)
4.89 Z3 (100+1/2WQCV)4.89 Z3 (100+1/2WQCV)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
MHFD-Detention, Version 4.06 (July 2022)
0.000
1.550
3.100
4.650
6.200
0.000
0.590
1.180
1.770
2.360
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MHFD-Detention_v4-06 Pond C - Full Spectrum Detention.xlsm, Basin 7/1/2025, 11:53 AM
Project:
Basin ID:
Estimated Estimated
Stage (ft) Volume (ac-ft) Outlet Type
Zone 1 (WQCV) 2.01 0.567 Orifice Plate
Zone 2 (EURV) 3.47 1.071 Orifice Plate
Z3 (100+1/2WQCV) 4.89 1.685 Weir&Pipe (Restrict)
Total (all zones) 3.323
User Input: Orifice at Underdrain Outlet (typically used to drain WQCV in a Filtration BMP)Calculated Parameters for Underdrain
Underdrain Orifice Invert Depth = N/A ft (distance below the filtration media surface) Underdrain Orifice Area = N/A ft2
Underdrain Orifice Diameter = N/A inches Underdrain Orifice Centroid = N/A feet
User Input: Orifice Plate with one or more orifices or Elliptical Slot Weir (typically used to drain WQCV and/or EURV in a sedimentation BMP)Calculated Parameters for Plate
Centroid of Lowest Orifice = 0.00 ft (relative to basin bottom at Stage = 0 ft) WQ Orifice Area per Row = 2.632E-02 ft2
Depth at top of Zone using Orifice Plate = 3.60 ft (relative to basin bottom at Stage = 0 ft) Elliptical Half-Width = N/A feet
Orifice Plate: Orifice Vertical Spacing = 14.00 inches Elliptical Slot Centroid = N/A feet
Orifice Plate: Orifice Area per Row = 3.79 sq. inches (use rectangular openings) Elliptical Slot Area = N/A ft2
User Input: Stage and Total Area of Each Orifice Row (numbered from lowest to highest)
Row 1 (required) Row 2 (optional) Row 3 (optional) Row 4 (optional) Row 5 (optional) Row 6 (optional) Row 7 (optional) Row 8 (optional)
Stage of Orifice Centroid (ft) 0.00 1.20 2.40
Orifice Area (sq. inches) 3.79 3.79 3.79
Row 9 (optional) Row 10 (optional) Row 11 (optional) Row 12 (optional) Row 13 (optional) Row 14 (optional) Row 15 (optional) Row 16 (optional)
Stage of Orifice Centroid (ft)
Orifice Area (sq. inches)
User Input: Vertical Orifice (Circular or Rectangular)Calculated Parameters for Vertical Orifice
Not Selected Not Selected Not Selected Not Selected
Invert of Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Area = N/A N/A ft2
Depth at top of Zone using Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Centroid = N/A N/A feet
Vertical Orifice Diameter = N/A N/A inches
User Input: Overflow Weir (Dropbox with Flat or Sloped Grate and Outlet Pipe OR Rectangular/Trapezoidal Weir and No Outlet Pipe) Calculated Parameters for Overflow Weir
grate Zone 3 Weir Not Selected Zone 3 Weir Not Selected
Overflow Weir Front Edge Height, Ho = 3.60 N/A ft (relative to basin bottom at Stage = 0 ft)Height of Grate Upper Edge, Ht =4.85 N/A feet
Overflow Weir Front Edge Length = 10.00 N/A feet Overflow Weir Slope Length = 5.15 N/A feet
Overflow Weir Grate Slope = 4.00 N/A H:V Grate Open Area / 100-yr Orifice Area = 12.66 N/A
Horiz. Length of Weir Sides = 5.00 N/A feet Overflow Grate Open Area w/o Debris = 35.87 N/A ft2
Overflow Grate Type = Type C Grate N/A Overflow Grate Open Area w/ Debris = 35.87 N/A ft2
Debris Clogging % = 0% N/A %
User Input: Outlet Pipe w/ Flow Restriction Plate (Circular Orifice, Restrictor Plate, or Rectangular Orifice)Calculated Parameters for Outlet Pipe w/ Flow Restriction Plate
Zone 3 Restrictor Not Selected Zone 3 Restrictor Not Selected
Depth to Invert of Outlet Pipe = 0.00 N/A ft (distance below basin bottom at Stage = 0 ft)Outlet Orifice Area = 2.83 N/A ft2
Outlet Pipe Diameter = 27.00 N/A inches Outlet Orifice Centroid = 0.85 N/A feet
Restrictor Plate Height Above Pipe Invert = 18.10 inches Half-Central Angle of Restrictor Plate on Pipe = 1.92 N/A radians
User Input: Emergency Spillway (Rectangular or Trapezoidal)Calculated Parameters for Spillway
Spillway Invert Stage= 5.30 ft (relative to basin bottom at Stage = 0 ft) Spillway Design Flow Depth= 0.50 feet
Spillway Crest Length = 68.00 feet Stage at Top of Freeboard = 6.30 feet
Spillway End Slopes = 4.00 H:V Basin Area at Top of Freeboard = 2.29 acres
Freeboard above Max Water Surface = 0.50 feet Basin Volume at Top of Freeboard = 5.95 acre-ft
Max Ponding Depth of Target Storage Volume =4.73 feet Discharge at Top of Freeboard = 245.46 cfs
Routed Hydrograph Results
Design Storm Return Period =WQCV EURV 2 Year 5 Year 10 Year 25 Year 50 Year 100 Year 500 Year
One-Hour Rainfall Depth (in) =N/A N/A 0.82 1.14 1.40 1.81 2.27 2.86 4.39
CUHP Runoff Volume (acre-ft) =0.567 1.638 1.076 1.610 2.076 2.863 3.728 4.867 7.790
Inflow Hydrograph Volume (acre-ft) =N/A N/A 1.076 1.610 2.076 2.863 3.728 4.867 7.790
CUHP Predevelopment Peak Q (cfs) =N/A N/A 0.2 2.1 5.1 12.9 19.5 29.1 51.5
OPTIONAL Override Predevelopment Peak Q (cfs) =N/A N/A
Predevelopment Unit Peak Flow, q (cfs/acre) =N/A N/A 0.01 0.10 0.24 0.61 0.92 1.38 2.44
Peak Inflow Q (cfs) =N/A N/A 16.2 24.0 30.4 43.5 56.5 74.4 117.8
Peak Outflow Q (cfs) =0.3 0.6 0.4 0.5 1.7 7.5 15.5 26.9 54.8
Ratio Peak Outflow to Predevelopment Q =N/A N/A N/A 0.3 0.3 0.6 0.8 0.9 1.1
Structure Controlling Flow =Plate Plate Plate Plate Overflow Weir 1 Overflow Weir 1 Overflow Weir 1 Outlet Plate 1 Spillway
Max Velocity through Grate 1 (fps) =N/A N/A N/A N/A 0.0 0.2 0.4 0.7 0.8
Max Velocity through Grate 2 (fps) =N/A N/A N/A N/A N/A N/A N/A N/A N/A
Time to Drain 97% of Inflow Volume (hours) =38 64 54 65 70 69 66 63 56
Time to Drain 99% of Inflow Volume (hours) =40 69 57 69 76 75 74 73 70
Maximum Ponding Depth (ft) =2.01 3.47 2.70 3.33 3.76 4.09 4.38 4.73 5.55
Area at Maximum Ponding Depth (acres) =0.56 0.94 0.72 0.90 1.03 1.14 1.24 1.40 1.82
Maximum Volume Stored (acre-ft) =0.568 1.646 1.003 1.518 1.922 2.291 2.636 3.097 4.389
DETENTION BASIN OUTLET STRUCTURE DESIGN
MHFD-Detention, Version 4.06 (July 2022)
Gateway at Prospect
Pond C
The user can override the default CUHP hydrographs and runoff volumes by entering new values in the Inflow Hydrographs table (Columns W through AF).
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond C - Full Spectrum Detention.xlsm, Outlet Structure 7/1/2025, 3:50 PM
COUNTA for Basin Tab = 1 Ao Dia WQ Plate Type Vert Orifice 1Vert Orifice 2
Count_Underdrain = 0 0.11(diameter = 3/8 inch)2 1 1
Count_WQPlate = 1 0.14(diameter = 7/16 inch)
Count_VertOrifice1 = 0 0.18(diameter = 1/2 inch)Outlet Plate 1 Outlet Plate 2 Drain Time Message Boolean
Count_VertOrifice2 = 0 0.24(diameter = 9/16 inch)4 1 5yr, <72hr 0
Count_Weir1 = 1 0.29(diameter = 5/8 inch)>5yr, <120hr 0
Count_Weir2 = 0 0.36(diameter = 11/16 inch)Max Depth Row
Count_OutletPipe1 = 1 0.42(diameter = 3/4 inch)WQCV 202
Count_OutletPipe2 = 0 0.50(diameter = 13/16 inch)2 Year 271
COUNTA_2 (Standard FSD Setup)= 1 0.58(diameter = 7/8 inch)EURV 348
Hidden Parameters & Calculations 0.67(diameter = 15/16 inch)5 Year 334
MaxPondDepth_Error? FALSE 0.76 (diameter = 1 inch)10 Year 377 Spillway Depth
Cd_Broad-Crested Weir 3.00 0.86(diameter = 1-1/16 inches)25 Year 410 0.50
WQ Plate Flow at 100yr depth = 0.71 0.97(diameter = 1-1/8 inches)50 Year 439
CLOG #1= 100% 1.08(diameter = 1-3/16 inches)100 Year 474 1 Z1_Boolean
n*Cdw #1 = 0.32 1.20(diameter = 1-1/4 inches)500 Year 556 1 Z2_Boolean
n*Cdo #1 = 1.45 1.32(diameter = 1-5/16 inches)Zone3_Pulldown Message 1 Z3_Boolean
Overflow Weir #1 Angle = 0.245 1.45(diameter = 1-3/8 inches)1 Opening Message
CLOG #2= N/A 1.59(diameter = 1-7/16 inches)Draintime Running
n*Cdw #2 = N/A 1.73(diameter = 1-1/2 inches)Outlet Boolean Outlet Rank Total (1 to 4)
n*Cdo #2 = N/A 1.88(diameter = 1-9/16 inches)Vertical Orifice 1 0 0 1
Overflow Weir #2 Angle = N/A 2.03(diameter = 1-5/8 inches)Vertical Orifice 2 0 0 Boolean
Underdrain Q at 100yr depth = 0.00 2.20(diameter = 1-11/16 inches)Overflow Weir 1 1 1 0 Max Depth
VertOrifice1 Q at 100yr depth = 0.00 2.36(diameter = 1-3/4 inches)Overflow Weir 2 0 0 0 500yr Depth
VertOrifice2 Q at 100yr depth = 0.00 2.54(diameter = 1-13/16 inches)Outlet Pipe 1 1 1 0 Freeboard
2.72(diameter = 1-7/8 inches)Outlet Pipe 2 0 0 1 Spillway
Count_User_Hydrographs 0 2.90(diameter = 1-15/16 inches)0 Spillway Length
CountA_3 (EURV & 100yr) = 1 3.09(diameter = 2 inches)FALSE Time Interval
CountA_4 (100yr Only) = 1 3.29(use rectangular openings)Button Visibility Boolean
COUNTA_5 (FSD Weir Only)= 0 0 WQCV Underdrain
COUNTA_6 (EURV Weir Only)= 1 1 WQCV Plate
0 EURV-WQCV Plate
Outlet1_Pulldown_Boolean 0 EURV-WQCV VertOriice
Outlet2_Pulldown_Boolean 1 Outlet 90% Qpeak
Outlet3_Pulldown_Boolean 0 Outlet Undetained
0 Weir Only 90% Qpeak
0 Five Year Ratio Plate
0 Five Year Ratio VertOrifice
EURV_draintime_user
Spillway Options
Offset
Overlapping
S-A-V-D Chart Axis Default X-axis Left Y-Axis Right Y-Axis
minimum bound 0.00 0 0
maximum bound 8.00 260,000 250
S-A-V-D Chart Axis Override X-axis Left Y-Axis Right Y-Axis
minimum bound
maximum bound
DETENTION BASIN OUTLET STRUCTURE DESIGN
MHFD-Detention, Version 4.06 (July 2022)
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PONDING DEPTH [ft]
User Area [ft^2]
Interpolated Area [ft^2]
Summary Area [ft^2]
Volume [ft^3]
Summary Volume [ft^3]
Outflow [cfs]
Summary Outflow [cfs]
MHFD-Detention_v4-06 Pond C - Full Spectrum Detention.xlsm, Outlet Structure 7/1/2025, 3:50 PM
Project:
Basin ID:
Depth Increment = ft
Watershed Information Top of Micropool -- 0.00 -- -- -- 169 0.004
Selected BMP Type =EDB -- 0.20 -- -- -- 354 0.008 49 0.001
Watershed Area = 2.94 acres -- 0.40 -- -- -- 835 0.019 163 0.004
Watershed Length = 560 ft -- 0.60 -- -- -- 1,458 0.033 386 0.009
Watershed Length to Centroid = 200 ft -- 0.80 -- -- -- 2,297 0.053 753 0.017
Watershed Slope = 0.010 ft/ft -- 1.00 -- -- -- 3,408 0.078 1,346 0.031
Watershed Imperviousness = 27.00% percent -- 1.20 -- -- -- 4,850 0.111 2,124 0.049
Percentage Hydrologic Soil Group A = 0.0% percent -- 1.32 -- -- -- 5,903 0.136 2,759 0.063
Percentage Hydrologic Soil Group B = 0.0% percent -- 1.40 -- -- -- 6,658 0.153 3,254 0.075
Percentage Hydrologic Soil Groups C/D = 100.0% percent -- 1.60 -- -- -- 8,491 0.195 4,750 0.109
Target WQCV Drain Time = 40.0 hours -- 1.80 -- -- -- 9,861 0.226 6,572 0.151
Location for 1-hr Rainfall Depths = User Input -- 2.00 -- -- -- 10,783 0.248 8,734 0.201
-- 2.20 -- -- -- 11,581 0.266 10,855 0.249
-- 2.40 -- -- -- 12,391 0.284 13,244 0.304
Optional User Overrides -- 3.40 -- -- -- 16,490 0.379 27,809 0.638
Water Quality Capture Volume (WQCV) = 0.035 acre-feet acre-feet -- -- -- --
Excess Urban Runoff Volume (EURV) = 0.071 acre-feet acre-feet -- -- -- --
2-yr Runoff Volume (P1 = 0.82 in.) = 0.042 acre-feet 0.82 inches -- -- -- --
5-yr Runoff Volume (P1 = 1.14 in.) = 0.086 acre-feet 1.14 inches -- -- -- --
10-yr Runoff Volume (P1 = 1.4 in.) = 0.138 acre-feet 1.40 inches -- -- -- --
25-yr Runoff Volume (P1 = 1.81 in.) = 0.249 acre-feet 1.81 inches -- -- -- --
50-yr Runoff Volume (P1 = 2.27 in.) = 0.360 acre-feet 2.27 inches -- -- -- --
100-yr Runoff Volume (P1 = 2.86 in.) = 0.520 acre-feet 2.86 inches -- -- -- --
500-yr Runoff Volume (P1 = 4.39 in.) = 0.918 acre-feet 4.39 inches -- -- -- --
Approximate 2-yr Detention Volume = 0.042 acre-feet -- -- -- --
Approximate 5-yr Detention Volume = 0.080 acre-feet -- -- -- --
Approximate 10-yr Detention Volume = 0.098 acre-feet -- -- -- --
Approximate 25-yr Detention Volume = 0.126 acre-feet -- -- -- --
Approximate 50-yr Detention Volume = 0.147 acre-feet -- -- -- --
Approximate 100-yr Detention Volume = 0.205 acre-feet -- -- -- --
-- -- -- --
Define Zones and Basin Geometry -- -- -- --
Zone 1 Volume (WQCV) = 0.035 acre-feet -- -- -- --
Zone 2 Volume (EURV - Zone 1) = 0.037 acre-feet -- -- -- --
Zone 3 (100yr + 1 / 2 WQCV - Zones 1 & 2) = 0.151 acre-feet -- -- -- --
Total Detention Basin Volume = 0.222 acre-feet -- -- -- --
Initial Surcharge Volume (ISV) = user ft 3 -- -- -- --
Initial Surcharge Depth (ISD) = user ft -- -- -- --
Total Available Detention Depth (Htotal) =user ft -- -- -- --
Depth of Trickle Channel (HTC) = user ft -- -- -- --
Slope of Trickle Channel (STC) =user ft/ft -- -- -- --
Slopes of Main Basin Sides (Smain) =user H:V -- -- -- --
Basin Length-to-Width Ratio (RL/W) =user -- -- -- --
-- -- -- --
Initial Surcharge Area (AISV) =user ft 2 -- -- -- --
Surcharge Volume Length (LISV) =user ft -- -- -- --
Surcharge Volume Width (WISV) =user ft -- -- -- --
Depth of Basin Floor (HFLOOR) =user ft -- -- -- --
Length of Basin Floor (LFLOOR) =user ft -- -- -- --
Width of Basin Floor (WFLOOR) =user ft -- -- -- --
Area of Basin Floor (AFLOOR) =user ft 2 -- -- -- --
Volume of Basin Floor (VFLOOR) =user ft 3 -- -- -- --
Depth of Main Basin (HMAIN) =user ft -- -- -- --
Length of Main Basin (LMAIN) =user ft -- -- -- --
Width of Main Basin (WMAIN) =user ft -- -- -- --
Area of Main Basin (AMAIN) =user ft 2 -- -- -- --
Volume of Main Basin (VMAIN) =user ft 3 -- -- -- --
Calculated Total Basin Volume (Vtotal) =user acre-feet -- -- -- --
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After providing required inputs above including 1-hour rainfall
depths, click 'Run CUHP' to generate runoff hydrographs using
the embedded Colorado Urban Hydrograph Procedure.
Volume
(ft 3)
Volume
(ac-ft)
Area
(acre)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
Optional
Override
Area (ft 2)
Length
(ft)
Optional
Override
Stage (ft)
Stage
(ft)
Stage - Storage
Description
Area
(ft 2)
Width
(ft)
Gateway at Prospect
Pond D
MHFD-Detention, Version 4.06 (July 2022)
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond D - Full Spectrum Detention.xlsm, Basin 7/1/2025, 12:19 PM
1 User Defined Stage-Area Booleans for Message
1 Equal Stage-Area Inputs Watershed L:W
1 CountA Watershed Lc:L
Watershed Slope
0 Calc_S_TC Booleans for CUHP
1 CUHP Inputs Complete
H_FLOOR 1 CUHP Results Calculated
L_FLOOR_OTHER
0.00 ISV 0.00 ISV
0.00 Floor 0.00 Floor
1.05 Zone 1 (WQCV) 1.05 Zone 1 (WQCV)
1.37 Zone 2 (EURV) 1.37 Zone 2 (EURV)
2.09 Z3 (100+1/2WQCV)2.09 Z3 (100+1/2WQCV)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
MHFD-Detention, Version 4.06 (July 2022)
0.000
0.160
0.320
0.480
0.640
0.000
0.095
0.190
0.285
0.380
0.00 1.00 2.00 3.00 4.00
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Area (acres)Volume (ac-ft)
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Length (ft)Width (ft)Area (sq.ft.)
MHFD-Detention_v4-06 Pond D - Full Spectrum Detention.xlsm, Basin 7/1/2025, 12:19 PM
Project:
Basin ID:
Estimated Estimated
Stage (ft) Volume (ac-ft) Outlet Type
Zone 1 (WQCV) 1.05 0.035 Orifice Plate
Zone 2 (EURV) 1.37 0.037 Orifice Plate
Z3 (100+1/2WQCV) 2.09 0.151 Weir&Pipe (Restrict)
Total (all zones) 0.222
User Input: Orifice at Underdrain Outlet (typically used to drain WQCV in a Filtration BMP)Calculated Parameters for Underdrain
Underdrain Orifice Invert Depth = N/A ft (distance below the filtration media surface) Underdrain Orifice Area = N/A ft2
Underdrain Orifice Diameter = N/A inches Underdrain Orifice Centroid = N/A feet
User Input: Orifice Plate with one or more orifices or Elliptical Slot Weir (typically used to drain WQCV and/or EURV in a sedimentation BMP)Calculated Parameters for Plate
Centroid of Lowest Orifice = 0.00 ft (relative to basin bottom at Stage = 0 ft) WQ Orifice Area per Row = 1.875E-03 ft2
Depth at top of Zone using Orifice Plate = 1.50 ft (relative to basin bottom at Stage = 0 ft) Elliptical Half-Width = N/A feet
Orifice Plate: Orifice Vertical Spacing = 5.55 inches Elliptical Slot Centroid = N/A feet
Orifice Plate: Orifice Area per Row = 0.27 sq. inches (diameter = 9/16 inch) Elliptical Slot Area = N/A ft2
User Input: Stage and Total Area of Each Orifice Row (numbered from lowest to highest)
Row 1 (required) Row 2 (optional) Row 3 (optional) Row 4 (optional) Row 5 (optional) Row 6 (optional) Row 7 (optional) Row 8 (optional)
Stage of Orifice Centroid (ft) 0.00 0.50 1.00
Orifice Area (sq. inches) 0.27 0.27 0.27
Row 9 (optional) Row 10 (optional) Row 11 (optional) Row 12 (optional) Row 13 (optional) Row 14 (optional) Row 15 (optional) Row 16 (optional)
Stage of Orifice Centroid (ft)
Orifice Area (sq. inches)
User Input: Vertical Orifice (Circular or Rectangular)Calculated Parameters for Vertical Orifice
Not Selected Not Selected Not Selected Not Selected
Invert of Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Area = N/A N/A ft2
Depth at top of Zone using Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Centroid = N/A N/A feet
Vertical Orifice Diameter = N/A N/A inches
User Input: Overflow Weir (Dropbox with Flat or Sloped Grate and Outlet Pipe OR Rectangular/Trapezoidal Weir and No Outlet Pipe) Calculated Parameters for Overflow Weir
grate Zone 3 Weir Not Selected Zone 3 Weir Not Selected
Overflow Weir Front Edge Height, Ho = 1.50 N/A ft (relative to basin bottom at Stage = 0 ft)Height of Grate Upper Edge, Ht =2.75 N/A feet
Overflow Weir Front Edge Length = 9.00 N/A feet Overflow Weir Slope Length = 5.15 N/A feet
Overflow Weir Grate Slope = 4.00 N/A H:V Grate Open Area / 100-yr Orifice Area = 42.54 N/A
Horiz. Length of Weir Sides = 5.00 N/A feet Overflow Grate Open Area w/o Debris = 32.28 N/A ft2
Overflow Grate Type = Type C Grate N/A Overflow Grate Open Area w/ Debris = 32.28 N/A ft2
Debris Clogging % = 0% N/A %
User Input: Outlet Pipe w/ Flow Restriction Plate (Circular Orifice, Restrictor Plate, or Rectangular Orifice)Calculated Parameters for Outlet Pipe w/ Flow Restriction Plate
Zone 3 Restrictor Not Selected Zone 3 Restrictor Not Selected
Depth to Invert of Outlet Pipe = 0.00 N/A ft (distance below basin bottom at Stage = 0 ft)Outlet Orifice Area = 0.76 N/A ft2
Outlet Pipe Diameter = 18.00 N/A inches Outlet Orifice Centroid = 0.39 N/A feet
Restrictor Plate Height Above Pipe Invert = 8.00 inches Half-Central Angle of Restrictor Plate on Pipe = 1.46 N/A radians
User Input: Emergency Spillway (Rectangular or Trapezoidal)Calculated Parameters for Spillway
Spillway Invert Stage= 2.40 ft (relative to basin bottom at Stage = 0 ft) Spillway Design Flow Depth= 0.37 feet
Spillway Crest Length = 7.50 feet Stage at Top of Freeboard = 3.27 feet
Spillway End Slopes = 4.00 H:V Basin Area at Top of Freeboard = 0.37 acres
Freeboard above Max Water Surface = 0.50 feet Basin Volume at Top of Freeboard = 0.59 acre-ft
Max Ponding Depth of Target Storage Volume =1.91 feet Discharge at Top of Freeboard = 31.24 cfs
Routed Hydrograph Results
Design Storm Return Period =WQCV EURV 2 Year 5 Year 10 Year 25 Year 50 Year 100 Year 500 Year
One-Hour Rainfall Depth (in) =N/A N/A 0.82 1.14 1.40 1.81 2.27 2.86 4.39
CUHP Runoff Volume (acre-ft) =0.035 0.071 0.042 0.086 0.138 0.249 0.360 0.520 0.918
Inflow Hydrograph Volume (acre-ft) =N/A N/A 0.042 0.086 0.138 0.249 0.360 0.520 0.918
CUHP Predevelopment Peak Q (cfs) =N/A N/A 0.0 0.4 0.9 2.1 3.2 4.8 8.4
OPTIONAL Override Predevelopment Peak Q (cfs) =N/A N/A
Predevelopment Unit Peak Flow, q (cfs/acre) =N/A N/A 0.01 0.12 0.30 0.72 1.09 1.62 2.87
Peak Inflow Q (cfs) =N/A N/A 0.5 1.0 1.5 2.9 4.2 5.9 10.1
Peak Outflow Q (cfs) =0.0 0.0 0.0 0.0 0.4 1.6 2.8 4.5 6.2
Ratio Peak Outflow to Predevelopment Q =N/A N/A N/A 0.1 0.5 0.8 0.9 0.9 0.7
Structure Controlling Flow =Plate Plate Plate Plate Overflow Weir 1 Overflow Weir 1 Overflow Weir 1 Outlet Plate 1 Spillway
Max Velocity through Grate 1 (fps) =N/A N/A N/A N/A 0.0 0.0 0.1 0.1 0.2
Max Velocity through Grate 2 (fps) =N/A N/A N/A N/A N/A N/A N/A N/A N/A
Time to Drain 97% of Inflow Volume (hours) =39 56 44 63 66 60 56 51 41
Time to Drain 99% of Inflow Volume (hours) =42 60 47 68 73 70 68 64 58
Maximum Ponding Depth (ft) =1.05 1.37 1.09 1.43 1.58 1.71 1.80 1.91 2.51
Area at Maximum Ponding Depth (acres) =0.09 0.15 0.09 0.16 0.19 0.21 0.22 0.24 0.29
Maximum Volume Stored (acre-ft) =0.035 0.072 0.038 0.079 0.107 0.131 0.151 0.176 0.336
The user can override the default CUHP hydrographs and runoff volumes by entering new values in the Inflow Hydrographs table (Columns W through AF).
DETENTION BASIN OUTLET STRUCTURE DESIGN
MHFD-Detention, Version 4.06 (July 2022)
Gateway at Prospect
Pond D
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond D - Full Spectrum Detention.xlsm, Outlet Structure 7/1/2025, 3:52 PM
COUNTA for Basin Tab = 1 Ao Dia WQ Plate Type Vert Orifice 1Vert Orifice 2
Count_Underdrain = 0 0.11(diameter = 3/8 inch)2 1 1
Count_WQPlate = 1 0.14(diameter = 7/16 inch)
Count_VertOrifice1 = 0 0.18(diameter = 1/2 inch)Outlet Plate 1 Outlet Plate 2 Drain Time Message Boolean
Count_VertOrifice2 = 0 0.24(diameter = 9/16 inch)4 1 5yr, <72hr 0
Count_Weir1 = 1 0.29(diameter = 5/8 inch)>5yr, <120hr 0
Count_Weir2 = 0 0.36(diameter = 11/16 inch)Max Depth Row
Count_OutletPipe1 = 1 0.42(diameter = 3/4 inch)WQCV 106
Count_OutletPipe2 = 0 0.50(diameter = 13/16 inch)2 Year 110
COUNTA_2 (Standard FSD Setup)= 1 0.58(diameter = 7/8 inch)EURV 138
Hidden Parameters & Calculations 0.67(diameter = 15/16 inch)5 Year 144
MaxPondDepth_Error? FALSE 0.76 (diameter = 1 inch)10 Year 159 Spillway Depth
Cd_Broad-Crested Weir 3.00 0.86(diameter = 1-1/16 inches)25 Year 172 0.37
WQ Plate Flow at 100yr depth = 0.03 0.97(diameter = 1-1/8 inches)50 Year 181
CLOG #1= 100% 1.08(diameter = 1-3/16 inches)100 Year 192 1 Z1_Boolean
n*Cdw #1 = 0.32 1.20(diameter = 1-1/4 inches)500 Year 252 1 Z2_Boolean
n*Cdo #1 = 1.45 1.32(diameter = 1-5/16 inches)Zone3_Pulldown Message 1 Z3_Boolean
Overflow Weir #1 Angle = 0.245 1.45(diameter = 1-3/8 inches)1 Opening Message
CLOG #2= N/A 1.59(diameter = 1-7/16 inches)Draintime Running
n*Cdw #2 = N/A 1.73(diameter = 1-1/2 inches)Outlet Boolean Outlet Rank Total (1 to 4)
n*Cdo #2 = N/A 1.88(diameter = 1-9/16 inches)Vertical Orifice 1 0 0 1
Overflow Weir #2 Angle = N/A 2.03(diameter = 1-5/8 inches)Vertical Orifice 2 0 0 Boolean
Underdrain Q at 100yr depth = 0.00 2.20(diameter = 1-11/16 inches)Overflow Weir 1 1 1 0 Max Depth
VertOrifice1 Q at 100yr depth = 0.00 2.36(diameter = 1-3/4 inches)Overflow Weir 2 0 0 0 500yr Depth
VertOrifice2 Q at 100yr depth = 0.00 2.54(diameter = 1-13/16 inches)Outlet Pipe 1 1 1 0 Freeboard
2.72(diameter = 1-7/8 inches)Outlet Pipe 2 0 0 1 Spillway
Count_User_Hydrographs 0 2.90(diameter = 1-15/16 inches)0 Spillway Length
CountA_3 (EURV & 100yr) = 1 3.09(diameter = 2 inches)FALSE Time Interval
CountA_4 (100yr Only) = 1 3.29(use rectangular openings)Button Visibility Boolean
COUNTA_5 (FSD Weir Only)= 0 0 WQCV Underdrain
COUNTA_6 (EURV Weir Only)= 1 1 WQCV Plate
0 EURV-WQCV Plate
Outlet1_Pulldown_Boolean 0 EURV-WQCV VertOriice
Outlet2_Pulldown_Boolean 1 Outlet 90% Qpeak
Outlet3_Pulldown_Boolean 0 Outlet Undetained
0 Weir Only 90% Qpeak
0 Five Year Ratio Plate
0 Five Year Ratio VertOrifice
EURV_draintime_user
Spillway Options
Offset
Overlapping
S-A-V-D Chart Axis Default X-axis Left Y-Axis Right Y-Axis
minimum bound 0.00 0 0
maximum bound 4.00 30,000 40
S-A-V-D Chart Axis Override X-axis Left Y-Axis Right Y-Axis
minimum bound
maximum bound
MHFD-Detention, Version 4.06 (July 2022)
DETENTION BASIN OUTLET STRUCTURE DESIGN
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500YR OUT
100YR IN
100YR OUT
50YR IN
50YR OUT
25YR IN
25YR OUT
10YR IN
10YR OUT
5YR IN
5YR OUT
2YR IN
2YR OUT
EURV IN
EURV OUT
WQCV IN
WQCV OUT
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PONDING DEPTH [ft]
User Area [ft^2]
Interpolated Area [ft^2]
Summary Area [ft^2]
Volume [ft^3]
Summary Volume [ft^3]
Outflow [cfs]
Summary Outflow [cfs]
MHFD-Detention_v4-06 Pond D - Full Spectrum Detention.xlsm, Outlet Structure 7/1/2025, 3:52 PM
Project:
Basin ID:
Depth Increment = ft
Watershed Information Top of Micropool -- 0.00 -- -- -- 76 0.002
Selected BMP Type =EDB -- 0.20 -- -- -- 258 0.006 31 0.001
Watershed Area = 4.92 acres -- 0.40 -- -- -- 528 0.012 107 0.002
Watershed Length = 469 ft -- 0.60 -- -- -- 832 0.019 240 0.006
Watershed Length to Centroid = 230 ft -- 0.80 -- -- -- 1,109 0.025 431 0.010
Watershed Slope = 0.015 ft/ft -- 1.00 -- -- -- 1,362 0.031 689 0.016
Watershed Imperviousness = 66.00% percent -- 1.20 -- -- -- 1,613 0.037 971 0.022
Percentage Hydrologic Soil Group A = 0.0% percent -- 1.40 -- -- -- 1,894 0.043 1,319 0.030
Percentage Hydrologic Soil Group B = 0.0% percent -- 1.60 -- -- -- 2,228 0.051 1,728 0.040
Percentage Hydrologic Soil Groups C/D = 100.0% percent -- 1.80 -- -- -- 2,615 0.060 2,208 0.051
Target WQCV Drain Time = 40.0 hours -- 2.00 -- -- -- 7,389 0.170 3,234 0.074
Location for 1-hr Rainfall Depths = User Input -- 2.20 -- -- -- 8,251 0.189 4,716 0.108
-- 2.40 -- -- -- 9,069 0.208 6,440 0.148
-- 2.60 -- -- -- 9,848 0.226 8,324 0.191
Optional User Overrides -- 2.80 -- -- -- 10,591 0.243 10,360 0.238
Water Quality Capture Volume (WQCV) = 0.106 acre-feet acre-feet -- 3.00 -- -- -- 11,286 0.259 12,654 0.290
Excess Urban Runoff Volume (EURV) = 0.314 acre-feet acre-feet -- 3.20 -- -- -- 11,906 0.273 14,854 0.341
2-yr Runoff Volume (P1 = 0.82 in.) = 0.194 acre-feet 0.82 inches -- 3.40 -- -- -- 12,522 0.287 17,291 0.397
5-yr Runoff Volume (P1 = 1.14 in.) = 0.299 acre-feet 1.14 inches -- 3.60 -- -- -- 13,138 0.302 19,851 0.456
10-yr Runoff Volume (P1 = 1.4 in.) = 0.396 acre-feet 1.40 inches -- 3.80 -- -- -- 13,932 0.320 22,550 0.518
25-yr Runoff Volume (P1 = 1.81 in.) = 0.570 acre-feet 1.81 inches -- 4.00 -- -- -- 14,800 0.340 25,562 0.587
50-yr Runoff Volume (P1 = 2.27 in.) = 0.757 acre-feet 2.27 inches -- 4.20 -- -- -- 15,740 0.361 28,459 0.653
100-yr Runoff Volume (P1 = 2.86 in.) = 1.007 acre-feet 2.86 inches -- 4.40 -- -- -- 16,789 0.385 31,701 0.728
500-yr Runoff Volume (P1 = 4.39 in.) = 1.647 acre-feet 4.39 inches -- 4.60 -- -- -- 18,007 0.413 35,169 0.807
Approximate 2-yr Detention Volume = 0.194 acre-feet -- 4.80 -- -- -- 20,261 0.465 39,176 0.899
Approximate 5-yr Detention Volume = 0.302 acre-feet -- 5.80 -- -- -- 27,505 0.631 63,059 1.448
Approximate 10-yr Detention Volume = 0.363 acre-feet -- -- -- --
Approximate 25-yr Detention Volume = 0.438 acre-feet -- -- -- --
Approximate 50-yr Detention Volume = 0.503 acre-feet -- -- -- --
Approximate 100-yr Detention Volume = 0.616 acre-feet -- -- -- --
-- -- -- --
Define Zones and Basin Geometry -- -- -- --
Zone 1 Volume (WQCV) = 0.106 acre-feet -- -- -- --
Zone 2 Volume (EURV - Zone 1) = 0.208 acre-feet -- -- -- --
Zone 3 (100yr + 1 / 2 WQCV - Zones 1 & 2) = 0.355 acre-feet -- -- -- --
Total Detention Basin Volume = 0.669 acre-feet -- -- -- --
Initial Surcharge Volume (ISV) = user ft 3 -- -- -- --
Initial Surcharge Depth (ISD) = user ft -- -- -- --
Total Available Detention Depth (Htotal) =user ft -- -- -- --
Depth of Trickle Channel (HTC) = user ft -- -- -- --
Slope of Trickle Channel (STC) =user ft/ft -- -- -- --
Slopes of Main Basin Sides (Smain) =user H:V -- -- -- --
Basin Length-to-Width Ratio (RL/W) =user -- -- -- --
-- -- -- --
Initial Surcharge Area (AISV) =user ft 2 -- -- -- --
Surcharge Volume Length (LISV) =user ft -- -- -- --
Surcharge Volume Width (WISV) =user ft -- -- -- --
Depth of Basin Floor (HFLOOR) =user ft -- -- -- --
Length of Basin Floor (LFLOOR) =user ft -- -- -- --
Width of Basin Floor (WFLOOR) =user ft -- -- -- --
Area of Basin Floor (AFLOOR) =user ft 2 -- -- -- --
Volume of Basin Floor (VFLOOR) =user ft 3 -- -- -- --
Depth of Main Basin (HMAIN) =user ft -- -- -- --
Length of Main Basin (LMAIN) =user ft -- -- -- --
Width of Main Basin (WMAIN) =user ft -- -- -- --
Area of Main Basin (AMAIN) =user ft 2 -- -- -- --
Volume of Main Basin (VMAIN) =user ft 3 -- -- -- --
Calculated Total Basin Volume (Vtotal) =user acre-feet -- -- -- --
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After providing required inputs above including 1-hour rainfall
depths, click 'Run CUHP' to generate runoff hydrographs using
the embedded Colorado Urban Hydrograph Procedure.
Volume
(ft 3)
Volume
(ac-ft)
Area
(acre)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
Optional
Override
Area (ft 2)
Length
(ft)
Optional
Override
Stage (ft)
Stage
(ft)
Stage - Storage
Description
Area
(ft 2)
Width
(ft)
Gateway at Prospect
Pond E
MHFD-Detention, Version 4.06 (July 2022)
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond E - Full Spectrum Detention.xlsm, Basin 7/1/2025, 1:54 PM
1 User Defined Stage-Area Booleans for Message
1 Equal Stage-Area Inputs Watershed L:W
1 CountA Watershed Lc:L
Watershed Slope
0 Calc_S_TC Booleans for CUHP
1 CUHP Inputs Complete
H_FLOOR 1 CUHP Results Calculated
L_FLOOR_OTHER
0.00 ISV 0.00 ISV
0.00 Floor 0.00 Floor
2.18 Zone 1 (WQCV) 2.18 Zone 1 (WQCV)
3.10 Zone 2 (EURV) 3.10 Zone 2 (EURV)
4.24 Z3 (100+1/2WQCV)4.24 Z3 (100+1/2WQCV)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
MHFD-Detention, Version 4.06 (July 2022)
0.000
0.365
0.730
1.095
1.460
0.000
0.160
0.320
0.480
0.640
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MHFD-Detention_v4-06 Pond E - Full Spectrum Detention.xlsm, Basin 7/1/2025, 1:54 PM
Project:
Basin ID:
Estimated Estimated
Stage (ft) Volume (ac-ft) Outlet Type
Zone 1 (WQCV) 2.18 0.106 Orifice Plate
Zone 2 (EURV) 3.10 0.208 Orifice Plate
Z3 (100+1/2WQCV) 4.24 0.355 Weir&Pipe (Restrict)
Total (all zones) 0.669
User Input: Orifice at Underdrain Outlet (typically used to drain WQCV in a Filtration BMP)Calculated Parameters for Underdrain
Underdrain Orifice Invert Depth = N/A ft (distance below the filtration media surface) Underdrain Orifice Area = N/A ft2
Underdrain Orifice Diameter = N/A inches Underdrain Orifice Centroid = N/A feet
User Input: Orifice Plate with one or more orifices or Elliptical Slot Weir (typically used to drain WQCV and/or EURV in a sedimentation BMP)Calculated Parameters for Plate
Centroid of Lowest Orifice = 0.00 ft (relative to basin bottom at Stage = 0 ft) WQ Orifice Area per Row = 3.889E-03 ft2
Depth at top of Zone using Orifice Plate = 3.30 ft (relative to basin bottom at Stage = 0 ft) Elliptical Half-Width = N/A feet
Orifice Plate: Orifice Vertical Spacing = 13.00 inches Elliptical Slot Centroid = N/A feet
Orifice Plate: Orifice Area per Row = 0.56 sq. inches (diameter = 13/16 inch) Elliptical Slot Area = N/A ft2
User Input: Stage and Total Area of Each Orifice Row (numbered from lowest to highest)
Row 1 (required) Row 2 (optional) Row 3 (optional) Row 4 (optional) Row 5 (optional) Row 6 (optional) Row 7 (optional) Row 8 (optional)
Stage of Orifice Centroid (ft) 0.00 1.10 2.20
Orifice Area (sq. inches) 0.56 0.56 0.56
Row 9 (optional) Row 10 (optional) Row 11 (optional) Row 12 (optional) Row 13 (optional) Row 14 (optional) Row 15 (optional) Row 16 (optional)
Stage of Orifice Centroid (ft)
Orifice Area (sq. inches)
User Input: Vertical Orifice (Circular or Rectangular)Calculated Parameters for Vertical Orifice
Not Selected Not Selected Not Selected Not Selected
Invert of Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Area = N/A N/A ft2
Depth at top of Zone using Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Centroid = N/A N/A feet
Vertical Orifice Diameter = N/A N/A inches
User Input: Overflow Weir (Dropbox with Flat or Sloped Grate and Outlet Pipe OR Rectangular/Trapezoidal Weir and No Outlet Pipe) Calculated Parameters for Overflow Weir
grate Zone 3 Weir Not Selected Zone 3 Weir Not Selected
Overflow Weir Front Edge Height, Ho = 3.30 N/A ft (relative to basin bottom at Stage = 0 ft)Height of Grate Upper Edge, Ht =4.05 N/A feet
Overflow Weir Front Edge Length = 10.00 N/A feet Overflow Weir Slope Length = 5.06 N/A feet
Overflow Weir Grate Slope = 6.66 N/A H:V Grate Open Area / 100-yr Orifice Area = 33.27 N/A
Horiz. Length of Weir Sides = 5.00 N/A feet Overflow Grate Open Area w/o Debris = 35.19 N/A ft2
Overflow Grate Type = Type C Grate N/A Overflow Grate Open Area w/ Debris = 35.19 N/A ft2
Debris Clogging % = 0% N/A %
User Input: Outlet Pipe w/ Flow Restriction Plate (Circular Orifice, Restrictor Plate, or Rectangular Orifice)Calculated Parameters for Outlet Pipe w/ Flow Restriction Plate
Zone 3 Restrictor Not Selected Zone 3 Restrictor Not Selected
Depth to Invert of Outlet Pipe = 0.00 N/A ft (distance below basin bottom at Stage = 0 ft)Outlet Orifice Area = 1.06 N/A ft2
Outlet Pipe Diameter = 18.00 N/A inches Outlet Orifice Centroid = 0.49 N/A feet
Restrictor Plate Height Above Pipe Invert = 10.40 inches Half-Central Angle of Restrictor Plate on Pipe = 1.73 N/A radians
User Input: Emergency Spillway (Rectangular or Trapezoidal)Calculated Parameters for Spillway
Spillway Invert Stage= 4.60 ft (relative to basin bottom at Stage = 0 ft) Spillway Design Flow Depth= 0.42 feet
Spillway Crest Length = 18.00 feet Stage at Top of Freeboard = 5.52 feet
Spillway End Slopes = 20.00 H:V Basin Area at Top of Freeboard = 0.58 acres
Freeboard above Max Water Surface = 0.50 feet Basin Volume at Top of Freeboard = 1.28 acre-ft
Max Ponding Depth of Target Storage Volume =3.85 feet Discharge at Top of Freeboard = 98.04 cfs
Routed Hydrograph Results
Design Storm Return Period =WQCV EURV 2 Year 5 Year 10 Year 25 Year 50 Year 100 Year 500 Year
One-Hour Rainfall Depth (in) =N/A N/A 0.82 1.14 1.40 1.81 2.27 2.86 4.39
CUHP Runoff Volume (acre-ft) =0.106 0.314 0.194 0.299 0.396 0.570 0.757 1.007 1.647
Inflow Hydrograph Volume (acre-ft) =N/A N/A 0.194 0.299 0.396 0.570 0.757 1.007 1.647
CUHP Predevelopment Peak Q (cfs) =N/A N/A 0.1 0.8 1.9 4.6 7.0 10.2 18.0
OPTIONAL Override Predevelopment Peak Q (cfs) =N/A N/A
Predevelopment Unit Peak Flow, q (cfs/acre) =N/A N/A 0.01 0.17 0.39 0.94 1.42 2.07 3.65
Peak Inflow Q (cfs) =N/A N/A 3.9 6.0 7.9 11.6 15.5 20.5 32.6
Peak Outflow Q (cfs) =0.0 0.1 0.1 0.1 0.2 2.5 5.9 9.3 13.0
Ratio Peak Outflow to Predevelopment Q =N/A N/A N/A 0.1 0.1 0.6 0.8 0.9 0.7
Structure Controlling Flow =Plate Plate Plate Plate Overflow Weir 1 Overflow Weir 1 Overflow Weir 1 Outlet Plate 1 Spillway
Max Velocity through Grate 1 (fps) =N/A N/A N/A N/A 0.0 0.1 0.2 0.3 0.3
Max Velocity through Grate 2 (fps) =N/A N/A N/A N/A N/A N/A N/A N/A N/A
Time to Drain 97% of Inflow Volume (hours) =38 72 55 71 82 79 76 73 67
Time to Drain 99% of Inflow Volume (hours) =41 77 59 76 88 87 86 84 80
Maximum Ponding Depth (ft) =2.18 3.09 2.56 2.99 3.33 3.50 3.64 3.85 4.72
Area at Maximum Ponding Depth (acres) =0.19 0.27 0.22 0.26 0.28 0.29 0.31 0.32 0.44
Maximum Volume Stored (acre-ft) =0.106 0.314 0.184 0.285 0.380 0.429 0.471 0.537 0.863
DETENTION BASIN OUTLET STRUCTURE DESIGN
MHFD-Detention, Version 4.06 (July 2022)
Gateway at Prospect
Pond E
The user can override the default CUHP hydrographs and runoff volumes by entering new values in the Inflow Hydrographs table (Columns W through AF).
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond E - Full Spectrum Detention.xlsm, Outlet Structure 7/1/2025, 1:55 PM
COUNTA for Basin Tab = 1 Ao Dia WQ Plate Type Vert Orifice 1Vert Orifice 2
Count_Underdrain = 0 0.11(diameter = 3/8 inch)2 1 1
Count_WQPlate = 1 0.14(diameter = 7/16 inch)
Count_VertOrifice1 = 0 0.18(diameter = 1/2 inch)Outlet Plate 1 Outlet Plate 2 Drain Time Message Boolean
Count_VertOrifice2 = 0 0.24(diameter = 9/16 inch)4 1 5yr, <72hr 0
Count_Weir1 = 1 0.29(diameter = 5/8 inch)>5yr, <120hr 0
Count_Weir2 = 0 0.36(diameter = 11/16 inch)Max Depth Row
Count_OutletPipe1 = 1 0.42(diameter = 3/4 inch)WQCV 219
Count_OutletPipe2 = 0 0.50(diameter = 13/16 inch)2 Year 257
COUNTA_2 (Standard FSD Setup)= 1 0.58(diameter = 7/8 inch)EURV 310
Hidden Parameters & Calculations 0.67(diameter = 15/16 inch)5 Year 300
MaxPondDepth_Error? FALSE 0.76 (diameter = 1 inch)10 Year 334 Spillway Depth
Cd_Broad-Crested Weir 3.00 0.86(diameter = 1-1/16 inches)25 Year 351 0.42
WQ Plate Flow at 100yr depth = 0.09 0.97(diameter = 1-1/8 inches)50 Year 365
CLOG #1= 100% 1.08(diameter = 1-3/16 inches)100 Year 386 1 Z1_Boolean
n*Cdw #1 = 0.46 1.20(diameter = 1-1/4 inches)500 Year 473 1 Z2_Boolean
n*Cdo #1 = 1.12 1.32(diameter = 1-5/16 inches)Zone3_Pulldown Message 1 Z3_Boolean
Overflow Weir #1 Angle = 0.149 1.45(diameter = 1-3/8 inches)1 Opening Message
CLOG #2= N/A 1.59(diameter = 1-7/16 inches)Draintime Running
n*Cdw #2 = N/A 1.73(diameter = 1-1/2 inches)Outlet Boolean Outlet Rank Total (1 to 4)
n*Cdo #2 = N/A 1.88(diameter = 1-9/16 inches)Vertical Orifice 1 0 0 1
Overflow Weir #2 Angle = N/A 2.03(diameter = 1-5/8 inches)Vertical Orifice 2 0 0 Boolean
Underdrain Q at 100yr depth = 0.00 2.20(diameter = 1-11/16 inches)Overflow Weir 1 1 1 0 Max Depth
VertOrifice1 Q at 100yr depth = 0.00 2.36(diameter = 1-3/4 inches)Overflow Weir 2 0 0 0 500yr Depth
VertOrifice2 Q at 100yr depth = 0.00 2.54(diameter = 1-13/16 inches)Outlet Pipe 1 1 1 0 Freeboard
2.72(diameter = 1-7/8 inches)Outlet Pipe 2 0 0 1 Spillway
Count_User_Hydrographs 0 2.90(diameter = 1-15/16 inches)0 Spillway Length
CountA_3 (EURV & 100yr) = 1 3.09(diameter = 2 inches)FALSE Time Interval
CountA_4 (100yr Only) = 1 3.29(use rectangular openings)Button Visibility Boolean
COUNTA_5 (FSD Weir Only)= 0 0 WQCV Underdrain
COUNTA_6 (EURV Weir Only)= 1 1 WQCV Plate
0 EURV-WQCV Plate
Outlet1_Pulldown_Boolean 0 EURV-WQCV VertOriice
Outlet2_Pulldown_Boolean 1 Outlet 90% Qpeak
Outlet3_Pulldown_Boolean 0 Outlet Undetained
0 Weir Only 90% Qpeak
0 Five Year Ratio Plate
0 Five Year Ratio VertOrifice
EURV_draintime_user
Spillway Options
Offset
Overlapping
S-A-V-D Chart Axis Default X-axis Left Y-Axis Right Y-Axis
minimum bound 0.00 0 0
maximum bound 6.00 60,000 100
S-A-V-D Chart Axis Override X-axis Left Y-Axis Right Y-Axis
minimum bound
maximum bound
DETENTION BASIN OUTLET STRUCTURE DESIGN
MHFD-Detention, Version 4.06 (July 2022)
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PONDING DEPTH [ft]
User Area [ft^2]
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Summary Area [ft^2]
Volume [ft^3]
Summary Volume [ft^3]
Outflow [cfs]
Summary Outflow [cfs]
MHFD-Detention_v4-06 Pond E - Full Spectrum Detention.xlsm, Outlet Structure 7/1/2025, 1:55 PM
Project:
Basin ID:
Depth Increment = ft
Watershed Information Top of Micropool -- 0.00 -- -- -- 119 0.003
Selected BMP Type =EDB -- 0.20 -- -- -- 196 0.004 30 0.001
Watershed Area = 12.20 acres -- 0.40 -- -- -- 904 0.021 133 0.003
Watershed Length = 1,180 ft -- 0.60 -- -- -- 2,402 0.055 472 0.011
Watershed Length to Centroid = 420 ft -- 0.80 -- -- -- 4,647 0.107 1,177 0.027
Watershed Slope = 0.010 ft/ft -- 1.00 -- -- -- 7,558 0.174 2,398 0.055
Watershed Imperviousness = 77.00% percent -- 1.20 -- -- -- 10,960 0.252 4,141 0.095
Percentage Hydrologic Soil Group A = 0.0% percent -- 1.40 -- -- -- 15,242 0.350 6,718 0.154
Percentage Hydrologic Soil Group B = 0.0% percent -- 1.60 -- -- -- 17,770 0.408 10,171 0.233
Percentage Hydrologic Soil Groups C/D = 100.0% percent -- 1.80 -- -- -- 20,063 0.461 13,954 0.320
Target WQCV Drain Time = 40.0 hours -- 1.99 -- -- -- 22,029 0.506 17,733 0.407
Location for 1-hr Rainfall Depths = User Input -- 2.00 -- -- -- 22,128 0.508 18,174 0.417
-- 2.20 -- -- -- 24,022 0.551 22,549 0.518
-- 2.40 -- -- -- 25,964 0.596 27,528 0.632
Optional User Overrides -- 2.60 -- -- -- 27,901 0.641 33,174 0.762
Water Quality Capture Volume (WQCV) = 0.316 acre-feet acre-feet -- 2.80 -- -- -- 29,838 0.685 38,948 0.894
Excess Urban Runoff Volume (EURV) = 0.920 acre-feet acre-feet -- 3.00 -- -- -- 31,783 0.730 45,110 1.036
2-yr Runoff Volume (P1 = 0.82 in.) = 0.590 acre-feet 0.82 inches -- 3.20 -- -- -- 33,447 0.768 51,299 1.178
5-yr Runoff Volume (P1 = 1.14 in.) = 0.886 acre-feet 1.14 inches -- 3.40 -- -- -- 35,173 0.807 58,143 1.335
10-yr Runoff Volume (P1 = 1.4 in.) = 1.147 acre-feet 1.40 inches -- 3.60 -- -- -- 36,975 0.849 65,709 1.508
25-yr Runoff Volume (P1 = 1.81 in.) = 1.592 acre-feet 1.81 inches -- 3.80 -- -- -- 38,858 0.892 73,293 1.683
50-yr Runoff Volume (P1 = 2.27 in.) = 2.078 acre-feet 2.27 inches -- 4.00 -- -- -- 40,904 0.939 81,269 1.866
100-yr Runoff Volume (P1 = 2.86 in.) = 2.720 acre-feet 2.86 inches -- 4.20 -- -- -- 42,789 0.982 89,211 2.048
500-yr Runoff Volume (P1 = 4.39 in.) = 4.367 acre-feet 4.39 inches -- 5.20 -- -- -- 50,249 1.154 136,157 3.126
Approximate 2-yr Detention Volume = 0.573 acre-feet -- -- -- --
Approximate 5-yr Detention Volume = 0.866 acre-feet -- -- -- --
Approximate 10-yr Detention Volume = 1.049 acre-feet -- -- -- --
Approximate 25-yr Detention Volume = 1.258 acre-feet -- -- -- --
Approximate 50-yr Detention Volume = 1.437 acre-feet -- -- -- --
Approximate 100-yr Detention Volume = 1.720 acre-feet -- -- -- --
-- -- -- --
Define Zones and Basin Geometry -- -- -- --
Zone 1 Volume (WQCV) = 0.316 acre-feet -- -- -- --
Zone 2 Volume (EURV - Zone 1) = 0.604 acre-feet -- -- -- --
Zone 3 (100yr + 1 / 2 WQCV - Zones 1 & 2) = 0.958 acre-feet -- -- -- --
Total Detention Basin Volume = 1.878 acre-feet -- -- -- --
Initial Surcharge Volume (ISV) = user ft 3 -- -- -- --
Initial Surcharge Depth (ISD) = user ft -- -- -- --
Total Available Detention Depth (Htotal) =user ft -- -- -- --
Depth of Trickle Channel (HTC) = user ft -- -- -- --
Slope of Trickle Channel (STC) =user ft/ft -- -- -- --
Slopes of Main Basin Sides (Smain) =user H:V -- -- -- --
Basin Length-to-Width Ratio (RL/W) =user -- -- -- --
-- -- -- --
Initial Surcharge Area (AISV) =user ft 2 -- -- -- --
Surcharge Volume Length (LISV) =user ft -- -- -- --
Surcharge Volume Width (WISV) =user ft -- -- -- --
Depth of Basin Floor (HFLOOR) =user ft -- -- -- --
Length of Basin Floor (LFLOOR) =user ft -- -- -- --
Width of Basin Floor (WFLOOR) =user ft -- -- -- --
Area of Basin Floor (AFLOOR) =user ft 2 -- -- -- --
Volume of Basin Floor (VFLOOR) =user ft 3 -- -- -- --
Depth of Main Basin (HMAIN) =user ft -- -- -- --
Length of Main Basin (LMAIN) =user ft -- -- -- --
Width of Main Basin (WMAIN) =user ft -- -- -- --
Area of Main Basin (AMAIN) =user ft 2 -- -- -- --
Volume of Main Basin (VMAIN) =user ft 3 -- -- -- --
Calculated Total Basin Volume (Vtotal) =user acre-feet -- -- -- --
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DETENTION BASIN STAGE-STORAGE TABLE BUILDER
Optional
Override
Area (ft 2)
Length
(ft)
Optional
Override
Stage (ft)
Stage
(ft)
Stage - Storage
Description
Area
(ft 2)
Width
(ft)
Gateway at Prospect
Pond F
MHFD-Detention, Version 4.06 (July 2022)
Volume
(ft 3)
Volume
(ac-ft)
Area
(acre)
After providing required inputs above including 1-hour rainfall
depths, click 'Run CUHP' to generate runoff hydrographs using
the embedded Colorado Urban Hydrograph Procedure.
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond F - Full Spectrum Detention.xlsm, Basin 7/1/2025, 1:37 PM
1 User Defined Stage-Area Booleans for Message
1 Equal Stage-Area Inputs Watershed L:W
1 CountA Watershed Lc:L
Watershed Slope
0 Calc_S_TC Booleans for CUHP
1 CUHP Inputs Complete
H_FLOOR 1 CUHP Results Calculated
L_FLOOR_OTHER
0.00 ISV 0.00 ISV
0.00 Floor 0.00 Floor
1.79 Zone 1 (WQCV) 1.79 Zone 1 (WQCV)
2.84 Zone 2 (EURV) 2.84 Zone 2 (EURV)
4.02 Z3 (100+1/2WQCV)4.02 Z3 (100+1/2WQCV)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
MHFD-Detention, Version 4.06 (July 2022)
0.000
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1.570
2.355
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0.580
0.870
1.160
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MHFD-Detention_v4-06 Pond F - Full Spectrum Detention.xlsm, Basin 7/1/2025, 1:37 PM
Project:
Basin ID:
Estimated Estimated
Stage (ft) Volume (ac-ft) Outlet Type
Zone 1 (WQCV) 1.79 0.316 Orifice Plate
Zone 2 (EURV) 2.84 0.604 Orifice Plate
Z3 (100+1/2WQCV) 4.02 0.958 Weir&Pipe (Restrict)
Total (all zones) 1.878
User Input: Orifice at Underdrain Outlet (typically used to drain WQCV in a Filtration BMP)Calculated Parameters for Underdrain
Underdrain Orifice Invert Depth = ft (distance below the filtration media surface) Underdrain Orifice Area =ft2
Underdrain Orifice Diameter = inches Underdrain Orifice Centroid = feet
User Input: Orifice Plate with one or more orifices or Elliptical Slot Weir (typically used to drain WQCV and/or EURV in a sedimentation BMP)Calculated Parameters for Plate
Centroid of Lowest Orifice = 0.00 ft (relative to basin bottom at Stage = 0 ft) WQ Orifice Area per Row = 1.285E-02 ft2
Depth at top of Zone using Orifice Plate = 3.00 ft (relative to basin bottom at Stage = 0 ft) Elliptical Half-Width = N/A feet
Orifice Plate: Orifice Vertical Spacing = 12.00 inches Elliptical Slot Centroid = N/A feet
Orifice Plate: Orifice Area per Row = 1.85 sq. inches (diameter = 1-1/2 inches) Elliptical Slot Area = N/A ft2
User Input: Stage and Total Area of Each Orifice Row (numbered from lowest to highest)
Row 1 (required) Row 2 (optional) Row 3 (optional) Row 4 (optional) Row 5 (optional) Row 6 (optional) Row 7 (optional) Row 8 (optional)
Stage of Orifice Centroid (ft) 0.00 1.00 2.00
Orifice Area (sq. inches) 1.85 1.85 1.85
Row 9 (optional) Row 10 (optional) Row 11 (optional) Row 12 (optional) Row 13 (optional) Row 14 (optional) Row 15 (optional) Row 16 (optional)
Stage of Orifice Centroid (ft)
Orifice Area (sq. inches)
User Input: Vertical Orifice (Circular or Rectangular)Calculated Parameters for Vertical Orifice
Not Selected Not Selected Not Selected Not Selected
Invert of Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Area = N/A N/A ft2
Depth at top of Zone using Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Centroid = N/A N/A feet
Vertical Orifice Diameter = N/A N/A inches
User Input: Overflow Weir (Dropbox with Flat or Sloped Grate and Outlet Pipe OR Rectangular/Trapezoidal Weir and No Outlet Pipe) Calculated Parameters for Overflow Weir
grate Zone 3 Weir Not Selected Zone 3 Weir Not Selected
Overflow Weir Front Edge Height, Ho = 3.20 N/A ft (relative to basin bottom at Stage = 0 ft)Height of Grate Upper Edge, Ht =4.20 N/A feet
Overflow Weir Front Edge Length = 5.00 N/A feet Overflow Weir Slope Length = 5.10 N/A feet
Overflow Weir Grate Slope = 5.00 N/A H:V Grate Open Area / 100-yr Orifice Area = 8.51 N/A
Horiz. Length of Weir Sides = 5.00 N/A feet Overflow Grate Open Area w/o Debris = 17.74 N/A ft2
Overflow Grate Type = Type C Grate N/A Overflow Grate Open Area w/ Debris = 17.74 N/A ft2
Debris Clogging % = 0% N/A %
User Input: Outlet Pipe w/ Flow Restriction Plate (Circular Orifice, Restrictor Plate, or Rectangular Orifice)Calculated Parameters for Outlet Pipe w/ Flow Restriction Plate
Zone 3 Restrictor Not Selected Zone 3 Restrictor Not Selected
Depth to Invert of Outlet Pipe = 0.00 N/A ft (distance below basin bottom at Stage = 0 ft)Outlet Orifice Area = 2.09 N/A ft2
Outlet Pipe Diameter = 21.00 N/A inches Outlet Orifice Centroid = 0.77 N/A feet
Restrictor Plate Height Above Pipe Invert = 17.00 inches Half-Central Angle of Restrictor Plate on Pipe = 2.24 N/A radians
User Input: Emergency Spillway (Rectangular or Trapezoidal)Calculated Parameters for Spillway
Spillway Invert Stage= 4.20 ft (relative to basin bottom at Stage = 0 ft) Spillway Design Flow Depth= 0.49 feet
Spillway Crest Length = 32.00 feet Stage at Top of Freeboard = 5.69 feet
Spillway End Slopes = 29.00 H:V Basin Area at Top of Freeboard = 1.15 acres
Freeboard above Max Water Surface = 1.00 feet Basin Volume at Top of Freeboard = 3.13 acre-ft
Max Ponding Depth of Target Storage Volume =4.04 feet Discharge at Top of Freeboard = 186.74 cfs
Routed Hydrograph Results
Design Storm Return Period =WQCV EURV 2 Year 5 Year 10 Year 25 Year 50 Year 100 Year 500 Year
One-Hour Rainfall Depth (in) =N/A N/A 0.82 1.14 1.40 1.81 2.27 2.86 4.39
CUHP Runoff Volume (acre-ft) =0.316 0.920 0.590 0.886 1.147 1.592 2.078 2.720 4.367
Inflow Hydrograph Volume (acre-ft) =N/A N/A 0.590 0.886 1.147 1.592 2.078 2.720 4.367
CUHP Predevelopment Peak Q (cfs) =N/A N/A 0.1 1.4 3.4 8.4 12.8 19.1 33.8
OPTIONAL Override Predevelopment Peak Q (cfs) =N/A N/A
Predevelopment Unit Peak Flow, q (cfs/acre) =N/A N/A 0.01 0.12 0.28 0.69 1.05 1.56 2.77
Peak Inflow Q (cfs) =N/A N/A 9.8 14.6 18.6 26.6 34.5 45.8 72.5
Peak Outflow Q (cfs) =0.1 0.2 0.2 0.2 0.3 2.3 6.2 14.0 37.3
Ratio Peak Outflow to Predevelopment Q =N/A N/A N/A 0.2 0.1 0.3 0.5 0.7 1.1
Structure Controlling Flow =Plate Plate Plate Plate Plate Overflow Weir 1 Overflow Weir 1 Overflow Weir 1 Spillway
Max Velocity through Grate 1 (fps) =N/A N/A N/A N/A N/A 0.1 0.3 0.8 1.1
Max Velocity through Grate 2 (fps) =N/A N/A N/A N/A N/A N/A N/A N/A N/A
Time to Drain 97% of Inflow Volume (hours) =38 72 57 71 82 86 84 82 76
Time to Drain 99% of Inflow Volume (hours) =40 76 60 75 87 93 93 91 88
Maximum Ponding Depth (ft) =1.80 2.84 2.27 2.73 3.09 3.49 3.74 4.04 4.49
Area at Maximum Ponding Depth (acres) =0.46 0.69 0.56 0.67 0.75 0.82 0.88 0.95 1.03
Maximum Volume Stored (acre-ft) =0.320 0.922 0.557 0.847 1.102 1.408 1.621 1.903 2.340
The user can override the default CUHP hydrographs and runoff volumes by entering new values in the Inflow Hydrographs table (Columns W through AF).
DETENTION BASIN OUTLET STRUCTURE DESIGN
MHFD-Detention, Version 4.06 (July 2022)
Gateway at Prospect
Pond F
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond F - Full Spectrum Detention.xlsm, Outlet Structure 7/1/2025, 1:40 PM
COUNTA for Basin Tab = 1 Ao Dia WQ Plate Type Vert Orifice 1Vert Orifice 2
Count_Underdrain = 0 0.11(diameter = 3/8 inch)2 1 1
Count_WQPlate = 1 0.14(diameter = 7/16 inch)
Count_VertOrifice1 = 0 0.18(diameter = 1/2 inch)Outlet Plate 1 Outlet Plate 2 Drain Time Message Boolean
Count_VertOrifice2 = 0 0.24(diameter = 9/16 inch)4 1 5yr, <72hr 0
Count_Weir1 = 1 0.29(diameter = 5/8 inch)>5yr, <120hr 0
Count_Weir2 = 0 0.36(diameter = 11/16 inch)Max Depth Row
Count_OutletPipe1 = 1 0.42(diameter = 3/4 inch)WQCV 181
Count_OutletPipe2 = 0 0.50(diameter = 13/16 inch)2 Year 228
COUNTA_2 (Standard FSD Setup)= 1 0.58(diameter = 7/8 inch)EURV 285
Hidden Parameters & Calculations 0.67(diameter = 15/16 inch)5 Year 274
MaxPondDepth_Error? FALSE 0.76 (diameter = 1 inch)10 Year 310 Spillway Depth
Cd_Broad-Crested Weir 3.00 0.86(diameter = 1-1/16 inches)25 Year 350 0.49
WQ Plate Flow at 100yr depth = 0.32 0.97(diameter = 1-1/8 inches)50 Year 375
CLOG #1= 100% 1.08(diameter = 1-3/16 inches)100 Year 405 1 Z1_Boolean
n*Cdw #1 = 0.39 1.20(diameter = 1-1/4 inches)500 Year 450 1 Z2_Boolean
n*Cdo #1 = 1.28 1.32(diameter = 1-5/16 inches)Zone3_Pulldown Message 1 Z3_Boolean
Overflow Weir #1 Angle = 0.197 1.45(diameter = 1-3/8 inches)1 Opening Message
CLOG #2= N/A 1.59(diameter = 1-7/16 inches)Draintime Running
n*Cdw #2 = N/A 1.73(diameter = 1-1/2 inches)Outlet Boolean Outlet Rank Total (1 to 4)
n*Cdo #2 = N/A 1.88(diameter = 1-9/16 inches)Vertical Orifice 1 0 0 1
Overflow Weir #2 Angle = N/A 2.03(diameter = 1-5/8 inches)Vertical Orifice 2 0 0 Boolean
Underdrain Q at 100yr depth = 0.00 2.20(diameter = 1-11/16 inches)Overflow Weir 1 1 1 0 Max Depth
VertOrifice1 Q at 100yr depth = 0.00 2.36(diameter = 1-3/4 inches)Overflow Weir 2 0 0 0 500yr Depth
VertOrifice2 Q at 100yr depth = 0.00 2.54(diameter = 1-13/16 inches)Outlet Pipe 1 1 1 1 Freeboard
2.72(diameter = 1-7/8 inches)Outlet Pipe 2 0 0 1 Spillway
Count_User_Hydrographs 0 2.90(diameter = 1-15/16 inches)0 Spillway Length
CountA_3 (EURV & 100yr) = 1 3.09(diameter = 2 inches)FALSE Time Interval
CountA_4 (100yr Only) = 1 3.29(use rectangular openings)Button Visibility Boolean
COUNTA_5 (FSD Weir Only)= 0 0 WQCV Underdrain
COUNTA_6 (EURV Weir Only)= 1 1 WQCV Plate
0 EURV-WQCV Plate
Outlet1_Pulldown_Boolean 0 EURV-WQCV VertOriice
Outlet2_Pulldown_Boolean 1 Outlet 90% Qpeak
Outlet3_Pulldown_Boolean 0 Outlet Undetained
0 Weir Only 90% Qpeak
0 Five Year Ratio Plate
0 Five Year Ratio VertOrifice
EURV_draintime_user
Spillway Options
Offset
Overlapping
S-A-V-D Chart Axis Default X-axis Left Y-Axis Right Y-Axis
minimum bound 0.00 0 0
maximum bound 6.00 140,000 190
S-A-V-D Chart Axis Override X-axis Left Y-Axis Right Y-Axis
minimum bound
maximum bound
MHFD-Detention, Version 4.06 (July 2022)
DETENTION BASIN OUTLET STRUCTURE DESIGN
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MHFD-Detention_v4-06 Pond F - Full Spectrum Detention.xlsm, Outlet Structure 7/1/2025, 1:40 PM
Project:
Basin ID:
Depth Increment = ft
Watershed Information Top of Micropool -- 0.00 -- -- -- 42 0.001
Selected BMP Type =EDB -- 0.20 -- -- -- 665 0.015 64 0.001
Watershed Area = 7.05 acres -- 0.40 -- -- -- 1,977 0.045 315 0.007
Watershed Length = 570 ft -- 0.60 -- -- -- 3,802 0.087 913 0.021
Watershed Length to Centroid = 310 ft -- 0.80 -- -- -- 6,199 0.142 1,913 0.044
Watershed Slope = 0.010 ft/ft -- 1.00 -- -- -- 8,719 0.200 3,405 0.078
Watershed Imperviousness = 70.00% percent -- 1.20 -- -- -- 11,510 0.264 5,313 0.122
Percentage Hydrologic Soil Group A = 0.0% percent -- 1.40 -- -- -- 14,444 0.332 7,879 0.181
Percentage Hydrologic Soil Group B = 0.0% percent -- 1.50 -- -- -- 16,089 0.369 9,549 0.219
Percentage Hydrologic Soil Groups C/D = 100.0% percent -- 1.60 -- -- -- 17,784 0.408 11,243 0.258
Target WQCV Drain Time = 40.0 hours -- 1.80 -- -- -- 21,572 0.495 15,178 0.348
Location for 1-hr Rainfall Depths = User Input -- 2.00 -- -- -- 25,847 0.593 19,920 0.457
-- 2.20 -- -- -- 30,277 0.695 25,231 0.579
-- 2.40 -- -- -- 34,455 0.791 31,662 0.727
Optional User Overrides -- 2.60 -- -- -- 38,605 0.886 39,312 0.902
Water Quality Capture Volume (WQCV) = 0.162 acre-feet acre-feet -- 2.80 -- -- -- 42,530 0.976 47,425 1.089
Excess Urban Runoff Volume (EURV) = 0.480 acre-feet acre-feet -- 3.80 -- -- -- 55,247 1.268 96,314 2.211
2-yr Runoff Volume (P1 = 0.82 in.) = 0.299 acre-feet 0.82 inches -- -- -- --
5-yr Runoff Volume (P1 = 1.14 in.) = 0.457 acre-feet 1.14 inches -- -- -- --
10-yr Runoff Volume (P1 = 1.4 in.) = 0.600 acre-feet 1.40 inches -- -- -- --
25-yr Runoff Volume (P1 = 1.81 in.) = 0.851 acre-feet 1.81 inches -- -- -- --
50-yr Runoff Volume (P1 = 2.27 in.) = 1.123 acre-feet 2.27 inches -- -- -- --
100-yr Runoff Volume (P1 = 2.86 in.) = 1.486 acre-feet 2.86 inches -- -- -- --
500-yr Runoff Volume (P1 = 4.39 in.) = 2.414 acre-feet 4.39 inches -- -- -- --
Approximate 2-yr Detention Volume = 0.297 acre-feet -- -- -- --
Approximate 5-yr Detention Volume = 0.457 acre-feet -- -- -- --
Approximate 10-yr Detention Volume = 0.551 acre-feet -- -- -- --
Approximate 25-yr Detention Volume = 0.664 acre-feet -- -- -- --
Approximate 50-yr Detention Volume = 0.760 acre-feet -- -- -- --
Approximate 100-yr Detention Volume = 0.923 acre-feet -- -- -- --
-- -- -- --
Define Zones and Basin Geometry -- -- -- --
Zone 1 Volume (WQCV) = 0.162 acre-feet -- -- -- --
Zone 2 Volume (EURV - Zone 1) = 0.318 acre-feet -- -- -- --
Zone 3 (100yr + 1 / 2 WQCV - Zones 1 & 2) = 0.524 acre-feet -- -- -- --
Total Detention Basin Volume = 1.004 acre-feet -- -- -- --
Initial Surcharge Volume (ISV) = user ft 3 -- -- -- --
Initial Surcharge Depth (ISD) = user ft -- -- -- --
Total Available Detention Depth (Htotal) =user ft -- -- -- --
Depth of Trickle Channel (HTC) = user ft -- -- -- --
Slope of Trickle Channel (STC) =user ft/ft -- -- -- --
Slopes of Main Basin Sides (Smain) =user H:V -- -- -- --
Basin Length-to-Width Ratio (RL/W) =user -- -- -- --
-- -- -- --
Initial Surcharge Area (AISV) =user ft 2 -- -- -- --
Surcharge Volume Length (LISV) =user ft -- -- -- --
Surcharge Volume Width (WISV) =user ft -- -- -- --
Depth of Basin Floor (HFLOOR) =user ft -- -- -- --
Length of Basin Floor (LFLOOR) =user ft -- -- -- --
Width of Basin Floor (WFLOOR) =user ft -- -- -- --
Area of Basin Floor (AFLOOR) =user ft 2 -- -- -- --
Volume of Basin Floor (VFLOOR) =user ft 3 -- -- -- --
Depth of Main Basin (HMAIN) =user ft -- -- -- --
Length of Main Basin (LMAIN) =user ft -- -- -- --
Width of Main Basin (WMAIN) =user ft -- -- -- --
Area of Main Basin (AMAIN) =user ft 2 -- -- -- --
Volume of Main Basin (VMAIN) =user ft 3 -- -- -- --
Calculated Total Basin Volume (Vtotal) =user acre-feet -- -- -- --
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After providing required inputs above including 1-hour rainfall
depths, click 'Run CUHP' to generate runoff hydrographs using
the embedded Colorado Urban Hydrograph Procedure.
Volume
(ft 3)
Volume
(ac-ft)
Area
(acre)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
Optional
Override
Area (ft 2)
Length
(ft)
Optional
Override
Stage (ft)
Stage
(ft)
Stage - Storage
Description
Area
(ft 2)
Width
(ft)
Gateway at Prospect
Pond G
MHFD-Detention, Version 4.06 (July 2022)
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond G - Full Spectrum Detention.xlsm, Basin 7/1/2025, 4:04 PM
1 User Defined Stage-Area Booleans for Message
1 Equal Stage-Area Inputs Watershed L:W
1 CountA Watershed Lc:L
Watershed Slope
0 Calc_S_TC Booleans for CUHP
1 CUHP Inputs Complete
H_FLOOR 1 CUHP Results Calculated
L_FLOOR_OTHER
0.00 ISV 0.00 ISV
0.00 Floor 0.00 Floor
1.33 Zone 1 (WQCV) 1.33 Zone 1 (WQCV)
2.04 Zone 2 (EURV) 2.04 Zone 2 (EURV)
2.72 Z3 (100+1/2WQCV)2.72 Z3 (100+1/2WQCV)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
MHFD-Detention, Version 4.06 (July 2022)
0.000
0.555
1.110
1.665
2.220
0.000
0.320
0.640
0.960
1.280
0.00 1.00 2.00 3.00 4.00
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MHFD-Detention_v4-06 Pond G - Full Spectrum Detention.xlsm, Basin 7/1/2025, 4:04 PM
Project:
Basin ID:
Estimated Estimated
Stage (ft) Volume (ac-ft) Outlet Type
Zone 1 (WQCV) 1.33 0.162 Orifice Plate
Zone 2 (EURV) 2.04 0.318 Orifice Plate
Z3 (100+1/2WQCV) 2.72 0.524 Weir&Pipe (Restrict)
Total (all zones) 1.004
User Input: Orifice at Underdrain Outlet (typically used to drain WQCV in a Filtration BMP)Calculated Parameters for Underdrain
Underdrain Orifice Invert Depth = N/A ft (distance below the filtration media surface) Underdrain Orifice Area = N/A ft2
Underdrain Orifice Diameter = N/A inches Underdrain Orifice Centroid = N/A feet
User Input: Orifice Plate with one or more orifices or Elliptical Slot Weir (typically used to drain WQCV and/or EURV in a sedimentation BMP)Calculated Parameters for Plate
Centroid of Lowest Orifice = 0.00 ft (relative to basin bottom at Stage = 0 ft) WQ Orifice Area per Row = 8.472E-03 ft2
Depth at top of Zone using Orifice Plate = 2.20 ft (relative to basin bottom at Stage = 0 ft) Elliptical Half-Width = N/A feet
Orifice Plate: Orifice Vertical Spacing = 9.00 inches Elliptical Slot Centroid = N/A feet
Orifice Plate: Orifice Area per Row = 1.22 sq. inches (diameter = 1-1/4 inches) Elliptical Slot Area = N/A ft2
User Input: Stage and Total Area of Each Orifice Row (numbered from lowest to highest)
Row 1 (required) Row 2 (optional) Row 3 (optional) Row 4 (optional) Row 5 (optional) Row 6 (optional) Row 7 (optional) Row 8 (optional)
Stage of Orifice Centroid (ft) 0.00 0.80 1.60
Orifice Area (sq. inches) 1.22 1.22 1.22
Row 9 (optional) Row 10 (optional) Row 11 (optional) Row 12 (optional) Row 13 (optional) Row 14 (optional) Row 15 (optional) Row 16 (optional)
Stage of Orifice Centroid (ft)
Orifice Area (sq. inches)
User Input: Vertical Orifice (Circular or Rectangular)Calculated Parameters for Vertical Orifice
Not Selected Not Selected Not Selected Not Selected
Invert of Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Area = N/A N/A ft2
Depth at top of Zone using Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Centroid = N/A N/A feet
Vertical Orifice Diameter = N/A N/A inches
User Input: Overflow Weir (Dropbox with Flat or Sloped Grate and Outlet Pipe OR Rectangular/Trapezoidal Weir and No Outlet Pipe) Calculated Parameters for Overflow Weir
grate Zone 3 Weir Not Selected Zone 3 Weir Not Selected
Overflow Weir Front Edge Height, Ho = 2.22 N/A ft (relative to basin bottom at Stage = 0 ft)Height of Grate Upper Edge, Ht =2.62 N/A feet
Overflow Weir Front Edge Length = 14.00 N/A feet Overflow Weir Slope Length = 4.02 N/A feet
Overflow Weir Grate Slope = 10.00 N/A H:V Grate Open Area / 100-yr Orifice Area = 21.78 N/A
Horiz. Length of Weir Sides = 4.00 N/A feet Overflow Grate Open Area w/o Debris = 39.17 N/A ft2
Overflow Grate Type = Type C Grate N/A Overflow Grate Open Area w/ Debris = 39.17 N/A ft2
Debris Clogging % = 0% N/A %
User Input: Outlet Pipe w/ Flow Restriction Plate (Circular Orifice, Restrictor Plate, or Rectangular Orifice)Calculated Parameters for Outlet Pipe w/ Flow Restriction Plate
Zone 3 Restrictor Not Selected Zone 3 Restrictor Not Selected
Depth to Invert of Outlet Pipe = 0.00 N/A ft (distance below basin bottom at Stage = 0 ft)Outlet Orifice Area = 1.80 N/A ft2
Outlet Pipe Diameter = 21.00 N/A inches Outlet Orifice Centroid = 0.68 N/A feet
Restrictor Plate Height Above Pipe Invert = 14.70 inches Half-Central Angle of Restrictor Plate on Pipe = 1.98 N/A radians
User Input: Emergency Spillway (Rectangular or Trapezoidal)Calculated Parameters for Spillway
Spillway Invert Stage= 2.80 ft (relative to basin bottom at Stage = 0 ft) Spillway Design Flow Depth= 0.51 feet
Spillway Crest Length = 24.00 feet Stage at Top of Freeboard = 4.31 feet
Spillway End Slopes = 4.00 H:V Basin Area at Top of Freeboard = 1.27 acres
Freeboard above Max Water Surface = 1.00 feet Basin Volume at Top of Freeboard = 2.21 acre-ft
Max Ponding Depth of Target Storage Volume =2.61 feet Discharge at Top of Freeboard = 96.89 cfs
Routed Hydrograph Results
Design Storm Return Period =WQCV EURV 2 Year 5 Year 10 Year 25 Year 50 Year 100 Year 500 Year
One-Hour Rainfall Depth (in) =N/A N/A 0.82 1.14 1.40 1.81 2.27 2.86 4.39
CUHP Runoff Volume (acre-ft) =0.162 0.480 0.299 0.457 0.600 0.851 1.123 1.486 2.414
Inflow Hydrograph Volume (acre-ft) =N/A N/A 0.299 0.457 0.600 0.851 1.123 1.486 2.414
CUHP Predevelopment Peak Q (cfs) =N/A N/A 0.1 1.0 2.4 5.9 8.9 13.0 23.1
OPTIONAL Override Predevelopment Peak Q (cfs) =N/A N/A
Predevelopment Unit Peak Flow, q (cfs/acre) =N/A N/A 0.01 0.15 0.35 0.83 1.26 1.85 3.27
Peak Inflow Q (cfs) =N/A N/A 5.6 8.5 11.0 15.9 20.9 28.1 44.7
Peak Outflow Q (cfs) =0.1 0.1 0.1 0.1 0.1 2.2 5.7 11.4 19.5
Ratio Peak Outflow to Predevelopment Q =N/A N/A N/A 0.1 0.1 0.4 0.6 0.9 0.8
Structure Controlling Flow =Plate Plate Plate Plate Plate Overflow Weir 1 Overflow Weir 1 Outlet Plate 1 Spillway
Max Velocity through Grate 1 (fps) =N/A N/A N/A N/A N/A 0.0 0.1 0.3 0.3
Max Velocity through Grate 2 (fps) =N/A N/A N/A N/A N/A N/A N/A N/A N/A
Time to Drain 97% of Inflow Volume (hours) =38 71 56 70 81 82 79 75 69
Time to Drain 99% of Inflow Volume (hours) =40 76 59 74 86 89 88 86 83
Maximum Ponding Depth (ft) =1.34 2.04 1.66 1.97 2.19 2.35 2.47 2.61 3.00
Area at Maximum Ponding Depth (acres) =0.31 0.61 0.43 0.57 0.68 0.77 0.82 0.89 1.03
Maximum Volume Stored (acre-ft) =0.165 0.481 0.283 0.434 0.572 0.696 0.791 0.902 1.280
DETENTION BASIN OUTLET STRUCTURE DESIGN
MHFD-Detention, Version 4.06 (July 2022)
Gateway at Prospect
Pond G
The user can override the default CUHP hydrographs and runoff volumes by entering new values in the Inflow Hydrographs table (Columns W through AF).
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond G - Full Spectrum Detention.xlsm, Outlet Structure 7/1/2025, 4:03 PM
COUNTA for Basin Tab = 1 Ao Dia WQ Plate Type Vert Orifice 1Vert Orifice 2
Count_Underdrain = 0 0.11(diameter = 3/8 inch)2 1 1
Count_WQPlate = 1 0.14(diameter = 7/16 inch)
Count_VertOrifice1 = 0 0.18(diameter = 1/2 inch)Outlet Plate 1 Outlet Plate 2 Drain Time Message Boolean
Count_VertOrifice2 = 0 0.24(diameter = 9/16 inch)4 1 5yr, <72hr 0
Count_Weir1 = 1 0.29(diameter = 5/8 inch)>5yr, <120hr 0
Count_Weir2 = 0 0.36(diameter = 11/16 inch)Max Depth Row
Count_OutletPipe1 = 1 0.42(diameter = 3/4 inch)WQCV 135
Count_OutletPipe2 = 0 0.50(diameter = 13/16 inch)2 Year 167
COUNTA_2 (Standard FSD Setup)= 1 0.58(diameter = 7/8 inch)EURV 205
Hidden Parameters & Calculations 0.67(diameter = 15/16 inch)5 Year 198
MaxPondDepth_Error? FALSE 0.76 (diameter = 1 inch)10 Year 220 Spillway Depth
Cd_Broad-Crested Weir 3.00 0.86(diameter = 1-1/16 inches)25 Year 236 0.51
WQ Plate Flow at 100yr depth = 0.16 0.97(diameter = 1-1/8 inches)50 Year 248
CLOG #1= 100% 1.08(diameter = 1-3/16 inches)100 Year 262 1 Z1_Boolean
n*Cdw #1 = 0.52 1.20(diameter = 1-1/4 inches)500 Year 301 1 Z2_Boolean
n*Cdo #1 = 0.97 1.32(diameter = 1-5/16 inches)Zone3_Pulldown Message 1 Z3_Boolean
Overflow Weir #1 Angle = 0.100 1.45(diameter = 1-3/8 inches)1 Opening Message
CLOG #2= N/A 1.59(diameter = 1-7/16 inches)Draintime Running
n*Cdw #2 = N/A 1.73(diameter = 1-1/2 inches)Outlet Boolean Outlet Rank Total (1 to 4)
n*Cdo #2 = N/A 1.88(diameter = 1-9/16 inches)Vertical Orifice 1 0 0 1
Overflow Weir #2 Angle = N/A 2.03(diameter = 1-5/8 inches)Vertical Orifice 2 0 0 Boolean
Underdrain Q at 100yr depth = 0.00 2.20(diameter = 1-11/16 inches)Overflow Weir 1 1 1 0 Max Depth
VertOrifice1 Q at 100yr depth = 0.00 2.36(diameter = 1-3/4 inches)Overflow Weir 2 0 0 0 500yr Depth
VertOrifice2 Q at 100yr depth = 0.00 2.54(diameter = 1-13/16 inches)Outlet Pipe 1 1 1 1 Freeboard
2.72(diameter = 1-7/8 inches)Outlet Pipe 2 0 0 1 Spillway
Count_User_Hydrographs 0 2.90(diameter = 1-15/16 inches)0 Spillway Length
CountA_3 (EURV & 100yr) = 1 3.09(diameter = 2 inches)FALSE Time Interval
CountA_4 (100yr Only) = 1 3.29(use rectangular openings)Button Visibility Boolean
COUNTA_5 (FSD Weir Only)= 0 0 WQCV Underdrain
COUNTA_6 (EURV Weir Only)= 1 1 WQCV Plate
0 EURV-WQCV Plate
Outlet1_Pulldown_Boolean 0 EURV-WQCV VertOriice
Outlet2_Pulldown_Boolean 1 Outlet 90% Qpeak
Outlet3_Pulldown_Boolean 0 Outlet Undetained
0 Weir Only 90% Qpeak
0 Five Year Ratio Plate
0 Five Year Ratio VertOrifice
EURV_draintime_user
Spillway Options
Offset
Overlapping
S-A-V-D Chart Axis Default X-axis Left Y-Axis Right Y-Axis
minimum bound 0.00 0 0
maximum bound 6.00 100,000 100
S-A-V-D Chart Axis Override X-axis Left Y-Axis Right Y-Axis
minimum bound
maximum bound
DETENTION BASIN OUTLET STRUCTURE DESIGN
MHFD-Detention, Version 4.06 (July 2022)
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PONDING DEPTH [ft]
User Area [ft^2]
Interpolated Area [ft^2]
Summary Area [ft^2]
Volume [ft^3]
Summary Volume [ft^3]
Outflow [cfs]
Summary Outflow [cfs]
MHFD-Detention_v4-06 Pond G - Full Spectrum Detention.xlsm, Outlet Structure 7/1/2025, 4:03 PM
Project:
Basin ID:
Depth Increment = 0.20 ft
Watershed Information Top of Micropool 0.00 11.5 11.5 133 0.003
Selected BMP Type =EDB ISV 0.45 11.5 11.5 133 0.003 60 0.001
Watershed Area = 16.72 acres 0.60 25.5 18.2 464 0.011 90 0.002
Watershed Length = 1,500 ft 0.80 67.1 38.2 2,564 0.059 365 0.008
Watershed Length to Centroid = 850 ft 1.00 108.7 58.2 6,327 0.145 1,226 0.028
Watershed Slope = 0.015 ft/ft 1.20 150.3 78.2 11,754 0.270 3,007 0.069
Watershed Imperviousness = 80.00% percent 1.40 191.9 98.2 18,846 0.433 6,039 0.139
Percentage Hydrologic Soil Group A = 0.0% percent 1.60 233.5 118.2 27,601 0.634 10,656 0.245
Percentage Hydrologic Soil Group B = 0.0% percent Floor 1.63 239.7 121.2 29,058 0.667 11,506 0.264
Percentage Hydrologic Soil Groups C/D = 100.0% percent 1.80 243.0 124.2 30,180 0.693 16,551 0.380
Target WQCV Drain Time = 40.0 hours Zone 1 (WQCV)1.92 244.9 126.1 30,889 0.709 20,215 0.464
Location for 1-hr Rainfall Depths = Thornton - Civic Center 2.00 246.2 127.4 31,365 0.720 22,705 0.521
2.20 249.4 130.6 32,571 0.748 29,098 0.668
2.40 252.6 133.8 33,797 0.776 35,735 0.820
Optional User Overrides 2.60 255.8 137.0 35,044 0.804 42,619 0.978
Water Quality Capture Volume (WQCV) = 0.457 acre-feet acre-feet 2.80 259.0 140.2 36,311 0.834 49,754 1.142
Excess Urban Runoff Volume (EURV) = 1.314 acre-feet acre-feet 3.00 262.2 143.4 37,599 0.863 57,144 1.312
2-yr Runoff Volume (P1 = 0.82 in.) = 0.862 acre-feet 0.82 inches Zone 2 (EURV)3.01 262.4 143.6 37,664 0.865 57,521 1.320
5-yr Runoff Volume (P1 = 1.14 in.) = 1.287 acre-feet 1.14 inches 3.20 265.4 146.6 38,907 0.893 64,795 1.487
10-yr Runoff Volume (P1 = 1.4 in.) = 1.657 acre-feet 1.40 inches 3.40 268.6 149.8 40,235 0.924 72,708 1.669
25-yr Runoff Volume (P1 = 1.81 in.) = 2.280 acre-feet 1.81 inches 3.60 271.8 153.0 41,585 0.955 80,890 1.857
50-yr Runoff Volume (P1 = 2.27 in.) = 2.964 acre-feet 2.27 inches 3.80 275.0 156.2 42,954 0.986 89,344 2.051
100-yr Runoff Volume (P1 = 2.86 in.) = 3.864 acre-feet 2.86 inches 4.00 278.2 159.4 44,344 1.018 98,073 2.251
500-yr Runoff Volume (P1 = 4.39 in.) = 6.175 acre-feet 4.39 inches 4.20 281.4 162.6 45,755 1.050 107,083 2.458
Approximate 2-yr Detention Volume = 0.820 acre-feet Z3 (100+1/2WQCV)4.39 284.4 165.6 47,114 1.082 115,905 2.661
Approximate 5-yr Detention Volume = 1.231 acre-feet 4.40 284.6 165.8 47,186 1.083 116,376 2.672
Approximate 10-yr Detention Volume = 1.493 acre-feet 4.60 287.8 169.0 48,637 1.117 125,958 2.892
Approximate 25-yr Detention Volume = 1.790 acre-feet 4.80 291.0 172.2 50,109 1.150 135,833 3.118
Approximate 50-yr Detention Volume = 2.043 acre-feet 5.00 294.2 175.4 51,602 1.185 146,003 3.352
Approximate 100-yr Detention Volume = 2.429 acre-feet 5.20 297.4 178.6 53,115 1.219 156,475 3.592
5.40 300.6 181.8 54,648 1.255 167,251 3.840
Define Zones and Basin Geometry 5.60 303.8 185.0 56,202 1.290 178,335 4.094
Zone 1 Volume (WQCV) = 0.457 acre-feet 5.80 307.0 188.2 57,776 1.326 189,733 4.356
Zone 2 Volume (EURV - Zone 1) = 0.856 acre-feet 6.00 310.2 191.4 59,371 1.363 201,447 4.625
Zone 3 (100yr + 1 / 2 WQCV - Zones 1 & 2) = 1.344 acre-feet 6.20 313.4 194.6 60,987 1.400 213,483 4.901
Total Detention Basin Volume = 2.658 acre-feet 6.40 316.6 197.8 62,622 1.438 225,843 5.185
Initial Surcharge Volume (ISV) = 60 ft 3 6.60 319.8 201.0 64,279 1.476 238,533 5.476
Initial Surcharge Depth (ISD) = 0.45 ft 6.80 323.0 204.2 65,955 1.514 251,556 5.775
Total Available Detention Depth (Htotal) =4.40 ft 7.00 326.2 207.4 67,653 1.553 264,916 6.082
Depth of Trickle Channel (HTC) = 0.08 ft 7.20 329.4 210.6 69,371 1.593 278,618 6.396
Slope of Trickle Channel (STC) =0.005 ft/ft 7.40 332.6 213.8 71,109 1.632 292,666 6.719
Slopes of Main Basin Sides (Smain) =8 H:V 7.60 335.8 217.0 72,867 1.673 307,063 7.049
Basin Length-to-Width Ratio (RL/W) =2 7.80 339.0 220.2 74,647 1.714 321,814 7.388
8.00 342.2 223.4 76,446 1.755 336,923 7.735
Initial Surcharge Area (AISV) =133 ft 2 8.20 345.4 226.6 78,266 1.797 352,394 8.090
Surcharge Volume Length (LISV) =11.5 ft 8.40 348.6 229.8 80,107 1.839 368,231 8.453
Surcharge Volume Width (WISV) =11.5 ft 8.60 351.8 233.0 81,968 1.882 384,438 8.825
Depth of Basin Floor (HFLOOR) =1.10 ft 8.80 355.0 236.2 83,850 1.925 401,020 9.206
Length of Basin Floor (LFLOOR) =240.3 ft 9.00 358.2 239.4 85,752 1.969 417,980 9.595
Width of Basin Floor (WFLOOR) =121.5 ft 9.20 361.4 242.6 87,674 2.013 435,322 9.994
Area of Basin Floor (AFLOOR) =29,206 ft 2 9.40 364.6 245.8 89,617 2.057 453,051 10.401
Volume of Basin Floor (VFLOOR) =11,480 ft 3 9.60 367.8 249.0 91,581 2.102 471,170 10.817
Depth of Main Basin (HMAIN) =2.77 ft 9.80 371.0 252.2 93,565 2.148 489,685 11.242
Length of Main Basin (LMAIN) =284.6 ft 10.00 374.2 255.4 95,569 2.194 508,598 11.676
Width of Main Basin (WMAIN) =165.8 ft 10.20 377.4 258.6 97,594 2.240 527,914 12.119
Area of Main Basin (AMAIN) =47,186 ft 2 10.40 380.6 261.8 99,640 2.287 547,637 12.572
Volume of Main Basin (VMAIN) =104,698 ft 3 10.60 383.8 265.0 101,706 2.335 567,771 13.034
Calculated Total Basin Volume (Vtotal) =2.669 acre-feet 10.80 387.0 268.2 103,792 2.383 588,320 13.506
11.00 390.2 271.4 105,899 2.431 609,289 13.987
11.20 393.4 274.6 108,026 2.480 630,681 14.478
11.40 396.6 277.8 110,174 2.529 652,501 14.979
11.60 399.8 281.0 112,342 2.579 674,752 15.490
11.80 403.0 284.2 114,531 2.629 697,439 16.011
12.00 406.2 287.4 116,740 2.680 720,566 16.542
12.20 409.4 290.6 118,970 2.731 744,137 17.083
12.40 412.6 293.8 121,220 2.783 768,155 17.634
12.60 415.8 297.0 123,491 2.835 792,626 18.196
12.80 419.0 300.2 125,782 2.888 817,553 18.768
13.00 422.2 303.4 128,094 2.941 842,941 19.351
13.20 425.4 306.6 130,426 2.994 868,792 19.945
13.40 428.6 309.8 132,779 3.048 895,112 20.549
13.60 431.8 313.0 135,152 3.103 921,905 21.164
13.80 435.0 316.2 137,545 3.158 949,174 21.790
14.00 438.2 319.4 139,959 3.213 976,925 22.427
14.20 441.4 322.6 142,394 3.269 1,005,160 23.075
14.40 444.6 325.8 144,849 3.325 1,033,884 23.735
14.60 447.8 329.0 147,325 3.382 1,063,101 24.405
14.80 451.0 332.2 149,821 3.439 1,092,815 25.088
15.00 454.2 335.4 152,337 3.497 1,123,030 25.781
15.20 457.4 338.6 154,874 3.555 1,153,751 26.486
15.40 460.6 341.8 157,431 3.614 1,184,981 27.203
15.60 463.8 345.0 160,009 3.673 1,216,725 27.932
15.80 467.0 348.2 162,608 3.733 1,248,986 28.673
16.00 470.2 351.4 165,227 3.793 1,281,769 29.425
16.20 473.4 354.6 167,866 3.854 1,315,078 30.190
16.40 476.6 357.8 170,526 3.915 1,348,917 30.967
16.60 479.8 361.0 173,206 3.976 1,383,290 31.756
16.80 483.0 364.2 175,907 4.038 1,418,201 32.557
17.00 486.2 367.4 178,628 4.101 1,453,654 33.371
17.20 489.4 370.6 181,370 4.164 1,489,653 34.198
17.40 492.6 373.8 184,132 4.227 1,526,203 35.037
17.60 495.8 377.0 186,915 4.291 1,563,308 35.889
17.80 499.0 380.2 189,718 4.355 1,600,971 36.753
18.00 502.2 383.4 192,542 4.420 1,639,196 37.631
18.20 505.4 386.6 195,386 4.485 1,677,989 38.521
18.40 508.6 389.8 198,250 4.551 1,717,352 39.425
18.60 511.8 393.0 201,135 4.617 1,757,290 40.342
18.80 515.0 396.2 204,041 4.684 1,797,807 41.272
19.00 518.2 399.4 206,967 4.751 1,838,908 42.216
After providing required inputs above including 1-hour rainfall
depths, click 'Run CUHP' to generate runoff hydrographs using
the embedded Colorado Urban Hydrograph Procedure.
Volume
(ft 3)
Volume
(ac-ft)
Area
(acre)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
Optional
Override
Area (ft 2)
Length
(ft)
Optional
Override
Stage (ft)
Stage
(ft)
Stage - Storage
Description
Area
(ft 2)
Width
(ft)
Gateway at Prospect
Pond H - Future
MHFD-Detention, Version 4.06 (July 2022)
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond H (Future) - Full Spectrum Detention.xlsm, Basin 6/25/2025, 10:03 AM
0 User Defined Stage-Area Booleans for Message
0 Equal Stage-Area Inputs Watershed L:W
1 CountA Watershed Lc:L
Watershed Slope
0 Calc_S_TC Booleans for CUHP
1 CUHP Inputs Complete
1.10 H_FLOOR 1 CUHP Results Calculated
L_FLOOR_OTHER
0.45 ISV 0.45 ISV
1.63 Floor 1.63 Floor
1.92 Zone 1 (WQCV) 1.92 Zone 1 (WQCV)
3.01 Zone 2 (EURV) 3.01 Zone 2 (EURV)
4.39 Z3 (100+1/2WQCV)4.39 Z3 (100+1/2WQCV)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
MHFD-Detention, Version 4.06 (July 2022)
0.000
10.555
21.110
31.665
42.220
0.000
1.190
2.380
3.570
4.760
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MHFD-Detention_v4-06 Pond H (Future) - Full Spectrum Detention.xlsm, Basin 6/25/2025, 10:03 AM
Project:
Basin ID:
Estimated Estimated
Stage (ft) Volume (ac-ft) Outlet Type
Zone 1 (WQCV) 1.92 0.457 Orifice Plate
Zone 2 (EURV) 3.01 0.856 Orifice Plate
Z3 (100+1/2WQCV) 4.39 1.344 Weir&Pipe (Restrict)
Total (all zones) 2.658
User Input: Orifice at Underdrain Outlet (typically used to drain WQCV in a Filtration BMP)Calculated Parameters for Underdrain
Underdrain Orifice Invert Depth = ft (distance below the filtration media surface) Underdrain Orifice Area =ft2
Underdrain Orifice Diameter = inches Underdrain Orifice Centroid = feet
User Input: Orifice Plate with one or more orifices or Elliptical Slot Weir (typically used to drain WQCV and/or EURV in a sedimentation BMP)Calculated Parameters for Plate
Centroid of Lowest Orifice = 0.00 ft (relative to basin bottom at Stage = 0 ft) WQ Orifice Area per Row = N/A ft2
Depth at top of Zone using Orifice Plate = 3.02 ft (relative to basin bottom at Stage = 0 ft) Elliptical Half-Width = N/A feet
Orifice Plate: Orifice Vertical Spacing = N/A inches Elliptical Slot Centroid = N/A feet
Orifice Plate: Orifice Area per Row = N/A sq. inches Elliptical Slot Area = N/A ft2
User Input: Stage and Total Area of Each Orifice Row (numbered from lowest to highest)
Row 1 (required) Row 2 (optional) Row 3 (optional) Row 4 (optional) Row 5 (optional) Row 6 (optional) Row 7 (optional) Row 8 (optional)
Stage of Orifice Centroid (ft) 0.00 1.00 2.00
Orifice Area (sq. inches) 2.25 2.25 4.00
Row 9 (optional) Row 10 (optional) Row 11 (optional) Row 12 (optional) Row 13 (optional) Row 14 (optional) Row 15 (optional) Row 16 (optional)
Stage of Orifice Centroid (ft)
Orifice Area (sq. inches)
User Input: Vertical Orifice (Circular or Rectangular)Calculated Parameters for Vertical Orifice
Not Selected Not Selected Not Selected Not Selected
Invert of Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Area = N/A N/A ft2
Depth at top of Zone using Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Centroid = N/A N/A feet
Vertical Orifice Diameter = N/A N/A inches
User Input: Overflow Weir (Dropbox with Flat or Sloped Grate and Outlet Pipe OR Rectangular/Trapezoidal Weir and No Outlet Pipe) Calculated Parameters for Overflow Weir
grate Zone 3 Weir Not Selected Zone 3 Weir Not Selected
Overflow Weir Front Edge Height, Ho = 3.10 N/A ft (relative to basin bottom at Stage = 0 ft)Height of Grate Upper Edge, Ht =4.10 N/A feet
Overflow Weir Front Edge Length = 3.00 N/A feet Overflow Weir Slope Length = 6.08 N/A feet
Overflow Weir Grate Slope = 6.00 N/A H:V Grate Open Area / 100-yr Orifice Area = 5.44 N/A
Horiz. Length of Weir Sides = 6.00 N/A feet Overflow Grate Open Area w/o Debris = 12.70 N/A ft2
Overflow Grate Type = Type C Grate N/A Overflow Grate Open Area w/ Debris = 12.70 N/A ft2
Debris Clogging % = 0% N/A %
User Input: Outlet Pipe w/ Flow Restriction Plate (Circular Orifice, Restrictor Plate, or Rectangular Orifice)Calculated Parameters for Outlet Pipe w/ Flow Restriction Plate
Zone 3 Restrictor Not Selected Zone 3 Restrictor Not Selected
Depth to Invert of Outlet Pipe = 0.00 N/A ft (distance below basin bottom at Stage = 0 ft)Outlet Orifice Area = 2.33 N/A ft2
Outlet Pipe Diameter = 24.00 N/A inches Outlet Orifice Centroid = 0.78 N/A feet
Restrictor Plate Height Above Pipe Invert = 16.70 inches Half-Central Angle of Restrictor Plate on Pipe = 1.97 N/A radians
User Input: Emergency Spillway (Rectangular or Trapezoidal)Calculated Parameters for Spillway
Spillway Invert Stage= 4.50 ft (relative to basin bottom at Stage = 0 ft) Spillway Design Flow Depth= 0.91 feet
Spillway Crest Length = 19.00 feet Stage at Top of Freeboard = 5.91 feet
Spillway End Slopes = 4.00 H:V Basin Area at Top of Freeboard = 1.35 acres
Freeboard above Max Water Surface = 0.50 feet Basin Volume at Top of Freeboard = 4.50 acre-ft
Max Ponding Depth of Target Storage Volume =4.23 feet Discharge at Top of Freeboard = 143.55 cfs
Routed Hydrograph Results
Design Storm Return Period =WQCV EURV 2 Year 5 Year 10 Year 25 Year 50 Year 100 Year 500 Year
One-Hour Rainfall Depth (in) =N/A N/A 0.82 1.14 1.40 1.81 2.27 2.86 4.39
CUHP Runoff Volume (acre-ft) =0.457 1.314 0.862 1.287 1.657 2.280 2.964 3.864 6.175
Inflow Hydrograph Volume (acre-ft) =N/A N/A 0.862 1.287 1.657 2.280 2.964 3.864 6.175
CUHP Predevelopment Peak Q (cfs) =N/A N/A 0.1 1.6 3.9 9.9 15.0 22.4 39.8
OPTIONAL Override Predevelopment Peak Q (cfs) =N/A N/A
Predevelopment Unit Peak Flow, q (cfs/acre) =N/A N/A 0.01 0.10 0.24 0.59 0.90 1.34 2.38
Peak Inflow Q (cfs) =N/A N/A 12.7 18.8 23.8 33.9 44.0 57.9 91.6
Peak Outflow Q (cfs) =0.2 0.4 0.3 0.4 1.1 5.2 11.8 20.9 44.7
Ratio Peak Outflow to Predevelopment Q =N/A N/A N/A 0.2 0.3 0.5 0.8 0.9 1.1
Structure Controlling Flow =Plate Plate Plate Plate Overflow Weir 1 Overflow Weir 1 Overflow Weir 1 Outlet Plate 1 Spillway
Max Velocity through Grate 1 (fps) =N/A N/A N/A N/A 0.1 0.4 0.9 1.6 1.8
Max Velocity through Grate 2 (fps) =N/A N/A N/A N/A N/A N/A N/A N/A N/A
Time to Drain 97% of Inflow Volume (hours) =38 71 58 71 79 78 76 74 68
Time to Drain 99% of Inflow Volume (hours) =40 75 61 75 83 84 83 82 79
Maximum Ponding Depth (ft) =1.92 3.01 2.39 2.90 3.28 3.61 3.90 4.23 5.00
Area at Maximum Ponding Depth (acres) =0.71 0.86 0.77 0.85 0.90 0.96 1.00 1.05 1.18
Maximum Volume Stored (acre-ft) =0.464 1.320 0.813 1.226 1.550 1.867 2.140 2.479 3.340
The user can override the default CUHP hydrographs and runoff volumes by entering new values in the Inflow Hydrographs table (Columns W through AF).
DETENTION BASIN OUTLET STRUCTURE DESIGN
MHFD-Detention, Version 4.06 (July 2022)
Gateway at Prospect
Pond H - Future
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond H (Future) - Full Spectrum Detention.xlsm, Outlet Structure 7/2/2025, 11:46 AM
COUNTA for Basin Tab = 1 Ao Dia WQ Plate Type Vert Orifice 1Vert Orifice 2
Count_Underdrain = 0 0.11(diameter = 3/8 inch)2 1 1
Count_WQPlate = 1 0.14(diameter = 7/16 inch)
Count_VertOrifice1 = 0 0.18(diameter = 1/2 inch)Outlet Plate 1 Outlet Plate 2 Drain Time Message Boolean
Count_VertOrifice2 = 0 0.24(diameter = 9/16 inch)4 1 5yr, <72hr 0
Count_Weir1 = 1 0.29(diameter = 5/8 inch)>5yr, <120hr 0
Count_Weir2 = 0 0.36(diameter = 11/16 inch)Max Depth Row
Count_OutletPipe1 = 1 0.42(diameter = 3/4 inch)WQCV 193
Count_OutletPipe2 = 0 0.50(diameter = 13/16 inch)2 Year 240
COUNTA_2 (Standard FSD Setup)= 1 0.58(diameter = 7/8 inch)EURV 302
Hidden Parameters & Calculations 0.67(diameter = 15/16 inch)5 Year 291
MaxPondDepth_Error? FALSE 0.76 (diameter = 1 inch)10 Year 329 Spillway Depth
Cd_Broad-Crested Weir 3.00 0.86(diameter = 1-1/16 inches)25 Year 362 0.91
WQ Plate Flow at 100yr depth = 0.49 0.97(diameter = 1-1/8 inches)50 Year 391
CLOG #1= 100% 1.08(diameter = 1-3/16 inches)100 Year 424 1 Z1_Boolean
n*Cdw #1 = 0.44 1.20(diameter = 1-1/4 inches)500 Year 501 1 Z2_Boolean
n*Cdo #1 = 1.17 1.32(diameter = 1-5/16 inches)Zone3_Pulldown Message 1 Z3_Boolean
Overflow Weir #1 Angle = 0.165 1.45(diameter = 1-3/8 inches)1 Opening Message
CLOG #2= N/A 1.59(diameter = 1-7/16 inches)Draintime Running
n*Cdw #2 = N/A 1.73(diameter = 1-1/2 inches)Outlet Boolean Outlet Rank Total (1 to 4)
n*Cdo #2 = N/A 1.88(diameter = 1-9/16 inches)Vertical Orifice 1 0 0 1
Overflow Weir #2 Angle = N/A 2.03(diameter = 1-5/8 inches)Vertical Orifice 2 0 0 Boolean
Underdrain Q at 100yr depth = 0.00 2.20(diameter = 1-11/16 inches)Overflow Weir 1 1 1 0 Max Depth
VertOrifice1 Q at 100yr depth = 0.00 2.36(diameter = 1-3/4 inches)Overflow Weir 2 0 0 0 500yr Depth
VertOrifice2 Q at 100yr depth = 0.00 2.54(diameter = 1-13/16 inches)Outlet Pipe 1 1 1 0 Freeboard
2.72(diameter = 1-7/8 inches)Outlet Pipe 2 0 0 1 Spillway
Count_User_Hydrographs 0 2.90(diameter = 1-15/16 inches)0 Spillway Length
CountA_3 (EURV & 100yr) = 1 3.09(diameter = 2 inches)FALSE Time Interval
CountA_4 (100yr Only) = 1 3.29(use rectangular openings)Button Visibility Boolean
COUNTA_5 (FSD Weir Only)= 0 0 WQCV Underdrain
COUNTA_6 (EURV Weir Only)= 1 1 WQCV Plate
0 EURV-WQCV Plate
Outlet1_Pulldown_Boolean 0 EURV-WQCV VertOriice
Outlet2_Pulldown_Boolean 1 Outlet 90% Qpeak
Outlet3_Pulldown_Boolean 0 Outlet Undetained
0 Weir Only 90% Qpeak
0 Five Year Ratio Plate
0 Five Year Ratio VertOrifice
EURV_draintime_user
Spillway Options
Offset
Overlapping
S-A-V-D Chart Axis Default X-axis Left Y-Axis Right Y-Axis
minimum bound 0.00 0 0
maximum bound 6.00 200,000 150
S-A-V-D Chart Axis Override X-axis Left Y-Axis Right Y-Axis
minimum bound
maximum bound
MHFD-Detention, Version 4.06 (July 2022)
DETENTION BASIN OUTLET STRUCTURE DESIGN
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PONDING DEPTH [ft]
User Area [ft^2]
Interpolated Area [ft^2]
Summary Area [ft^2]
Volume [ft^3]
Summary Volume [ft^3]
Outflow [cfs]
Summary Outflow [cfs]
MHFD-Detention_v4-06 Pond H (Future) - Full Spectrum Detention.xlsm, Outlet Structure 7/2/2025, 11:46 AM
Outflow Hydrograph Workbook Filename:
Inflow Hydrographs
The user can override the calculated inflow hydrographs from this workbook with inflow hydrographs developed in a separate program.
SOURCE CUHP CUHP CUHP CUHP CUHP CUHP CUHP CUHP CUHP
Time Interval TIME WQCV [cfs] EURV [cfs] 2 Year [cfs] 5 Year [cfs] 10 Year [cfs] 25 Year [cfs] 50 Year [cfs] 100 Year [cfs] 500 Year [cfs]
5.00 min 0:00:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
0:05:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
0:10:00 0.00 0.00 0.00 0.00 0.00 0.00 0.27 0.44 2.32
0:15:00 0.00 0.00 0.55 1.96 2.89 2.36 3.72 4.42 8.28
0:20:00 0.00 0.00 4.48 7.08 9.05 6.56 8.87 11.18 19.39
0:25:00 0.00 0.00 10.45 15.77 20.48 14.64 19.61 24.51 41.20
0:30:00 0.00 0.00 12.73 18.81 23.77 30.11 39.46 49.67 79.51
0:35:00 0.00 0.00 11.88 17.35 21.75 33.91 44.01 57.89 91.60
0:40:00 0.00 0.00 10.67 15.29 19.15 32.51 42.00 55.22 87.08
0:45:00 0.00 0.00 9.23 13.43 16.97 28.99 37.42 50.38 79.38
0:50:00 0.00 0.00 7.96 11.85 14.78 26.27 33.88 45.45 71.55
0:55:00 0.00 0.00 6.90 10.27 12.89 22.68 29.25 40.05 63.04
1:00:00 0.00 0.00 6.16 9.13 11.60 19.55 25.23 35.41 55.76
1:05:00 0.00 0.00 5.66 8.35 10.72 17.35 22.41 32.16 50.67
1:10:00 0.00 0.00 4.98 7.69 9.95 15.17 19.62 27.48 43.37
1:15:00 0.00 0.00 4.35 6.85 9.19 13.26 17.18 23.33 36.87
1:20:00 0.00 0.00 3.76 5.90 8.06 11.18 14.45 18.92 29.95
1:25:00 0.00 0.00 3.23 5.08 6.74 9.33 12.05 15.08 23.93
1:30:00 0.00 0.00 2.83 4.46 5.72 7.51 9.68 11.85 18.88
1:35:00 0.00 0.00 2.62 4.14 5.14 6.10 7.88 9.41 15.12
1:40:00 0.00 0.00 2.52 3.71 4.77 5.27 6.82 7.96 12.87
1:45:00 0.00 0.00 2.46 3.37 4.51 4.74 6.13 7.02 11.40
1:50:00 0.00 0.00 2.42 3.13 4.32 4.38 5.67 6.36 10.39
1:55:00 0.00 0.00 2.14 2.95 4.09 4.12 5.34 5.90 9.67
2:00:00 0.00 0.00 1.89 2.73 3.73 3.96 5.12 5.56 9.14
2:05:00 0.00 0.00 1.46 2.11 2.87 3.05 3.95 4.23 6.96
2:10:00 0.00 0.00 1.10 1.57 2.14 2.26 2.92 3.11 5.12
2:15:00 0.00 0.00 0.82 1.17 1.59 1.69 2.18 2.32 3.82
2:20:00 0.00 0.00 0.61 0.87 1.17 1.25 1.62 1.73 2.85
2:25:00 0.00 0.00 0.45 0.63 0.85 0.91 1.18 1.28 2.10
2:30:00 0.00 0.00 0.32 0.45 0.62 0.66 0.85 0.92 1.52
2:35:00 0.00 0.00 0.23 0.32 0.44 0.48 0.62 0.67 1.10
2:40:00 0.00 0.00 0.15 0.22 0.31 0.34 0.44 0.47 0.78
2:45:00 0.00 0.00 0.09 0.14 0.20 0.22 0.29 0.31 0.51
2:50:00 0.00 0.00 0.05 0.08 0.11 0.13 0.17 0.18 0.30
2:55:00 0.00 0.00 0.02 0.04 0.05 0.06 0.08 0.09 0.14
3:00:00 0.00 0.00 0.01 0.01 0.01 0.02 0.02 0.03 0.04
3:05:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
3:10:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
3:15:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
3:20:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
3:25:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
3:30:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
3:35:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
3:40:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
3:45:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
3:50:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
3:55:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
4:00:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
4:05:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
4:10:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
4:15:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
4:20:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
4:25:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
4:30:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
4:35:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
4:40:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
4:45:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
4:50:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
4:55:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
5:00:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
5:05:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
5:10:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
5:15:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
5:20:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
5:25:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
5:30:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
5:35:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
5:40:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
5:45:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
5:50:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
5:55:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
6:00:00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
DETENTION BASIN OUTLET STRUCTURE DESIGN
MHFD-Detention_v4-06 Pond H (Future) - Full Spectrum Detention.xlsm, Outlet Structure 7/2/2025, 11:46 AM
Summary Stage-Area-Volume-Discharge Relationships
The user can create a summary S-A-V-D by entering the desired stage increments and the remainder of the table will populate automatically.
The user should graphically compare the summary S-A-V-D table to the full S-A-V-D table in the chart to confirm it captures all key transition points.
Stage Area Area Volume Volume Total
Outflow
[ft][ft 2][acres][ft 3][ac-ft] [cfs]
MHFD-Detention, Version 4.06 (July 2022)
DETENTION BASIN OUTLET STRUCTURE DESIGN
Stage - Storage
Description
For best results, include the
stages of all grade slope
changes (e.g. ISV and Floor)
from the S-A-V table on
Sheet 'Basin'.
Also include the inverts of all
outlets (e.g. vertical orifice,
overflow grate, and spillway,
where applicable).
MHFD-Detention_v4-06 Pond H (Future) - Full Spectrum Detention.xlsm, Outlet Structure 7/2/2025, 11:46 AM
Project:
Basin ID:
Depth Increment = ft
Watershed Information Top of Micropool -- 0.00 -- -- -- 18 0.000
Selected BMP Type =EDB -- 0.20 -- -- -- 307 0.007 29 0.001
Watershed Area = 20.98 acres -- 0.40 -- -- -- 755 0.017 131 0.003
Watershed Length = 1,500 ft -- 0.60 -- -- -- 1,436 0.033 358 0.008
Watershed Length to Centroid = 850 ft -- 0.80 -- -- -- 2,229 0.051 724 0.017
Watershed Slope = 0.010 ft/ft -- 1.00 -- -- -- 3,078 0.071 1,255 0.029
Watershed Imperviousness = 13.00% percent -- 1.20 -- -- --3,985 0.091 1,922 0.044
Percentage Hydrologic Soil Group A = 0.0% percent -- 1.40 -- -- -- 5,117 0.117 2,821 0.065
Percentage Hydrologic Soil Group B = 0.0% percent -- 1.60 -- -- -- 6,013 0.138 3,984 0.091
Percentage Hydrologic Soil Groups C/D = 100.0% percent -- 1.80 -- -- -- 7,676 0.176 5,353 0.123
Target WQCV Drain Time = 40.0 hours -- 1.96 -- -- -- 9,627 0.221 6,738 0.155
Location for 1-hr Rainfall Depths = Thornton - Civic Center -- 2.00 -- -- -- 10,186 0.234 7,134 0.164
-- 2.20 -- -- -- 13,064 0.300 9,329 0.214
-- 2.40 -- -- -- 15,805 0.363 12,188 0.280
Optional User Overrides -- 2.60 -- -- -- 18,439 0.423 15,770 0.362
Water Quality Capture Volume (WQCV) = 0.146 acre-feet acre-feet -- 2.80 -- -- -- 20,978 0.482 19,712 0.453
Excess Urban Runoff Volume (EURV) = 0.232 acre-feet acre-feet -- 3.00 -- -- -- 23,455 0.538 24,155 0.555
2-yr Runoff Volume (P1 = 0.82 in.) = 0.124 acre-feet 0.82 inches -- 3.20 -- -- -- 25,804 0.592 28,824 0.662
5-yr Runoff Volume (P1 = 1.14 in.) = 0.373 acre-feet 1.14 inches -- 3.40 -- -- -- 28,102 0.645 34,191 0.785
10-yr Runoff Volume (P1 = 1.4 in.) = 0.727 acre-feet 1.40 inches -- 3.60 -- -- -- 30,343 0.697 40,316 0.926
25-yr Runoff Volume (P1 = 1.81 in.) = 1.536 acre-feet 1.81 inches -- 3.80 -- -- -- 32,460 0.745 46,597 1.070
50-yr Runoff Volume (P1 = 2.27 in.) = 2.330 acre-feet 2.27 inches -- 4.00 -- -- -- 38,309 0.879 53,673 1.232
100-yr Runoff Volume (P1 = 2.86 in.) = 3.497 acre-feet 2.86 inches -- 4.20 -- -- -- 40,837 0.937 61,180 1.405
500-yr Runoff Volume (P1 = 4.39 in.) = 6.381 acre-feet 4.39 inches -- -- -- --
Approximate 2-yr Detention Volume = 0.131 acre-feet ---- -- --
Approximate 5-yr Detention Volume = 0.311 acre-feet ---- -- --
Approximate 10-yr Detention Volume = 0.417 acre-feet -- -- -- --
Approximate 25-yr Detention Volume = 0.562 acre-feet -- -- -- --
Approximate 50-yr Detention Volume = 0.653 acre-feet -- -- -- --
Approximate 100-yr Detention Volume = 0.994 acre-feet -- -- -- --
-- -- -- --
Define Zones and Basin Geometry -- -- -- --
Zone 1 Volume (WQCV) = 0.146 acre-feet -- -- -- --
Zone 2 Volume (EURV - Zone 1) = 0.086 acre-feet -- -- ----
Zone 3 (100yr + 1 / 2 WQCV - Zones 1 & 2) = 0.835 acre-feet -- -- -- --
Total Detention Basin Volume = 1.067 acre-feet -- -- -- --
Initial Surcharge Volume (ISV) = user ft 3 -- -- -- --
Initial Surcharge Depth (ISD) = user ft -- -- -- --
Total Available Detention Depth (Htotal) = user ft -- -- -- --
Depth of Trickle Channel (HTC) = user ft -- -- -- --
Slope of Trickle Channel (STC) = user ft/ft -- -- -- --
Slopes of Main Basin Sides (Smain) = user H:V -- -- -- --
Basin Length-to-Width Ratio (RL/W) = user -- -- -- --
-- -- -- --
Initial Surcharge Area (AISV) =user ft 2 -- -- -- --
Surcharge Volume Length (LISV) =user ft -- -- -- --
Surcharge Volume Width (WISV) =user ft -- -- -- --
Depth of Basin Floor (HFLOOR) =user ft -- -- -- --
Length of Basin Floor (LFLOOR) =user ft -- -- -- --
Width of Basin Floor (WFLOOR) =user ft -- -- -- --
Area of Basin Floor (AFLOOR) =user ft 2 -- -- -- --
Volume of Basin Floor (VFLOOR) =user ft 3 -- -- -- --
Depth of Main Basin (HMAIN) =user ft -- -- -- --
Length of Main Basin (LMAIN) =user ft -- -- -- --
Width of Main Basin (WMAIN) =user ft -- -- -- --
Area of Main Basin (AMAIN) =user ft 2 -- -- -- --
Volume of Main Basin (VMAIN) =user ft 3 -- -- -- --
Calculated Total Basin Volume (Vtotal) =user acre-feet -- -- -- --
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After providing required inputs above including 1-hour rainfall
depths, click 'Run CUHP' to generate runoff hydrographs using
the embedded Colorado Urban Hydrograph Procedure.
Volume
(ft 3)
Volume
(ac-ft)
Area
(acre)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
Optional
Override
Area (ft 2)
Length
(ft)
Optional
Override
Stage (ft)
Stage
(ft)
Stage - Storage
Description
Area
(ft 2)
Width
(ft)
Gateway at Prospect
Pond I - Interim (Basins H & I)
MHFD-Detention, Version 4.06 (July 2022)
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond I (Interim) - Full Spectrum Detention, Basin 8/14/2025, 11:22 AM
1 User Defined Stage-Area Booleans for Message
1 Equal Stage-Area Inputs Watershed L:W
1 CountA Watershed Lc:L
Watershed Slope
0 Calc_S_TC Booleans for CUHP
1 CUHP Inputs Complete
H_FLOOR 1 CUHP Results Calculated
L_FLOOR_OTHER
0.00 ISV 0.00 ISV
0.00 Floor 0.00 Floor
1.92 Zone 1 (WQCV) 1.92 Zone 1 (WQCV)
2.25 Zone 2 (EURV) 2.25 Zone 2 (EURV)
3.80 Z3 (100+1/2WQCV)3.80 Z3 (100+1/2WQCV)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
MHFD-Detention, Version 4.06 (July 2022)
0.000
0.355
0.710
1.065
1.420
0.000
0.235
0.470
0.705
0.940
0.00 1.50 3.00 4.50 6.00
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Stage (ft.)
Area (acres)Volume (ac-ft)
0
10300
20600
30900
41200
0
5
10
15
20
0.00 1.50 3.00 4.50 6.00
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Stage (ft)
Length (ft)Width (ft)Area (sq.ft.)
MHFD-Detention_v4-06 Pond I (Interim) - Full Spectrum Detention, Basin 8/14/2025, 11:22 AM
Project:
Basin ID:
Estimated Estimated
Stage (ft) Volume (ac-ft) Outlet Type
Zone 1 (WQCV) 1.92 0.146 Orifice Plate
Zone 2 (EURV) 2.25 0.086 Orifice Plate
Z3 (100+1/2WQCV) 3.80 0.835 Weir&Pipe (Restrict)
Total (all zones) 1.067
User Input: Orifice at Underdrain Outlet (typically used to drain WQCV in a Filtration BMP)Calculated Parameters for Underdrain
Underdrain Orifice Invert Depth = N/A ft (distance below the filtration media surface) Underdrain Orifice Area = N/A ft2
Underdrain Orifice Diameter = N/A inches Underdrain Orifice Centroid = N/A feet
User Input: Orifice Plate with one or more orifices or Elliptical Slot Weir (typically used to drain WQCV and/or EURV in a sedimentation BMP)Calculated Parameters for Plate
Centroid of Lowest Orifice = 0.00 ft (relative to basin bottom at Stage = 0 ft) WQ Orifice Area per Row =5.278E-03 ft2
Depth at top of Zone using Orifice Plate = 2.30 ft (relative to basin bottom at Stage = 0 ft) Elliptical Half-Width = N/A feet
Orifice Plate: Orifice Vertical Spacing = 9.00 inches Elliptical Slot Centroid = N/A feet
Orifice Plate: Orifice Area per Row = 0.76 sq. inches (diameter = 1 inch) Elliptical Slot Area = N/A ft2
User Input: Stage and Total Area of Each Orifice Row (numbered from lowest to highest)
Row 1 (required) Row 2 (optional) Row 3 (optional) Row 4 (optional) Row 5 (optional) Row 6 (optional) Row 7 (optional) Row 8 (optional)
Stage of Orifice Centroid (ft) 0.00 0.80 1.60
Orifice Area (sq. inches) 0.76 0.76 0.76
Row 9 (optional) Row 10 (optional) Row 11 (optional) Row 12 (optional) Row 13 (optional) Row 14 (optional) Row 15 (optional) Row 16 (optional)
Stage of Orifice Centroid (ft)
Orifice Area (sq. inches)
User Input: Vertical Orifice (Circular or Rectangular)Calculated Parameters for Vertical Orifice
Not Selected Not Selected Not Selected Not Selected
Invert of Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Area =N/A N/A ft2
Depth at top of Zone using Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Centroid = N/A N/A feet
Vertical Orifice Diameter = N/A N/A inches
User Input: Overflow Weir (Dropbox with Flat or Sloped Grate and Outlet Pipe OR Rectangular/Trapezoidal Weir and No Outlet Pipe) Calculated Parameters for Overflow Weir
grate Zone 3 Weir Not Selected Zone 3 Weir Not Selected
Overflow Weir Front Edge Height, Ho = 2.80 N/A ft (relative to basin bottom at Stage = 0 ft)Height of Grate Upper Edge, Ht =3.80 N/A feet
Overflow Weir Front Edge Length = 10.00 N/A feet Overflow Weir Slope Length = 6.08 N/A feet
Overflow Weir Grate Slope = 6.00 N/A H:V Grate Open Area / 100-yr Orifice Area = 11.78 N/A
Horiz. Length of Weir Sides = 6.00 N/A feet Overflow Grate Open Area w/o Debris = 42.34 N/A ft2
Overflow Grate Type = Type C Grate N/A Overflow Grate Open Area w/ Debris = 42.34 N/A ft2
Debris Clogging % = 0% N/A %
User Input: Outlet Pipe w/ Flow Restriction Plate (Circular Orifice, Restrictor Plate, or Rectangular Orifice)Calculated Parameters for Outlet Pipe w/ Flow Restriction Plate
Zone 3 Restrictor Not Selected Zone 3 Restrictor Not Selected
Depth to Invert of Outlet Pipe = 0.00 N/A ft (distance below basin bottom at Stage = 0 ft)Outlet Orifice Area = 3.59 N/A ft2
Outlet Pipe Diameter = 30.00 N/A inches Outlet Orifice Centroid = 0.96 N/A feet
Restrictor Plate Height Above Pipe Invert = 20.60 inches Half-Central Angle of Restrictor Plate on Pipe =1.95 N/A radians
User Input: Emergency Spillway (Rectangular or Trapezoidal)Calculated Parameters for Spillway
Spillway Invert Stage= 4.20 ft (relative to basin bottom at Stage = 0 ft) Spillway Design Flow Depth= 1.08 feet
Spillway Crest Length = 8.00 feet Stage at Top of Freeboard = 5.94 feet
Spillway End Slopes = 1.00 H:V Basin Area at Top of Freeboard = 0.94 acres
Freeboard above Max Water Surface = 0.66 feet Basin Volume at Top of Freeboard = 1.41 acre-ft
Max Ponding Depth of Target Storage Volume =3.65 feet Discharge at Top of Freeboard = 31.14 cfs
Routed Hydrograph Results
Design Storm Return Period =WQCV EURV 2 Year 5 Year 10 Year 25 Year 50 Year 100 Year 500 Year
One-Hour Rainfall Depth (in) =N/A N/A 0.82 1.14 1.40 1.81 2.27 2.86 4.39
CUHP Runoff Volume (acre-ft) =0.146 0.232 0.124 0.373 0.727 1.536 2.330 3.497 6.381
Inflow Hydrograph Volume (acre-ft) =N/A N/A 0.124 0.373 0.727 1.536 2.330 3.497 6.381
CUHP Predevelopment Peak Q (cfs) =N/A N/A 0.2 2.0 5.0 12.5 19.0 28.3 50.3
OPTIONAL Override Predevelopment Peak Q (cfs) =N/A N/A
Predevelopment Unit Peak Flow, q (cfs/acre) =N/A N/A 0.01 0.10 0.24 0.60 0.90 1.35 2.40
Peak Inflow Q (cfs) =N/A N/A 1.1 3.4 6.4 14.0 20.6 30.1 52.4
Peak Outflow Q (cfs) =0.1 0.1 0.1 0.1 1.9 8.7 15.4 25.7 31.1
Ratio Peak Outflow to Predevelopment Q =N/A N/A N/A 0.0 0.4 0.7 0.8 0.9 0.6
Structure Controlling Flow =Plate Plate Plate Plate Overflow Weir 1 Overflow Weir 1 Overflow Weir 1 Overflow Weir 1 N/A
Max Velocity through Grate 1 (fps) =N/A N/A N/A N/A 0.0 0.2 0.4 0.6 0.7
Max Velocity through Grate 2 (fps) =N/A N/A N/A N/A N/A N/A N/A N/A N/A
Time to Drain 97% of Inflow Volume (hours) =38 49 36 65 73 66 60 53 39
Time to Drain 99% of Inflow Volume (hours) =40 52 38 69 81 77 73 70 62
Maximum Ponding Depth (ft) =1.92 2.25 1.72 2.57 2.97 3.25 3.43 3.65 4.20
Area at Maximum Ponding Depth (acres) =0.21 0.32 0.16 0.41 0.53 0.60 0.65 0.71 0.94
Maximum Volume Stored (acre-ft) =0.146 0.233 0.109 0.345 0.539 0.692 0.804 0.954 1.414
DETENTION BASIN OUTLET STRUCTURE DESIGN
MHFD-Detention, Version 4.06 (July 2022)
Gateway at Prospect
Pond I - Interim (Basins H & I)
The user can override the default CUHP hydrographs and runoff volumes by entering new values in the Inflow Hydrographs table (Columns W through AF).
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond I (Interim) - Full Spectrum Detention, Outlet Structure 8/14/2025, 11:23 AM
COUNTA for Basin Tab = 1 Ao Dia WQ Plate Type Vert Orifice 1Vert Orifice 2
Count_Underdrain = 0 0.11(diameter = 3/8 inch)2 1 1
Count_WQPlate = 1 0.14(diameter = 7/16 inch)
Count_VertOrifice1 = 0 0.18(diameter = 1/2 inch)Outlet Plate 1 Outlet Plate 2 Drain Time Message Boolean
Count_VertOrifice2 = 0 0.24(diameter = 9/16 inch)4 1 5yr, <72hr 0
Count_Weir1 = 1 0.29(diameter = 5/8 inch)>5yr, <120hr 0
Count_Weir2 = 0 0.36(diameter = 11/16 inch)Max Depth Row
Count_OutletPipe1 = 1 0.42(diameter = 3/4 inch)WQCV 193
Count_OutletPipe2 = 0 0.50(diameter = 13/16 inch)2 Year 173
COUNTA_2 (Standard FSD Setup)= 1 0.58(diameter = 7/8 inch)EURV 226
Hidden Parameters & Calculations 0.67(diameter = 15/16 inch)5 Year 258
MaxPondDepth_Error? FALSE 0.76 (diameter = 1 inch)10 Year 298 Spillway Depth
Cd_Broad-Crested Weir 3.00 0.86(diameter = 1-1/16 inches)25 Year 326 1.08
WQ Plate Flow at 100yr depth = 0.13 0.97(diameter = 1-1/8 inches)50 Year 344
CLOG #1= 100% 1.08(diameter = 1-3/16 inches)100 Year 366 1 Z1_Boolean
n*Cdw #1 = 0.44 1.20(diameter = 1-1/4 inches)500 Year 421 1 Z2_Boolean
n*Cdo #1 = 1.17 1.32(diameter = 1-5/16 inches)Zone3_Pulldown Message 1 Z3_Boolean
Overflow Weir #1 Angle = 0.165 1.45(diameter = 1-3/8 inches)1 Opening Message
CLOG #2= N/A 1.59(diameter = 1-7/16 inches)Draintime Running
n*Cdw #2 = N/A 1.73(diameter = 1-1/2 inches)Outlet Boolean Outlet Rank Total (1 to 4)
n*Cdo #2 = N/A 1.88(diameter = 1-9/16 inches)Vertical Orifice 1 0 0 1
Overflow Weir #2 Angle = N/A 2.03(diameter = 1-5/8 inches)Vertical Orifice 2 0 0 Boolean
Underdrain Q at 100yr depth = 0.00 2.20(diameter = 1-11/16 inches)Overflow Weir 1 1 1 0 Max Depth
VertOrifice1 Q at 100yr depth = 0.00 2.36(diameter = 1-3/4 inches)Overflow Weir 2 0 0 0 500yr Depth
VertOrifice2 Q at 100yr depth = 0.00 2.54(diameter = 1-13/16 inches)Outlet Pipe 1 1 1 1 Freeboard
2.72(diameter = 1-7/8 inches)Outlet Pipe 2 0 0 1 Spillway
Count_User_Hydrographs 0 2.90(diameter = 1-15/16 inches)0 Spillway Length
CountA_3 (EURV & 100yr) = 1 3.09(diameter = 2 inches)FALSE Time Interval
CountA_4 (100yr Only) = 1 3.29(use rectangular openings)Button Visibility Boolean
COUNTA_5 (FSD Weir Only)= 0 0 WQCV Underdrain
COUNTA_6 (EURV Weir Only)= 1 1 WQCV Plate
0 EURV-WQCV Plate
Outlet1_Pulldown_Boolean 0 EURV-WQCV VertOriice
Outlet2_Pulldown_Boolean 1 Outlet 90% Qpeak
Outlet3_Pulldown_Boolean 0 Outlet Undetained
0 Weir Only 90% Qpeak
0 Five Year Ratio Plate
0 Five Year Ratio VertOrifice
EURV_draintime_user
Spillway Options
Offset
Overlapping
S-A-V-D Chart Axis Default X-axis Left Y-Axis Right Y-Axis
minimum bound 0.00 0 0
maximum bound 6.00 70,000 40
S-A-V-D Chart Axis Override X-axis Left Y-Axis Right Y-Axis
minimum bound
maximum bound
DETENTION BASIN OUTLET STRUCTURE DESIGN
MHFD-Detention, Version 4.06 (July 2022)
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WQCV
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PONDING DEPTH [ft]
User Area [ft^2]
Interpolated Area [ft^2]
Summary Area [ft^2]
Volume [ft^3]
Summary Volume [ft^3]
Outflow [cfs]
Summary Outflow [cfs]
MHFD-Detention_v4-06 Pond I (Interim) - Full Spectrum Detention, Outlet Structure 8/14/2025, 11:23 AM
Project:
Basin ID:
Depth Increment = ft
Watershed Information Top of Micropool -- 0.00 -- -- -- 18 0.000
Selected BMP Type =EDB -- 0.20 -- -- -- 307 0.007 32 0.001
Watershed Area = 4.26 acres -- 0.40 -- -- -- 755 0.017 139 0.003
Watershed Length = 712 ft -- 0.60 -- -- -- 1,436 0.033 358 0.008
Watershed Length to Centroid = 504 ft -- 0.80 -- -- -- 2,229 0.051 724 0.017
Watershed Slope = 0.020 ft/ft -- 1.00 -- -- -- 3,078 0.071 1,255 0.029
Watershed Imperviousness = 76.00% percent -- 1.20 -- -- --3,985 0.091 1,961 0.045
Percentage Hydrologic Soil Group A = 0.0% percent -- 1.40 -- -- -- 5,117 0.117 2,871 0.066
Percentage Hydrologic Soil Group B = 0.0% percent -- 1.60 -- -- -- 5,849 0.134 3,968 0.091
Percentage Hydrologic Soil Groups C/D = 100.0% percent -- 1.80 -- -- -- 6,372 0.146 5,190 0.119
Target WQCV Drain Time = 40.0 hours -- 1.96 -- -- -- 6,794 0.156 6,243 0.143
Location for 1-hr Rainfall Depths = User Input -- 2.00 -- -- -- 6,900 0.158 6,517 0.150
-- 2.20 -- -- -- 7,414 0.170 7,949 0.182
-- 2.40 -- -- -- 7,915 0.182 9,481 0.218
Optional User Overrides -- 2.60 -- -- -- 8,420 0.193 11,115 0.255
Water Quality Capture Volume (WQCV) = 0.108 acre-feet acre-feet -- 2.80 -- -- -- 8,951 0.205 12,852 0.295
Excess Urban Runoff Volume (EURV) = 0.317 acre-feet acre-feet -- 3.00 -- -- -- 9,520 0.219 14,699 0.337
2-yr Runoff Volume (P1 = 0.82 in.) = 0.202 acre-feet 0.82 inches -- 3.20 -- -- -- 10,117 0.232 16,663 0.383
5-yr Runoff Volume (P1 = 1.14 in.) = 0.305 acre-feet 1.14 inches -- 3.40 -- -- -- 10,732 0.246 18,748 0.430
10-yr Runoff Volume (P1 = 1.4 in.) = 0.395 acre-feet 1.40 inches -- 3.60 -- -- -- 11,361 0.261 20,957 0.481
25-yr Runoff Volume (P1 = 1.81 in.) = 0.550 acre-feet 1.81 inches -- 3.80 -- -- -- 12,003 0.276 23,294 0.535
50-yr Runoff Volume (P1 = 2.27 in.) = 0.719 acre-feet 2.27 inches -- 4.00 -- -- -- 16,511 0.379 26,145 0.600
100-yr Runoff Volume (P1 = 2.86 in.) = 0.943 acre-feet 2.86 inches -- 4.20 -- -- -- 17,632 0.405 29,559 0.679
500-yr Runoff Volume (P1 = 4.39 in.) = 1.516 acre-feet 4.39 inches -- -- -- --
Approximate 2-yr Detention Volume = 0.197 acre-feet ---- -- --
Approximate 5-yr Detention Volume = 0.299 acre-feet ---- -- --
Approximate 10-yr Detention Volume = 0.361 acre-feet -- -- -- --
Approximate 25-yr Detention Volume = 0.434 acre-feet -- -- -- --
Approximate 50-yr Detention Volume = 0.496 acre-feet -- -- -- --
Approximate 100-yr Detention Volume = 0.594 acre-feet -- -- -- --
-- -- -- --
Define Zones and Basin Geometry -- -- -- --
Zone 1 Volume (WQCV) = 0.108 acre-feet -- -- -- --
Zone 2 Volume (EURV - Zone 1) = 0.208 acre-feet -- -- ----
Zone 3 (100yr + 1 / 2 WQCV - Zones 1 & 2) = 0.332 acre-feet -- -- -- --
Total Detention Basin Volume = 0.648 acre-feet -- -- -- --
Initial Surcharge Volume (ISV) = user ft 3 -- -- -- --
Initial Surcharge Depth (ISD) = user ft -- -- -- --
Total Available Detention Depth (Htotal) = user ft -- -- -- --
Depth of Trickle Channel (HTC) = user ft -- -- -- --
Slope of Trickle Channel (STC) = user ft/ft -- -- -- --
Slopes of Main Basin Sides (Smain) = user H:V -- -- -- --
Basin Length-to-Width Ratio (RL/W) = user -- -- -- --
-- -- -- --
Initial Surcharge Area (AISV) =user ft 2 -- -- -- --
Surcharge Volume Length (LISV) =user ft -- -- -- --
Surcharge Volume Width (WISV) =user ft -- -- -- --
Depth of Basin Floor (HFLOOR) =user ft -- -- -- --
Length of Basin Floor (LFLOOR) =user ft -- -- -- --
Width of Basin Floor (WFLOOR) =user ft -- -- -- --
Area of Basin Floor (AFLOOR) =user ft 2 -- -- -- --
Volume of Basin Floor (VFLOOR) =user ft 3 -- -- -- --
Depth of Main Basin (HMAIN) =user ft -- -- -- --
Length of Main Basin (LMAIN) =user ft -- -- -- --
Width of Main Basin (WMAIN) =user ft -- -- -- --
Area of Main Basin (AMAIN) =user ft 2 -- -- -- --
Volume of Main Basin (VMAIN) =user ft 3 -- -- -- --
Calculated Total Basin Volume (Vtotal) =user acre-feet -- -- -- --
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DETENTION BASIN STAGE-STORAGE TABLE BUILDER
Optional
Override
Area (ft 2)
Length
(ft)
Optional
Override
Stage (ft)
Stage
(ft)
Stage - Storage
Description
Area
(ft 2)
Width
(ft)
Gateway at Prospect
Pond I - Future
MHFD-Detention, Version 4.06 (July 2022)
Volume
(ft 3)
Volume
(ac-ft)
Area
(acre)
After providing required inputs above including 1-hour rainfall
depths, click 'Run CUHP' to generate runoff hydrographs using
the embedded Colorado Urban Hydrograph Procedure.
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond I (Future) - Full Spectrum Detention, Basin 8/14/2025, 11:24 AM
1 User Defined Stage-Area Booleans for Message
1 Equal Stage-Area Inputs Watershed L:W
1 CountA Watershed Lc:L
Watershed Slope
0 Calc_S_TC Booleans for CUHP
1 CUHP Inputs Complete
H_FLOOR 1 CUHP Results Calculated
L_FLOOR_OTHER
0.00 ISV 0.00 ISV
0.00 Floor 0.00 Floor
1.73 Zone 1 (WQCV) 1.73 Zone 1 (WQCV)
2.91 Zone 2 (EURV) 2.91 Zone 2 (EURV)
4.13 Z3 (100+1/2WQCV)4.13 Z3 (100+1/2WQCV)
DETENTION BASIN STAGE-STORAGE TABLE BUILDER
MHFD-Detention, Version 4.06 (July 2022)
0.000
0.170
0.340
0.510
0.680
0.000
0.105
0.210
0.315
0.420
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MHFD-Detention_v4-06 Pond I (Future) - Full Spectrum Detention, Basin 8/14/2025, 11:24 AM
Project:
Basin ID:
Estimated Estimated
Stage (ft) Volume (ac-ft) Outlet Type
Zone 1 (WQCV) 1.73 0.108 Orifice Plate
Zone 2 (EURV) 2.91 0.208 Orifice Plate
Z3 (100+1/2WQCV) 4.13 0.332 Weir&Pipe (Restrict)
Total (all zones) 0.648
User Input: Orifice at Underdrain Outlet (typically used to drain WQCV in a Filtration BMP)Calculated Parameters for Underdrain
Underdrain Orifice Invert Depth = N/A ft (distance below the filtration media surface) Underdrain Orifice Area = N/A ft2
Underdrain Orifice Diameter = N/A inches Underdrain Orifice Centroid = N/A feet
User Input: Orifice Plate with one or more orifices or Elliptical Slot Weir (typically used to drain WQCV and/or EURV in a sedimentation BMP)Calculated Parameters for Plate
Centroid of Lowest Orifice = 0.00 ft (relative to basin bottom at Stage = 0 ft) WQ Orifice Area per Row =4.931E-03 ft2
Depth at top of Zone using Orifice Plate = 3.00 ft (relative to basin bottom at Stage = 0 ft) Elliptical Half-Width = N/A feet
Orifice Plate: Orifice Vertical Spacing = 11.50 inches Elliptical Slot Centroid = N/A feet
Orifice Plate: Orifice Area per Row = 0.71 sq. inches (diameter = 15/16 inch) Elliptical Slot Area = N/A ft2
User Input: Stage and Total Area of Each Orifice Row (numbered from lowest to highest)
Row 1 (required) Row 2 (optional) Row 3 (optional) Row 4 (optional) Row 5 (optional) Row 6 (optional) Row 7 (optional) Row 8 (optional)
Stage of Orifice Centroid (ft) 0.00 1.00 2.00
Orifice Area (sq. inches) 0.71 0.71 0.71
Row 9 (optional) Row 10 (optional) Row 11 (optional) Row 12 (optional) Row 13 (optional) Row 14 (optional) Row 15 (optional) Row 16 (optional)
Stage of Orifice Centroid (ft)
Orifice Area (sq. inches)
User Input: Vertical Orifice (Circular or Rectangular)Calculated Parameters for Vertical Orifice
Not Selected Not Selected Not Selected Not Selected
Invert of Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Area =N/A N/A ft2
Depth at top of Zone using Vertical Orifice = N/A N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Centroid = N/A N/A feet
Vertical Orifice Diameter = N/A N/A inches
User Input: Overflow Weir (Dropbox with Flat or Sloped Grate and Outlet Pipe OR Rectangular/Trapezoidal Weir and No Outlet Pipe) Calculated Parameters for Overflow Weir
grate Zone 3 Weir Not Selected Zone 3 Weir Not Selected
Overflow Weir Front Edge Height, Ho = 3.00 N/A ft (relative to basin bottom at Stage = 0 ft)Height of Grate Upper Edge, Ht =4.00 N/A feet
Overflow Weir Front Edge Length = 10.00 N/A feet Overflow Weir Slope Length = 6.08 N/A feet
Overflow Weir Grate Slope = 6.00 N/A H:V Grate Open Area / 100-yr Orifice Area = 121.91 N/A
Horiz. Length of Weir Sides = 6.00 N/A feet Overflow Grate Open Area w/o Debris = 42.34 N/A ft2
Overflow Grate Type = Type C Grate N/A Overflow Grate Open Area w/ Debris = 42.34 N/A ft2
Debris Clogging % = 0% N/A %
User Input: Outlet Pipe w/ Flow Restriction Plate (Circular Orifice, Restrictor Plate, or Rectangular Orifice)Calculated Parameters for Outlet Pipe w/ Flow Restriction Plate
Zone 3 Restrictor Not Selected Zone 3 Restrictor Not Selected
Depth to Invert of Outlet Pipe = 0.00 N/A ft (distance below basin bottom at Stage = 0 ft)Outlet Orifice Area = 0.35 N/A ft2
Outlet Pipe Diameter = 30.00 N/A inches Outlet Orifice Centroid = 0.18 N/A feet
Restrictor Plate Height Above Pipe Invert = 3.70 inches Half-Central Angle of Restrictor Plate on Pipe = 0.72 N/A radians
User Input: Emergency Spillway (Rectangular or Trapezoidal)Calculated Parameters for Spillway
Spillway Invert Stage= 4.20 ft (relative to basin bottom at Stage = 0 ft) Spillway Design Flow Depth= 0.68 feet
Spillway Crest Length = 8.00 feet Stage at Top of Freeboard = 5.54 feet
Spillway End Slopes = 1.00 H:V Basin Area at Top of Freeboard = 0.40 acres
Freeboard above Max Water Surface = 0.66 feet Basin Volume at Top of Freeboard = 0.68 acre-ft
Max Ponding Depth of Target Storage Volume =4.09 feet Discharge at Top of Freeboard = 3.35 cfs
Routed Hydrograph Results
Design Storm Return Period =WQCV EURV 2 Year 5 Year 10 Year 25 Year 50 Year 100 Year 500 Year
One-Hour Rainfall Depth (in) =N/A N/A 0.82 1.14 1.40 1.81 2.27 2.86 4.39
CUHP Runoff Volume (acre-ft) =0.108 0.317 0.202 0.305 0.395 0.550 0.719 0.943 1.516
Inflow Hydrograph Volume (acre-ft) =N/A N/A 0.202 0.305 0.395 0.550 0.719 0.943 1.516
CUHP Predevelopment Peak Q (cfs) =N/A N/A 0.0 0.4 1.1 2.6 3.9 5.9 10.5
OPTIONAL Override Predevelopment Peak Q (cfs) =N/A N/A
Predevelopment Unit Peak Flow, q (cfs/acre) =N/A N/A 0.01 0.10 0.25 0.61 0.93 1.38 2.46
Peak Inflow Q (cfs) =N/A N/A 3.0 4.6 5.8 8.4 10.9 14.4 23.0
Peak Outflow Q (cfs) =0.1 0.1 0.1 0.1 0.7 2.9 3.1 3.3 3.4
Ratio Peak Outflow to Predevelopment Q =N/A N/A N/A 0.2 0.7 1.1 0.8 0.6 0.3
Structure Controlling Flow =Plate Plate Plate Plate Overflow Weir 1 Outlet Plate 1 Outlet Plate 1 Outlet Plate 1 N/A
Max Velocity through Grate 1 (fps) =N/A N/A N/A N/A 0.0 0.1 0.1 0.1 0.1
Max Velocity through Grate 2 (fps) =N/A N/A N/A N/A N/A N/A N/A N/A N/A
Time to Drain 97% of Inflow Volume (hours) =38 69 56 68 73 70 68 65 60
Time to Drain 99% of Inflow Volume (hours) =40 73 59 72 78 77 76 75 74
Maximum Ponding Depth (ft) =1.73 2.91 2.25 2.77 3.08 3.23 3.56 4.09 4.20
Area at Maximum Ponding Depth (acres) =0.14 0.21 0.17 0.20 0.22 0.23 0.26 0.39 0.40
Maximum Volume Stored (acre-ft) =0.109 0.318 0.189 0.289 0.355 0.387 0.468 0.635 0.679
The user can override the default CUHP hydrographs and runoff volumes by entering new values in the Inflow Hydrographs table (Columns W through AF).
DETENTION BASIN OUTLET STRUCTURE DESIGN
MHFD-Detention, Version 4.06 (July 2022)
Gateway at Prospect
Pond I - Future
Example Zone Configuration (Retention Pond)
MHFD-Detention_v4-06 Pond I (Future) - Full Spectrum Detention, Outlet Structure 8/14/2025, 12:02 PM
COUNTA for Basin Tab = 1 Ao Dia WQ Plate Type Vert Orifice 1Vert Orifice 2
Count_Underdrain = 0 0.11(diameter = 3/8 inch)2 1 1
Count_WQPlate = 1 0.14(diameter = 7/16 inch)
Count_VertOrifice1 = 0 0.18(diameter = 1/2 inch)Outlet Plate 1 Outlet Plate 2 Drain Time Message Boolean
Count_VertOrifice2 = 0 0.24(diameter = 9/16 inch)4 1 5yr, <72hr 0
Count_Weir1 = 1 0.29(diameter = 5/8 inch)>5yr, <120hr 0
Count_Weir2 = 0 0.36(diameter = 11/16 inch)Max Depth Row
Count_OutletPipe1 = 1 0.42(diameter = 3/4 inch)WQCV 174
Count_OutletPipe2 = 0 0.50(diameter = 13/16 inch)2 Year 226
COUNTA_2 (Standard FSD Setup)= 1 0.58(diameter = 7/8 inch)EURV 292
Hidden Parameters & Calculations 0.67(diameter = 15/16 inch)5 Year 278
MaxPondDepth_Error? FALSE 0.76 (diameter = 1 inch)10 Year 309 Spillway Depth
Cd_Broad-Crested Weir 3.00 0.86(diameter = 1-1/16 inches)25 Year 324 0.68
WQ Plate Flow at 100yr depth = 0.12 0.97(diameter = 1-1/8 inches)50 Year 357
CLOG #1= 100% 1.08(diameter = 1-3/16 inches)100 Year 410 1 Z1_Boolean
n*Cdw #1 = 0.44 1.20(diameter = 1-1/4 inches)500 Year 421 1 Z2_Boolean
n*Cdo #1 = 1.17 1.32(diameter = 1-5/16 inches)Zone3_Pulldown Message 1 Z3_Boolean
Overflow Weir #1 Angle = 0.165 1.45(diameter = 1-3/8 inches)1 Opening Message
CLOG #2= N/A 1.59(diameter = 1-7/16 inches)Draintime Running
n*Cdw #2 = N/A 1.73(diameter = 1-1/2 inches)Outlet Boolean Outlet Rank Total (1 to 4)
n*Cdo #2 = N/A 1.88(diameter = 1-9/16 inches)Vertical Orifice 1 0 0 1
Overflow Weir #2 Angle = N/A 2.03(diameter = 1-5/8 inches)Vertical Orifice 2 0 0 Boolean
Underdrain Q at 100yr depth = 0.00 2.20(diameter = 1-11/16 inches)Overflow Weir 1 1 1 0 Max Depth
VertOrifice1 Q at 100yr depth = 0.00 2.36(diameter = 1-3/4 inches)Overflow Weir 2 0 0 0 500yr Depth
VertOrifice2 Q at 100yr depth = 0.00 2.54(diameter = 1-13/16 inches)Outlet Pipe 1 1 1 1 Freeboard
2.72(diameter = 1-7/8 inches)Outlet Pipe 2 0 0 1 Spillway
Count_User_Hydrographs 0 2.90(diameter = 1-15/16 inches)0 Spillway Length
CountA_3 (EURV & 100yr) = 1 3.09(diameter = 2 inches)FALSE Time Interval
CountA_4 (100yr Only) = 1 3.29(use rectangular openings)Button Visibility Boolean
COUNTA_5 (FSD Weir Only)= 0 0 WQCV Underdrain
COUNTA_6 (EURV Weir Only)= 1 1 WQCV Plate
0 EURV-WQCV Plate
Outlet1_Pulldown_Boolean 0 EURV-WQCV VertOriice
Outlet2_Pulldown_Boolean 1 Outlet 90% Qpeak
Outlet3_Pulldown_Boolean 0 Outlet Undetained
0 Weir Only 90% Qpeak
0 Five Year Ratio Plate
0 Five Year Ratio VertOrifice
EURV_draintime_user
Spillway Options
Offset
Overlapping
S-A-V-D Chart Axis Default X-axis Left Y-Axis Right Y-Axis
minimum bound 0.00 0 0
maximum bound 6.00 30,000 10
S-A-V-D Chart Axis Override X-axis Left Y-Axis Right Y-Axis
minimum bound
maximum bound
MHFD-Detention, Version 4.06 (July 2022)
DETENTION BASIN OUTLET STRUCTURE DESIGN
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PONDING DEPTH [ft]
User Area [ft^2]
Interpolated Area [ft^2]
Summary Area [ft^2]
Volume [ft^3]
Summary Volume [ft^3]
Outflow [cfs]
Summary Outflow [cfs]
MHFD-Detention_v4-06 Pond I (Future) - Full Spectrum Detention, Outlet Structure 8/14/2025, 12:02 PM
GATEWAY AT PROSPECT
APPENDIX
epsgroupinc.com Arizona | Colorado
C.3 Weir Calculations
Weir Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Tuesday, Jul 1 2025
Pond C - Spillway
Trapezoidal Weir
Crest = Sharp
Bottom Length (ft) = 68.00
Total Depth (ft) = 1.00
Side Slope (z:1) = 4.00
Calculations
Weir Coeff. Cw = 3.10
Compute by: Known Q
Known Q (cfs) = 74.40
Highlighted
Depth (ft) = 0.50
Q (cfs) = 74.40
Area (sqft) = 35.00
Velocity (ft/s) = 2.13
Top Width (ft) = 72.00
0 10 20 30 40 50 60 70 80 90 100
Depth (ft) Depth (ft)Pond C - Spillway
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
1.50 1.50
2.00 2.00
Length (ft)Weir W.S.
Weir Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Tuesday, Jul 1 2025
Pond D - Spillway
Trapezoidal Weir
Crest = Sharp
Bottom Length (ft) = 4.00
Total Depth (ft) = 1.00
Side Slope (z:1) = 4.00
Calculations
Weir Coeff. Cw = 3.10
Compute by: Known Q
Known Q (cfs) = 4.50
Highlighted
Depth (ft) = 0.42
Q (cfs) = 4.500
Area (sqft) = 2.39
Velocity (ft/s) = 1.89
Top Width (ft) = 7.36
0 2 4 6 8 10 12 14 16
Depth (ft) Depth (ft)Pond D - Spillway
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
1.50 1.50
2.00 2.00
Length (ft)Weir W.S.
Weir Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Tuesday, Jul 1 2025
Pond E - Spillway
Trapezoidal Weir
Crest = Sharp
Bottom Length (ft) = 18.00
Total Depth (ft) = 1.00
Side Slope (z:1) = 4.00
Calculations
Weir Coeff. Cw = 3.10
Compute by: Known Q
Known Q (cfs) = 20.50
Highlighted
Depth (ft) = 0.49
Q (cfs) = 20.50
Area (sqft) = 9.78
Velocity (ft/s) = 2.10
Top Width (ft) = 21.92
0 5 10 15 20 25 30 35 40
Depth (ft) Depth (ft)Pond E - Spillway
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
1.50 1.50
2.00 2.00
Length (ft)Weir W.S.
Weir Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Tuesday, Jul 1 2025
Pond F - Spillway
Trapezoidal Weir
Crest = Sharp
Bottom Length (ft) = 32.00
Total Depth (ft) = 1.00
Side Slope (z:1) = 4.00
Calculations
Weir Coeff. Cw = 3.10
Compute by: Known Q
Known Q (cfs) = 45.80
Highlighted
Depth (ft) = 0.58
Q (cfs) = 45.80
Area (sqft) = 19.91
Velocity (ft/s) = 2.30
Top Width (ft) = 36.64
0 5 10 15 20 25 30 35 40 45 50
Depth (ft) Depth (ft)Pond F - Spillway
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
1.50 1.50
2.00 2.00
Length (ft)Weir W.S.
Weir Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Tuesday, Jul 1 2025
Pond G - Spillway
Trapezoidal Weir
Crest = Sharp
Bottom Length (ft) = 24.00
Total Depth (ft) = 1.00
Side Slope (z:1) = 4.00
Calculations
Weir Coeff. Cw = 3.10
Compute by: Known Q
Known Q (cfs) = 28.10
Highlighted
Depth (ft) = 0.51
Q (cfs) = 28.10
Area (sqft) = 13.28
Velocity (ft/s) = 2.12
Top Width (ft) = 28.08
0 5 10 15 20 25 30 35 40 45
Depth (ft) Depth (ft)Pond G - Spillway
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
1.50 1.50
2.00 2.00
Length (ft)Weir W.S.
Channel Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Monday, Jul 7 2025
B2 Sidewalk Culvert Channel
Rectangular
Bottom Width (ft) = 4.00
Total Depth (ft) = 0.66
Invert Elev (ft) = 1.00
Slope (%) = 0.60
N-Value = 0.012
Calculations
Compute by: Known Q
Known Q (cfs) = 3.40
Highlighted
Depth (ft) = 0.25
Q (cfs) = 3.400
Area (sqft) = 1.00
Velocity (ft/s) = 3.40
Wetted Perim (ft) = 4.50
Crit Depth, Yc (ft) = 0.29
Top Width (ft) = 4.00
EGL (ft) = 0.43
0 .5 1 1.5 2 2.5 3 3.5 4 4.5 5
Elev (ft) Depth (ft)Section
0.75 -0.25
1.00 0.00
1.25 0.25
1.50 0.50
1.75 0.75
2.00 1.00
Reach (ft)
Weir Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Monday, Jul 7 2025
Sidewalk Culvert B2 - 100-year
Rectangular Weir
Crest = Sharp
Bottom Length (ft) = 4.00
Total Depth (ft) = 0.66
Calculations
Weir Coeff. Cw = 3.33
Compute by: Known Q
Known Q (cfs) = 3.40
Highlighted
Depth (ft) = 0.40
Q (cfs) = 3.400
Area (sqft) = 1.61
Velocity (ft/s) = 2.11
Top Width (ft) = 4.00
0 .5 1 1.5 2 2.5 3 3.5 4 4.5 5
Depth (ft) Depth (ft)Sidewalk Culvert B2 - 100-year
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
Length (ft)Weir W.S.
Channel Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Monday, Jul 7 2025
G2 Sidewalk Culvert Channel
Rectangular
Bottom Width (ft) = 4.00
Total Depth (ft) = 0.66
Invert Elev (ft) = 1.00
Slope (%) = 0.60
N-Value = 0.012
Calculations
Compute by: Known Q
Known Q (cfs) = 9.14
Highlighted
Depth (ft) = 0.46
Q (cfs) = 9.140
Area (sqft) = 1.84
Velocity (ft/s) = 4.97
Wetted Perim (ft) = 4.92
Crit Depth, Yc (ft) = 0.55
Top Width (ft) = 4.00
EGL (ft) = 0.84
0 .5 1 1.5 2 2.5 3 3.5 4 4.5 5
Elev (ft) Depth (ft)Section
0.75 -0.25
1.00 0.00
1.25 0.25
1.50 0.50
1.75 0.75
2.00 1.00
Reach (ft)
Weir Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Monday, Jul 7 2025
Sidewalk Culvert G2 Curb Opening - 100-year
Rectangular Weir
Crest = Sharp
Bottom Length (ft) = 8.00
Total Depth (ft) = 0.66
Calculations
Weir Coeff. Cw = 3.33
Compute by: Known Q
Known Q (cfs) = 9.14
Highlighted
Depth (ft) = 0.49
Q (cfs) = 9.140
Area (sqft) = 3.92
Velocity (ft/s) = 2.33
Top Width (ft) = 8.00
0 1 2 3 4 5 6 7 8 9 10
Depth (ft) Depth (ft)Sidewalk Culvert G2 Curb Opening - 100-year
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
Length (ft)Weir W.S.
Channel Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Monday, Jul 7 2025
G4 Sidewalk Culvert Channel
Rectangular
Bottom Width (ft) = 4.00
Total Depth (ft) = 0.66
Invert Elev (ft) = 1.00
Slope (%) = 0.60
N-Value = 0.012
Calculations
Compute by: Known Q
Known Q (cfs) = 5.06
Highlighted
Depth (ft) = 0.32
Q (cfs) = 5.060
Area (sqft) = 1.28
Velocity (ft/s) = 3.95
Wetted Perim (ft) = 4.64
Crit Depth, Yc (ft) = 0.37
Top Width (ft) = 4.00
EGL (ft) = 0.56
0 .5 1 1.5 2 2.5 3 3.5 4 4.5 5
Elev (ft) Depth (ft)Section
0.75 -0.25
1.00 0.00
1.25 0.25
1.50 0.50
1.75 0.75
2.00 1.00
Reach (ft)
Weir Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Monday, Jul 7 2025
Sidewalk Culvert G4 Curb Opening - 100-year
Rectangular Weir
Crest = Sharp
Bottom Length (ft) = 4.00
Total Depth (ft) = 0.66
Calculations
Weir Coeff. Cw = 3.33
Compute by: Known Q
Known Q (cfs) = 5.06
Highlighted
Depth (ft) = 0.52
Q (cfs) = 5.060
Area (sqft) = 2.10
Velocity (ft/s) = 2.41
Top Width (ft) = 4.00
0 .5 1 1.5 2 2.5 3 3.5 4 4.5 5
Depth (ft) Depth (ft)Sidewalk Culvert G4 Curb Opening - 100-year
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
Length (ft)Weir W.S.
Channel Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Monday, Jul 7 2025
I2 Sidewalk Culvert Channel
Rectangular
Bottom Width (ft) = 8.00
Total Depth (ft) = 0.66
Invert Elev (ft) = 1.00
Slope (%) = 0.60
N-Value = 0.012
Calculations
Compute by: Known Q
Known Q (cfs) = 17.08
Highlighted
Depth (ft) = 0.43
Q (cfs) = 17.08
Area (sqft) = 3.44
Velocity (ft/s) = 4.97
Wetted Perim (ft) = 8.86
Crit Depth, Yc (ft) = 0.53
Top Width (ft) = 8.00
EGL (ft) = 0.81
0 1 2 3 4 5 6 7 8 9 10
Elev (ft) Depth (ft)Section
0.75 -0.25
1.00 0.00
1.25 0.25
1.50 0.50
1.75 0.75
2.00 1.00
Reach (ft)
Weir Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Monday, Jul 7 2025
Sidewalk Culvert I2 Curb Opening - 100-year
Rectangular Weir
Crest = Sharp
Bottom Length (ft) = 12.00
Total Depth (ft) = 0.66
Calculations
Weir Coeff. Cw = 3.33
Compute by: Known Q
Known Q (cfs) = 17.08
Highlighted
Depth (ft) = 0.57
Q (cfs) = 17.08
Area (sqft) = 6.81
Velocity (ft/s) = 2.51
Top Width (ft) = 12.00
0 2 4 6 8 10 12 14 16
Depth (ft) Depth (ft)Sidewalk Culvert I2 Curb Opening - 100-year
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
Length (ft)Weir W.S.
GATEWAY AT PROSPECT
APPENDIX
epsgroupinc.com Arizona | Colorado
C.5 Riprap Calculations
Gateway at Prospect
Circular
D or Da,
Pipe
Diameter
(ft)
H or Ha,
Culvert
Height
(ft)
W,
Culvert
Width
(ft)
Yt/D Q/D1.5 Q/D2.5 Yt/H Q/WH0.5
Storm Line A 14.92 2.00 0.80 0.40 5.28 2.64 N/A N/A 5.00 2.64 2.98 8.65 Type M 9.00 8.00 2.0
Storm Line B 9.30 1.50 0.60 0.40 5.06 3.37 N/A N/A 4.70 3.37 1.86 7.52 Type M 8.00 6.00 2.0
Storm Line C 36.61 2.50 1.00 0.40 9.26 3.70 N/A N/A 3.70 3.70 7.32 17.84 Type M 18.00 10.00 2.0
Storm Line D 8.59 1.25 0.50 0.40 6.15 4.92 N/A N/A 2.40 4.92 1.72 5.25 Type M 6.00 5.00 2.0
Storm Line E 103.70 4.00 1.60 0.40 12.96 3.24 N/A N/A 4.20 3.24 20.74 37.64 Type M 38.00 18.00 2.0
Storm Line F 13.70 2.50 1.00 0.40 3.47 1.39 N/A N/A 6.40 1.39 2.74 1.54 Type M 8.00 10.00 2.0
Storm Line G 26.90 2.25 0.90 0.40 7.97 3.54 N/A N/A 4.00 3.54 5.38 14.91 Type M 15.00 9.00 2.0
Storm Line H 4.50 1.50 0.60 0.40 2.45 1.63 N/A N/A 6.20 1.63 0.90 0.00 Type M 5.00 6.00 2.0
Storm Line I 14.00 1.75 0.70 0.40 6.05 3.46 N/A N/A 4.00 3.46 2.80 9.00 Type M 9.00 7.00 2.0
Storm Line J 67.70 3.00 1.20 0.40 13.03 4.34 N/A N/A 3.10 4.34 13.54 25.68 Type M 26.00 15.00 2.0
Storm Line K 4.13 1.25 0.50 0.40 2.96 2.36 N/A N/A 5.20 2.36 0.83 2.09 Type M 4.00 5.00 2.0
Date: 07/02/2025
Spec
Length
of
Riprap
(ft)
Box Culvert
Yt,
Tailwater
Depth
(ft)
Culvert Parameters
At=Q/V (ft)
By: S. Thomas
CALCULATE
Froude
Parameter
Q/D2.5
Max 6.0
or
Q/WH1.5
Max 8.0
Riprap
Type
(From
Figure
MD-21 or
MD-22)
Project: 892-002
Urban Drainage
pg MD-107
L=
1/(2tanq)*
[At/Yt)-W]
(ft)
INPUT
Storm Line/Culvert
Label
Design
Discharge
(cfs)
Expansion
Factor
1/(2tanq)
(From
Figure
MD-23 or
MD-24)
OUTPUT
CALCULATIONS FOR RIPRAP PROTECTION AT PIPE OUTLETS
Circular
Pipe
(Figure MD-21)
Rectangular
Pipe
(Figure MD-22)Spec
Width
of
Riprap
(ft)
2*d50,
Depth
of
Riprap
(ft)
for L/2
GATEWAY AT PROSPECT
APPENDIX
epsgroupinc.com Arizona | Colorado
APPENDIX D
Cooper Slough HEC-RAS Model
COOPER SLOUGH CO
2698.69
2400
2100
1800
1500
1200
900
600
300
0
COOPER SLOUGH CO
Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S.E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl
(cfs)(ft)(ft)(ft)(ft)(ft/ft)(ft/s)(sq ft)(ft)
COOPER SLOUGH CO 2698.69 10-yr 474 4910.86 4915.5 4913.55 4915.67 0.002726 3.31 143.11 69.39 0.35
COOPER SLOUGH CO 2400 10-yr 474 4910.64 4915.18 4912.38 4915.25 0.000773 2.03 232.94 85.79 0.2
COOPER SLOUGH CO 2100 10-yr 474 4910.43 4914.95 4912.16 4915.01 0.000779 2.04 232.65 87.11 0.2
COOPER SLOUGH CO 1800 10-yr 474 4910.21 4914.78 4911.68 4914.82 0.00048 1.66 285.76 222.4 0.16
COOPER SLOUGH CO 1500 10-yr 474 4909.99 4914.63 4911.51 4914.67 0.000524 1.68 282.22 101.85 0.16
COOPER SLOUGH CO 1200 10-yr 474 4909.77 4914.51 4911.11 4914.55 0.000337 1.42 333.82 134.31 0.13
COOPER SLOUGH CO 900 10-yr 474 4909.4 4914.24 4911.78 4914.35 0.001445 2.66 177.95 105.62 0.26
COOPER SLOUGH CO 600 10-yr 474 4909.01 4913.49 4911.88 4913.71 0.003392 3.75 131.83 93.76 0.4
COOPER SLOUGH CO 300 10-yr 474 4908.43 4912.35 4910.93 4912.59 0.004076 3.94 120.38 48.43 0.43
COOPER SLOUGH CO 0 10-yr 474 4907.72 4909.45 4909.45 4909.97 0.029383 5.79 81.84 78.93 1
Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S.E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl
(cfs)(ft)(ft)(ft)(ft)(ft/ft)(ft/s)(sq ft)(ft)
COOPER SLOUGH CO 2698.69 100-yr 1274 4910.86 4917.85 4915.4 4918.13 0.002878 4.19 305.46 117.31 0.38
COOPER SLOUGH CO 2400 100-yr 1274 4910.64 4917.42 4913.77 4917.57 0.001172 3.12 408.25 109.49 0.25
COOPER SLOUGH CO 2100 100-yr 1274 4910.43 4917.04 4913.58 4917.2 0.001252 3.21 399.2 126.65 0.26
COOPER SLOUGH CO 1800 100-yr 1274 4910.21 4916.97 4912.94 4917 0.000299 1.68 1011.91 394.96 0.13
COOPER SLOUGH CO 1500 100-yr 1274 4909.99 4916.77 4912.79 4916.87 0.000691 2.51 559.99 210.46 0.2
COOPER SLOUGH CO 1200 100-yr 1274 4909.77 4916.6 4912.26 4916.68 0.000562 2.3 579.91 207.88 0.18
COOPER SLOUGH CO 900 100-yr 1274 4909.4 4916.06 4913.48 4916.35 0.0025 4.29 308.92 162.48 0.37
COOPER SLOUGH CO 600 100-yr 1274 4909.01 4915.28 4913.99 4915.52 0.002953 4.38 370.07 211.51 0.39
COOPER SLOUGH CO 300 100-yr 1274 4908.43 4913.65 -4914.23 0.006392 6.4 242.84 150.66 0.57
COOPER SLOUGH CO 0 100-yr 1274 4907.72 4913.91 4910.49 4913.93 0.000144 1.15 1239.46 300 0.09
10-Year HEC-RAS Results
100-Year HEC-RAS Results
0 500 1000 1500 2000 2500 3000
4906
4908
4910
4912
4914
4916
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Main Channel Distance (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 10-yr
WS 10-yr
Crit 10-yr
Ground
COOPER SLOUGH CO COOPER SLOUGH CO
0 50 100 150 200 250 300
4910
4912
4914
4916
4918
4920
4922
4924
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 10-yr
WS 10-yr
Crit 10-yr
Ground
Ineff
Bank Sta
.045 .045 .045
0 50 100 150 200 250 300
4904
4906
4908
4910
4912
4914
4916
4918
4920
4922
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 10-yr
WS 10-yr
Crit 10-yr
Ground
Ineff
Bank Sta
.045 .045 .045
0 50 100 150 200 250 300
4900
4905
4910
4915
4920
4925
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 10-yr
WS 10-yr
Crit 10-yr
Ground
Ineff
Bank Sta
.045 .045 .045
0 100 200 300 400 500
4910
4912
4914
4916
4918
4920
4922
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 10-yr
WS 10-yr
Crit 10-yr
Ground
Ineff
Bank Sta
.045 .045 .045
0 50 100 150 200 250 300
4908
4910
4912
4914
4916
4918
4920
4922
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 10-yr
WS 10-yr
Crit 10-yr
Ground
Ineff
Bank Sta
.045 .045 .045
0 50 100 150 200 250 300
4908
4910
4912
4914
4916
4918
4920
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 10-yr
WS 10-yr
Crit 10-yr
Ground
Ineff
Bank Sta
.045 .045 .045
0 50 100 150 200 250 300
4908
4910
4912
4914
4916
4918
4920
4922
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 10-yr
WS 10-yr
Crit 10-yr
Ground
Ineff
Bank Sta
.045 .045 .045
0 50 100 150 200 250 300
4908
4910
4912
4914
4916
4918
4920
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 10-yr
WS 10-yr
Crit 10-yr
Ground
Ineff
Bank Sta
.045 .045 .045
0 50 100 150 200 250 300
4908
4909
4910
4911
4912
4913
4914
4915
4916
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 10-yr
WS 10-yr
Crit 10-yr
Ground
Bank Sta
.045 .045 .045
0 50 100 150 200 250 300
4907.5
4908.0
4908.5
4909.0
4909.5
4910.0
4910.5
4911.0
4911.5
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 10-yr
WS 10-yr
Crit 10-yr
Ground
Bank Sta
.045 .045 .045
0 500 1000 1500 2000 2500 3000
4906
4908
4910
4912
4914
4916
4918
4920
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Main Channel Distance (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 100-yr
WS 100-yr
Crit 100-yr
Ground
COOPER SLOUGH CO COOPER SLOUGH CO
0 50 100 150 200 250 300
4910
4912
4914
4916
4918
4920
4922
4924
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 100-yr
WS 100-yr
Crit 100-yr
Ground
Ineff
Bank Sta
.045 .045 .045
0 50 100 150 200 250 300
4904
4906
4908
4910
4912
4914
4916
4918
4920
4922
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 100-yr
WS 100-yr
Crit 100-yr
Ground
Ineff
Bank Sta
.045 .045 .045
0 50 100 150 200 250 300
4900
4905
4910
4915
4920
4925
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 100-yr
WS 100-yr
Crit 100-yr
Ground
Ineff
Bank Sta
.045 .045 .045
0 100 200 300 400 500
4910
4912
4914
4916
4918
4920
4922
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 100-yr
WS 100-yr
Crit 100-yr
Ground
Ineff
Bank Sta
.045 .045 .045
0 50 100 150 200 250 300
4908
4910
4912
4914
4916
4918
4920
4922
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 100-yr
WS 100-yr
Crit 100-yr
Ground
Ineff
Bank Sta
.045 .045 .045
0 50 100 150 200 250 300
4908
4910
4912
4914
4916
4918
4920
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 100-yr
WS 100-yr
Crit 100-yr
Ground
Ineff
Bank Sta
.045 .045 .045
0 50 100 150 200 250 300
4908
4910
4912
4914
4916
4918
4920
4922
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 100-yr
WS 100-yr
Crit 100-yr
Ground
Ineff
Bank Sta
.045 .045 .045
0 50 100 150 200 250 300
4908
4910
4912
4914
4916
4918
4920
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 100-yr
WS 100-yr
Crit 100-yr
Ground
Ineff
Bank Sta
.045 .045 .045
0 50 100 150 200 250 300
4908
4909
4910
4911
4912
4913
4914
4915
4916
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 100-yr
WS 100-yr
Ground
Bank Sta
.045 .045 .045
0 50 100 150 200 250 300
4907
4908
4909
4910
4911
4912
4913
4914
COOPER SLOUGH CORRIDOR Plan: Plan 01 8/13/2025
Station (ft)
El
e
v
a
t
i
o
n
(
f
t
)
Legend
EG 100-yr
WS 100-yr
Crit 100-yr
Ground
Bank Sta
.045 .045 .045
CITY OF FORT COLLINS
UPPER COOPER SLOUGH BASIN
SELECTED PLAN OF IMPROVEMENTS
February 2021
Prepared for:
Department of Utilities
700 Wood Street
Fort Collins, CO 80522
(970) 221‐6589
Prepared by:
7000 S. Yosemite Street, Suite 120
Centennial CO 80112
(303) 221‐0802
www.iconeng.com
ANHEUSER BUSCH (AB)
PLANT
Sod Farm Diversion
Q diverted = 752 cfs
Proposed Sod Farm Pond
S = 164 AF
Max WSE = 5033.2 ft
Berm along southern end at 5037.0 ft
Sod Farm Pond Outlet Pipe
into No. 8 Outlet Ditch
36" RCP with a 33.6" Orifice
Q = 54 cfs
Mountain Vista Diversion
From No8 Outlet Ditch
Q
=
2
5
0
c
f
s
Q = 8
9
c
f
s
Assume Full Development
of AB Lands with 100yr ->
2yr Detention (On-Site)
Mountain Vista Diversion
May Be Conveyed In
Open Channel or Pipe through
Montava Development
Proposed C&S/ Crumb
Detention Pond (426)
S = 193 AF
WSE = 4987.0 ft
Qin = 903 cfs
New AB Pond Outfall
Overflow Flume
Discharges into Cooper Slough
Q = 304 cfs
Existing AB 425 Pond Outlet
Remains Connected to L&W Canal
Q = 385 cfs
Existing AB Pond 425
S = 47 AF
Max WSE = 4983.5
Qin = 732 cfs
Remove Existing Flow Spill At CSRR
Provide Open Channel to Convey
Flows on West Side of RR
Combined Outlow From
C&S/ Crumb and L&W Canal Spill
Q = 639 cfs
Proposed E. Vine Dr. Culverts
(3) 8' x 4' RCBC
Q = 678 cfs
Proposed E. Mulberry St. Culverts
(2) 6' x 11' RCBC
Q = 1050 cfs
COOPER SLOUGH
Canal Spill to Dry Creek
Q = 0 cfs
Canal Spill
Q = 421 cfs
Q
=
7
7
8
c
f
s
Q
=
3
5
7
c
f
s
Q =
2
2
9
c
f
s
Q
=
3
3
9
c
f
s
Q =
1
0
0
2
c
f
s
Q
=
3
7
4
c
f
s
NO
.
8
O
U
T
L
E
T
D
I
T
C
H
LARIME
R
&
W
E
L
D
C
A
N
A
L
CO
L
O
R
A
D
O
&
S
O
U
T
H
E
R
N
R
A
I
L
R
O
A
D
BOXELDER WATERSHED
DRY CREEK WATERSHED
COOPER SLOUGH WATERSHED
BLACK HOLLOW OUTFALL CHANNEL
IMPROVEMENTS FROM 2006 MASTER
PLAN NOT INCLUDED IN 2021 UPDATE
Q =
2
5
0
c
f
s
N. Poudre Reservoir No. 6
Add 8-inch Iron Sill Plate to
Spillway
Q = 547 cfs
S = 679 AF
Max WSE = 5163.2'
Proposed (2) 6'x11' RCBC
to Lake Canal
SH-14
Proposed Channel
to Box Elder Creek
Channel and Bank Improvements
along Cooper Slough
Pond A
S = 82 AF
Max WSE = 5019.6 ft
Qout = 778 cfs
Montava Swale
Q = 778 cfs
Q
=
1
4
9
c
f
s
Overflow Pond
S = 20.3 AF
WSE = 4980.2 ft
Qin = 112 cfs
Proposed C&S/ Crumb Outfalls:
42" RCP to AB Pond = 102 cfs
3ft x 13.5ft RCBC to AB Pond
(3ft above Pond inv) = 331 cfs
Spill to Overflow Pond = 112cfs
Overflow Pond Outfall
into L&W Canal
48" RCP with a 44.4" Orifice
Qout = 103 cfs
Proposed (3) 3'x15' RCBC
under Lake Canal
Proposed Channel
Proposed culverts
for local drainage
MONTAVA
DEVELOPMENT
MT VISTA AND TIMBERLINE ROAD
MIXED-USED DEVELOPMENT
WATER'S EDGE
DEVELOPMENT
COUNTRY CLUB
RESERVE
DEVELOPMENT
Existing 24-in Culvert
Capaity = 21cfs
Culvert Crossing
(3) 10'X3' RCBC
Q = 888cfs
Proposed Channel
Formalize Spill from
Lake Canal
E VINE DR
IN
T
E
R
S
T
A
T
E
2
5
S
B
E MULBERRY ST
GI
D
D
I
N
G
S
R
D
TU
R
N
B
E
R
R
Y
R
D
RICHARDS LAKE RD
MOUNTAIN VISTA DR
E LIN
C
O
L
N
A
V
E
S TIMB
E
R
L
I
N
E
R
D
COUNTRY CLUB RD
E COUNTY ROAD 48
§¨¦25
§¨¦25
Cooper Slough Selected Plan (2021)
Figure 3: Selected Plan Projects $
0 0.5
Miles
Legend
swale
Overflow_Pond
Pond_A
C&S_Pond
AB_Pond
CRUMB_OUTLET
Sod Farm Pond
Proposed_Channel
Proposed Culvert
Montava Dev Boundary
Waters Edge Dev Boundary
Cooper Slough Basin Boundary
MtVista
!
! !
! !Anheuser Busch Property
Cooper Slough 23
Selected Plan
February 2021
Figure 15: Mountain Vista and Timberline Road Mixed‐Use Development
2.9 Improvements South of Mulberry Street (SH‐14)
Approximately 1050 cfs flows south along Cooper Slough to Mulberry Street. There, the flow is currently
conveyed under Mulberry Street (SH‐14) through dual 48‐inch diameter culverts with approximately 200
cfs capacity. All flow in excess of this 200 cfs backs up and overtops the roadway. Commercial
development upstream and downstream of Mulberry are at risk of flooding as a result. Floodwater
overtopping Mulberry ultimately enters and spills from the Lake Canal prior to reaching Boxelder Creek.
The following improvements are proposed to convey the 100‐year storm event from Mulberry Street to
Boxelder Creek.
2.9.1 Mulberry Street (SH‐14) Crossing
At Mulberry Street (EPA SWMM node 406. Lower Model), dual (2) 6ft high by 11ft wide RCBCs are
proposed to convey the 1050 cfs discharge without overtopping. The installation of these culverts will
remove the existing Cooper Slough split flow path to the east of the crossing location.
The water can be conveyed to the Lake Canal through either an open channel or culvert system. The
Cooper Slough channel improvements would consist of a channel 6 feet deep, with a bottom width of 13
feet. The channel would contain a low flow channel in the bottom to convey the base flows. Due to the
size of the channel, and land acquisition required, the extension of the dual (2) 6ft high by 11ft
1
Blaine Mathisen
From:Craig Jacobson <cjacobson@iconeng.com>
Sent:Thursday, April 1, 2021 6:23 PM
To:Stephanie Thomas; Daniel Evans; jim@tbgroup.us
Cc:Jaclyn Michaelsen; Blaine Mathisen; Adam Boese
Subject:RE: Gateway - Cooper Slough Improvements
Hi Stephanie,
In essence you are correct in that statement. Our models for the master plan direct all of the stormwater into the
proposed culvert systems and downstream into the Cooper Slough Channel. The 100-year flow is 1050cfs at Mulberry
and increases to 1274cfs further downstream as shown in the figure below. It was noted in the report that the existing
pipes could be used to take on the base flows to maintain water rights. This flow would ultimately follow the Lake Canal
towards BEC. This could reduce the overall flow in the channel by approximately 200cfs as you indicated. However, you
should note that we have not confirmed the actual capacity of the Lake Canal and that the entirety of the 200cfs can fit
and will not spill back out to Cooper Slough, and that a control structure from the Lake Canal does exist about half way
down, as shown by the figure where the flow change is at. So from that perspective, it a bit hard to say if the flow
reduction would exist continuously all the way to BEC.
Let us know if you have any questions. Thanks.
Craig
To help protect your privacy, Microsoft Office prevented automatic download of this picture from the
Internet.
Craig Jacobson, PE, CFM
Principal
7000 S. Yosemite St, Suite 120, Centennial, CO 80112
(303) 221-0802(o) (303) 898-9717(c) | www.iconeng.com | cjacobson@iconeng.com
The information contained in this e-mail is confidential and may be protected by legal privilege. If you are not the intended recipient of this e-
mail, the use of this information is prohibited. If you have received this in error, please notify us immediately and delete this copy from your
system. Thank you for your cooperation. ICON Engineering, Inc.
2
From: Stephanie Thomas <stephanie@northernengineering.com>
Sent: Thursday, April 1, 2021 11:09 AM
To: Daniel Evans <daevans@fcgov.com>; jim@tbgroup.us
Cc: Craig Jacobson <cjacobson@iconeng.com>; Jaclyn Michaelsen <jmichaelsen@iconeng.com>; Blaine Mathisen
<blaine@northernengineering.com>; Adam Boese <adam@northernengineering.com>
Subject: RE: Gateway - Cooper Slough Improvements
Dan
I can’t help but notice that the 100-year flow increased from 1050 cfs to 1274 cfs. This is an increase of 224 cfs or 21%.
The Cooper Slough report indicated that about 200 cfs would still pass through the 48” dual culverts. Is this 224 cfs
related to the amount that would continue through the existing culverts? If that is the case, it would seem to me that
the channel through Gateway would be required to pass the events shown below minus 200 cfs?
Am I interpreting this correctly?
Thank you.
Stephanie Thomas, PE
Project Manager
301 N. Howes Street, Suite 100 | Fort Collins, CO 80521
D: 970.568.5412
O: 970.221.4158
Home Office: 970-658-1035
northernengineering.com
Improving quality of life in our communities.
3
From: Daniel Evans <daevans@fcgov.com>
Sent: Wednesday, March 31, 2021 5:09 PM
To: Stephanie Thomas <stephanie@northernengineering.com>; jim@tbgroup.us
Cc: Craig Jacobson <cjacobson@iconeng.com>; Jaclyn Michaelsen <jmichaelsen@iconeng.com>
Subject: FW: Gateway - Cooper Slough Improvements
Stephanie and Jim,
Icon ran the 2, 5, 10, 25, 50 and 100-year flows for the Upper Cooper Slough channel and are highlighted in yellow
below.
Let us know if the need anything else.
Dan
From: Craig Jacobson <cjacobson@iconeng.com>
Sent: Wednesday, March 31, 2021 2:09 PM
To: Daniel Evans <daevans@fcgov.com>; Jaclyn Michaelsen <jmichaelsen@iconeng.com>
Subject: [EXTERNAL] RE: Gateway - Cooper Slough Improvements
Hey Dan,
Here are the flows that Jackie came up with. We just went ahead and modeled them top to bottom, including through
the LWC. Let me know if you need any of the models. We can discuss later today. Thanks
Craig
Low Flow Summary - Upper Cooper Slough (DS of Larimer and Weld Canal)
Junction/Link ID Description 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr
Junction 866 US Vine Drive 15 24 31 246 419 678
Junction 413 US Railroad 81 126 160 253 438 680
Junction 7417 DS Railroad 13 16 20 246 418 678
Junction 928 US Mulberry 202 317 415 579 775 1048
Link C4 Channel DS Lake Canal 219 352 474 685 935 1274
Junction 884 Confluence with BEC 494 723 945 1586 2403 3157
From: Daniel Evans <daevans@fcgov.com>
Sent: Wednesday, March 17, 2021 9:51 AM
To: Craig Jacobson <cjacobson@iconeng.com>; Jaclyn Michaelsen <jmichaelsen@iconeng.com>
Cc: Ken Sampley <KSampley@fcgov.com>
Subject: RE: Gateway - Cooper Slough Improvements
Yes, we did evaluate the 2 and 10-year from Montava. Looks like there are No Spills from the L&W in the 2-year so flow
to the outfall channel will just be from downstream contributing basins, and not a lot of flow from the 10-year….
From: Daniel Evans
Sent: Wednesday, March 17, 2021 9:11 AM
To: Craig Jacobson <cjacobson@iconeng.com>; Jaclyn Michaelsen <jmichaelsen@iconeng.com>
4
Cc: Ken Sampley <KSampley@fcgov.com>
Subject: FW: Gateway - Cooper Slough Improvements
Craig and Jackie,
Northern is requesting the full range of flows to design the outfall channel for Upper Cooper. I don’t see that in the
Selected Plan as we only evaluated the 100-year.
I know we looked at the more frequent events during the Montava analysis to make sure they did not adversely impact
downstream properties so do we have these flow values?
If not, how much of an effort would it be to get those to Northern?
Dan
From: Stephanie Thomas <stephanie@northernengineering.com>
Sent: Tuesday, March 16, 2021 1:34 PM
To: Matt Simpson <masimpson@fcgov.com>; Daniel Evans <daevans@fcgov.com>; Theodore Bender
<tbender@fcgov.com>
Cc: Blaine Mathisen <blaine@northernengineering.com>
Subject: [EXTERNAL] Gateway - Cooper Slough Improvements
Matt, Dan and Ted
We are looking at the Cooper Slough improvements along the Gateway north parcel. We would like to look at a tiered
channel with a 2-yr, 10-yr, and 100-yr channel. We will be looking at other storm events for comparison as well.
The Cooper Slough report doesn’t have any flow data for events other than the 100-year in this reach. Would you
please tell us what flow is expected for the 2-yr, 10-yr, 25-yr, 50-yr and 100-yr? Or can you please contact ICON and ask
them to send us this information?
Thank you.
Stephanie Thomas, PE
Project Manager
301 N. Howes Street, Suite 100 | Fort Collins, CO 80521
D: 970.568.5412
O: 970.221.4158
Home Office: 970-658-1035
northernengineering.com
Improving quality of life in our communities.
GATEWAY AT PROSPECT
APPENDIX
epsgroupinc.com Arizona | Colorado
APPENDIX E
FEMA Firmette
PANEL LOCATOR
NATIONAL FLOOD INSURANCE PROGRAMFLOOD INSURANCE RATE MAP
LARIMER COUNTY, COLORADO
Panel Contains:
COMMUNITY NUMBER PANEL SUFFIX
VERSION NUMBER
MAP NUMBER
EFFECTIVE DATE
1.1.1.0
08069C0984H
MAY 2, 2012
NOTES TO USERS
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LARIMER COUNTYFORT COLLINS, CITY OF
County Name
SCALE
Map Projection:Universal Transverse MercatorNAD 1983 UTM Zone 13NWestern Hemisphere; Vertical Datum: NAVD 88
FLOOD HAZARD INFORMATION
080101080102 09840984 HH
))))
))))
))))
Larimer CountyUnincorporated Areas080101
Larimer CountyUnincorporated Areas080101
Larimer CountyUnincorporated Areas080101
Larimer CountyUnincorporated Areas080101
City of Fort Collins080102
City of Fort Collins080102
City of Fort Collins080102
City of Fort Collins080102
22
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Larimer CountyUnincorporated Areas080101
DAR
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DRIV
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Sherry DriveOverflow
INTERSTATE25FRONTAGE ROAD
FRONTAGE ROAD NFRONTAGE ROAD S
COUNTRYSIDE
DELOZIER
DR
KENWOOD
DR
MAR
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CT
EAST PROSPECT ROAD
COLLINS
AIRE LN
INTERNATIONAL
BOULEVARD
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ANDREAST
JO
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TIMBERLINEROAD
LINCOLN AVE
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BOX ELDER DRIVE
KI
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BUCKEYE ST
REDMAN DRIVE
STOCKTON
AVE
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Larimer CountyUnincorporated Areas080101
SH
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SM
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LOCUST ST
FRONTAGE ROAD
IN
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FRONTAGE
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BOXELDER
DRIVE
SUM
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MULBERRY ST
MULBERRY STREET
DR
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RAILR
O
A
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RIVERBEND CT.
40°33'45.0"
105°01'52.5"498000mE 499000mE 105°00'00"
40°33'45.0"
4491000mN
4492000mN
4493000mN
40°35'37.5"
105°00'00"3135000 FT105°01'52.5"
40°35'37.5"
1455000 FT
1450000 FT
§¨¦25
RAILROAD
NOTE: MAP AREA SHOWN ON THIS PANEL
IS LOCATED WITHIN TOWNSHIP 7 NORTH,
RANGE 68 WEST.
REVISED
AREA
4896.1
4923.0
4898.6
4898.1
4920.7
4898.4
4913.0
4923.1
491
3
.
6
490
9
.
7
4905.2
FLOODING EFFECTS FROM
CACHE LA POUDRE RIVER SPLIT R PATH
4919.9
4921.3
49
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.
9
4940.0
4917.5
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49
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4
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8
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4939
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4920.5
FLOODWAY CONTAINED
IN CULVERT
4916.9
%,BF
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4923.6
4918.9
4916.9
4945.7
Cache La PoudreRiver L Path
4930.5
49
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.
3
4942.0
4930.7
4945.6
4937.7
%,Z
%,T
%,S
%,BH
%,D
%,M
%,BJ
%,BK
%,P
%,N
%,O
%,U
%,B
%,V
%,Y
%,A
%,X
%,H
%,B
%,C
%,G
%,D
%,C
%,M
%,E%,BI
%,A
%,F
%,G
%,R
%,L
%,N
%,C
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%,K
%,A
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%,J
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48874890
4884
4892
4891
4886
4892
4902
4903
Bridge
Boxelder DitchDiversion Dam
4904
4905
4904
4893
4906
490
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4893
4901
4884
48854899
49
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9
4898
4894
490
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489548964897
4891
4897
4900
4896
4892
4894
4895
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Boxelder Creek
Boxelder Creek
Cache La PoudreRiver
Lake Ca
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Cache La Poudre Reservoir Inlet
BoxelderCreek
CooperSlough
%,BL
ZONE
AE
SpringCreek
ZONE
AE
ZONE AE
ZONE AO
(DEPTH 2)
Cache La PoudreReservoir Inlet
ZONE
AE
ZONE AE
ZONE A
City of Fort Collins080102
ZONE AE
ZONE AE
%,A
ZONE AE ZONE
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Cache La Poudre RiverSplit R Path
BoxelderCreek
ZONE
AE
ZONE AE
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%,AA
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1%-ANNUAL-CHANCE
FLOOD DISCHARGE
CONTAINED IN CULVERT
ZONE
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(DEPTH 2)
ZONE
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4949.2
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4920.6
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1%-ANNUAL-CHANCE FLOOD
DISCHARGE CONTAINED
IN CULVERT
4902.3%,F
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FLOOD DISCHARGE
CONTAINED
IN CULVERT
Bridge
490
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4897.1%,D
4895.7%,C
48
9
2
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Cooper SloughOverflow
Culvert
Culvert
Culvert
PANEL OF 1420 9840250500125
Meters
0 1,000 2,000500
Feet
1 inch = 500 feet 1:6,000
1001
1011
0981 0982
0992
0983 10030984
LarimerCounty
*PANEL NOT PRINTED
SPECIAL FLOODHAZARD AREAS
OTHER AREAS OFFLOOD HAZARD
OTHERAREAS
GENERALSTRUCTURES
Without Base Flood Elevation (BFE)
With BFE or Depth
Regulatory Floodway
Area of Undetermined Flood Hazard
Area of Minimal Flood Hazard
Zone A,V, A99 Zone AE, AO, AH, VE, AR
Zone X
Zone D
HTTP://MSC.FEMA.GOV
THE INFORMATION DEPICTED ON THIS MAP AND SUPPORTINGDOCUMENTATION ARE ALSO AVAILABLE IN DIGITAL FORMAT AT
SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT
Cross Sections with 1% Annual ChanceWater Surface Elevation
Coastal Transect
OTHERFEATURES
Profile BaselineHydrographic FeatureBase Flood Elevation Line (BFE)Limit of StudyJurisdiction Boundary
Coastal Transect Baseline
17.5
0.2% Annual Chance Flood Hazard, Areas of 1% annual chance flood with average depth less than one foot or with drainage areas of less than one square mileFuture Conditions 1% Annual Chance Flood HazardArea with Reduced Flood Risk due to LeveeSee Notes.
Zone X
Zone X
Zone X
!(8
%,E 18.2
NO SCREEN
Levee, Dike, or Floodwall
Channel, Culvert, or Storm Sewer
Area with Flood Risk due to Levee Zone D
This map includes approximate boundaries of the CBRS for informational purposes only. Flood insurance
is not available within CBRS areas for structures that are newly built or substantially
improved on or after the date(s) indicated on the map. For more information
see http://www.fws.gov/cbra, the FIS Report, or call the U.S. Fish and Wildlife Service
Customer Service Center at 1-800-344-WILD.
CBRS Area Otherwise Protected Area
For information and questions about this Flood Insurance Rate Map (FIRM), available products associated
with this FIRM, including historic versions, the current map date for each FIRM panel, how to order
products, or the National Flood Insurance Program (NFIP) in general, please call the
FEMA Map Information eXchange at 1-877-FEMA-MAP (1-877-336-2627) or visit the FEMA Flood
Map Service Center website at http://msc.fema.gov. Available products may include previously
issued Letters of Map Change, a Flood Insurance Study Report, and/or digital versions of this map.
Many of these products can be ordered or obtained directly from the website.
Communities annexing land on adjacent FIRM panels must obtain a current copy of the adjacent panel as well as
the current FIRM Index. These may be ordered directly from the Flood Map Service Center at the number listed
above.
For community and countywide map dates refer to the Flood Insurance Study Report for this jurisdiction.
To determine if flood insurance is available in this community, contact your Insurance agent or call the National
Flood Insurance Program at 1-800-638-6620.
Base map information shown on this FIRM was derived from U.S. Census Bureau TIGER files, dated 2010,
and digital data provided by Flood County Geospatial Coordinator, dated 2010.
Local vertical monuments were used to create this map. To obtain current monument information,
please contact the [community contact information, phone number] or visit the website at [website address].
ACCREDITED LEVEE: Check with your local community to obtain more information, such as
the estimated level of protection provided (which may exceed the 1-percent-annual-chance level) and Emergency
Action Plan, on the levee system(s) shown as providing protection for areas on this panel. To mitigate flood
risk in residual risk areas, property owners and residents are encouraged to consider flood insurance and
floodproofing or other protective measures. For more information on flood insurance, interested parties should
visit http://www.fema.gov/national-flood-insurance-program.
PROVISIONALLY ACCREDITED LEVEE: Check with your local community to obtain more
information, such as the estimated level of protection provided (which may exceed the 1-percent- annual-chance
level) and Emergency Action Plan, on the levee system(s) shown as providing protection for areas on this panel.
To maintain accreditation, the levee owner or community is required to submit the data and documentation
necessary to comply with Section 65.10 of the NFIP regulations by (_____, _____). If the community or owner
does not provide the necessary data and documentation or if the data and documentation provided indicate the
levee system does not comply with Section 65.10 requirements, FEMA will revise the flood hazard and risk
information for this area to reflect de-accreditation of the levee system. To mitigate flood risk in residual
risk areas, property owners and residents are encouraged to consider flood insurance and floodproofing or other
protective measures. For more information on flood insurance, interested parties should visit
http://www.fema.gov/national-flood-insurance-program.
LIMIT OF MODERATE WAVE ACTION: Zone AE has been divided by a Limit of Moderate Wave Action (LiMWA).
The LiMWA represents the approximate landward limit of the 1.5-foot breaking wave. The effects of wave
hazards between the Zone VE and the LiMWA (or between the shoreline and the LiMWA for areas where
Zone VE is not identified) will be similar to, but less severe than, those in the Zone VE.
and Incorporated Areas
COASTAL BARRIER RESOURCES SYSTEM (CBRS)
Limit of Moderate Wave Action (LiMWA)# #
REVISED TO
REFLECT LOMR
EFFECTIVE: February 21, 2019
GATEWAY AT PROSPECT
APPENDIX
epsgroupinc.com Arizona | Colorado
APPENDIX F
Erosion Control Report
GATEWAY AT PROSPECT
APPENDIX
epsgroupinc.com Arizona | Colorado
EROSION CONTROL REPORT
A comprehensive Erosion and Sediment Control Plan (along with associated details) has been included with the final
construction drawings. It should be noted; however, any such Erosion and Sediment Control Plan serves only as a general
guide to the Contractor. Staging and/or phasing of the BMPs depicted, and additional or different BMPs from those
included may be necessary during construction, or as required by the authorities having jurisdiction.
It shall be the responsibility of the Contractor to ensure erosion control measures are properly maintained and followed.
The Erosion and Sediment Control Plan is intended to be a living document, constantly adapting to site conditions and
needs. The Contractor shall update the location of BMPs as they are installed, removed, or modified in conjunction with
construction activities. It is imperative to appropriately reflect the current site conditions at all times.
The Erosion and Sediment Control Plan shall address both temporary measures to be implemented during construction,
as well as permanent erosion control protection. Best Management Practices from the Volume 3, Chapter 7 –
Construction BMPs will be utilized. Measures may include, but are not limited to, silt fencing and/or wattles along the
disturbed perimeter, gutter protection in the adjacent roadways, and inlet protection at existing and proposed storm
inlets. Vehicle tracking control pads, spill containment and clean-up procedures, designated concrete washout areas,
dumpsters, and job site restrooms shall also be provided by the Contractor.
Grading and Erosion Control Notes can be found on Sheet 3 of the PICP. The Final Utility Plans will also contain a full-size
Erosion Control Plan as well as a separate sheet dedicated to Erosion Control Details. In addition to this report and the
referenced plan sheets, the Contractor shall be aware of, and adhere to, the applicable requirements outlined in any
existing Development Agreement(s) of record, as well as the Development Agreement, to be recorded prior to issuance
of the Development Construction Permit. Also, the Site Contractor for this project may be required to secure a
Stormwater Construction General Permit from the Colorado Department of Public Health and Environment (CDPHE),
Water Quality Control Division – Stormwater Program, before commencing any earth disturbing activities. Prior to
securing said permit, the Site Contractor shall develop a comprehensive Storm Water Management Plan (SWMP)
pursuant to CDPHE requirements and guidelines. The SWMP will further describe and document the ongoing activities,
inspections, and maintenance of construction BMPs.
GATEWAY AT PROSPECT
APPENDIX
epsgroupinc.com Arizona | Colorado
MAP POCKET
DR1- Drainage Exhibit
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E E E E E
/ / / / / / / /
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SS SS
24
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8" SS
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ELEC
VAULT
ELEC
X
OHU OHU OHU
/ /
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/ / / / / / / // / / / / / / // / / / / / / /
GAS
GAS
CONTROL
IRR
CONTROL
IRR
VAULT
ELECH2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
F.O.
F.O.
ELEC
ELEC
VAULT
ELEC
VAULT
ELEC
VAULT
ELEC
VAULT
ELEC
VAULT
ELEC
AC
W
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BL BL BL
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SS SS SS SS SS
SD
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SD
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W
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12" W 12" W
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V.P.
H2O
6" W 6" W
/ / / / / / / /
/ / / / / / / /
/ / / / / / / /
/ / / / / / / /
/ / / / / / / // / / / / / / // / / / / / / // / / / / / / /
12" W
12" W
ST
ST
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P
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P
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P
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NISP
24" CASING
12" CARRIER
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X X X X
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OHU OHU OHU
OHU
OH
U
OHU
OHU
OH
U
OH
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OH
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OH
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U
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U
OWNER:
ANDERSON
KENNTH E &
JULIE ANN
OWNER:
DEADMOND
LARRY L &
NANCY K
OWNER:
CULBERT SON
DAVID M
OWNER: SEA
STAR LIMITED
PARTNERSHIP
OWNER:
DESELMS
ROBERT A &
K DENISE
OWNER: 1303
FRONTAGE
HOLDINGS LLC
OWNER: GLANZ
THOMAS J/LAURA P
OWNER:
MOODY
MARILYN
JOANNE
OWNER:
WHITE
WESLEY R
ANGELA M
OWNER:
BADE
CARLA M
OWNER:
K AND M
COMPANY
OWNER:
BOARD OF GOVERNORS
CSU SYSTEM
PROSPECT ROAD
FR
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E
L
D
E
R
C
R
E
E
K
EXISTING 79.98'
ROW
TRACT F
FUTURE
DEVELOPMENT
TRACT J
OPEN SPACE
DETRACT G
OPEN SPACE
TRACT H
FUTURE
DEVELOPMENT
TRACT B
FUTURE
DEVELOPMENT
TRACT C
FUTURE
DEVELOPMENT
TRACT E
OPEN SPACE
DE
TRACT A
OPEN SPACE
DE
TRACT K
FUTURE
DEVELOPMENT
ST
R
E
E
T
B
STR
E
E
T
E
STREET
D
EROSION BUFFER
LIMITS (TYP.)
FEMA 100-YR
FLOODWAY
FEMA 100-YR
FLOODPLAIN
BOXELDER CREEK
NATURAL HABITAT
BUFFER ZONE (NHBZ)
EXISTING
CDOT ROW
FEMA 100-YR
FLOODPLAIN
FEMA 100-YR
FLOODPLAIN
CDOT ROW
DRAINAGE EASEMENT
TO THE CITY OF FORT COLLINS
RECEPTION NO. 20160018474
NATURAL HABITAT
BUFFER ZONE (NHBZ)
EX. TOP OF BANK
NATURAL HABITAT
BUFFER ZONE (NHBZ)
EX. TOP OF BANK
INTERIM POND B
POND C
INTERIM POND I
POND E
POND D
POND F
POND G
7087
BFE=4903.00
7342 R
BFE=4903.63
7749 S
BFE=4904.69
7999.
7
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BFE=4900.80
PROPOSED 100-YR
FLOODPLAIN
PROPOSED 100-YR
FLOODWAY
TRACT D
FUTURE
DEVELOPMENT
TRACT I
OPEN SPACE
DE
BOXELDER CREEK
100-YEAR OVERFLOW
CHANNEL
PROPOSED 100-YR
FLOODPLAIN
PROPOSED 100-YR
FLOODWAY
Sheet
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FLD1
FL
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B
I
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127
NORTH
CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU
DIG, GRADE, OR EXCAVATE FOR THE MARKING OF
UNDERGROUND MEMBER UTILITIES.
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
Know what'sbelow.
before you dig.Call
R
KEYMAP
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PROSPECT RD
IN
T
E
R
S
T
A
T
E
-
2
5
( IN FEET )
1 inch = ft.
Feet0100100
100
200 300
EXISTING ELECTRIC E
LEGEND:
G
T
EXISTING STORM SEWER ST
EXISTING TELEPHONE
EXISTING GAS
NOTES:
1.THE SIZE, TYPE AND LOCATION OF ALL KNOWN UNDERGROUND UTILITIES ARE
APPROXIMATE WHEN SHOWN ON THESE DRAWINGS. IT SHALL BE THE
RESPONSIBILITY OF THE CONTRACTOR TO VERIFY THE EXISTENCE OF ALL
UNDERGROUND UTILITIES IN THE AREA OF THE WORK. BEFORE COMMENCING NEW
CONSTRUCTION, THE CONTRACTOR SHALL BE RESPONSIBLE FOR LOCATING ALL
UNDERGROUND UTILITIES AND SHALL BE RESPONSIBLE FOR ALL UNKNOWN
UNDERGROUND UTILITIES.
2.CONTRACTOR SHALL BE RESPONSIBLE FOR COORDINATING DEMOLITION, REMOVAL,
REPLACEMENT, AND DISPOSAL OF ALL FACILITIES AND MATERIAL.
3.ALL SYMBOLS ARE ONLY GRAPHICALLY REPRESENTED AND ARE NOT TO SCALE.
4.ALL ACTIVITIES WITHIN THE FLOODPLAIN ARE SUBJECT TO THE REQUIREMENTS OF
CHAPTER 10 OF THE FORT COLLINS MUNICIPAL CODE.
5.ANY CONSTRUCTION ACTIVITIES, NONSTRUCTURAL DEVELOPMENT (ROADS, CURB
CUTS, DRIVEWAYS, SIDEWALKS, TRAILS, VEGETATION, ETC.) IN THE REGULATORY
FLOODWAY MUST BE PRECEDED BY A NO RISE CERTIFICATION, WHICH MUST BE
PREPARED BY A PROFESSIONAL ENGINEER LICENSED IN THE STATE OF COLORADO.
6.ANY WORK WITHIN THE MAPPED BOXELDER CREEK EROSION BUFFER ZONE MUST
BE PRECEDED BY A CHANNEL STABILITY ANALYSIS PREPARED BY A PROFESSIONAL
ENGINEER LICENSED IN THE STATE OF COLORADO.
7.NO STORAGE OF MATERIALS OR EQUIPMENT SHALL BE ALLOWED IN THE
FLOODWAY, WHETHER TEMPORARY (DURING CONSTRUCTION) OR PERMANENT.
EXISTING SANITARY SEWER SS
EXISTING WATER W
EXISTING FENCE X
PROPERTY BOUNDARY
EXISTING RIGHT-OF-WAY
EXISTING MAJOR CONTOUR
EXISTING MINOR CONTOUR
5015
5013
BUFFER ZONE BL
FEMA 100-YR HIGH-RISK FLOODPLAIN
FEMA 100-YR FLOODWAY
EXISTING TOP OF BANK
EXISTING EDGE OF WATER
NATURAL HABITAT BUFFER ZONE
PROPOSED 100-YR FLOODPLAIN
PROPOSED CROSS-SECTION
9314
BFE=4910.77
PROPOSED 100-YR FLOODWAY
FLD1
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OH
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OH
E
OH
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OH
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OH
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XX
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T
S
FO
S
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S
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FO
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H2O
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W
W
V.P.
OWNER:
NORMANDIN
KIM WOWNER:
JORDAN
DAVID W
OWNER:
SILVERTIP
REALTY LLC
OWNER: HIXON
TIMOTHY R
OWNER: 913
SMITHFIELD
LLC
OWNER: R W
PROPERTIES
OWNER:
AMERIGAS
PROPANE LP
OWNER:
SCHNORR
GARY L TRUST
OWNER: CT
ENTERPRISES
LLC
OWNER: 901
HOLDING
COMPANY LLP
OWNER: DAKA
PROPERTIES LLC
OWNER: FORNEY
INDUSTRIES INC
OWNER: 3824
CANAL LLC
OWNER: 3800
CANAL DR LLC
OWNER: AMERICAN
BUILDERS AND
CONTRACTORS
OWNER: CANAL
HOLDINGS LLC
OWNER: BALLA
INVESTMENTS LLC
OWNER: RASS
HOLDINGS LLC
OWNER: RASS
HOLDINGS LLC
OWNER:DEAN
ANDREW G
OWNER: BALDWIN
R/JANELLE R
OWNER: CROISSANT
OWNER: SLATE
ROBERT STEPHEN
OW
N
E
R
:
S
H
E
A
F
O
R
SH
E
R
Y
L
OWNER: SLATE
ROBERT STEPHEN
OWNER: MARTINEZ
RONALD A/LINDA
OWNER: GONZALES
M/CAROLINA G
OWNER: US
MOBILE MODULAR
OWNER: US
MODULAR
SALES CO
OWNER:
AMERIGAS
PROPANE LP
TRACT B
FUTURE
DEVELOPMENT
TIMNATH
R
E
S
E
R
V
O
I
R
I
N
L
E
T
C
A
N
A
L
IRRIGATION POND
TRACT A
OPEN SPACE
DE
TRACT D
FUTURE
DEVELOPMENT
A1
PUD1
a1
B1
C1
BO
X
E
L
D
E
R
C
R
E
E
K
TIM
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T
C
A
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LAKE
C
A
N
A
L
LAK
E
C
A
N
A
L
FUTURE COOPER SLOUGH BOX
CULVERT (TO BE BUILT BY
OTHERS)
1050 CFS (100-YR)
FUT
U
R
E
C
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E
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H
(
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FUTU
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C
O
O
P
E
R
S
L
O
U
G
H
(
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)
COOPER SLOUGH
ADDITIONAL
224 CFS (100-YR)
FUTURE COOPER
SLOUGH GRADING
(BY OTHERS)
TRACT C
FUTURE
DEVELOPMENT
Rational Flow Summary | Final Basin Flow Rates
BASIN
TOTAL
AREA
(acres)
Tc2
(min)
Tc100
(min)
C2 C100 Q2
(cfs)
Q100
(cfs)
A1 29.57 13.8 13.8 0.20 0.25 11.53 50.39
B1 66.71 18.9 18.9 0.54 0.67 60.32 262.65
B2 0.35 5.0 5.0 0.77 0.97 0.78 3.40
B3 0.17 5.0 5.0 0.77 0.97 0.38 1.67
C1 20.77 6.5 6.5 0.85 1.00 47.13 193.35
C2 0.36 5.0 5.0 0.79 0.98 0.82 3.57
D1 2.07 10.9 10.9 0.20 0.25 0.90 3.93
D2 0.86 5.0 5.0 0.85 1.00 2.09 8.59
E1 3.08 7.2 7.2 0.65 0.81 5.04 22.00
E2 1.85 5.3 5.3 0.65 0.81 3.42 14.92
F1 9.43 5.9 5.9 0.85 1.00 22.12 90.81
F2 0.36 5.0 5.0 0.77 0.97 0.80 3.47
F3 0.42 5.0 5.0 0.79 0.98 0.95 4.13
F4 0.79 5.0 5.0 0.77 0.97 1.73 7.57
F5 1.20 6.9 6.9 0.45 0.57 1.40 6.13
G1 5.28 5.0 5.0 0.76 0.95 11.43 49.89
G2 0.92 5.0 5.0 0.85 1.00 2.23 9.14
G3 0.35 5.0 5.0 0.85 1.00 0.84 3.45
G4 0.51 5.0 5.0 0.85 1.00 1.23 5.06
H1 15.97 6.9 6.9 0.85 1.00 35.22 144.59
H2 0.75 5.0 5.0 0.85 1.00 1.83 7.51
I1 2.54 5.0 5.0 0.76 0.95 5.52 24.11
I2 1.72 5.0 5.0 0.85 1.00 4.16 17.08
BOX1 5.53 8.2 8.2 0.20 0.25 2.65 11.58
BOX2 4.66 8.2 8.2 0.20 0.25 2.24 9.77
PUD1 3.13 8.1 8.1 0.20 0.25 1.50 6.55
Combined Basins
Basin B (B1, B2 and B3)67.23 20.8 20.8 0.20 0.25 53.42 232.99
Basin C (C1 and C2)21.13 14.4 14.4 0.54 0.67 34.03 141.80
Basin D (D1 and D2)2.94 10.9 10.9 0.77 0.97 2.50 10.88
Basin E (E1 and E2)4.92 12.8 12.8 0.77 0.97 6.45 28.16
Basin F (F1, F2, F3, F4 and F5)12.20 13.9 13.9 0.85 1.00 19.23 83.12
Basin G (G1, G2, G3, G4)7.05 12.1 12.1 0.79 0.98 11.32 49.41
Basin H (H1 and H2)16.72 14.7 14.7 0.20 0.25 26.94 110.62
Basin I (I1 and I2)4.26 11.6 11.6 0.85 1.00 7.10 30.98
Rational Flow Summary | Interim Basin Flow Rates
BASIN
TOTAL
AREA
(acres)
Tc2
(min)
Tc100
(min)
C2 C100 Q2
(cfs)
Q100
(cfs)
A1 29.57 13.8 13.8 0.20 0.25 11.53 50.39
B1 66.71 20.8 20.8 0.20 0.25 21.15 92.22
B2 0.35 5.0 5.0 0.77 0.97 0.78 3.40
B3 0.17 5.0 5.0 0.77 0.97 0.38 1.67
C1 20.77 14.4 14.4 0.20 0.25 7.98 34.84
C2 0.36 5.0 5.0 0.79 0.98 0.82 3.57
D1 2.07 10.9 10.9 0.20 0.25 0.90 3.93
D2 0.86 5.0 5.0 0.85 1.00 2.09 8.59
E1 3.08 12.8 12.8 0.20 0.25 1.24 5.42
E2 1.85 5.3 5.3 0.65 0.81 3.42 14.92
F1 9.43 13.9 13.9 0.20 0.25 3.68 16.07
F2 0.36 5.0 5.0 0.77 0.97 0.80 3.47
F3 0.42 5.0 5.0 0.79 0.98 0.95 4.13
F4 0.79 5.0 5.0 0.77 0.97 1.73 7.57
F5 1.20 6.9 6.9 0.45 0.57 1.40 6.13
G1 5.28 12.1 12.1 0.24 0.30 2.59 11.30
G2 0.92 5.0 5.0 0.85 1.00 2.23 9.14
G3 0.35 5.0 5.0 0.85 1.00 0.84 3.45
G4 0.51 5.0 5.0 0.85 1.00 1.23 5.06
H1 15.97 14.7 14.7 0.22 0.27 6.51 28.41
H2 0.75 5.0 5.0 0.85 1.00 1.83 7.51
I1 2.54 8.5 8.5 0.20 0.25 1.19 5.21
I2 1.72 5.0 5.0 0.85 1.00 4.16 17.08
BOX1 5.53 8.2 8.2 0.20 0.25 2.65 11.58
BOX2 4.66 8.2 8.2 0.20 0.25 2.24 9.77
PUD1 3.13 8.1 8.1 0.20 0.25 1.50 6.55
Combined Basins
Basin B (B1, B2 and B3)67.23 20.8 20.8 0.20 0.25 21.79 95.04
Basin C (C1 and C2)21.13 14.4 14.4 0.20 0.25 8.12 35.45
Basin D (D1 and D2)2.94 10.9 10.9 0.77 0.97 2.50 10.88
Basin E (E1 and E2)4.92 12.8 12.8 0.77 0.97 3.66 15.97
Basin F (F1, F2, F3, F4 and F5)12.20 13.9 13.9 0.20 0.25 7.28 31.79
Basin G (G1, G2, G3, G4)7.05 12.1 12.1 0.79 0.98 5.68 24.80
Basin H (H1 and H2)16.72 14.7 14.7 0.20 0.25 7.73 33.72
Basin I (I1 and I2)4.26 11.6 11.6 0.85 1.00 4.12 17.94
Basin H & I 20.98 16.9 16.9 0.20 0.25 10.76 46.87
Pond Summaries
Pond ID
Tributary
Area
Interim
Impervious
Final
Impervious
Interim 100-yr
Storage
Interim
WQCV + EURV
Interim
Release Rate
Final 100-yr
Storage
Final
WQCV + EURV
Final Release
Rate
(acre)(%)(%)ac-ft (elev.)ac-ft (elev.)(cfs)ac-ft (elev.)ac-ft (elev.)(cfs)
Pond B 67.23 3%46%1.726 (4908.38)0.152 (4904.54)96.00 7.07 (TBD)*2.907 (TBD)*103.7*
Pond C 21.13 n/a 79%n/a n/a n/a 3.323 (4907.89)1.638 (4906.47)26.90
Pond D 2.94 n/a 27%n/a n/a n/a 0.222 (4904.69)0.072 (4903.97)4.50
Pond E 4.92 n/a 66%n/a n/a n/a 0.669 (4901.84)0.314 (4900.70)9.30
Pond F 12.20 n/a 77%n/a n/a n/a 1.878 (4905.02)0.92 (4903.84)14.00
Pond G 7.05 n/a 70%n/a n/a n/a 1.004 (4901.72)0.48 (4901.04)11.40
Pond H 16.72 13%
80%1.067 (4902.80)0.232 (4901.25)25.70
2.658 (TBD)*1.313 (TBD)*20.9*
Pond I 4.26 76%0.648 (4903.13)0.316 (4901.91)3.30
* Future required pond volumes and WSELs to be determined at time of development and once pond layout and grading is known.
KEYMAP
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PROSPECT RD
IN
T
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S
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E
-
2
5
DR1
DR
A
I
N
A
G
E
E
X
H
I
B
I
T
125
LEGEND:
PROPOSED STORM SEWER
PROPOSED CURB & GUTTER
PROPERTY BOUNDARY
PROPOSED STORM INLET
EXISTING CURB & GUTTER
PROPOSED OVERLAND FLOW
EXISTING MAJOR CONTOUR
PROPOSED MAJOR CONTOUR
RUNOFF SUMMARY:
A2
a3
DRAINAGE BASIN ID
EXISTING STORM SEWER
PROPOSED DIRECT FLOW
BASIN DELINEATION
1. REFER TO "DRAINAGE REPORT FOR GATEWAY AT PROSPECT DATED 08/15/2025"
PREPARED BY EPS GROUP FOR ADDITIONAL INFORMATION.
2. REFER TO FLOODPLAIN EXHIBIT ON SHEET FLD1 FOR MORE INFORMATION ON THE
FLOODPLAIN.
NOTES:
( IN FEET )
0
1 INCH = 100 FEET
100 100 200 300
Sheet
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DRAINAGE
BASIN AREA
DR1
DETENTION SUMMARY:
MATCHLINE - SEE SHEET DR2
FEMA 100-YR FLOODPLAIN
FEMA 100-YR FLOODWAY
EROSION BUFFER LIMITS BL
PROPOSED 100-YR FLOODPLAIN
PROPOSED 100-YR FLOODWAY
NATURAL HABITAT BUFFER ZONE
T ST S
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X X X X
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X
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X
X
X
X
X
OHU OHU OHU OHU
OH
U
OHU OHU
OH
U
OH
U
OH
U
OH
U
OH
U
OH
U
OH
U
OH
U
OH
U
OH
U
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FO
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XX
X
X
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XX
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XXXX
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XX
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X X
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X
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X
T T T T
OH
E
OH
E
OH
E
OH
E
OH
E
OH
E
OH
E
OH
E
OH
E
SS
10
"
S
S
10
"
S
S
10
"
S
S
10
"
S
S
10
"
S
S
10
"
S
S
10
"
S
S
10" SS
27
"
A
B
D
N
S
S
27
"
A
B
D
N
S
S
27
"
A
B
D
N
S
S
27
"
A
B
D
N
S
S
27" A
B
D
N
S
S
E E E E E
/ / / / / / / /
T
T
W
W W
W
W
S
W
FO
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/ / / / / / / // / / / / / / // / / / / / / /
GAS
GAS
CONTROL
IRR
CONTROL
IRR
VAULT
ELEC
F.O.
F.O.
F.O.
ELEC
ELEC
VAULT
ELEC
VAULT
ELEC
VAULT
ELEC
VAULT
ELEC
VAULT
ELEC
AC
S
H2O
H2O
W
T
FES
H2O
H2O
W
H2O
H2O
W
ELEC
FE S
VAULT
ELECVAULT
ELEC
TRAFFICVAULTE
VAULT
ELECTRAFFIC
VAULT ELEC
H2OHYD
T ST S
VAULTELEC
ELEC
VAULTELEC
VAULTELEC
S
FES
D
X
X
X
X
X
X
X
W
W
TT
OHU OHU
30" SS S
S
12" W 12" W 12" W
FES
W
W
H2O
H2O
H2O
H2O
HYD
W
W
ST
ST
ST
12" W 12" W
W
HYD
V.P.
V.P.
H2O
6" W 6" W 6" W
/ / / / / / / /
/ / / / / / / /
/ / / / / / / // / / / / / / /
/ / / / / / / // / / / / / / // / / / / / / // / / / / / / /
12" W
12" W
ST
ST
ST
ST
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E
OW
N
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R
:
C
U
L
B
E
R
T
SO
N
D
A
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I
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M
OWNER: 1303
FRONTAGE
HOLDINGS LLC
OWNER:
GLANZ
THOMAS
J/LAURA P
WESLEY R
ANGELA M
OW
N
E
R
:
B
A
D
E
CA
R
L
A
M
OWNER:
K AND M
COMPANY OWNER:
BOARD OF GOVERNORS
CSU SYSTEM
OWNER: 1303
FRONTAGE
HOLDINGS LLC
OW
N
E
R
:
1
3
0
3
FR
O
N
T
A
G
E
HO
L
D
I
N
G
S
L
L
C
ST
R
E
E
T
B
FRONTAGE ROAD
SW
FR
O
N
T
A
G
E
R
D
TEMPORARY
SWALE
EXISTING BOX
CULVERTS EXISTING BOX
CULVERTS
FR
O
N
T
A
G
E
R
O
A
D
BO
X
E
L
D
E
R
C
R
E
E
K
BOXELDER CREEK
NATURAL HABITAT
BUFFER ZONE
TRACT H
FUTURE
DEVELOPMENT
NODE 887
(PER FORT COLLINS
SWMM MODEL)NODE 886
(PER FORT COLLINS
SWMM MODEL)
BOXELDER CREEK
100-YR OVERFLOW
CHANNEL
0.3%
PROSPECT ROAD
STORM DRAIN A
SEE SHEET ST1
STORM DRAIN B
SEE SHEET ST1 STORM DRAIN C
SEE SHEET ST2
STORM DRAIN E
SEE SHEET ST4
STORM DRAIN L
SEE SHEET ST6
STORM DRAIN G
SEE SHEET ST5
STORM DRAIN H
SEE SHEET ST5
STORM DRAIN I
SEE SHEET ST5
STORM DRAIN J
SEE SHEET ST5
INLET A3
INLET A2
OUTLET B2
OUTLET E4
4.4%
OUTLET H2
OUTFALL G2
TRACT J
OPEN SPACE
DE
TRACT K
FUTURE
DEVELOPMENT
TRACT F
FUTURE
DEVELOPMENT
TRACT E
OPEN SPACE
DE
TRACT I
OPEN SPACE
DE
BOXELDER CREEK
NATURAL HABITAT
BUFFER ZONE
STR
E
E
T
E
STREET
D
PROPOSED
BRIDGE
STORM DRAIN K
SEE SHEET ST6
STORM DRAIN C2
SEE SHEET ST3
PROPOSED 100-YR
FLOODPLAIN
STORM DRAIN N
SEE SHEET ST7
STORM DRAIN F
SEE SHEET ST4
STORM DRAIN O
SEE SHEET ST7
STORM DRAIN D
SEE SHEET ST3
OUTLET C7
OUTLET C2.2
B1
C1
E1
G1
H1
D1
D2
F3
C2
E2
BOX1
F1
F2
BOX2
H2
F4
F5
G2
G3
B2
B3
b1
f2
d1
I1
e1
f1
c2
c1
h2
d2
e2
g1
g2
I2
g3
b2
b3
f4
f5
f3
I1
H1
I2
G4
POND D
INTERIM
POND I
POND E
POND F
INTERIM
POND B
POND G
POND C
g4
FUTURE POND H
(LAYOUT DEPENDENT
ON FUTURE SITE PLAN)
PUD1
RAIN GARDEN E2
RAIN GARDEN I2
RAIN GARDEN D2
RAIN GARDEN G3
RAIN GARDEN C2
RAIN GARDEN B2
EXISTING INLET
DIVERTS FLOW TO
SOUTH
STORM DRAIN M
SEE SHEET ST6
PUD
IRRIGATION DITCH GATE IS OPEN
WHEN DITCH IS NOT RUNNING.
EXISTING FLOWS IN DITCH ARE
EXISTING INTERCEPTED COOPER
SLOUGH STORMWATER FLOWS
PER FC MODEL= 203 CFS (10-YR)
INLET O2
INLET K5
PIPE END M1
INLET L1
INLET D3
INLET N2
INLET N3
INLET F8
INLET F7
FUTURE POND B
(LAYOUT DEPENDENT
ON FUTURE SITE PLAN)
TRACT C
FUTURE
DEVELOPMENT
Rational Flow Summary | Final Basin Flow Rates
BASIN
TOTAL
AREA
(acres)
Tc2
(min)
Tc100
(min)
C2 C100 Q2
(cfs)
Q100
(cfs)
A1 29.57 13.8 13.8 0.20 0.25 11.53 50.39
B1 66.71 18.9 18.9 0.54 0.67 60.32 262.65
B2 0.35 5.0 5.0 0.77 0.97 0.78 3.40
B3 0.17 5.0 5.0 0.77 0.97 0.38 1.67
C1 20.77 6.5 6.5 0.85 1.00 47.13 193.35
C2 0.36 5.0 5.0 0.79 0.98 0.82 3.57
D1 2.07 10.9 10.9 0.20 0.25 0.90 3.93
D2 0.86 5.0 5.0 0.85 1.00 2.09 8.59
E1 3.08 7.2 7.2 0.65 0.81 5.04 22.00
E2 1.85 5.3 5.3 0.65 0.81 3.42 14.92
F1 9.43 5.9 5.9 0.85 1.00 22.12 90.81
F2 0.36 5.0 5.0 0.77 0.97 0.80 3.47
F3 0.42 5.0 5.0 0.79 0.98 0.95 4.13
F4 0.79 5.0 5.0 0.77 0.97 1.73 7.57
F5 1.20 6.9 6.9 0.45 0.57 1.40 6.13
G1 5.28 5.0 5.0 0.76 0.95 11.43 49.89
G2 0.92 5.0 5.0 0.85 1.00 2.23 9.14
G3 0.35 5.0 5.0 0.85 1.00 0.84 3.45
G4 0.51 5.0 5.0 0.85 1.00 1.23 5.06
H1 15.97 6.9 6.9 0.85 1.00 35.22 144.59
H2 0.75 5.0 5.0 0.85 1.00 1.83 7.51
I1 2.54 5.0 5.0 0.76 0.95 5.52 24.11
I2 1.72 5.0 5.0 0.85 1.00 4.16 17.08
BOX1 5.53 8.2 8.2 0.20 0.25 2.65 11.58
BOX2 4.66 8.2 8.2 0.20 0.25 2.24 9.77
PUD1 3.13 8.1 8.1 0.20 0.25 1.50 6.55
Combined Basins
Basin B (B1, B2 and B3)67.23 20.8 20.8 0.20 0.25 53.42 232.99
Basin C (C1 and C2)21.13 14.4 14.4 0.54 0.67 34.03 141.80
Basin D (D1 and D2)2.94 10.9 10.9 0.77 0.97 2.50 10.88
Basin E (E1 and E2)4.92 12.8 12.8 0.77 0.97 6.45 28.16
Basin F (F1, F2, F3, F4 and F5)12.20 13.9 13.9 0.85 1.00 19.23 83.12
Basin G (G1, G2, G3, G4)7.05 12.1 12.1 0.79 0.98 11.32 49.41
Basin H (H1 and H2)16.72 14.7 14.7 0.20 0.25 26.94 110.62
Basin I (I1 and I2)4.26 11.6 11.6 0.85 1.00 7.10 30.98
Rational Flow Summary | Interim Basin Flow Rates
BASIN
TOTAL
AREA
(acres)
Tc2
(min)
Tc100
(min)
C2 C100 Q2
(cfs)
Q100
(cfs)
A1 29.57 13.8 13.8 0.20 0.25 11.53 50.39
B1 66.71 20.8 20.8 0.20 0.25 21.15 92.22
B2 0.35 5.0 5.0 0.77 0.97 0.78 3.40
B3 0.17 5.0 5.0 0.77 0.97 0.38 1.67
C1 20.77 14.4 14.4 0.20 0.25 7.98 34.84
C2 0.36 5.0 5.0 0.79 0.98 0.82 3.57
D1 2.07 10.9 10.9 0.20 0.25 0.90 3.93
D2 0.86 5.0 5.0 0.85 1.00 2.09 8.59
E1 3.08 12.8 12.8 0.20 0.25 1.24 5.42
E2 1.85 5.3 5.3 0.65 0.81 3.42 14.92
F1 9.43 13.9 13.9 0.20 0.25 3.68 16.07
F2 0.36 5.0 5.0 0.77 0.97 0.80 3.47
F3 0.42 5.0 5.0 0.79 0.98 0.95 4.13
F4 0.79 5.0 5.0 0.77 0.97 1.73 7.57
F5 1.20 6.9 6.9 0.45 0.57 1.40 6.13
G1 5.28 12.1 12.1 0.24 0.30 2.59 11.30
G2 0.92 5.0 5.0 0.85 1.00 2.23 9.14
G3 0.35 5.0 5.0 0.85 1.00 0.84 3.45
G4 0.51 5.0 5.0 0.85 1.00 1.23 5.06
H1 15.97 14.7 14.7 0.22 0.27 6.51 28.41
H2 0.75 5.0 5.0 0.85 1.00 1.83 7.51
I1 2.54 8.5 8.5 0.20 0.25 1.19 5.21
I2 1.72 5.0 5.0 0.85 1.00 4.16 17.08
BOX1 5.53 8.2 8.2 0.20 0.25 2.65 11.58
BOX2 4.66 8.2 8.2 0.20 0.25 2.24 9.77
PUD1 3.13 8.1 8.1 0.20 0.25 1.50 6.55
Combined Basins
Basin B (B1, B2 and B3)67.23 20.8 20.8 0.20 0.25 21.79 95.04
Basin C (C1 and C2)21.13 14.4 14.4 0.20 0.25 8.12 35.45
Basin D (D1 and D2)2.94 10.9 10.9 0.77 0.97 2.50 10.88
Basin E (E1 and E2)4.92 12.8 12.8 0.77 0.97 3.66 15.97
Basin F (F1, F2, F3, F4 and F5)12.20 13.9 13.9 0.20 0.25 7.28 31.79
Basin G (G1, G2, G3, G4)7.05 12.1 12.1 0.79 0.98 5.68 24.80
Basin H (H1 and H2)16.72 14.7 14.7 0.20 0.25 7.73 33.72
Basin I (I1 and I2)4.26 11.6 11.6 0.85 1.00 4.12 17.94
Basin H & I 20.98 16.9 16.9 0.20 0.25 10.76 46.87
Pond Summaries
Pond ID
Tributary
Area
Interim
Impervious
Final
Impervious
Interim 100-yr
Storage
Interim
WQCV + EURV
Interim
Release Rate
Final 100-yr
Storage
Final
WQCV + EURV
Final Release
Rate
(acre)(%)(%)ac-ft (elev.)ac-ft (elev.)(cfs)ac-ft (elev.)ac-ft (elev.)(cfs)
Pond B 67.23 3%46%1.726 (4908.38)0.152 (4904.54)96.00 7.07 (TBD)*2.907 (TBD)*103.7*
Pond C 21.13 n/a 79%n/a n/a n/a 3.323 (4907.89)1.638 (4906.47)26.90
Pond D 2.94 n/a 27%n/a n/a n/a 0.222 (4904.69)0.072 (4903.97)4.50
Pond E 4.92 n/a 66%n/a n/a n/a 0.669 (4901.84)0.314 (4900.70)9.30
Pond F 12.20 n/a 77%n/a n/a n/a 1.878 (4905.02)0.92 (4903.84)14.00
Pond G 7.05 n/a 70%n/a n/a n/a 1.004 (4901.72)0.48 (4901.04)11.40
Pond H 16.72 13%
80%1.067 (4902.80)0.232 (4901.25)25.70
2.658 (TBD)*1.313 (TBD)*20.9*
Pond I 4.26 76%0.648 (4903.13)0.316 (4901.91)3.30
* Future required pond volumes and WSELs to be determined at time of development and once pond layout and grading is known.
LEGEND:
RUNOFF SUMMARY:
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( IN FEET )
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1 INCH = 100 FEET
100 100 200 300
DETENTION SUMMARY:
KEYMAP
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PROSPECT RD
IN
T
E
R
S
T
A
T
E
-
2
5
DR2
MATCHLINE - SEE SHEET DR1
PROPOSED STORM SEWER
PROPOSED CURB & GUTTER
PROPERTY BOUNDARY
PROPOSED STORM INLET
EXISTING CURB & GUTTER
PROPOSED OVERLAND FLOW
EXISTING MAJOR CONTOUR
PROPOSED MAJOR CONTOUR
A2
a3
DRAINAGE BASIN ID
EXISTING STORM SEWER
PROPOSED DIRECT FLOW
BASIN DELINEATION
1. REFER TO "DRAINAGE REPORT FOR GATEWAY AT PROSPECT DATED 08/15/2025"
PREPARED BY EPS GROUP FOR ADDITIONAL INFORMATION.
2. REFER TO FLOODPLAIN EXHIBIT ON SHEET FLD1 FOR MORE INFORMATION ON THE
FLOODPLAIN.
NOTES:
DRAINAGE
BASIN AREA
FEMA 100-YR FLOODPLAIN
FEMA 100-YR FLOODWAY
EROSION BUFFER LIMITS BL
PROPOSED 100-YR FLOODPLAIN
PROPOSED 100-YR FLOODWAY
NATURAL HABITAT BUFFER ZONE