HomeMy WebLinkAboutGATEWAY AT PROSPECT - BDR200010 - DOCUMENT MARKUPS - ROUND 2 - DRAINAGE REPORT
PRELIMINARY DRAINAGE REPORT
GATEWAY AT PROSPECT
Fort Collins, Colorado
June 8th, 2020
Prepared for:
Fort Collins / I-25 Interchange, LLC
2 North Cascade Avenue, Suite 1490
Colorado Springs, CO 80903
Prepared by:
301 North Howes Street, Suite 100
Fort Collins, Colorado 80521
Phone: 970.221.4158 Fax: 970.221.4159
www.northernengineering.com
Project Number: 892-002
This Drainage Report is consciously provided as a PDF.
Please consider the environment before printing this document in its entirety.
When a hard copy is absolutely necessary, we recommend double-sided printing.
June 8th, 2020
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Preliminary Drainage Report for
Gateway at Prospect
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report for
your review. This report accompanies the Preliminary Development Review submittal for the
proposed Gateway at Prospect project.
This report has been prepared in accordance to 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 that 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,
NORTHERN ENGINEERING SERVICES, INC.
Blaine Mathisen, EI Stephanie Thomas, PE
Project Engineer Project Manager
Gateway at Prospect
Final Drainage Report
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION ................................................................... 1
A. Location ............................................................................................................................................. 1
B. Description of Property ..................................................................................................................... 2
C. Floodplain.......................................................................................................................................... 2
II. DRAINAGE BASINS AND SUB-BASINS ....................................................................... 4
A. Major Basin Description .................................................................................................................... 4
B. Sub-Basin Description ....................................................................................................................... 4
III. DRAINAGE DESIGN CRITERIA ................................................................................... 6
A. Regulations........................................................................................................................................ 6
B. Four Step Process .............................................................................................................................. 6
C. Development Criteria Reference and Constraints ............................................................................ 7
D. Hydrological Criteria ......................................................................................................................... 7
E. Hydraulic Criteria .............................................................................................................................. 8
F. Floodplain Regulations Compliance .................................................................................................. 8
G. Modifications of Criteria ................................................................................................................... 8
IV. DRAINAGE FACILITY DESIGN .................................................................................... 8
A. General Concept ............................................................................................................................... 8
B. Specific Details ................................................................................................................................ 12
V. CONCLUSIONS ...................................................................................................... 17
A. Compliance with Standards ............................................................................................................ 17
B. Drainage Concept ............................................................................................................................ 18
References ....................................................................................................................... 19
APPENDICES:
APPENDIX A – Hydrologic Computations
APPENDIX B – Hydraulic Computations
B.1 – Storm Sewers (For Future Use)
B.2 – Inlets (For Future Use)
B.3 – Detention Facilities (WQCV, EURV, and Total Volume)
APPENDIX C – Water Quality Design Computations
APPENDIX D – Erosion Control Report
Gateway at Prospect
Final Drainage Report
LIST OF FIGURES:
Figure 1 - Vicinity Map ........................................................................................................ 1
Figure 2 - Existing FEMA Floodplains ..................................................................................... 3
Figure 3 - Existing City Floodplains ........................................................................................ 3
Figure 4 - Snapshot of Existing Ayers Associates SWMM Model ................................................. 5
Figure 5 - Snapshot of Ultimate Pond SWMM Model ............................................................. 16
LIST OF TABLES:
Table 1 - Land Use - Percent Impervious (Per Table 4.1.2 FCSCM) ........................................... 2
Table 2 - Flowrates for Project Specific Nodes via SWMM ........................................................ 5
Table 3 - Interim Pond Summary ........................................................................................ 14
Table 4 - Ultimate Pond Summary ...................................................................................... 14
Table 5 - SWMM Existing v. Interim Conditions Summary ...................................................... 17
Table 6 - SWMM Existing v. Ultimate Conditions Summary .................................................... 17
MAP POCKET:
DR1 - Drainage Exhibit
Gateway at Prospect
Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
Figure 1 - Vicinity Map
2. 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.
3. 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 just east of the existing Boxelder
Estates 1st Replat.
4. Zoning across the site includes Low-Density Mixed Use (LMN), Medium-Density
Mixed Use (MMN), Employment District (E), Commercial District (C), Urban Estate
(UE). Currently the existing lot does not have any stormwater or water quality
facilities.
5. 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.
Gateway at Prospect
Drainage Report 2
Table 1 - Land Use - Percent Impervious (Per Table 4.1.2 FCSCM)
B. Description of Property
1. Gateway at Prospect is approximately 182.30 net acres including the existing frontage
road.
2. Gateway at Prospect is proposing to realign the I-25 West Frontage Road and
installing two collector streets with utilities using master planning concepts. A span
bridge or culvert (to be decided at final) 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, as well as 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 collector roads will get detained and water quality will also be
provided via extended detention. However, there will be no LID treatment for the
interim condition. 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.
C. Floodplain
1. The subject property is located in a FEMA floodplain but not a City regulatory
floodplain.
2. The Gateway at Prospect project will be pursuing a CLOMR/LOMR with this project.
Gateway at Prospect
Drainage Report 3
This CLOMR/LOMR will revise the floodplain and floodway along the Boxelder Creek
within the limits of this project. This CLOMR/LOMR will effectively limit the extents of
the floodplain and allow for the installation of a bridge over the Boxelder Creek.
The CLOMR/LOMR will not be detailed in this report but will rather be a separate
report and model. The CLOMR/LOMR will be pursued concurrently with this proposal.
More grading and bridge details will be provided at final design.
Figure 2 - Existing FEMA Floodplains
Figure 3 - Existing City Floodplains
Gateway at Prospect
Drainage Report 4
II. DRAINAGE BASINS AND SUB-BASINS
A. 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,
where it ends 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
B. Sub-Basin 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 situated within the
Gateway at Prospect site. In normal flowing conditions the Boxelder Creek flows
within its typical channel and heads south through an 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.
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 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 that downstream infrastructure will not be impacted by
future developments within the Gateway at Prospect property.
Gateway at Prospect
Drainage Report 5
Figure 4 - Snapshot of Existing Ayers Associates SWMM Model
2. There are some important nodes to take note of within this model. Node 884 which is
the closest upstream node prior to 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
as well as the emergency overflow channel. A more in-depth explanation can be found
later in the report.
Table 2 - Flowrates for Project Specific Nodes via SWMM
3. Gateway at Prospect is located towards the 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 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 collector streets, utilities, and the span
bridge or culvert is installed, there 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
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
Gateway at Prospect
Drainage Report 6
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. All future developments must follow Fort Collins Stormwater Criteria Manual for LID
sizing and implementation.
6. 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.
III. DRAINAGE DESIGN CRITERIA
A. Regulations
Gateway at Prospect is proposing to utilize 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 that the Gateway at Prospect project will not cause
damage to downstream infrastructure and/or cause more maintenance than historic
conditions. Full spectrum guidelines laid out by Mile High Flood Control District were
followed.
B. Four Step Process
The overall stormwater management strategy employed with Gateway at Prospect project
utilizes the “Four Step Process” to minimize adverse impacts of urbanization on receiving
waters. The following is a description of how the proposed development has incorporated
each step.
Step 1 – Employ Runoff Reduction Practices
Gateway at Prospect will be reducing runoff 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 produces outflow hydrographs that, other than a small release rate of
the excess urban runoff volume (EURV), replicates the shape of pre-development
hydrographs. Full spectrum detention modeling shows reduction of urban runoff peaks to
levels similar to pre-development conditions over an entire watershed, even with multiple
independent detention facilities. For a thorough in-depth explanation on 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 development of the future development tracts within the Gateway at
Prospect. Each development will be responsible to implement 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.
Gateway at Prospect
Drainage Report 7
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 that 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 pre-development
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, during the interim condition there will be large swaths of greenspace
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 the 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 which
include riprap pads, erosion control blankets, scour pads.
The Gateway at Prospect project aims to protect the existing Boxelder Creek by limiting
any increases beyond the historic 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 prior to the 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 and is not
applicable for this project. Future developments must implement site specific BMPs.
C. 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 the 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 off pre-development conditions both
the interim and future developments will have approximately the same release rates.
Therefore, future developments will not be hindered by the size storm lines that are
installed by Gateway at Prospect.
3. Future developments are responsible for their own LID calculations and
implementation.
D. 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
Gateway at Prospect
Drainage Report 8
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.
E. 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 I.C.1, above, the subject property is subject to regulatory
floodplain restrictions and development code.
4. Gateway at Prospect intends to maintain downstream integrity of the Boxelder Creek
to fullest extent possible.
F. Floodplain Regulations Compliance
1. No occupied structures are being proposed with the Gateway Prospect project. A
bridge structure is proposed with this project. This structure will be subject to
floodplain regulations. However, future developments within this project area me be
subject to all floodplain regulations.
G. Modifications of Criteria
Gateway at Prospect is requesting that full spectrum detention as laid out by the Mile
High Flood Control District be substituted for the Fort Collins Stormwater Criteria
detention requirements.
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objectives of Gateway at Prospect is to provide detention and water quality
for the interim conditions as well as layout a comprehensive master plan for future
developments to utilize. Additionally, maintaining Boxelder Creek stabilization is of the
utmost importance.
2. Excluding the Boxelder Creek and Cache La Poudre River Inlet there are no off-site
Gateway at Prospect
Drainage Report 9
flows draining onto the existing property.
3. 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.
4. Gateway at Prospect project is composed of nine major drainage basins, designated
as Basins A, B, C, D, E, F, G, BOX, and PUD. The drainage patterns for each major
basin are described below.
Basin A
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 B
During the interim condition Basin B will be undeveloped except for a small portion of
the new collector street discharging onto it. During the ultimate condition Basin B is
zoned to have low-density residential and urban estate districts. Basin B will discharge
into the Boxelder Creek via an RCP pipe that is sized to the ultimate release rate of
Pond B.
Basin C
Basin C is composed of two sub basins, Basin C1 and Basin C2.
Basin C1
During the interim condition Basin C1 will overland flow from northeast to the
southwest to Interim 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 HDPE pipe to Boxelder Creek. Basin C1 is adjacent to Boxelder
Creek so it might be advantageous for the future developments to stagger their ponds
adjacent to the creek and therefore might have several stubs to the Boxelder Creek.
However, the sum of those release rates must be less than or equal to the 100-year
release rate specified for Pond C below and in the Appendix.
Basin C2
Basin C2 encompasses half the right of way for the new collector road and half the
span bridge or culvert section. Basin C2 has the same condition in the interim and
ultimate conditions. Basin C2 will convey runoff to Pond C via sidewalk culvert into a
swale. Basin C2 must be detained and treated during the interim and ultimate
conditions within Basin C.
Gateway at Prospect
Drainage Report 10
Basin D
Basin D is composed of two sub basins, Basin D1 and Basin D2. Basin D is the only
major drainage basin that does not have an interim condition.
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 HDPE pipe.
Basin D2
Basin D2 encompasses a portion of the entire R.O.W associated with the I-25
frontage road re-alignment. Runoff generated in Basin D2 is conveyed to inlets within
the R.O.W which will route the runoff to Pond D found within Basin D1.
Basin E
Basin E is composed of three sub basins, Basin E1, E2, and E3.
Basin E1
During the interim condition Basin E1 will remain undeveloped with the exception for
a swale and Interim Pond E. In the ultimate condition Basin E1 will be built out per its
zoning designation of medium density mixed-use. In the ultimate condition Basin E1
might choose to have several ponds instead of just one in the southern section of the
basin because it is adjacent to the Boxelder Creek. However, the sum of those release
rates must be less than or equal to the 100-year release rate specified for Pond E
below and in the Appendix.
Basin E2
Basin E2 is comprised of the collector 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 except for a small portion near the northwest
corner of the basin which during the ultimate condition will be built as low-density
mixed use. Runoff from Basin E2 is conveyed to Interim Pond E via storm pipe. This
storm pipe is sized for the ultimate condition. If in the future Interim Pond E is
relocated Basin E2 will need to be routed to a new pond within Basin E.
Basin E3
Basin E3 is comprised of half the right of way for the new collector roads internal to
the project site as well has half the span bridge or culvert section. Runoff is conveyed
to a sidewalk culvert and then to a temporary swale during the interim condition
which conveys runoff to Interim Pond E. Basin E3 will remain unchanged in the
ultimate condition. In the ultimate condition Basin E3 must be detained and treated
within Basin E. Future developments can reroute Basin E3 to a separate pond within
Basin E and get rid of the swale. However, the sum of the release rates within in
Basin E must be less than or equal to the 100-year release rate specified for Pond E
below and in the Appendix.
Gateway at Prospect
Drainage Report 11
Basin F
Basin F will remain undeveloped and green space during the interim condition and
therefore will not require an interim pond. In the ultimate condition Basin F is zoned
as commercial use and will be required to detain and treat runoff. In the ultimate
condition Basin F can discharge directly to Boxelder Creek or tie into a proposed storm
line running adjacent to the Prospect Road. A manhole will be installed with Gateway
at Prospect to provide a connection to this storm line. Additionally, this storm line will
be designed to convey the ultimate release rate.
Basin G
Basin G is comprised of two sub basins, Basin G1 and Basin G2.
Basin G1
Basin G1 will remain undeveloped and green space during the interim condition with
the exception for Interim Pond G and a small portion of the roundabout. In the
ultimate condition Basin G will be used for a commercial district. Basin G1 will be
routed to Interim Pond G which will discharge to Boxelder Creek via storm line. This
storm line will be sized to convey the future 100-year max release rate for all of Basin
G.
Basin G2
Basin G2 encompasses a portion of the entire R.O.W associated with the I-25 frontage
road realignment. Basin G2 does not have an interim condition and will be routed to
Interim Pond G via storm line. If in the ultimate design of the commercial district
Interim Pond G is relocated Basin G2 must be detained and treated within Basin G
Basin BOX
Basin BOX is associated with the Boxelder Creek and is comprised of two sub basins,
Basin BOX1 and Basin BOX2. As mentioned earlier it is very important to Gateway at
Prospect to maintain stabilization within this drainageway. Ayers Associates put
together a comprehensive SWMM model showing historic flows through the Boxelder
Creek/Cooper Slough Basin. Fortunately, there are some exact nodes within this model
that will allow Northern Engineering to see the exact impacts Gateway at Prospect will
have on the Boxelder Creek during the interim and ultimate conditions.
Basin BOX1
Basin BOX1 is associated with the Boxelder Creek that is downstream of the proposed
span bridge or culvert that will be installed with Gateway at Prospect
Mentioned earlier there is an emergency overflow weir within the Boxelder Creek on
this site. This overflow weir is denoted as Divider 885 in Ayers Associates SWMM
model and this is found within Basin BOX1.
Gateway at Prospect
Drainage Report 12
Basin BOX2
Basin BOX2 is associated with the Boxelder Creek that is upstream of the proposed
span bridge or culvert that will be installed with Gateway at Prospect. Node 884 in
the Ayers Associates SWMM model represents the start of this basin.
Basin PUD1
Basin PUD1 is associated with the Cache La Poudre Inlet Canal. Basin PUD1 runs
west to east and conveys offsite 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 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.
B. Specific Details
1. Gateway at Prospect is located near the end of the Boxelder Creek/Cooper Slough
Basin and will be discharging into the Boxelder Creek. In order to maintain
stabilization 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
prior to when the peak flowrates within Boxelder Creek occur. In beating the peak
Gateway at Prospect can guarantee that it will not be adversely impacting
downstream infrastructure.
2. Gateway at Prospect is proposing to provide 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 four interim ponds (Interim Pond B, Interim Pond C, Interim Pond E,
and Interim Pond G) and one final pond (Pond D) installed with Gateway at Prospect.
4. Information regarding future ponds for ultimate condition for Pond B, Pond C, Pond E,
Pond F, and Pond G are detailed below and in Appendix B.
5. 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.
Several ponds (Pond B, Pond C, Pond E, Pond G) will have interim ponds. Pond D
will be built out to its ultimate condition per the Gateway at Prospect plans. Lastly
Pond F will not have an interim pond condition because Basin F during the interim
condition remains unchanged from the existing condition.
For ponds that will be constructed in the future, and not with Gateway at Prospect
(i.e. Pond B, Pond C, Pond E, Pond F, and Pond G), 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 each basin instead of one large pond.
Gateway at Prospect
Drainage Report 13
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.
Pond B
Pond B is associated with Basin B. During the interim condition Pond B will have a
total volume of 1.429 ac-ft with a max release rate of 95.9 cfs. Interim Pond B will
also be providing 0.098 ac-ft of water quality capture volume (WQCV) and excess
urban runoff volume (EURV) via extended detention. In the ultimate condition Pond B
will have a total volume of 6.614 ac-ft with 2.897 ac-ft of WQCV and EURV via
extended detention and have a max release rate of 91.1 cfs. As previously stated, the
final volume is not the controlling factor but rather the 91.1 cfs release rate from
Basin B. Therefore, in the future Basin B can have a total release rate of 91.1 cfs.
Additionally, Basin B must also provide a minimum of 2.897 ac-ft of WQCV and
EURV via extended detention along with LID measures as laid forth in the Fort Collins
Stormwater Criteria Manual.
Pond C
Pond C is associated with Basin C. During the interim condition Pond C will have a
total volume of 0.613 ac-ft with a max release rate of 30.9 cfs. Interim Pond C will
also be providing 0.055 ac-ft of water quality capture volume (WQCV) and excess
urban runoff volume (EURV) via extended detention. In the ultimate condition Pond C
will have a total volume of 3.530 ac-ft with 1.914 ac-ft of WQCV and EURV via
extended detention and have a max release rate of 29.6 cfs. As previously stated, the
final volume is not the controlling factor but rather the 29.6 cfs release rate from
Basin C. Therefore, in the future Basin C can have a total release rate of 29.6 cfs.
Additionally, Basin C must also provide a minimum of 1.914 ac-ft of WQCV and
EURV via extended detention along with LID measures as laid forth in the Fort Collins
Stormwater Criteria Manual.
Pond D
Pond D is associated with Basin D. Pond D will not have an interim condition
because Basin D is being built out to its ultimate condition. Therefore, Pond D will
have a total volume of 3.530 ac-ft while providing 0.118 ac-ft of WQCV and EURV
via extended detention. Pond D will have a max release rate of 5.8 cfs.
Pond E
Pond E is associated with Basin E. During the interim condition Pond E will have a
total volume of 0.943 ac-ft with a max release rate of 31.0 cfs. Interim Pond E will
also be providing 0.225 ac-ft of water quality capture volume (WQCV) and excess
urban runoff volume (EURV) via extended detention. In the ultimate condition Pond E
will have a total volume of 2.375 ac-ft with 1.184 ac-ft of WQCV and EURV via
extended detention and have a max release rate of 31.9 cfs. As previously stated, the
final volume is not the controlling factor but rather the 31.9 cfs release rate from
Basin E. Therefore, in the future Basin E can have a total release rate of 31.9 cfs.
Additionally, Basin E must also provide a minimum of 1.184 ac-ft of WQCV and
EURV via extended detention along with LID measures as laid forth in the Fort Collins
Stormwater Criteria Manual.
Pond F
Pond F is associated with Basin F. There is no interim Pond F because Basin F
Gateway at Prospect
Drainage Report 14
remains unchanged with the Gateway at Prospect development. However, in the
future Pond F must have a total volume of 0.854 ac-ft, with 0.454 ac-ft of WQCV
and EURV via extended detention. Pond F will have a max release rate of 10.1 cfs.
Therefore, in the future Basin F can have a total release rate of 10.1 cfs and must
also provide LID measures as laid forth in the Fort Collins Stormwater Criteria Manual.
Pond G
Pond G is associated with Basin G. During the interim condition Pond G will have a
total volume of 0.896 ac-ft with a max release rate of 30.9 cfs. Interim Pond B will
also be providing 0.140 ac-ft of water quality capture volume (WQCV) and excess
urban runoff volume (EURV) via extended detention. In the ultimate condition Pond G
will have a total volume of 3.625 ac-ft with 1.920 ac-ft of WQCV and EURV via
extended detention and have a max release rate of 33.1 cfs. As previously stated, the
final volume is not the controlling factor but rather the 33.1 cfs release rate from
Basin G. Therefore, in the future Basin G can have a total release rate of 33.1 cfs.
Additionally, Basin G must also provide a minimum of 1.920 ac-ft of WQCV and
EURV via extended detention along with LID measures as laid forth in the Fort Collins
Stormwater Criteria Manual.
Pond Summary
Pond sizing and associated release rates were calculated via full spectrum detention
methods. All interim and final ponds will be releasing to Boxelder Creek. By utilizing
full spectrum detention, it allows Gateway at Prospect and future developments to
maintain downstream infrastructure within the Boxelder Creek by beating the peak.
By utilizing the hydrographs produced by full spectrum in conjunction with Ayers
Associates Boxelder Creek/Cooper Slough Basin SWMM models allows for verification
that downstream integrity within the Boxelder Creek will be maintained. Further
explanation on this can be found in the following section.
Table 3 - Interim Pond Summary
Table 4 - Ultimate Pond Summary
Pond ID Storage (ac-ft) WQCV + EURV (ac-ft) Release Rate (cfs)
Interim Pond B 1.429 0.098 95.9
Interim Pond C 0.613 0.055 30.9
Pond D N/A N/A N/A
Interim Pond E 0.943 0.225 31.0
Pond F N/A N/A N/A
Interim Pond G 0.896 0.140 30.9
Pond ID Final Storage (ac-ft)* WQCCV + EURV (ac-ft) Final Release Rate (cfs)
Pond B 6.614 2.897 91.1
Pond C 3.530 1.914 29.6
Pond D 0.305 0.118 5.8
Pond E 2.375 1.184 31.9
Pond F 0.854 0.454 10.1
Pond G 3.625 1.920 33.1
Gateway at Prospect
Drainage Report 15
*Future Developments can choose to do several ponds instead of one large pond.
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 pre-development flows. The pre-development 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 difference in
volumes have an impact on 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.
6. Full Spectrum and SWMM Analysis
As previously stated, one of Gateway at Prospects main goals is to maintain
downstream integrity of the Boxelder Creek and emergency overflow channel. The
main way this is achievable is by utilizing full spectrum detention to “beat the peak”.
The “beat the peak” concept is when you discharge the sites runoff at a certain rate to
guarantee that you are not increasing the peak flowrate in the drainageway by the
compounding peak discharge from the site concurrently with the peak flow in the
drainageway. In general, the Boxelder Creek has a peaking time within the Gateway at
Prospect project is roughly 14.20 hours after the initial storm. This can be seen in
Appendix C.
Ayers and Associates put together a SWMM model in 2018 that modeled the
Boxelder Creek/Cooper Slough Basin in its entirety. By utilizing this SWMM model in
conjunction with the hydrographs produced by full spectrum, the impacts of the
Gateway at Prospect and the future associated developments on the Boxelder Creek
were modeled.
There are four main junctions with the Ayers and Associates SWMM model that are
directly applicable to the Gateway at Prospect project. Gateway at Prospect utilized
these four junctions to compare the existing, interim, and ultimate 100-year flow rates
at these known locations.
Gateway at Prospect
Drainage Report 16
Figure 5 - Snapshot of Ultimate Pond SWMM Model
Node 884
Node 884 represents the junction upstream of the Gateway at Prospect project.
Therefore, this node is a control point and the flow rate will remain unchanged from
existing condition to the ultimate condition. The flowrate leaving Node 884 in all
three scenarios is 3377.99 cfs.
Divider 885
Divider 885 represents the location in Boxelder Creek where the emergency overflow
is located, which has previously been described. This is the first junction that you can
see the negligible impact that Gateway at Prospect will have on Boxelder Creek in the
interim and ultimate condition. Pond B, Pond C, and Pond D discharge into Boxelder
Creek Upstream of Divider 885. At the existing condition Divider 885 has a flowrate
of 3377.89 cfs. In the interim condition Divider 885 max flow rate is raised to
3378.02 cfs and up to 3378.79 cfs during the ultimate condition. The slight increase
to peak flow rate in the Boxelder Creek is due to the required 40-hour release of the
WQCV and EURV of Ponds B, C, and D. The peak flow rate within Divider 885 occurs
roughly around 14.17 hours after the storm event. Therefore, there will be a slight
increase in runoff that is driven by the release of the WQCV and EURV. However, this
change is extremely negligible in the grand scheme of the entire basin and therefore it
can be said that the integrity of Boxelder Creek at Divider 885 will be maintained.
Node 886
Node 886 is the next downstream node within the typical Boxelder Creek flow path.
Node 886 will be the closest downstream nodes for Pond F and Pond G where
impacts can be analyzed. In the existing condition Node 886 had a flow rate of
950.98 cfs, in the interim condition 951.12, and in the ultimate condition 951.41
cfs. Again, this increase is driven by the 40-hr drain time of the WQCV and EURV
from upstream ponds. However, once again the impact is negligible, and it can be
concluded that the integrity of Boxelder Creek will be maintained at Node 886.
Gateway at Prospect
Drainage Report 17
Node 887
Node 887 is associated with the first node down stream of the emergency overflow
path within Boxelder Creek. Node 887 sees most of the 100-year event generated
within the Boxelder Creek/Cooper Slough Basin with an existing flowrate of 2426.9
cfs. In the interim condition the flow rate at Node 887 is 2427.17 cfs and 2428.22
cfs in the ultimate condition. These increases in flowrates can once again be
associated with the 40-hr release time for the WQCV and EURV. Pond E in the
interim condition discharges directly into this overflow spillway.
All these junctions are depicted on the Drainage Exhibit found in the map packet for
additional comprehension ease.
SWMM Summary
By utilizing full spectrum detention Gateway at Prospect, it is expected that the
Boxelder Creek downstream integrity will not be impacted during the interim and
ultimate conditions. The slight increases in the peak flowrates are a result of the 40-
hr drain times for the WQCV and EURV.
Table 5 - SWMM Existing v. Interim Conditions Summary
Table 6 - SWMM Existing v. Ultimate Conditions Summary
Additionally, by utilizing full spectrum Gateway at Prospect has shown that it is in fact
beating the peak within the Boxelder Creek, which was stated to be roughly 14.20
hours after the initial storm. During both the interim and ultimate conditions all the
ponds are peaking at roughly 1 hour after the initial storm. This is illustrated in the
profiles found with in Appendix C.
Please refer to the Appendix for a more comprehensive breakdown in calculations and
locations. Additionally, the SWMM model can be provided to whomever requests
access to it but for the sake of comprehension and reducing the overall sheet count of
this report the SWMM results have been stripped down to include only information
that is relevant to the Gateway and Prospect project.
V. CONCLUSIONS
A. Compliance with Standards
1. The drainage design proposed with 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
SWMM ID
Ayers Associate Boxelder Basin
Model 100-YR Flow Rates (cfs)Interim 100-YR Flow Rates (cfs) Increase in Flow Rates (cfs)
Node 884 3377.99 3377.99 0.00
Divider 885 3377.89 3378.02 0.13
Node 886 950.98 951.12 0.14
Node 887 2426.9 2427.17 0.27
SWMM ID
Ayers Associate Boxelder Basin
Model 100-YR Flow Rates (cfs)Ultimate 100-YR Flow Rates (cfs) Increase in Flow Rates (cfs)
Node 884 3377.99 3377.99 0.00
Divider 885 3377.89 3378.79 0.90
Node 886 950.98 951.41 0.43
Node 887 2426.9 2428.22 1.32
Gateway at Prospect
Drainage Report 18
this divergence from the detention standards set in the FCSCM
2. The drainage design proposed with 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 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.
B. Drainage Concept
1. The drainage design proposed with this project will effectively limit potential damage
associated with its stormwater runoff. Gateway at Prospect will install interim ponds
and one final pond. Additionally, it has set out the guidelines for future development to
follow in order to ensure downstream integrity of Boxelder Creek. Gateway at Prospect
utilized full spectrum detention as a mechanism to “beat the peak” of the Boxelder
Creek.
2. The proposed Gateway at Prospect development will not impact the Master Drainage
Plan recommendations for the Boxelder and Cooper Slough major drainage basin.
Gateway at Prospect
Drainage Report 19
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 Stephanie
Thomas at Northern Engineering, May 3rd 2016
APPENDIX A
HYDROLOGIC COMPUTATIONS
Gateway at Prospect
Project:Gateway at Prospect
Calculations By:B. Mathisen
Date:April 21, 2020
CHARACTER OF SURFACE1: Percentage
Impervious
Streets, Parking Lots, Roofs, Alleys, and Drives:
Asphalt ……....……………...……….....…...……………….…………………………………………………………..100%
Concrete …….......……………….….……….………………..….……………………………………………………..90%
Gravel ……….…………………….….…………………………..………………………………………………………40%
Roofs …….…….………………..……………….………………………………………………………………………90%
Lawns and Landscaping
Sandy Soil 2%
Clayey Soil 2%
ROW ROW Width Asphalt Concrete Area Landscaped Area Percent Impervious
LF LF LF SF %
ROW (Collector 66' ROW)66 38 15 13 78%
ROW (Collector 84' ROW)84 50 15 19 76%
UPDATED TO FCSCM RUNOFF COEFFICENTS
SITE SPECIFIC % IMPERVIOUSNESS
4/21/20203:38 PM P:\892-002\Drainage\Hydrology\889-002_Proposed Rational Calcs (Interim).xlsx
Gateway at ProspectCHARACTER OF SURFACE1: PercentageImperviousDevelopedProject:Gateway at ProspectROW (Collector 84' ROW)76%Calculations By:Blaine MathisenROW (Collector 66' ROW)78%Date:April 21, 2020Urban Estate30%Low Density Residential50%Medium Density Residential70%Commercial 80%Park25%Unimproved AreasUndeveloped, Greenbelts, agricultural2%Lawns Sandy Soil2%Notes:Basin IDBasin Area(ac)Area of Collector 66' R.O.W(ac)Area ofCollector 84' R.O.W(ac)Area ofUrban Estate(ac)Area ofLow Density Residential(ac)Area ofMedium Density Residential(ac)Area ofCommercial(ac)Area ofPark(ac)Area of Undeveloped, Greenbelts, Agricultural(ac)Composite% Imperv.2-yearComposite RunoffCoefficient5-yearComposite RunoffCoefficient10-yearComposite RunoffCoefficient100-yearComposite Runoff CoefficientA1 29.57 0.00 0.00 0.00 0.00 0.00 0.00 0.00 29.57 2% 0.01 0.05 0.15 0.49B1 67.01 0.40 0.00 0.00 0.00 0.00 0.00 0.00 66.61 2% 0.01 0.05 0.15 0.49C1 23.88 0.00 0.00 0.00 0.00 0.00 0.00 0.00 23.88 2% 0.01 0.05 0.15 0.49C2 0.48 0.48 0.00 0.00 0.00 0.00 0.00 0.00 0.00 76% 0.60 0.65 0.68 0.79D1 2.11 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2.11 2% 0.01 0.05 0.15 0.49D2 1.57 0.00 1.57 0.00 0.00 0.00 0.00 0.00 0.00 78% 0.60 0.65 0.68 0.79E1 14.43 0.00 0.00 0.00 0.00 0.00 0.00 0.00 14.43 2% 0.01 0.05 0.15 0.49E2 3.45 2.04 0.00 0.00 0.00 0.00 0.00 0.00 1.41 46% 0.34 0.40 0.46 0.67E3 0.97 0.97 0.00 0.00 0.00 0.00 0.00 0.00 0.00 76% 0.60 0.65 0.68 0.79F1 5.78 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5.78 2% 0.01 0.05 0.15 0.49G1 23.26 0.00 0.42 0.00 0.00 0.00 0.00 0.00 22.83 3% 0.01 0.05 0.15 0.49G2 1.51 0.00 1.31 0.00 0.00 0.00 0.00 0.00 0.20 68% 0.51 0.56 0.61 0.75BOX1 3.58 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.58 2% 0.01 0.05 0.15 0.49BOX2 1.57 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.57 2% 0.01 0.05 0.15 0.49PUD1 3.13 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.13 2% 0.01 0.05 0.15 0.49Total182.303.893.310.000.000.000.000.00175.10 5% 0.03 0.08 0.17 0.50Combined BasinsBasin C (C1 and C2)24.36 0.48 0.00 0.00 0.00 0.00 0.00 0.00 23.883% 0.01 0.05 0.15 0.49Basin D (D1 and D2)3.68 0.00 1.57 0.00 0.00 0.00 0.00 0.00 2.1135% 0.26 0.32 0.39 0.63Basin E (E1, E2, and E3)18.85 3.01 0.00 0.00 0.00 0.00 0.00 0.00 15.8414% 0.06 0.12 0.21 0.52Basin G (G1 and G2)24.77 0.00 1.74 0.00 0.00 0.00 0.00 0.00 23.037% 0.03 0.08 0.17 0.50INTERIM BASIN % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS2) Runoff Coefficients are taken from the Mile High Flood Control District, Chapter 6, Table 6-5, Soil Group C.1) Percentage impervious taken from Fort Collins Stormwater Criteria Manual, Chapter 5, Table 4.1-2 and Table 4.1-3
Gateway at ProspectOverland Flow, Time of Concentration:Project:Gateway at ProspectCalculations By:Blaine MathisenDate:April 21, 2020Gutter/Swale Flow, Time of Concentration:Tt = L / 60V (UDFCD USDCM, Volume 1, Chapter 6, Equation 6-4)Tc = Ti + Tt (UDFCD USDCM, Volume 1, Chapter 6, Equation 6-2)Velocity (Gutter Flow), V = 20·S½ (UDFCD USDCM, Volume 1, Chapter 6, Table 6-2)Velocity (Swale Flow), V = 15·S½ (UDFCD USDCM, Volume 1, Chapter 6, Table 6-2)Time of ConcentrationIs Length >500' ?C5Slope,S(%)TiSlope,S(%)Velocity,V(ft/s)Tt(min)Slope,S(%)Velocity,V(ft/s)Tt(min)Urban TcCheckTc(min)A1Yes0.050.52%65.6N/AN/AN/AN/AN/AN/An/a65.6Interim Pond BB1No0.054.00%21.00.75%1.735.8N/AN/AN/A15.015.0C1No0.053.75%17.51.20%2.193.8N/AN/AN/A13.913.9c2C2No0.65N/AN/A1.10%2.103.9N/AN/AN/A12.75.0D1No0.0523.33%3.7N/AN/AN/AN/AN/AN/A10.25.0d2D2No0.65N/AN/A0.49%1.415.9N/AN/AN/A12.85.9E1No0.055.00%11.3N/AN/AN/AN/AN/AN/A10.610.6e2E2No0.40N/AN/A0.76%1.759.4N/AN/AN/A15.59.4e3E3No0.65N/AN/A1.10%2.103.9N/AN/AN/A12.75.0F1No0.054.00%10.52.67%3.270.4N/AN/AN/A10.810.8G1No0.053.00%18.90.80%1.792.3N/AN/AN/A12.512.5g2G2No0.56N/AN/A1.72%2.633.7N/AN/AN/A13.25.0BOX1No0.05N/AN/AN/AN/AN/A0.71%1.279.213.99.2BOX2No0.05N/AN/AN/AN/AN/A0.13%0.5329.715.315.3PUD1No0.05 N/A N/A N/A N/A N/A 0.09% 0.45 99.6 25.0 25.0Interim Pond CBasin C (C1 and C2)No0.05N/AN/A1.10%2.103.9N/AN/AN/A12.75.0Final Pond DBasin D (D1 and D2)No0.3223.33%2.7N/AN/AN/AN/AN/AN/A10.25.0Interim Pond EBasin E (E1, E2, and E3)No0.12N/AN/A1.10%2.103.9N/AN/AN/A12.75.0Interim Pond GBasin G (G1 and G2)No0.08 N/A N/A 1.72% 2.63 3.7 N/A N/A N/A 13.2 5.0INTERIM DEVELOPED DIRECT TIME OF CONCENTRATION FOR INDIVIDUAL BASINSGutter Flow 1 Swale FlowDesignPointBasinOverland Flow(UDFCD USDCM, Volume 1, ()3151.1395.0SLCTi-=
Gateway at ProspectRational Method Equation:Project:Calculations By:Date:Rainfall Intensity:A129.5765.6 0.01 0.15 0.49 1.32 2.25 4.60 0.39 9.98 66.66Interim Pond BB167.0115.0 0.01 0.15 0.49 1.87 3.19 6.52 1.25 32.06 214.08C123.8813.9 0.01 0.15 0.49 1.95 3.34 6.82 0.47 11.96 79.74c2C20.485.0 0.60 0.68 0.79 2.85 4.87 9.95 0.82 1.59 3.78D12.115.0 0.01 0.15 0.49 2.85 4.87 9.95 0.06 1.54 10.29d2D21.575.9 0.60 0.68 0.79 2.76 4.72 9.63 2.60 5.04 11.95E114.4310.6 0.01 0.15 0.49 2.17 3.71 7.57 0.31 8.02 53.53e2E23.459.4 0.34 0.46 0.67 2.30 3.93 8.03 2.70 6.24 18.56e3E30.975.0 0.60 0.68 0.79 2.85 4.87 9.95 1.65 3.20 7.60F15.7810.8 0.01 0.15 0.49 2.17 3.71 7.57 0.13 3.21 21.45G123.2612.5 0.01 0.15 0.49 2.02 3.45 7.04 0.47 12.02 80.22g2G21.515.0 0.51 0.61 0.75 2.85 4.87 9.95 2.20 4.50 11.30BOX13.589.2 0.01 0.15 0.49 2.30 3.93 8.03 0.08 2.11 14.07BOX21.5715.3 0.01 0.15 0.49 1.87 3.19 6.52 0.03 0.75 5.00PUD13.1325.0 0.01 0.15 0.49 1.43 2.44 4.98 0.04 1.14 7.63Interim Pond C Basin C (C1 and C2) 24.36 5.0 0.01 0.15 0.49 2.85 4.87 9.95 0.69 17.80 118.77Final Pond D Basin D (D1 and D2) 3.68 5.0 0.26 0.39 0.63 2.85 4.87 9.95 2.73 6.99 23.08Interim Pond E Basin E (E1, E2, and E3) 18.85 5.0 0.06 0.21 0.52 2.85 4.87 9.95 3.22 19.28 97.52Interim Pond G Basin G (G1 and G2) 24.77 5.0 0.03 0.17 0.50 2.85 4.87 9.95 2.12 20.51 123.23Combined BasinsIntensity,i2(in/hr)Intensity, i100(in/hr)NotesINTERIM DEVELOPED RUNOFF COMPUTATIONS FOR INDIVIDUAL BASINSDesignPointBasin(s)Area, A(acres)Tc(min)Flow,Q2(cfs)Flow,Q100(cfs)C2C100Rainfall Intensity taken from the Larimer County Stormwater Design Standards, Adopted June 20, 2005, Figure RA-3.C10Intensity,i10(in/hr)Flow,Q10(cfs)Gateway at ProspectBlaine MathisenApril 21, 2020()()()AiCCQf=
Gateway at ProspectBASINTOTALAREA(acres)Tc(min)C2C100Q2(cfs)Q100(cfs)A129.5765.60.010.490.3966.66B167.0115.00.010.491.25214.08C123.8813.90.010.490.4779.74C20.485.00.600.790.823.78D12.115.00.010.490.0610.29D21.575.90.600.792.6011.95E114.4310.60.010.490.3153.53E23.459.40.340.672.7018.56E30.975.00.600.791.657.60F15.7810.80.010.490.1321.45G123.2612.50.010.490.4780.22G21.515.00.510.752.2011.30BOX13.589.20.010.490.0814.07BOX21.5715.30.010.490.035.00PUD1 3.13 25.0 0.01 0.49 0.04 7.63Basin C (C1 and C2)24.365.00.010.490.69118.77Basin D (D1 and D2)3.685.00.260.632.7323.08Basin E (E1, E2, and E3)18.855.00.060.523.2297.52Basin G (G1 and G2) 24.77 5.0 0.03 0.50 2.12 123.23Rational Flow Summary | Developed Basin Flow Rates4/21/20203:38 PMP:\892-002\Drainage\Hydrology\889-002_Proposed Rational Calcs (Interim).xlsx\Summary Tables
Gateway at ProspectCHARACTER OF SURFACE1: PercentageImperviousDevelopedProject:Gateway at ProspectROW (Collector 84' ROW)76%Calculations By:Blaine MathisenROW (Collector 66' ROW)78%Date:April 21, 2020Urban Estate30%Low Density Residential50%Medium Density Residential70%Commercial 80%Park25%Unimproved AreasUndeveloped, Greenbelts, agricultural2%Lawns Sandy Soil2%Notes:Basin IDBasin Area(ac)Area of Collector 66' R.O.W(ac)Area ofCollector 84' R.O.W(ac)Area ofUrban Estate(ac)Area ofLow Density Residential(ac)Area ofMedium Density Residential(ac)Area ofCommercial(ac)Area ofPark(ac)Area of Undeveloped, Greenbelts, Agricultural(ac)Composite% Imperv.2-yearComposite RunoffCoefficient5-yearComposite RunoffCoefficient10-yearComposite RunoffCoefficient100-yearComposite Runoff CoefficientA1 29.57 0.00 0.00 0.00 0.00 0.00 0.00 0.00 29.57 2% 0.01 0.05 0.15 0.49B1 67.01 0.40 0.00 13.56 52.96 0.00 0.00 0.00 0.09 46% 0.34 0.40 0.46 0.67C1 23.88 0.00 0.00 0.00 0.00 0.00 23.88 0.00 0.00 80% 0.65 0.69 0.72 0.81C2 0.48 0.48 0.00 0.00 0.00 0.00 0.00 0.00 0.00 76% 0.60 0.65 0.68 0.79D1 2.11 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2.11 2% 0.01 0.05 0.15 0.49D2 1.57 0.00 1.57 0.00 0.00 0.00 0.00 0.00 0.00 78% 0.60 0.65 0.68 0.79E1 14.43 0.00 0.00 0.00 0.00 14.04 0.00 0.00 0.39 68% 0.51 0.56 0.61 0.75E2 3.45 2.04 0.00 0.00 0.18 0.00 0.00 0.00 1.22 48% 0.34 0.40 0.46 0.67E3 0.97 0.97 0.00 0.00 0.00 0.00 0.00 0.00 0.00 76% 0.60 0.65 0.68 0.79F1 5.78 0.00 0.31 0.00 0.00 0.00 5.47 0.00 0.00 80% 0.65 0.69 0.72 0.81G1 23.26 0.00 0.42 0.00 0.00 0.00 22.83 0.00 0.00 80% 0.65 0.69 0.72 0.81G2 1.51 0.00 1.31 0.00 0.00 0.00 0.00 0.00 0.20 68% 0.51 0.56 0.61 0.75BOX1 3.58 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.58 2% 0.01 0.05 0.15 0.49BOX2 1.57 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.57 2% 0.01 0.05 0.15 0.49PUD1 3.13 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.13 2% 0.01 0.05 0.15 0.49Total182.303.893.6213.5653.1514.0452.190.0041.86 49% 0.34 0.40 0.46 0.67Combined BasinsBasin C (C1 and C2)24.36 0.48 0.00 0.00 0.00 0.00 23.88 0.00 0.0080% 0.65 0.69 0.72 0.81Basin D (D1 and D2)3.68 0.00 1.57 0.00 0.00 0.00 0.00 0.00 2.1135% 0.26 0.32 0.39 0.63Basin E (E1, E2, and E3)18.85 3.01 0.00 0.00 0.18 14.04 0.00 0.00 1.6265% 0.51 0.56 0.61 0.75Basin G (G1 and G2)24.77 0.00 1.74 0.00 0.00 0.00 22.83 0.00 0.2079% 0.60 0.65 0.68 0.79BASIN % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS2) Runoff Coefficients are taken from the Mile High Flood Control District, Chapter 6, Table 6-5, Soil Group C.1) Percentage impervious taken from the Fort Collins Stormwater Criteria Manual, Chapter 5, Table 4.1-2 and Table 4.1-3
Gateway at ProspectOverland Flow, Time of Concentration:Project:Gateway at ProspectCalculations By:Blaine MathisenDate:April 21, 2020Gutter/Swale Flow, Time of Concentration:Tt = L / 60V (UDFCD USDCM, Volume 1, Chapter 6, Equation 6-4)Tc = Ti + Tt (UDFCD USDCM, Volume 1, Chapter 6, Equation 6-2)Velocity (Gutter Flow), V = 20·S½ (UDFCD USDCM, Volume 1, Chapter 6, Table 6-2)Velocity (Swale Flow), V = 15·S½ (UDFCD USDCM, Volume 1, Chapter 6, Table 6-2)Time of ConcentrationIs Length >500' ?C5Slope,S(%)TiSlope,S(%)Velocity,V(ft/s)Tt(min)Slope,S(%)Velocity,V(ft/s)Tt(min)Urban TcCheckTc(min)A1Yes0.05 0.52% 65.6 N/A N/A N/A N/A N/A N/A n/a 65.6Pond BB1No0.40 4.00% 14.0 0.75% 1.73 5.8 N/A N/A N/A 15.0 15.0C1No0.69 3.75% 6.8 1.20% 2.19 3.8 N/A N/A N/A 13.9 10.6c2C2No0.65 N/A N/A 1.10% 2.10 3.9 N/A N/A N/A 12.7 5.0D1No0.05 23.33% 3.7 N/A N/A N/A N/A N/A N/A 10.2 5.0d2D2No0.65 N/A N/A 0.49% 1.41 5.9 N/A N/A N/A 12.8 5.9E1No0.56 5.00% 5.8 N/A N/A N/A N/A N/A N/A 10.6 5.8e2E2No0.40 N/A N/A 0.76% 1.75 9.4 N/A N/A N/A 15.5 9.4e3E3No0.65 N/A N/A 1.10% 2.10 3.9 N/A N/A N/A 12.7 5.0Pond FF1No0.69 4.00% 4.1 2.67% 3.27 0.4 N/A N/A N/A 10.8 5.0G1No0.69 3.00% 7.4 0.80% 1.79 2.3 N/A N/A N/A 12.5 9.7g2G2No0.56 N/A N/A 1.72% 2.63 3.7 N/A N/A N/A 13.2 5.0BOX1No0.05 N/A N/A N/A N/A N/A 0.71% 1.27 9.2 13.9 9.2BOX2No0.05 N/A N/A N/A N/A N/A 0.13% 0.53 29.7 15.3 15.3PUD1No0.05 N/A N/A N/A N/A N/A 0.09% 0.45 99.6 25.0 25.0Pond CBasin C (C1 and C2)No0.69 N/A N/A 1.10% 2.10 3.9 N/A N/A N/A 12.7 5.0Pond DBasin D (D1 and D2)No0.32 23.33% 2.7 N/A N/A N/A N/A N/A N/A 10.2 5.0Pond EBasin E (E1, E2, and E3)No0.56 N/A N/A 1.10% 2.10 3.9 N/A N/A N/A 12.7 5.0Pond GBasin G (G1 and G2)No0.65 N/A N/A 1.72% 2.63 3.7 N/A N/A N/A 13.2 5.0DEVELOPED DIRECT TIME OF CONCENTRATION FOR INDIVIDUAL BASINSGutter Flow 1 Swale FlowDesignPointBasinOverland Flow(UDFCD USDCM, Volume 1, ()3151.1395.0SLCTi-=
Gateway at ProspectRational Method Equation:Project:Calculations By:Date:Rainfall Intensity:A1 29.5765.6 0.01 0.15 0.49 1.32 2.25 4.60 0.39 9.98 66.66Pond B B1 67.0115.0 0.34 0.46 0.67 1.87 3.19 6.52 42.60 98.33 292.72C1 23.8810.6 0.65 0.72 0.81 2.17 3.71 7.57 33.68 63.70 146.42c2 C2 0.485.0 0.60 0.68 0.79 2.85 4.87 9.95 0.82 1.59 3.78D1 2.115.0 0.01 0.15 0.49 2.85 4.87 9.95 0.06 1.54 10.29d2 D2 1.575.9 0.60 0.68 0.79 2.76 4.72 9.63 2.60 5.04 11.95E1 14.435.8 0.51 0.61 0.75 2.76 4.72 9.63 20.31 41.51 104.23e2 E2 3.459.4 0.34 0.46 0.67 2.30 3.93 8.03 2.70 6.24 18.56e3 E3 0.975.0 0.60 0.68 0.79 2.85 4.87 9.95 1.65 3.20 7.60Pond F F1 5.785.0 0.65 0.72 0.81 2.85 4.87 9.95 10.71 20.28 46.61G1 23.269.7 0.65 0.72 0.81 2.26 3.86 7.88 34.09 64.55 148.34g2 G2 1.515.0 0.51 0.61 0.75 2.85 4.87 9.95 2.20 4.50 11.30BOX1 3.589.2 0.01 0.15 0.49 2.30 3.93 8.03 0.08 2.11 14.07BOX2 1.5715.3 0.01 0.15 0.49 1.87 3.19 6.52 0.03 0.75 5.00PUD13.1325.0 0.01 0.15 0.49 1.43 2.44 4.98 0.04 1.14 7.63Pond C Basin C (C1 and C2) 24.36 5.0 0.65 0.72 0.81 2.85 4.87 9.95 45.13 85.42 196.34Pond D Basin D (D1 and D2) 3.68 5.0 0.26 0.39 0.63 2.85 4.879.95 2.73 6.99 23.08Pond E Basin E (E1, E2, and E3) 18.85 5.0 0.51 0.61 0.75 2.85 4.87 9.95 27.40 55.99 140.65Pond G Basin G (G1 and G2) 24.77 5.0 0.60 0.68 0.79 2.85 4.87 9.95 42.36 82.03 194.70Combined BasinsIntensity,i2(in/hr)Intensity, i100(in/hr)NotesDEVELOPED RUNOFF COMPUTATIONS FOR INDIVIDUAL BASINSDesignPointBasin(s)Area, A(acres)Tc(min)Flow,Q2(cfs)Flow,Q100(cfs)C2C100Rainfall Intensity taken from the Larimer County Stormwater Design Standards, Adopted June 20, 2005, Figure RA-3.C10Intensity,i10(in/hr)Flow,Q10(cfs)Gateway at ProspectBlaine MathisenApril 21, 2020()()()AiCCQf=
Gateway at ProspectBASINTOTALAREA(acres)Tc(min)C2C100Q2(cfs)Q100(cfs)A129.5765.60.010.490.3966.66B167.0115.00.340.6742.60292.72C123.8810.60.650.8133.68146.42C20.485.00.600.790.823.78D12.115.00.010.490.0610.29D21.575.90.600.792.6011.95E114.435.80.510.7520.31104.23E23.459.40.340.672.7018.56E30.975.00.600.791.657.60F15.785.00.650.8110.7146.61G123.269.70.650.8134.09148.34G21.515.00.510.752.2011.30BOX13.589.20.010.490.0814.07BOX21.5715.30.010.490.035.00PUD1 3.13 25.0 0.01 0.49 0.04 7.63Basin C (C1 and C2)24.365.00.650.8145.13196.34Basin D (D1 and D2)3.685.00.260.632.7323.08Basin E (E1, E2, and E3)18.855.00.510.7527.40140.65Basin G (G1 and G2) 24.77 5.0 0.60 0.79 42.36 194.70Rational Flow Summary | Developed Basin Flow Rates4/21/20203:39 PMP:\892-002\Drainage\Hydrology\889-002_Proposed Rational Calcs (Final Master Planning).xlsx\Summary Tables
1-hr point (in)1.04 1.73 2.71
Duration (min) 2-Year Intensity (in/hr) 10-Year Intensity (in/hr) 100-Year Intensity (in/hr)
2.00 3 4
5 2.85 4.87 9.95
5.5 2.76 4.72 9.63
6 2.67 4.56 9.31
6.5 2.60 4.44 9.06
7 2.52 4.31 8.80
7.5 2.46 4.21 8.59
8 2.40 4.10 8.38
8.5 2.35 4.02 8.21
9 2.30 3.93 8.03
9.5 2.26 3.86 7.88
10 2.21 3.78 7.72
10.5 2.17 3.71 7.57
11 2.13 3.63 7.42
12 2.09 3.57 7.29
12 2.05 3.50 7.16
12.5 2.02 3.45 7.04
13 1.98 3.39 6.92
13.5 1.95 3.34 6.82
14 1.92 3.29 6.71
14.5 1.90 3.24 6.62
15 1.87 3.19 6.52
15.5 1.84 3.14 6.41
16 1.81 3.08 6.30
16.5 1.78 3.04 6.20
17 1.75 2.99 6.10
17.5 1.73 2.95 6.01
18 1.70 2.90 5.92
18.5 1.68 2.86 5.84
19 1.65 2.82 5.75
19.5 1.63 2.78 5.68
20 1.61 2.74 5.60
20.5 1.59 2.71 5.53
21 1.56 2.67 5.46
21.5 1.55 2.64 5.39
22 1.53 2.61 5.32
22.5 1.51 2.58 5.26
23 1.49 2.55 5.20
23.5 1.48 2.52 5.15
24 1.46 2.49 5.09
24.5 1.45 2.47 5.04
25 1.43 2.44 4.98
25.5 1.42 2.42 4.93
26 1.40 2.39 4.87
26.5 1.39 2.37 4.83
27 1.37 2.34 4.78
27.5 1.36 2.32 4.74
28 1.34 2.29 4.69
28.5 1.33 2.27 4.65
29 1.32 2.25 4.60
29.5 1.31 2.23 4.56
30 1.30 2.21 4.52
Fort Collins Rainfall Intensity - Duration - Frequency Table
30.5 1.29 2.19 4.47
31 1.27 2.16 4.42
31.5 1.26 2.14 4.38
32 1.24 2.12 4.33
32.5 1.23 2.10 4.29
33 1.22 2.08 4.24
33.5 1.21 2.06 4.20
34 1.19 2.04 4.16
34.5 1.18 2.02 4.12
35 1.17 2 4.08
35.5 1.16 1.98 4.045
36 1.15 1.96 4.01
36.5 1.14 1.945 3.97
37 1.13 1.93 3.93
37.5 1.12 1.91 3.9
38 1.11 1.89 3.87
38.5 1.1 1.875 3.835
39 1.09 1.86 3.8
39.5 1.08 1.845 3.77
40 1.07 1.83 3.74
40.5 1.06 1.815 3.71
41 1.05 1.8 3.68
41.5 1.045 1.785 3.65
42 1.04 1.77 3.62
42.5 1.03 1.755 3.59
43 1.02 1.74 3.56
43.5 1.015 1.73 3.535
44 1.01 1.72 3.51
44.5 1 1.705 3.485
45 0.99 1.69 3.46
45.5 0.985 1.68 3.435
46 0.98 1.67 3.41
46.5 0.97 1.655 3.385
47 0.96 1.64 3.36
47.5 0.955 1.63 3.335
48 0.95 1.62 3.31
48.5 0.945 1.61 3.29
49 0.94 1.6 3.27
49.5 0.93 1.59 3.25
50 0.92 1.58 3.23
50.5 0.915 1.57 3.205
51 0.91 1.56 3.18
51.5 0.905 1.55 3.16
52 0.9 1.54 3.14
52.5 0.895 1.53 3.12
53 0.89 1.52 3.1
53.5 0.885 1.51 3.085
54 0.88 1.5 3.07
54.5 0.875 1.49 3.05
55 0.87 1.48 3.03
55.5 0.865 1.475 3.01
56 0.86 1.47 2.99
56.5 0.855 1.46 2.975
57 0.85 1.45 2.96
57.5 0.845 1.44 2.94
58 0.84 1.43 2.92
58.5 0.835 1.425 2.905
59 0.83 1.42 2.89
59.5 0.825 1.41 2.875
60 0.82 1.4 2.86
60.5 0.815 1.392 2.846
61 0.81 1.384 2.832
61.5 0.805 1.376 2.818
62 0.8 1.368 2.804
62.5 0.795 1.36 2.79
63 0.79 1.352 2.776
63.5 0.785 1.344 2.762
64 0.78 1.336 2.748
64.5 0.775 1.328 2.734
65 0.77 1.32 2.72
65.5 0.766 1.313 2.707
66 0.762 1.306 2.694
66.5 0.758 1.299 2.681
67 0.754 1.292 2.668
67.5 0.75 1.285 2.655
68 0.746 1.278 2.642
68.5 0.742 1.271 2.629
69 0.738 1.264 2.616
69.5 0.734 1.257 2.603
70 0.73 1.25 2.59
70.5 0.726 1.244 2.579
71 0.722 1.238 2.568
71.5 0.718 1.232 2.557
72 0.714 1.226 2.546
72.5 0.71 1.22 2.535
73 0.706 1.214 2.524
73.5 0.702 1.208 2.513
74 0.698 1.202 2.502
74.5 0.694 1.196 2.491
75 0.69 1.19 2.48
75.5 0.687 1.185 2.47
76 0.684 1.18 2.46
76.5 0.681 1.175 2.45
77 0.678 1.17 2.44
77.5 0.675 1.165 2.43
78 0.672 1.16 2.42
78.5 0.669 1.155 2.41
79 0.666 1.15 2.4
79.5 0.663 1.145 2.39
80 0.66 1.14 2.38
80.5 0.657 1.135 2.371
81 0.654 1.13 2.362
81.5 0.651 1.125 2.353
82 0.648 1.12 2.344
82.5 0.645 1.115 2.335
83 0.642 1.11 2.326
83.5 0.639 1.105 2.317
84 0.636 1.1 2.308
84.5 0.633 1.095 2.299
85 0.63 1.09 2.29
85.5 0.628 1.086 2.282
86 0.626 1.082 2.274
86.5 0.624 1.078 2.266
87 0.622 1.074 2.258
87.5 0.62 1.07 2.25
88 0.618 1.066 2.242
88.5 0.616 1.062 2.234
89 0.614 1.058 2.226
89.5 0.612 1.054 2.218
90 0.61 1.05 2.21
90.5 0.613 1.054 2.218
91 0.616 1.058 2.226
91.5 0.619 1.062 2.234
92 0.622 1.066 2.242
92.5 0.625 1.07 2.25
93 0.628 1.074 2.258
93.5 0.631 1.078 2.266
94 0.634 1.082 2.274
94.5 0.637 1.086 2.282
95 0.58 1.01 2.13
95.5 0.578 1.006 2.123
96 0.576 1.002 2.116
96.5 0.574 0.998 2.109
97 0.572 0.994 2.102
97.5 0.57 0.99 2.095
98 0.568 0.986 2.088
98.5 0.566 0.982 2.081
99 0.564 0.978 2.074
99.5 0.562 0.974 2.067
100 0.56 0.97 2.06
100.5 0.558 0.967 2.054
101 0.556 0.964 2.048
101.5 0.554 0.961 2.042
102 0.552 0.958 2.036
102.5 0.55 0.955 2.03
103 0.548 0.952 2.024
103.5 0.546 0.949 2.018
104 0.544 0.946 2.012
104.5 0.542 0.943 2.006
105 0.54 0.94 2
105.5 0.538 0.937 1.994
106 0.536 0.934 1.988
106.5 0.534 0.931 1.982
107 0.532 0.928 1.976
107.5 0.53 0.925 1.97
108 0.528 0.922 1.964
108.5 0.526 0.919 1.958
109 0.524 0.916 1.952
109.5 0.522 0.913 1.946
110 0.52 0.91 1.94
110.5 0.519 0.907 1.935
111 0.518 0.904 1.93
111.5 0.517 0.901 1.925
112 0.516 0.898 1.92
112.5 0.515 0.895 1.915
113 0.514 0.892 1.91
113.5 0.513 0.889 1.905
114 0.512 0.886 1.9
114.5 0.511 0.883 1.895
115 0.51 0.88 1.89
115.5 0.508 0.878 1.885
116 0.506 0.876 1.88
116.5 0.504 0.874 1.875
117 0.502 0.872 1.87
117.5 0.5 0.87 1.865
118 0.498 0.868 1.86
118.5 0.496 0.866 1.855
119 0.494 0.864 1.85
119.5 0.492 0.862 1.845
120 0.49 0.86 1.84
Purpose:This workbook aids in the estimation of stormwater detention basin sizing and
outlet routing based on the modified puls routing method for urban watersheds.
Several different BMP types and various outlet configurations can be sized.
Function:1. Approximates the stage-area-volume relationship for a detention basin based
on watershed parameters and basin geometry parameters. Also evaluates
existing user-defined basin stage-area relationships.
2. Sizes filtration media orifice, outlet orifices, elliptical slots, weirs, trash racks,
and develops stage-discharge relationships. Uses the Modified Puls method to
route a series of hydrographs (i.e., 2-, 5-, 10-, 25-, 50-, 100- and 500-year) and
calibrates the peak discharge out of the basin to match the pre-development
peak discharges for the watershed.
Content: This workbook consists of the following sheets:
Basin Tabulates stage-area-volume relationship estimates based on watershed parameters
Outlet Structure Tabulates a stage-discharge relationship for the user-defined outlet structure (inlet control).
Reference Provides reference equations and figures.
User Tips and Tools Provides instructions and video links to assist in using this workbook. Includes a stage-area calculator.
BMP Zone Images Provides images of typical BMP zone confirgurations corresponding with Zone pulldown selections.
Acknowledgements:Spreadsheet Development Team:
Ken MacKenzie, P.E., Holly Piza, P.E.
Mile High Flood District
Derek N. Rapp, P.E.
Peak Stormwater Engineering, LLC
Dr. James C.Y. Guo, Ph.D., P.E.
Professor, Department of Civil Engineering, University of Colorado at Denver
Comments?Direct all comments regarding this spreadsheet workbook to:MHFD E-Mail
Revisions?Check for revised versions of this or any other workbook at:Downloads
DETENTION BASIN DESIGN WORKBOOK
MHFD-Detention, Version 4.02 (February 2020)
Mile High Flood District
Denver, Colorado
www.mhfd.org
Pond G (Future) - Full Spectrum Detention.xlsm, Intro 4/16/2020, 3:34 PM
Project:
Basin ID:
Depth Increment = 0.50 ft
Watershed Information Top of Micropool 0.00 16.9 16.9 285 0.007
Selected BMP Type =EDB ISV 0.50 16.9 16.9 285 0.007 143 0.003
Watershed Area = 67.01 acres 1.00 16.9 16.9 285 0.007 285 0.007
Watershed Length = 2,370 ft 1.50 143.9 58.6 8,427 0.193 2,022 0.046
Watershed Length to Centroid = 1,150 ft 2.00 270.9 100.2 27,151 0.623 10,476 0.240
Watershed Slope = 0.010 ft/ft 2.50 397.9 141.9 56,459 1.296 30,938 0.710
Watershed Imperviousness = 46.00% percent Zone 1 (WQCV)2.76 463.9 163.6 75,882 1.742 48,080 1.104
Percentage Hydrologic Soil Group A = 0.0% percent 3.00 524.9 183.6 96,350 2.212 68,699 1.577
Percentage Hydrologic Soil Group B = 0.0% percent Zone 2 (EURV)3.49 649.4 224.4 145,712 3.345 127,589 2.929
Percentage Hydrologic Soil Groups C/D = 100.0% percent 3.50 651.9 225.2 146,825 3.371 129,052 2.963
Target WQCV Drain Time = 40.0 hours Floor 3.59 674.8 232.7 157,034 3.605 142,723 3.276
Location for 1-hr Rainfall Depths = Thornton - Civic Center 4.00 678.0 236.0 160,022 3.674 207,719 4.769
Zone 3 (100-year)4.50 682.0 240.0 163,694 3.758 288,646 6.626
5.00 686.0 244.0 167,398 3.843 371,418 8.527
Optional User Overrides 5.50 690.0 248.0 171,134 3.929 456,050 10.469
Water Quality Capture Volume (WQCV) = 1.092 acre-feet acre-feet 6.00 694.0 252.0 174,902 4.015 542,558 12.455
Excess Urban Runoff Volume (EURV) = 2.897 acre-feet acre-feet 6.50 698.0 256.0 178,703 4.102 630,957 14.485
2-yr Runoff Volume (P1 = 0.86 in.) = 2.010 acre-feet 0.86 inches 7.00 702.0 260.0 182,535 4.190 721,265 16.558
5-yr Runoff Volume (P1 = 1.14 in.) = 3.140 acre-feet 1.14 inches 7.50 706.0 264.0 186,399 4.279 813,497 18.675
10-yr Runoff Volume (P1 = 1.43 in.) = 4.619 acre-feet 1.43 inches 8.00 710.0 268.0 190,295 4.369 907,670 20.837
25-yr Runoff Volume (P1 = 1.93 in.) = 7.669 acre-feet 1.93 inches 8.50 714.0 272.0 194,223 4.459 1,003,798 23.044
50-yr Runoff Volume (P1 = 2.39 in.) = 10.340 acre-feet 2.39 inches 9.00 718.0 276.0 198,183 4.550 1,101,898 25.296
100-yr Runoff Volume (P1 = 2.91 in.) = 13.604 acre-feet 2.91 inches 9.50 722.0 280.0 202,176 4.641 1,201,987 27.594
500-yr Runoff Volume (P1 = 4.39 in.) = 22.571 acre-feet 4.39 inches 10.00 726.0 284.0 206,200 4.734 1,304,079 29.938
Approximate 2-yr Detention Volume = 1.844 acre-feet 10.50 730.0 288.0 210,256 4.827 1,408,192 32.328
Approximate 5-yr Detention Volume = 2.933 acre-feet 11.00 734.0 292.0 214,344 4.921 1,514,340 34.764
Approximate 10-yr Detention Volume = 3.597 acre-feet 11.50 738.0 296.0 218,464 5.015 1,622,541 37.248
Approximate 25-yr Detention Volume = 4.622 acre-feet 12.00 742.0 300.0 222,616 5.111 1,732,810 39.780
Approximate 50-yr Detention Volume = 5.281 acre-feet 12.50 746.0 304.0 226,801 5.207 1,845,163 42.359
Approximate 100-yr Detention Volume = 6.614 acre-feet 13.00 750.0 308.0 231,017 5.303 1,959,616 44.987
13.50 754.0 312.0 235,265 5.401 2,076,185 47.663
Define Zones and Basin Geometry 14.00 758.0 316.0 239,545 5.499 2,194,886 50.388
Zone 1 Volume (WQCV) = 1.092 acre-feet 14.50 762.0 320.0 243,857 5.598 2,315,735 53.162
Zone 2 Volume (EURV - Zone 1) = 1.805 acre-feet 15.00 766.0 324.0 248,201 5.698 2,438,749 55.986
Zone 3 Volume (100-year - Zones 1 & 2) = 3.717 acre-feet 15.50 770.0 328.0 252,578 5.798 2,563,942 58.860
Total Detention Basin Volume = 6.614 acre-feet 16.00 774.0 332.0 256,986 5.900 2,691,332 61.784
Initial Surcharge Volume (ISV) = 143 ft 3 16.50 778.0 336.0 261,426 6.002 2,820,933 64.760
Initial Surcharge Depth (ISD) = 0.50 ft 17.00 782.0 340.0 265,898 6.104 2,952,763 67.786
Total Available Detention Depth (Htotal) = 4.50 ft 17.50 786.0 344.0 270,402 6.208 3,086,837 70.864
Depth of Trickle Channel (HTC) = 0.50 ft 18.00 790.0 348.0 274,938 6.312 3,223,171 73.994
Slope of Trickle Channel (STC) = 0.004 ft/ft 18.50 794.0 352.0 279,507 6.417 3,361,781 77.176
Slopes of Main Basin Sides (Smain) = 4 H:V 19.00 798.0 356.0 284,107 6.522 3,502,683 80.411
Basin Length-to-Width Ratio (RL/W) = 3 19.50 802.0 360.0 288,739 6.629 3,645,893 83.698
20.00 806.0 364.0 293,403 6.736 3,791,427 87.039
Initial Surcharge Area (AISV) =285 ft 2 20.50 810.0 368.0 298,099 6.843 3,939,301 90.434
Surcharge Volume Length (LISV) =16.9 ft 21.00 814.0 372.0 302,828 6.952 4,089,532 93.883
Surcharge Volume Width (WISV) =16.9 ft 21.50 818.0 376.0 307,588 7.061 4,242,134 97.386
Depth of Basin Floor (HFLOOR) =2.59 ft 22.00 822.0 380.0 312,380 7.171 4,397,125 100.944
Length of Basin Floor (LFLOOR) =674.8 ft 22.50 826.0 384.0 317,204 7.282 4,554,519 104.557
Width of Basin Floor (WFLOOR) =232.7 ft 23.00 830.0 388.0 322,060 7.393 4,714,334 108.226
Area of Basin Floor (AFLOOR) =157,034 ft 2 23.50 834.0 392.0 326,948 7.506 4,876,585 111.951
Volume of Basin Floor (VFLOOR) =141,599 ft 3 24.00 838.0 396.0 331,869 7.619 5,041,288 115.732
Depth of Main Basin (HMAIN) =0.91 ft 24.50 842.0 400.0 336,821 7.732 5,208,459 119.570
Length of Main Basin (LMAIN) =682.0 ft 25.00 846.0 404.0 341,805 7.847 5,378,114 123.465
Width of Main Basin (WMAIN) =240.0 ft 25.50 850.0 408.0 346,821 7.962 5,550,269 127.417
Area of Main Basin (AMAIN) =163,694 ft 2 26.00 854.0 412.0 351,869 8.078 5,724,940 131.427
Volume of Main Basin (VMAIN) =145,921 ft 3 26.50 858.0 416.0 356,949 8.194 5,902,143 135.495
Calculated Total Basin Volume (Vtotal) =6.607 acre-feet 27.00 862.0 420.0 362,062 8.312 6,081,895 139.621
27.50 866.0 424.0 367,206 8.430 6,264,210 143.806
28.00 870.0 428.0 372,382 8.549 6,449,106 148.051
28.50 874.0 432.0 377,590 8.668 6,636,598 152.355
29.00 878.0 436.0 382,830 8.789 6,826,701 156.719
29.50 882.0 440.0 388,102 8.910 7,019,433 161.144
30.00 886.0 444.0 393,407 9.031 7,214,809 165.629
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 4.02 (February 2020)
ExampleZone Configuration (Retention Pond)
Pond B (Future) - Full Spectrum Detention.xlsm, Basin 4/16/2020, 2:37 PM
Project:
Basin ID:
Estimated Estimated
Stage (ft) Volume (ac-ft) Outlet Type
Zone 1 (WQCV) 2.76 1.092 Orifice Plate
Zone 2 (EURV) 3.49 1.805 Orifice Plate
Zone 3 (100-year) 4.50 3.717 Weir&Pipe (Rect.)
Total (all zones) 6.614
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
Invert of Lowest Orifice = 0.00 ft (relative to basin bottom at Stage = 0 ft) WQ Orifice Area per Row = 2.535E-02 ft2
Depth at top of Zone using Orifice Plate = 3.49 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 = 3.65 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 1.16 2.33
Orifice Area (sq. inches) 3.65 3.65 3.65
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 = 3.49 N/A ft (relative to basin bottom at Stage = 0 ft)Height of Grate Upper Edge, Ht =4.74 N/A feet
Overflow Weir Front Edge Length = 15.00 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 = 5.85 N/A
Horiz. Length of Weir Sides = 5.00 N/A feet Overflow Grate Open Area w/o Debris = 69.58 N/A ft2
Overflow Grate Open Area % = 90% N/A %, grate open area/total area Overflow Grate Open Area w/ Debris = 55.66 N/A ft2
Debris Clogging % = 20% 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 Rectangular Not Selected Zone 3 Rectangular Not Selected
Depth to Invert of Outlet Pipe = 0.00 N/A ft (distance below basin bottom at Stage = 0 ft)Outlet Orifice Area = 11.90 N/A ft2
Rectangular Orifice Width = 46.80 N/A inches Outlet Orifice Centroid = 1.53 N/A feet
Rectangular Orifice Height = 36.60 inches Half-Central Angle of Restrictor Plate on Pipe = N/A N/A radians
User Input: Emergency Spillway (Rectangular or Trapezoidal)Calculated Parameters for Spillway
Spillway Invert Stage= 4.80 ft (relative to basin bottom at Stage = 0 ft) Spillway Design Flow Depth= 0.97 feet
Spillway Crest Length = 63.00 feet Stage at Top of Freeboard = 6.77 feet
Spillway End Slopes = 4.00 H:V Basin Area at Top of Freeboard = 4.15 acres
Freeboard above Max Water Surface = 1.00 feet Basin Volume at Top of Freeboard = 15.60 acre-ft
Max Ponding Depth of Target Storage Volume =4.74 feet Discharge at Top of Freeboard = 706.05 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 0.86 1.14 1.43 1.93 2.39 2.91 4.39
CUHP Runoff Volume (acre-ft) =1.092 2.897 2.010 3.140 4.619 7.669 10.340 13.604 22.571
Inflow Hydrograph Volume (acre-ft) =N/A N/A 2.010 3.140 4.619 7.669 10.340 13.604 22.571
CUHP Predevelopment Peak Q (cfs) =N/A N/A 0.7 7.6 19.8 51.7 75.2 105.7 182.4
OPTIONAL Override Predevelopment Peak Q (cfs) =N/A N/A
Predevelopment Unit Peak Flow, q (cfs/acre) =N/A N/A 0.01 0.11 0.30 0.77 1.12 1.58 2.72
Peak Inflow Q (cfs) =N/A N/A 26.1 42.0 61.5 109.1 145.5 189.9 307.1
Peak Outflow Q (cfs) =0.4 0.5 0.5 0.8 8.5 32.5 56.1 91.1 190.8
Ratio Peak Outflow to Predevelopment Q =N/A N/A N/A 0.1 0.4 0.6 0.7 0.9 1.0
Structure Controlling Flow =Plate Overflow Weir 1 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 0.0 0.1 0.5 0.8 1.3 1.6
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 80 61 85 86 83 80 76 66
Time to Drain 99% of Inflow Volume (hours) =40 83 63 88 91 90 89 87 84
Maximum Ponding Depth (ft) =2.76 3.49 3.14 3.52 3.77 4.16 4.42 4.74 5.35
Area at Maximum Ponding Depth (acres) =1.74 3.35 2.51 3.40 3.63 3.70 3.74 3.80 3.90
Maximum Volume Stored (acre-ft) =1.104 2.929 1.908 2.996 3.892 5.321 6.326 7.533 9.843
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 4.02 (February 2020)
Gateway at Prospect
Pond B (Future)
Example Zone Configuration (Retention Pond)
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)3 1 5yr, <72hr 1 1
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 277 Watershed Constraint Check
Count_OutletPipe2 = 0 0.50(diameter = 13/16 inch)2 Year 315 Slope 0.010
COUNTA_2 (Standard FSD Setup)= 1 0.58(diameter = 7/8 inch)EURV 350 Shape 1.92
Hidden Parameters & Calculations 0.67(diameter = 15/16 inch)5 Year 353
MaxPondDepth_Error? FALSE 0.76 (diameter = 1 inch)10 Year 378 Spillway Depth
Cd_Broad-Crested Weir 3.00 0.86(diameter = 1-1/16 inches)25 Year 417 0.97
WQ Plate Flow at 100yr depth = 0.69 0.97(diameter = 1-1/8 inches)50 Year 443
CLOG #1=72%1.08(diameter = 1-3/16 inches)100 Year 475 1 Z1_Boolean
Cdw #1 = 0.89 1.20(diameter = 1-1/4 inches)500 Year 536 1 Z2_Boolean
Cdo #1 = 0.69 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=0%1.59(diameter = 1-7/16 inches)Draintime Running
Cdw #2 = #VALUE! 1.73(diameter = 1-1/2 inches)Outlet Boolean Outlet Rank Total (1 to 4)
Cdo #2 = #VALUE! 1.88(diameter = 1-9/16 inches)Vertical Orifice 1 0 0
1
Overflow Weir #2 Angle =#VALUE!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 8.00 680,000 710
S-A-V-D Chart Axis Override X-axis Left Y-Axis Right Y-Axis
minimum bound
maximum bound
MHFD-Detention, Version 4.00 (December 2019)
DETENTION BASIN OUTLET STRUCTURE DESIGN
0
50
100
150
200
250
300
350
0.1 1 10FLOW [cfs]TIME [hr]
500YR IN
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
0
1
2
3
4
5
6
0.1 1 10 100PONDING DEPTH [ft]DRAIN TIME [hr]
500YR
100YR
50YR
25YR
10YR
5YR
2YR
EURV
WQCV
0
100
200
300
400
500
600
700
0
100,000
200,000
300,000
400,000
500,000
600,000
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 OUTFLOW [cfs]AREA [ft^2], VOLUME [ft^3]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]
Outflow Hydrograph Workbook Filename:.\Pond B - Outflow Hydrographs.xlsx
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 0.61 0.68 3.15
0:15:00 0.00 0.00 0.97 2.60 4.03 3.67 5.67 6.37 12.22
0:20:00 0.00 0.00 6.71 10.23 13.74 10.79 14.48 18.06 35.16
0:25:00 0.00 0.00 17.55 26.82 41.41 27.21 40.79 53.25 102.52
0:30:00 0.00 0.00 25.14 40.08 60.10 76.76 106.69 134.89 229.13
0:35:00 0.00 0.00 26.10 41.98 61.51 104.47 141.05 183.36 300.07
0:40:00 0.00 0.00 24.39 38.64 56.24 109.10 145.46 189.88 307.12
0:45:00 0.00 0.00 21.69 34.37 50.36 101.93 135.39 180.02 290.08
0:50:00 0.00 0.00 19.27 30.89 44.98 93.65 124.28 165.87 267.21
0:55:00 0.00 0.00 17.26 27.66 40.23 83.95 111.64 151.13 243.62
1:00:00 0.00 0.00 15.43 24.58 35.91 74.48 99.25 137.53 221.57
1:05:00 0.00 0.00 13.84 21.85 32.05 65.95 87.97 124.96 201.31
1:10:00 0.00 0.00 12.34 19.88 29.48 56.72 76.12 107.66 174.64
1:15:00 0.00 0.00 11.14 18.21 27.77 49.76 67.35 92.99 152.16
1:20:00 0.00 0.00 10.15 16.49 25.47 43.42 58.87 79.21 130.39
1:25:00 0.00 0.00 9.27 14.85 22.50 37.78 51.15 66.83 110.54
1:30:00 0.00 0.00 8.43 13.30 19.56 32.27 43.58 56.12 93.30
1:35:00 0.00 0.00 7.60 11.83 16.82 27.13 36.54 46.45 77.74
1:40:00 0.00 0.00 6.79 10.13 14.35 22.39 30.09 37.62 63.53
1:45:00 0.00 0.00 6.08 8.53 12.21 18.07 24.19 29.66 50.95
1:50:00 0.00 0.00 5.61 7.41 10.86 14.41 19.35 23.32 41.38
1:55:00 0.00 0.00 5.03 6.75 9.93 12.25 16.58 19.47 35.49
2:00:00 0.00 0.00 4.49 6.23 9.03 10.89 14.81 17.01 31.70
2:05:00 0.00 0.00 3.72 5.19 7.48 8.85 12.06 13.55 25.58
2:10:00 0.00 0.00 2.97 4.11 5.93 6.83 9.30 10.25 19.52
2:15:00 0.00 0.00 2.35 3.23 4.65 5.25 7.15 7.65 14.72
2:20:00 0.00 0.00 1.86 2.54 3.62 4.02 5.46 5.66 11.03
2:25:00 0.00 0.00 1.46 1.98 2.79 3.07 4.15 4.21 8.31
2:30:00 0.00 0.00 1.14 1.52 2.12 2.33 3.14 3.20 6.33
2:35:00 0.00 0.00 0.88 1.16 1.59 1.75 2.35 2.41 4.77
2:40:00 0.00 0.00 0.68 0.87 1.20 1.32 1.77 1.84 3.64
2:45:00 0.00 0.00 0.52 0.66 0.92 1.01 1.35 1.42 2.82
2:50:00 0.00 0.00 0.38 0.48 0.69 0.76 1.01 1.07 2.11
2:55:00 0.00 0.00 0.27 0.34 0.48 0.54 0.73 0.76 1.49
3:00:00 0.00 0.00 0.17 0.23 0.32 0.37 0.48 0.51 0.99
3:05:00 0.00 0.00 0.10 0.14 0.19 0.22 0.29 0.30 0.59
3:10:00 0.00 0.00 0.05 0.07 0.09 0.11 0.15 0.15 0.29
3:15:00 0.00 0.00 0.02 0.03 0.03 0.04 0.05 0.05 0.09
3:20:00 0.00 0.00 0.00 0.01 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
APPENDIX C
SWMM ANALYSIS OF BOXELDER CREEK