HomeMy WebLinkAboutTHE QUARRY BY WATERMARK - FDP210016 - SUBMITTAL DOCUMENTS - ROUND 3 - DRAINAGE REPORT
PRELIMINARY DRAINAGE REPORT
THE QUARRY BY WATERMARK
FORT COLLINS, COLORADO
October 20, 2021
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FORT COLLINS
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FORT COLLINS | GREELEY COVER LETTER
October 20, 2021
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, CO 80521
RE: PRELIMINARY DRAINAGE REPORT FOR
THE QUARRY BY WATERMARK
Dear Staff,
Northern Engineering is pleased to submit this Preliminary Drainage Report for your review. This report
accompanies the combined Preliminary Plan submittal for the proposed The Quarry by Watermark
This report has been prepared in accordance with the Fort Collins Stormwater Criteria Manual (FCSCM) and
serves to document the stormwater impacts associated with the proposed The Quarry by Watermark housing
project. We understand that review by the City of Fort Collins is to assure general compliance with standardized
criteria contained in the FCSCM.
If you should have any questions as you review this report, please feel free to contact us.
Sincerely,
NORTHERN ENGINEERING SERVICES, INC.
CASSANDRA UNGERMAN, EI DANNY WEBER, PE
Project Engineer Project Manager
I hereby attest that this report for the preliminary drainage design for The Quarry by Watermark was prepared by
me or under my direct supervision, in accordance with the provisions of the Fort Collins Stormwater Criteria
Manual. I understand that the City of Fort Collins does not and will not assume liability for drainage facilities
designed by others.
Registered professional engineer must affix their seal with signature and date. (for final report)
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FORT COLLINS | GREELEY TABLE OF CONTENTS
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION ................................................................ 1
II. DRAINAGE BASINS AND SUB-BASINS ..................................................................... 4
III. DRAINAGE DESIGN CRITERIA ................................................................................ 4
IV. DRAINAGE FACILITY DESIGN ................................................................................. 7
V. CONCLUSIONS .................................................................................................. 11
VI. REFERENCES .................................................................................................... 11
TABLES AND FIGURES
Figure 1 – Vicinity Map ........................................................................................................1
Figure 2 – Aerial Photograph ..............................................................................................2
Table 1 - Groundwater Elevations vs. Proposed Elevations………………………………3
Figure 3 – FEMA Firmette (Map Numbers 08069CO978G and 08069CO979H) ..................3
Table 2 - LID Summary………………………………………………………………………..6
Table 3 - Detention Summary………………………………………………………………10
Table 4 - Allowable Release Summary…………………………………………………….10
APPENDICES
APPENDIX A – HYDROLOGIC COMPUTATIONS
APPENDIX B – HYDRAULIC COMPUTATIONS
B.1 – Detention Ponds
B.2 – Water Quality
B.3 – Storm Sewers
B.4 – Inlets
B.5 – Overtopping Analysis
B.6 – Channels, Weirs, and Swales
B.7 – Erosion Control Mat Calculations
APPENDIX C – LID EXHIBIT
APPENDIX D – SWMM MODELING
APPENDIX E – USDA SOILS REPORT
APPENDIX F – FEMA FIRMETTE
MAP POCKET
DR1 – DRAINAGE EXHIBIT
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I. GENERAL LOCATION AND DESCRIPTION
A. LOCATION
Vicinity Map
Figure 1 – Vicinity Map
The Quarry by Watermark project site is located in the northwest quarter of Section 23, Township
7 North, Range 69 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer, State
of Colorado.
The project site (refer to Figure 1) is bordered to the north by Hobbit Street; to the east by Canal
Importation Ditch; to the south by Spring Creek; and to the west by Shields Street.
Spring Creek and Canal Importation Ditch are major drainageways located adjacent to the
project site. The confluence of Spring Creek and Canal Importation Ditch is in the southeast
corner of the site.
B. DESCRIPTION OF PROPERTY
The Quarry by Watermark comprises of ± 19.38 acres.
The site is currently an undeveloped parcel surrounded by multi-family to the north, west, and
south and single-family homes to the east.
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Figure 2 – Aerial Photograph
The existing groundcover consists of short grasses. The existing on-site runoff generally drains
from the northwest to the southeast across flat grades (e.g., <1.00%) into the Canal Importation
Ditch. From there, the drainage continues through Canal Importation Ditch to Spring Creek, and
on to the Cache La Poudre River.
According to the United States Department of Agriculture (USDA) Natural Resources
Conservation Service (NRCS) Soil Survey website:
(http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx),
the site consists primarily of Altvan-Satanta loams (Hydrologic Soil Group B) and Nunn clay loam
(Hydrological Soil Group C).
SpringCreek and Canal Importation Ditch are the only major drainageways within or adjacent to
the project site.
Groundwater was found to be present approximately 9-11 feet below existing ground elevations.
Proposed site development will maintain a minimum of 2 feet between these existing
groundwater levels and proposed ground levels. The highest amount of cut on the site occurs
where the proposed detention ponds will be located. In these locations we are cutting
approximately 5-7 feet which will allow for greater than 2 feet of separation between the pond
bottom and the existing groundwater levels. Table 1, below, shows elevations of existing ground,
groundwater, and proposed ground to demonstrate that minimum required separation is met.
The proposed development will consist of eight (8) apartment buildings and ten (10) duplex units
containing a total of 313 units with detached garages. Other proposed improvements include
parking lots, sidewalks, pool, clubhouse, and landscaping.
The proposed land use is multi-family. This is a permitted use in the Medium-Density Mixed-Use
Neighborhood District (MMN).
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Table 1 - Groundwater Elevations vs. Proposed Elevations
Pond 1 Pond 2
Existing Ground Elevation 5014.74 5017.29
Groundwater Elevation 5003.74 5006.29
Proposed Elevation 5008.06 5012.38
Note: These values are approximate based on borings provided for the site
C. FLOODPLAIN
1. The eastern and southern edges of the site are in a FEMA regulatory floodplain; however, the
developable project area is outside of the FEMA floodplain. In particular, the FEMA designated
100-year floodplain Basins E1 and E2 on the Drainage Exhibit include the FEMA regulatory
floodplains for Spring Creek and Canal Importation Ditch (Map Numbers 08069CO978G and
08069CO979H and effective date of May 2, 2012). The eastern portion on this site, along the Canal
Importation Ditch, is located within the City of Fort Collins Regulatory floodplain/floodway. No
development is proposed within Basins E1 and E2. A copy of the FEMA Firmette is provided in
Appendix G.
2. We have analyzed the FEMA Floodplain map and cross sections for Spring Creek and Canal
Importation Ditch and determined that the highest base flood elevation adjacent to the project
site is 5016 (NAVD88). Furthermore, the buildings all maintain a minimum of 12” between the
finished floor elevation and the top of bank along the south and east side of the property.
3. This project is in compliance with Chapter 10 of the City Municipal Code and a floodplain use
permit will be obtained for utility work in the floodplain/floodway.
Figure 3 – FEMA Firmette (Map Numbers 08069CO978G and 08069CO979H)
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II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
The north and east halves of The Quarry by Watermark is located within the City of Fort Collins Canal
Importation major drainage basin. The southwest quarter of the site is located within the City of Fort
Collins Spring Creek major drainage basin. Specifically, the project site is situated at the confluence
of the Spring Creek and Canal Importation major drainage basins. Detention requirements for this
basin are to detain the difference between the 100-yr developed inflow rate and the historic 2-year
release rate.
B. Sub-Basin Description
The outfall for the project site is at the confluence of Springs Creek and Canal Importation Basins.
The existing subject site can be defined with twelve (12) sub-basins that encompasses the entire
project site and three (3) offsite basins that drain onto the project site.
The existing site runoff generally drains from northwest-to-southeast and into the Canal
Importation Ditch.
The project site receives runoff from Shields Street and Hobbit Street.
III. DRAINAGE DESIGN CRITERIA
A. OPTIONAL PROVISIONS
There are no optional provisions outside of the FCSCM proposed with the Quarry by Watermark.
B. STORMWATER MANAGEMENT STRATEGY
The overall stormwater management strategy employed with The Quarry by Watermark 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. The first consideration taken in trying to reduce the
stormwater impacts of this development is the site selection itself. By choosing an already developed
site with public storm sewer currently in place, the burden is significantly less than developing a
vacant parcel absent of any infrastructure.
The Quarry by Watermark aims to reduce runoff peaks, volumes and pollutant loads from frequently
occurring storm events (i.e., water quality (i.e., 80th percentile) and 2-year storm events) by
implementing Low Impact Development (LID) strategies. Wherever practical, runoff will be routed
across landscaped areas or through a rain garden or water quality pond. These LID practices reduce
the overall amount of impervious area, while at the same time Minimizing Directly Connected
Impervious Areas (MDCIA). The combined LID/MDCIA techniques will be implemented, where
practical, throughout the development, thereby slowing runoff and increasing opportunities for
infiltration.
Step 2 – Implement BMPs that Provide a Water Quality Capture Volume (WQCV) with Slow
Release. The efforts taken in Step 1 will help to minimize excess runoff from frequently occurring
storm events; however, urban development of this intensity will still have stormwater runoff leaving
the site. The primary water quality treatment will occur between underground vaults located at the
south end of the project and a single rain garden along the east side of the property. The remaining
runoff will be treated for water quality in the proposed detention ponds along the Spring Creek.
Step 3 – Stabilize Drainageways. As stated in Section I.B.6, above, the Spring Creek and Canal
Importation drainage is adjacent to the subject site, however no changes to the channel are proposed
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with this project. While this step may not seem applicable to The Quarry by Watermark, the proposed
project indirectly helps achieve stabilized drainageways, nonetheless. Once again, site selection has a
positive effect on stream stabilization. By developing an infill site with stormwater infrastructure,
combined with LID and MDCIA strategies, the likelihood of bed and bank erosion and the frequency of
erosive flows are reduced. Furthermore, this project will pay one-time stormwater development fees,
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.
C. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS
The subject property is not part of any Overall Development Plan (ODP) drainage study or similar
“development/project” drainage master plan.
The site plan is constrained to the north and west by public streets, to the south by Spring Creek,
and to the east by the Canal Importation Ditch.
D. HYDROLOGICAL CRITERIA
The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as depicted in Figure 3.4-1
of the FCSCM, serve as the source for all hydrologic computations associated with The Quarry by
Watermark development. Tabulated data contained in Table 3.4-1 has been utilized for Rational
Method runoff calculations.
The Rational Method has been used to estimate peak developed stormwater runoff from
drainage basins within the developed site for the 2-year, 10-year, and 100-year design storms.
Peak runoff discharges determined using this methodology have been used to check the street
capacities, inlets, swales, and storm drain lines.
Two 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.
E. HYDRAULIC CRITERIA
The drainage facilities proposed with The Quarry by Watermark project are designed in
accordance with criteria outlined in the FCSCM.
As stated in Section I.C.1, above, the subject property is located next to a FEMA designated
floodplain but is not located within the floodplain limits.
F. FLOODPLAIN REGULATIONS COMPLIANCE
As previously mentioned, this project is adjacent to a FEMA regulated floodplain. The
developable area of the project is located outside of the floodplain, and as such, it will not be
subject to any floodplain regulations. However, two storm outfalls and a small portion of the
access trail will be located within the floodway, and that work will be subject to the applicable
floodplain regulations of Chapter 10 of the City Municipal Code.
Despite most of the project not being located within the floodplain, consideration has been given
to the floodplain elevations as they relate to the proposed buildings and the finished floors have
been elevated accordingly.
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G. MODIFICATIONS OF CRITERIA
There are no optional provisions outside of the FCSCM proposed with the Quarry by Watermark.
H. CONFORMANCE WITH WATER QUALITY TREATMENT CRITERIA
City Code requires that 100% of runoff from impervious surfaces in a project site shall receive some
sort of water quality treatment. This project proposes to provide water quality treatment using
several methods. A single rain garden will be located along the east edge of the site. Two separate
areas along the south side of the site will use underground chambers for treatment. Both areas will
discharge into two proposed detention ponds that will provide water quality for the remainder of the
site before discharge into the Canal Importation Basin. Due to the physical constraints associated
with an infill project of this nature and the prohibition of providing water quality facilities within the
public right-of-way, there are some small, narrow areas around the perimeter of the project that
cannot be captured. The uncaptured areas tend to be narrow strips of concrete flatwork that link the
building entrances to the public sidewalks as well as small planter beds between the building and
public sidewalks or property lines.
While these small areas will not receive formal water quality treatment, most areas will still see some
treatment as runoff is directed across through the landscaped areas or across the landscaped
parkways before reaching the roadway curb and gutter.
I. CONFORMANCE WITH LOW IMPACT DEVELOPMENT (LID)
The project site will conform with the requirement to treat a minimum of 75% of the project site using
a LID technique. A single rain garden and underground chambers will be used to capture and filter or
infiltrate the water quality capture volume.
J. SIZING OF LID FACILITIES
Rain Gardens/Underground Chambers
1. The rain gardens and chambers were sized by first determining the required water quality
capture volume (WQCV) for Basins B1-B10 for the rain garden and Basins A2 & D5-7 for the
chambers. A 12-hour drain time was used in this calculation.
2. Once the WQCV was identified, each rain garden and chamber area were sized for its respective
WQCV. The rain gardens will be constructed with a biomedia filter and underdrain. An
overflow drain will be provided in each rain garden and weir for chambers to pass storms
greater than the WQCV.
Water Quality Pond
1. The water quality pond was sized by first determining the required water quality capture
volume (WQCV) for Basins D1 and A1. Offsite flows from Basins OS1 and OS2 (Shields Street)
will be treated in the water quality ponds. A 40-hour drain time was used in this calculation.
The WQCV that resulted was approximately 9060 ft3, which includes the additional 20%
2. Once the WQCV was identified, the water quality pond was sized to provide the WQCV. An
outlet control structure with overflow will be provided to pass storms greater than the WQCV.
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Table 2 – LID Summary
LID ID Area (ft2) Weighted %
Impervious
Volume per
UD-BMP
(ft3)
Vol. w/ 20%
increase per
FC Manual
(ft3)
Impervious
area (ft2)
Rain Garden
A
318,413 71% 7,243 8,692 225,001
Stormtech 1 76,238 77% 1,578 1,894 58,703
Stormtech 2 81,341 58% 1,247 1,496 47,552
IV. DRAINAGE FACILITY DESIGN
A. GENERAL CONCEPT
1. The main objective of The Quarry by Watermark drainage design is to maintain existing
drainage patterns, while not adversely impacting adjacent properties.
2. All storm drains on the site have been designed to convey 100-yr flows, except storm line 1
which is designed for the 2-yr storm.
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. Drainage for the project site has been analyzed using twenty-five (25) onsite drainage sub-
basins, designated as sub-basins A1- A2, B1-B10, C1-C2, D1-D7, E1-E2, and F1-F2. Furthermore,
there are three (3) offsite drainage sub-basins designated as sub-basins OS1, OS2, and OS3.
The drainage patterns anticipated for the basins are further described below.
Sub-Basins A1
Sub-Basin A1 encompasses approximately 7% of the total site area. Basin A1 contains Detention
Pond 1 which is the collection point of all B sub-basins on site before release into the Canal
Importation Ditch. This pond, in conjunction with Detention Pond 2, will moderate the release
rate into the ditch during the Major Storm. An outlet structure with a restrictor plate will be
installed with Pond 1 and an outfall pipe will be used for the discharge into the Canal Importation
Ditch. Scour protection will be provided at the outfall into the ditch in order to lessen the site’s
impact on the ditch. Storm drain 5-2, which serves as the outfall for both detention ponds, has a
release rate of 1 cfs. Emergency Overflow from this pond will be directed into the Canal
Importation Ditch.
Sub-Basins A2
Sub-Basin A2 encompasses approximately 9% of the total site area. Basin A2 is comprised
primarily of roof area, concrete flatwork, parking lot and landscaped areas. This basin will drain
into a valley pan and curb and gutter located in the parking lot and be captured by an inlet and
storm drain. Sub-Basin A2 is the collection point of overflow from basins B1-B10. These overflows
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will pass over a series of weirs on their way to Sub-Basin A2 and ultimately drain to the inlet at DP
A2. Minor flows from this area will be treated by Stormtech Chambers 1, located just south of the
collection point. Major flows will bypass the Stormtech Chambers and proceed to Detention
Pond 1. Inlet 2-5 serves as the collection point for all flows and separates major and minor flows
using a weir inside the inlet. The top of weir elevation is set at the top of chamber elevation
(5011.55) to ensure the chambers are fully inundated before major flows are collected. All B
basins will be detained in the pond, but Sub-basin A2 will be passed through the spillway for
Pond 1 and will not be detained as part of the “area trade” as discussed in Section IV.B, below.
Sub-Basin B1 – B10
Sub-Basins B1 through B10 encompass approximately 36% the total site area. Basin B1, mainly
comprised of Rain Garden A, will be the main treatment method for the B sub-basins. Minor flows
will be treated in this rain garden, while flows from larger storms will proceed to Detention Pond
1 and to the Canal Importation ditch. An underdrain is proposed underneath Rain Garden A and
will outfall into the Canal Importation ditch. The remaining sub-basins (B2-B10) are comprised
primarily of roof area, concrete flatwork, parking lot, and landscaped areas. The sub-basins will
drain into a valley pan and curb & gutter located within each sub-basin and towards a common
storm sewer. This common storm sewer will discharge into Rain Garden A. Storm sewer 1,
which conveys flows for all B basins, is sized for the minor storm event. Excess flows will continue
through the site over a series of weirs and ultimately into basin A2 where minor flows will be
treated by Storm Chamber 1 and then continue to Detention Pond 1. Major flows will proceed to
Detention Pond 1 and then to the Canal Importation Ditch.
Sub-Basin C1
Sub-basin C1 is comprised of an existing ditch along the north property line (Ditch C). This
existing ditch conveys runoff from OS3 (Hobbit Street) and discharges directly into the Canal
Importation Ditch. This is an existing condition and there will be no added flows or change in
drainage patterns.
Sub-Basin C2
This sub-basin is comprised primarily of roof area, concrete flatwork, and landscaped areas.
Flows from the sub-basin will flow east into a proposed landscape drain and will be routed
through Storm sewer 1 to Rain Garden A. From Rain Garden A, flows will proceed to Detention
Pond 1, then to the Canal Importation.
Sub-Basin D1
Sub-Basin D1 encompasses approximately 5% the total site area. This basin contains Detention
Pond 2, which will collect runoff from Sub-Basins D, F, and the offsite flows from Shields (OS1 &
OS2). Detention Pond 2 will serve as the water quality pond for the remaining basins that are not
treated with LID. An outlet structure will be constructed with a water quality plate and restrictor
plate. The outfall for Pond 2 will discharge around Pond 1. The pond is designed to handle a total
inflow rate of approximately 49 cfs. Emergency overflow from detention pond 2 will flow through
the overflow channel and spill into detention pond 1 prior to discharging into the Canal
Importation Ditch.
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Sub-Basin D2
Sub-Basin D2 encompasses approximately 1% the total site area. This sub-basin is comprised
primarily of landscaped areas. No development is proposed in this area and flows from the sub-
basin will discharge directly into Spring Creek.
Sub-Basin D3
This sub-basin is comprised primarily of roof area, concrete flatwork, parking lot, and landscaped
areas. The sub-basin will drain into a common storm sewer via curb and gutter. The storm sewer
will collect drainage from Sub-Basins OS1 and OS2, and discharge into Detention Pond 2. This
storm drain will capture only the 2-year flows from these basins. The 100-yr flows will continue
into Sub-Basin D4 via overland flow and curb and gutter flow towards the sidewalk chase that
will direct flows to Detention Pond 2. Flows will then proceed to the Canal Importation Ditch.
Sub-Basin D4
Sub-basin D4 encompasses approximately 4% of the total site area and is comprised of roof area,
concrete flatwork, parking lot, and landscaped areas. Runoff from this basin flows via curb and
gutter and overland flow to a proposed sidewalk chase that ultimately conveys the flow to
Detention Pond 2. Flows will then proceed to the Canal Importation Ditch.
Sub-Basin D5-D7
Sub-Basins D5-D7 encompass approximately 9% the total site area. These sub-basins are
comprised primarily of roof area, concrete flatwork, parking lot, and landscaped areas. The sub-
basins will drain into a common storm sewer via valley pans and curb and gutter. The storm
sewer will collect drainage from all the sub-basins and discharge into Stormtech Chambers 2.
The WQCV will be captured in these chambers during minor storm events. Larger flows will
bypass the chamber weir, set at 5013.75, and discharge directly into Detention Pond 2. Flows
will then proceed to the Canal Importation Ditch. Storm sewer will be sized to convey major
storms.
Sub-Basin E1
Sub-basin E1 encompasses approximately 17% the total site area. This sub-basin comprises of
the Spring Creek flood plain. No improvements, except for storm sewer outfalls and a small
portion of the access trail, are proposed within this sub-basin.
Sub-Basin E2
Sub-basin E2 encompasses approximately 7% the total site area. This sub-basin comprises of the
Canal Importation flood plain. No improvements, except for storm sewer outfalls, are proposed
within this sub-basin.
Sub-Basins F1 & F2
Sub-basins F1 and F2 encompass approximately 1% the total site area. These sub-basins are
comprised primarily of concrete flatwork and landscaped areas. Flows from the sub-basin will
drain into curb and gutter along Shield Street. The curb and gutter will then convey the flows to
the intersection of Shields Street and Stuart Street (also the west entrance of the site), into Sub-
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Basins D3 and D4, and ultimately Detention Pond 2. Flows will then proceed to the Canal
Importation Ditch.
Sub-Basin OS1 & OS2
Offsite Sub-Basins OS1 and OS2 consist of the west edge of Shields Street that directly impacts
the project site. These sub-basins are comprised primarily of asphalt, concrete flatwork, and a
landscaped parkway. Flows from the sub-basin will drain into curb and gutter along Shields
Street. The curb and gutter will then convey the flows to the intersection of Shields Street and
Stuart Street (also the west entrance of the site), into Sub-Basins D3 and D4, and ultimately into
Water Quality Pond D. 1.7 of the 2.5 acres will be detained and treated in Pond 2. The remaining
0.8 acres will pass through the detention pond.
Sub-Basin OS3
Offsite Sub-Basin OS3 consists of Hobbit Street north of the project site. This sub-basin is
comprised primarily of asphalt and concrete flatwork. Flows from the sub-basin will drain into
curb and gutter along Hobbit Street. The curb and gutter will then convey the flows to Ditch C
and ultimately into the Canal Importation Ditch.
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of this report.
B. SPECIFIC DETAILS
Two detention ponds are proposed with this development and will detain up to the 100-yr storm
event and release at or below the caluclated release rate. A SWMM model was created to
determine the detention volumes. See Appendix C for more detail. See Table 3 for detention
summary and Table 4 for an allowable release summary.
Table 3 – Detention Summary
Table 4 – Allowable Release Summary
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LID treatment is being provided within Rain Garden A and Stormtech Chambers 1 & 2. These treat
approxmiately 85% of the site impervious runoff which is more than the required LID treatement
of 75%. Please see the LID exhibt and calculations in Appendix C. The remainder of water quality
will be provided by extended detention.
Detention allowable release rate is based on computed 2-year historic flow for the overall
property. We have added historic flow from Right-of-Way area in addition to the property. Basins
OS1 and OS2 (Please see Historic Drainage Exhibit), with a combined area of 2.28 acres, will be
taken into Pond 2 and will be detained. Thus, we have added 2-year historic flow from these
basins to the site allowable release. We proposed an “area trade” which allows for the free
release of developed basin A2, with an area of 1.75 acres. We will detain 1.75 acres of offsite
basins OS1 and OS2 (combined area of 2.28 acres), and in exchange, we will be allowed to free
release basin A2. Based on historic flow computations provided in the appendix, the summation
of onsite historic 2-year flow and 2-year flows from Basins OS1 and OS2 is 6.3 cfs (as summarized
in Table 3). We propose to release slightly below this rate as shown in Table 4, above.
Stormwater facility Standard Operations Procedures (SOP) will be provided by the City of Fort
Collins in the Development Agreement.
Final Design details, and construction documentation shall be provided to the City of Fort Collins
for review prior to Final Development Plan approval.
V. CONCLUSIONS
A. COMPLIANCE WITH STANDARDS
The drainage design proposed with The Quarry by Watermark complies with the City of Fort
Collins Master Drainage Plan for the Spring Creek and Canal Importation Basins.
The project is adjacent to the Spring Creek and Canal Importation FEMA regulatory floodplains.
However, the development is constructed outside of the floodplains, and buildings are located
18-inches above the base flood elevation. No improvements are proposed within the FEMA
regulated floodplains. All applicable provisions within Chapter 10 of the City Municipal Code
shall be adhered to.
The drainage plan and stormwater management measures proposed with The Quarry by
Watermark project are compliant with all applicable State and Federal regulations governing
stormwater discharge.
B. DRAINAGE CONCEPT
The drainage plan and stormwater management measures proposed with The Quarry by
Watermark project are compliant with all applicable State and Federal regulations governing
stormwater discharge.
The Quarry by Watermark will not impact the Master Drainage Plan recommendations for the
Canal Importation and Spring Creek major drainage basin.
NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE QUARRY BY WATERMARK
FORT COLLINS | GREELEY 12 | 29
VI. REFERENCES
Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, as adopted by Ordinance No. 159,
2018, and referenced in Section 26-500 of the City of Fort Collins Municipal Code.
Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation Service, United
States Department of Agriculture.
Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control District, Wright-
McLaughlin Engineers, Denver, Colorado, Revised April 2008.
NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE QUARRY BY WATERMARK
FORT COLLINS | GREELEY EROSION CONTROL REPORT
APPENDIX A
HYDROLOGIC COMPUTATIONS
Runoff
Coefficient 1
Percent
Impervious1
0.95 100%
0.95 90%
0.50 40%
0.50 40%
0.20 2%
0.20 2%
Basin ID Basin Area
(sq.ft.)
Basin Area
(acres)
Asphalt,
Concrete (acres)Rooftop (acres) Gravel (acres) Pavers (acres)
Undeveloped:
Greenbelts,
Agriculture
(acres)
Lawns, Clayey
Soil, Flat Slope <
2% (acres)
Percent
Impervious
C2*Cf
Cf = 1.00
C5*Cf
Cf = 1.00
C10*Cf
Cf = 1.00
C100*Cf
Cf = 1.25
H-A1 44,062 1.012 0.000 0.000 0.000 0.000 1.012 0.000 2%0.20 0.20 0.20 0.25
H-A2 6,773 0.155 0.000 0.000 0.000 0.000 0.155 0.000 2%0.20 0.20 0.20 0.25
H-B1 110,004 2.525 0.000 0.000 0.000 0.000 2.525 0.000 2%0.20 0.20 0.20 0.25
H-B2 170,633 3.917 0.015 0.000 0.000 0.000 3.902 0.000 2%0.20 0.20 0.20 0.25
H-B3 19,023 0.437 0.020 0.000 0.000 0.000 0.417 0.000 6%0.23 0.23 0.23 0.29
H-C1 32,204 0.739 0.000 0.000 0.000 0.000 0.739 0.000 2%0.20 0.20 0.20 0.25
H-C2 238,190 5.468 0.009 0.000 0.000 0.000 5.459 0.000 2%0.20 0.20 0.20 0.25
H-D1 7,509 0.172 0.000 0.000 0.000 0.000 0.172 0.000 2%0.20 0.20 0.20 0.25
H-E1 147,424 3.384 0.283 0.019 0.000 0.000 3.082 0.000 11%0.27 0.27 0.27 0.33
H-E2 60,287 1.384 0.143 0.002 0.000 0.000 1.239 0.000 12%0.28 0.28 0.28 0.35
H-F1 1,947 0.045 0.028 0.000 0.000 0.000 0.000 0.017 64%0.67 0.67 0.67 0.84
H-F2 7,695 0.177 0.094 0.000 0.000 0.000 0.000 0.082 54%0.60 0.60 0.60 0.75
OS1 21,067 0.484 0.407 0.000 0.000 0.000 0.000 0.077 84%0.83 0.83 0.83 1.00
OS2 78,428 1.800 1.706 0.000 0.000 0.000 0.000 0.094 95%0.91 0.91 0.91 1.00
Comb
OS1,
OS2 99,495 2.284 0.000 0.000 0.000 0.000 0.000 2.284 2%0.20 0.20 0.20 0.25
OS3 20,406 0.468 0.405 0.000 0.000 0.000 0.000 0.063 87%0.25 0.25 0.25 0.31
Total-
Onsite 630,531 14.475 0.167 0.000 0.000 0.000 14 0.099 3%0.20 0.20 0.20 0.25
Lawns and Landscaping:
Combined Basins
2) Composite Runoff Coefficient adjusted per Table 3.2-3 of the Fort Collins
Stormwater Manual (FCSM).
Lawns, Clayey Soil, Flat Slope < 2%
USDA SOIL TYPE: C
Undeveloped: Greenbelts, Agriculture Composite Runoff Coefficient 2
1) Runoff coefficients per Tables 3.2-1 & 3.2 of the FCSM. Percent impervious per Tables 4.1-2 & 4.1-3 of the FCSM.
EXISTING RUNOFF COEFFICIENT CALCULATIONS
Asphalt, Concrete
Rooftop
Gravel
Pavers
The Quarry by Watermark
A.Cvar
October 18, 2021
Project:
Calculations By:
Date:
Character of Surface
Streets, Parking Lots, Roofs, Alleys, and Drives:
Page 1 of 11
Project:
Date:
Where:
Length
(ft)
Elev
Up
Elev
Down
Slope
(%)
Ti
2-Yr
(min)
Ti
10-Yr
(min)
Ti
100-Yr
(min)
Length
(ft)
Elev
Up
Elev
Down
Slope
(%)Surface Roughness
(n)
Flow
Area3
(sq.ft.)
WP
3
(ft)
Hydraulic
Radius (ft)
Velocity
(ft/s)
Tt
(min)
Max.
Tc
(min)
Comp.
Tc 2-Yr
(min)
Tc
2-Yr
(min)
Comp.
Tc 10-Yr
(min)
Tc
10-Yr
(min)
Comp.
Tc 100-Yr
(min)
Tc
100-Yr
(min)
h-a1 H-A1 200 15.34 10.61 2.37%17.9 17.9 16.9 159 10.61 7.95 1.67%Swale (4:1)0.025 4.00 8.25 0.48 4.76 0.56 11.99 18.42 11.99 18.42 11.99 17.43 11.99
h-a2 H-A2 45 15.23 14.59 1.42%10.0 10.0 9.5 N/A Swale (4:1)4.00 8.25 N/A N/A 0.00 10.25 10.04 10.04 10.04 10.04 9.48 9.48
h-b1 H-B1 200 14.80 13.63 0.59%28.5 28.5 26.9 278 13.63 11.74 0.68%Swale (8:1)0.025 8.00 16.12 0.50 3.08 1.50 12.66 29.96 12.66 29.96 12.66 28.38 12.66
h-b2 H-B2 148 17.33 16.31 0.69%23.1 23.1 21.8 365 16.31 13.44 0.79%Swale (8:1)0.025 8.00 16.12 0.50 3.31 1.84 12.85 24.94 12.85 24.94 12.85 23.63 12.85
h-b3 H-B3 52 17.33 16.20 2.17%9.0 9.0 8.4 180 16.20 15.20 0.56%Swale (4:1)0.025 4.00 8.25 0.48 2.74 1.09 11.29 10.11 10.11 10.11 10.11 9.50 9.50
h-c1 H-C1 90 17.23 10.63 7.33%8.2 8.2 7.8 175 10.63 10.10 0.30%Swale (4:1)0.025 4.00 8.25 0.48 2.02 1.44 11.47 9.66 9.66 9.66 9.66 9.20 9.20
h-c2 H-C2 60 17.48 16.29 1.98%10.4 10.4 9.8 826 16.29 13.33 0.36%Swale (8:1)0.025 8.00 16.12 0.50 2.24 6.16 14.92 16.52 14.92 16.52 14.92 15.94 14.92
h-d1 H-D1 60 19.31 17.33 3.30%8.8 8.8 8.3 N/A Swale (4:1)4.00 8.25 N/A N/A 0.00 10.33 8.75 8.75 8.75 8.75 8.26 8.26
h-e1 H-E1 65 17.28 11.43 9.00%6.0 6.0 5.6 1272 11.43 3.16 0.65%Floodplain 0.045 46.50 23.32 1.99 4.23 5.01 17.43 11.05 11.05 11.05 11.05 10.57 10.57
h-e2 H-E2 40 14.10 7.58 16.30%3.8 3.8 3.5 735 7.58 4.17 0.46%Floodplain 0.035 18.00 13.00 1.38 3.60 3.40 14.31 7.23 7.23 7.23 7.23 6.91 6.91
h-f1 H-F1 22 18.47 17.99 2.18%2.9 2.9 1.8 175 17.99 17.00 0.57%Gutter 0.012 3.61 19.18 0.19 3.07 0.95 11.09 3.84 5.00 3.84 5.00 2.70 5.00
h-f2 H-F2 40 20.24 19.49 1.88%4.8 4.8 3.4 570 19.49 16.79 0.47%Gutter 0.012 3.61 19.18 0.19 2.81 3.38 13.39 8.18 8.18 8.18 8.18 6.74 6.74
os1 OS1 30 22.53 21.47 3.53%1.8 1.8 0.7 420 21.47 16.95 1.08%Gutter 0.012 3.61 19.18 0.19 4.23 1.65 12.50 3.47 5.00 3.47 5.00 2.33 5.00
os2 OS2 26 36.00 34.55 5.58%1.0 1.0 0.5 1738 34.55 16.79 1.02%Gutter 0.012 3.61 19.18 0.19 4.12 7.02 19.80 8.04 8.04 8.04 8.04 7.56 7.56
Comb
OS1,
OS2
Comb
OS1,
OS2
26 36.00 34.55 5.58% 5.9 5.9 5.9 1738 34.55 16.79 1.02% Gutter 0.012 3.61 19.18 0.19 4.12 7.02 19.80 12.94 12.94 12.94 12.94 12.94 12.94
os3 OS3 32 20.10 20.05 0.16%16.7 16.7 15.5 615 20.05 12.88 1.17%Gutter 0.012 3.61 19.18 0.19 4.40 2.33 13.59 19.02 13.59 19.02 13.59 17.79 13.59
Total-
Onsite
Total-
Onsite 62 20.17 17.96 3.56% 10.6 10.6 10.6 843 17.96 12.80 0.61% Swale (8:1) 0.025 8.00 16.12 0.50 2.92 4.81 15.03 15.41 15.03 15.41 15.03 15.41 15.03
R = Hydraulic Radius (feet)
S = Longitudinal Slope, feet/feet
Maximum Tc:
Combined Basins
Design
Point Basin
Overland Flow Channelized Flow Time of Concentration
Channelized Flow, Velocity:Channelized Flow, Time of Concentration:
V = Velocity (ft/sec)
n = Roughness Coefficient
October 18, 2021
EXISTING TIME OF CONCENTRATION COMPUTATIONS
Overland Flow, Time of Concentration:
Calculations By:
The Quarry by Watermark
A.Cvar
(Equation 3.3-2 per Fort Collins Stormwater Manual)=1.87 1.1 − ∗
=1.49 ∗
/∗(Equation 5-4 per Fort Collins Stormwater Manual)
=180 + 10
(Equation 3.3-5 per Fort Collins Stormwater Manual)
=∗ 60
(Equation 5-5 per Fort Collins Stormwater Manual)
Notes:
1) Add 5000 to all elevations.
2) Per Fort Collins Stormwater Manual, minimum Tc = 5 min.
3) Assume a water depth of 6" and a typical curb and gutter per Larimer County Urban Street Standard Detail 701 for curb and gutter channelized flow. Assume a water depth of 1', fixed side slopes, and a triangular swale section for grass
channelized flow. Assume a water depth of 1', 4:1 side slopes, and a 2' wide valley pan for channelized flow in a valley pan.
Page 2 of 11
Tc2 Tc10 Tc100 C2 C10 C100
I2
(in/hr)
I10
(in/hr)
I100
(in/hr)
Q2
(cfs)
Q10
(cfs)
Q100
(cfs)
h-a1 H-A1 1.012 11.99 11.99 11.99 0.20 0.20 0.25 2.09 3.57 7.29 0.4 0.7 1.8
h-a2 H-A2 0.155 10.04 10.04 9.48 0.20 0.20 0.25 2.21 3.78 8.03 0.1 0.1 0.3
h-b1 H-B1 2.525 12.66 12.66 12.66 0.20 0.20 0.25 2.02 3.45 7.04 1.0 1.7 4.4
h-b2 H-B2 3.917 12.85 12.85 12.85 0.20 0.20 0.25 2.02 3.45 7.04 1.6 2.7 7.0
h-b3 H-B3 0.437 10.11 10.11 9.50 0.23 0.23 0.29 2.21 3.78 8.03 0.2 0.4 1.0
h-c1 H-C1 0.739 9.66 9.66 9.20 0.20 0.20 0.25 2.26 3.86 8.03 0.3 0.6 1.5
h-c2 H-C2 5.468 14.92 14.92 14.92 0.20 0.20 0.25 1.90 3.24 6.62 2.1 3.6 9.1
h-d1 H-D1 0.172 8.75 8.75 8.26 0.20 0.20 0.25 2.35 4.02 8.38 0.1 0.1 0.4
h-e1 H-E1 3.384 11.05 11.05 10.57 0.27 0.27 0.33 2.13 3.63 7.57 1.9 3.3 8.6
h-e2 H-E2 1.384 7.23 7.23 6.91 0.28 0.28 0.35 2.52 4.31 9.06 1.0 1.7 4.4
h-f1 H-F1 0.045 5.00 5.00 5.00 0.67 0.67 0.84 2.85 4.87 9.95 0.1 0.1 0.4
h-f2 H-F2 0.177 8.18 8.18 6.74 0.60 0.60 0.75 2.40 4.10 9.06 0.3 0.4 1.2
os1 OS1 0.484 5.00 5.00 5.00 0.83 0.83 1.00 2.85 4.87 9.95 1.1 2.0 4.8
os2 OS2 1.800 8.04 8.04 7.56 0.91 0.91 1.00 2.40 4.10 8.59 3.9 6.7 15.5
Comb OS1, OS2 Comb OS1, OS2 2.284 12.94 12.94 12.94 0.20 0.20 0.25 2.02 3.45 7.04 0.9 1.6 4.0
os3 OS3 0.468 13.59 13.59 13.59 0.25 0.25 0.31 1.95 3.34 6.82 0.2 0.4 1.0
Total-Onsite Total-Onsite 14.475 15.03 15.03 15.03 0.20 0.20 0.25 1.87 3.19 6.52 5.4 9.2 23.6
Total-Onsite Basins Include: H-A1 H-A2 H-B1 H-B2 H-B3 H-C1 H-C2 H-F1 H-F2
EXISTING DIRECT RUNOFF COMPUTATIONS
Intensity Flow
The Quarry by Watermark
A.Cvar
October 18, 2021
Project:
Calculations By:
Date:
Rational Equation: Q = CiA (Equation 6-1 per MHFD)
Design
Point Basin Area
(acres)
Runoff C
Combined Basins
Intensity, I from Fig. 3.4.1 Fort Collins Stormwater Manual
Tc (Min)
Page 3 of 11
CHARACTER OF SURFACE1:
Percentage
Impervious
2-yr Runoff
Coefficient
10-yr Runoff
Coefficient
100-yr Runoff
Coefficient
Developed
Asphalt .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………100%0.95 0.95 1.19
Concrete .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………100%0.95 0.95 1.19
Rooftop .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………90%0.95 0.95 1.19
Gravel .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………40%0.50 0.50 0.63
Pavers .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………40%0.50 0.50 0.63
Landscape or Pervious Surface
Playgrounds .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………25%0.35 0.35 0.44
Lawns Clayey Soil .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………2%0.25 0.25 0.31
Lawns Sandy Soil .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………2%0.15 0.15 0.19
Notes:
Basin ID Basin Area
(ac)
Area of
Asphalt/Con
crete
(ac)
Area of
Concrete
(ac)
Area of
Rooftop
(ac)
Area of
Gravel
(ac)
Area of
Pavers
(ac)
Area of
Playgrounds
(ac)
Area of Lawns
(ac)
Composite
% Imperv.
2-year
Composite Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
A1 1.310 0.036 0.00 0.009 0.00 0.00 0.00 1.265 5%0.27 0.27 0.34
A2 1.761 1.220 0.00 0.133 0.00 0.00 0.00 0.408 77%0.79 0.79 0.98
B1 0.617 0.051 0.00 0.152 0.00 0.00 0.00 0.414 32%0.48 0.48 0.60
B2 0.536 0.248 0.00 0.191 0.00 0.00 0.00 0.097 79%0.82 0.82 1.00
B3 2.415 1.597 0.00 0.633 0.00 0.00 0.00 0.185 90%0.90 0.90 1.00
B4 0.288 0.241 0.00 0.022 0.00 0.00 0.00 0.025 91%0.89 0.89 1.00
B5 0.480 0.007 0.00 0.269 0.00 0.00 0.00 0.205 53%0.65 0.65 0.82
B6 0.868 0.576 0.00 0.292 0.00 0.00 0.00 0.000 97%0.95 0.95 1.00
B7 0.796 0.607 0.00 0.131 0.00 0.00 0.00 0.058 91%0.90 0.90 1.00
B8 0.491 0.037 0.00 0.241 0.00 0.00 0.00 0.213 53%0.65 0.65 0.81
B9 0.460 0.293 0.00 0.167 0.00 0.00 0.00 0.000 96%0.95 0.95 1.00
B10 0.206 0.050 0.00 0.020 0.00 0.00 0.00 0.136 34%0.49 0.49 0.61
C1 0.106 0.000 0.00 0.000 0.00 0.00 0.00 0.106 2%0.25 0.25 0.31
C2 0.162 0.007 0.00 0.080 0.00 0.00 0.00 0.075 50%0.62 0.62 0.78
D1 0.979 0.060 0.00 0.000 0.00 0.00 0.00 0.919 8%0.29 0.29 0.37
D2 0.219 0.000 0.00 0.000 0.00 0.00 0.00 0.219 2%0.25 0.25 0.31
D3 0.214 0.104 0.00 0.080 0.00 0.00 0.00 0.030 82%0.85 0.85 1.00
D4 0.768 0.600 0.00 0.130 0.00 0.00 0.00 0.038 93%0.92 0.92 1.00
D5 1.072 0.670 0.00 0.318 0.00 0.00 0.00 0.084 89%0.90 0.90 1.00
D6 0.068 0.009 0.00 0.033 0.00 0.00 0.00 0.026 58%0.69 0.69 0.86
D7 0.639 0.067 0.00 0.033 0.00 0.00 0.00 0.539 17%0.36 0.36 0.45
E1 3.384 0.283 0.00 0.270 0.00 0.00 0.00 0.000 16%0.16 0.16 0.19
E2 1.384 0.143 0.00 0.019 0.00 0.00 0.00 0.000 12%0.11 0.11 0.14
F1 0.045 0.028 0.00 0.002 0.00 0.00 0.00 0.015 67%0.72 0.72 0.90
F2 0.177 0.094 0.00 0.000 0.00 0.00 0.00 0.083 54%0.62 0.62 0.78
OS1 0.484 0.407 0.00 0.000 0.00 0.00 0.00 0.077 84%0.84 0.84 1.00
OS2 1.800 1.706 0.00 0.000 0.00 0.00 0.00 0.094 95%0.91 0.91 1.00
OS3 0.873 0.750 0.00 0.000 0.00 0.00 0.00 0.123 87%0.86 0.86 1.00
Detention Pond 1 (A1, B1-B10) 8.466 3.327 0.000 1.690 0.000 0.000 0.000 0.984 57% 0.59 0.59 0.74
Detention Pond 2 (OS1, OS2, D1,
D2, D3, D4, D5, D6, D7, F1, F2)6.464 4.495 0.004 0.596 0.000 0.000 0.000 2.246 79% 0.84 0.84 1.04
DEVELOPED 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
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 A1 0.27 0.34 5 5.00%2.0 1.9 570 1.61%0.015 0.59 8.88 1.1 13.2 3.1 2.9 5.0 5.0
a2 A2 0.79 0.98 50 2.00%3.3 1.3 915 0.50%0.015 0.59 4.95 3.1 15.4 6.3 4.3 6.3 5.0
b1 B1 0.48 0.60 240 2.46%13.3 10.7 0 N/A 0.015 N/A N/A N/A 11.3 13.3 10.7 11.3 10.7
b2 B2 0.82 1.00 60 5.00%2.4 0.8 87 1.03%0.015 0.59 7.11 0.2 10.8 2.6 1.1 5.0 5.0
b3 B3 0.90 1.00 130 2.46%3.2 1.6 610 0.79%0.015 0.59 6.20 1.6 14.1 4.8 3.2 5.0 5.0
b4 B4 0.89 1.00 40 2.00%2.0 0.9 162 0.68%0.015 0.59 5.76 0.5 11.1 2.4 1.4 5.0 5.0
b5 B5 0.65 0.82 50 2.80%4.2 2.6 51 1.06%0.038 0.50 2.54 0.3 10.6 4.6 3.0 5.0 5.0
b6 B6 0.95 1.00 96 2.29%2.1 1.4 227 0.97%0.015 0.59 6.88 0.5 11.8 2.6 1.9 5.0 5.0
b7 B7 0.90 1.00 62 2.29%2.2 1.1 250 0.60%0.015 0.59 5.43 0.8 11.7 3.0 1.9 5.0 5.0
b8 B8 0.65 0.81 10 17.10%1.0 0.7 291 0.42%0.015 0.59 4.54 1.1 11.7 2.1 1.7 5.0 5.0
b9 B9 0.95 1.00 90 2.69%1.9 1.3 43 0.49%0.015 0.59 4.88 0.1 10.7 2.1 1.4 5.0 5.0
b10 B10 0.49 0.61 70 3.23%6.5 5.2 0 N/A 0.015 0.59 N/A N/A 10.4 6.5 5.2 6.5 5.2
c1 C1 0.25 0.31 13 12.85%2.4 2.3 190 0.87%0.038 0.50 2.31 1.4 11.1 3.8 3.6 5.0 5.0
c2 C2 0.62 0.78 40 6.33%3.1 2.0 0 N/A 0.015 n/a N/A N/A 10.2 3.1 2.0 5.0 5.0
d1 D1 0.29 0.37 40 15.03%3.9 3.5 200 0.51%0.015 0.59 4.99 0.7 11.3 4.6 4.2 5.0 5.0
d2 D2 0.25 0.31 100 1.42%14.1 13.1 0 N/A 0.015 n/a N/A N/A 10.6 14.1 13.1 10.6 10.6
d3 D3 0.85 1.00 40 2.57%2.2 0.9 60 0.50%0.015 0.19 2.32 0.4 10.6 2.6 1.3 5.0 5.0
d4 D4 0.92 1.00 82 1.87%2.5 1.4 185 0.50%0.015 0.19 2.33 1.3 11.5 3.8 2.7 5.0 5.0
d5 D5 0.90 1.00 40 1.00%2.4 1.2 277 0.96%0.015 0.19 3.21 1.4 11.8 3.8 2.6 5.0 5.0
d6 D6 0.69 0.86 40 2.35%3.6 2.1 25 0.68%0.015 0.59 5.76 0.1 10.4 3.7 2.2 5.0 5.0
d7 D7 0.36 0.45 40 3.18%6.0 5.2 280 0.64%0.015 0.59 5.59 0.8 11.8 6.8 6.1 6.8 6.1
e1 E1 0.16 0.19 65 9.00%6.8 6.6 1272 0.65%0.056 1.99 3.39 6.2 17.4 13.1 12.8 13.1 12.8
e2 E2 0.11 0.14 40 16.30%4.6 4.5 735 0.46%0.044 1.38 2.86 4.3 14.3 8.9 8.8 8.9 8.8
f1 F1 0.72 0.90 22 2.18%2.6 1.4 175 0.57%0.015 0.19 2.47 1.2 11.1 3.8 2.5 5.0 5.0
f2 F2 0.62 0.78 40 1.88%4.6 3.1 570 0.47%0.015 0.19 2.26 4.2 13.4 8.8 7.3 8.8 7.3
os1 OS1 0.84 1.00 30 3.53%1.7 0.7 420 1.08%0.015 0.19 3.41 2.1 12.5 3.8 2.7 5.0 5.0
os2 OS2 0.91 1.00 26 5.58%1.0 0.5 1738 1.02%0.015 0.19 3.32 8.7 19.8 9.8 9.3 9.8 9.3
os3 OS3 0.86 1.00 18 2.06% 1.5 0.6 615 1.38% 0.015 0.19 3.85 2.7 13.5 4.2 3.3 5.0 5.0
DEVELOPED DIRECT TIME OF CONCENTRATION
Channelized Flow
Design
Point Basin
Overland Flow Time of Concentration
Frequency Adjustment Factor:
(Equation 3.3-2 FCSCM)
(Equation 5-5 FCSCM)
(Equation 5-4 FCSCM)
(Equation 3.3-5 FCSCM)
Table 3.2-3 FCSCM
Therefore Tc2=Tc10 Notes:
1) Add 5000 to all elevations.
2) Per Fort Collins Stormwater Manual, minimum Tc = 5 min.
3) Assume a water depth of 6" and a typical curb and gutter per Larimer County
Urban Street Standard Detail 701 for curb and gutter channelized flow. Assume a
water depth of 1', fixed side slopes, and a triangular swale section for grass
channelized flow. Assume a water depth of 1', 4:1 side slopes, and a 2' wide valley
pan for channelized flow in a valley pan.
Rational Method Equation:
Rainfall Intensity:
a1 A1 1.31 5.0 5.0 0.27 0.34 2.85 4.87 9.95 1.01 1.72 4.43
a2 A2 1.76 5.0 5.0 0.79 0.98 2.85 2.85 9.95 3.97 3.97 17.17
b1 B1 0.62 10.7 10.7 0.48 0.60 2.17 2.17 7.57 0.64 0.64 2.80
b2 B2 0.54 5.0 5.0 0.82 1.00 2.85 2.85 9.95 1.25 1.25 5.33
b3 B3 2.42 5.0 5.0 0.90 1.00 2.85 2.85 9.95 6.20 6.20 24.03
b4 B4 0.29 5.0 5.0 0.89 1.00 2.85 2.85 9.95 0.73 0.73 2.87
b5 B5 0.48 5.0 5.0 0.65 0.82 2.85 2.85 9.95 0.89 0.89 3.92
b6 B6 0.87 5.0 5.0 0.95 1.00 2.85 2.85 9.95 2.35 2.35 8.64
b7 B7 0.80 5.0 5.0 0.90 1.00 2.85 2.85 9.95 2.04 2.04 7.92
b8 B8 0.49 5.0 5.0 0.65 0.81 2.85 2.85 9.95 0.91 0.91 3.96
b9 B9 0.46 5.0 5.0 0.95 1.00 2.85 2.85 9.95 1.24 1.24 4.57
b10 B10 0.21 5.2 5.2 0.49 0.61 2.85 2.85 9.95 0.29 0.29 1.25
c1 C1 0.11 5.0 5.0 0.25 0.31 2.85 2.85 9.95 0.08 0.08 0.33
c2 C2 0.16 5.0 5.0 0.62 0.78 2.85 2.85 9.95 0.29 0.29 1.26
d1 D1 0.98 5.0 5.0 0.29 0.37 2.85 2.85 9.95 0.81 0.81 3.60
d2 D2 0.22 10.6 10.6 0.25 0.31 2.17 2.17 7.57 0.12 0.12 0.51
d3 D3 0.21 5.0 5.0 0.85 1.00 2.85 2.85 9.95 0.52 0.52 2.13
d4 D4 0.77 5.0 5.0 0.92 1.00 2.85 2.85 9.95 2.01 2.01 7.64
d5 D5 1.07 5.0 5.0 0.90 1.00 2.85 2.85 9.95 2.75 2.75 10.67
d6 D6 0.07 5.0 5.0 0.69 0.86 2.85 2.85 9.95 0.13 0.13 0.58
d7 D7 0.64 6.1 6.1 0.36 0.45 2.67 2.67 9.31 0.61 0.61 2.68
e1 E1 3.38 12.8 12.8 0.16 0.19 2.02 2.02 7.04 1.09 1.09 4.53
e2 E2 1.38 8.8 8.8 0.11 0.14 2.35 2.35 8.21 0.36 0.36 1.59
f1 F1 0.05 5.0 5.0 0.72 0.90 2.85 2.85 9.95 0.09 0.09 0.40
f2 F2 0.18 7.3 7.3 0.62 0.78 2.52 2.52 8.80 0.28 0.28 1.21
os1 OS1 0.48 5.0 5.0 0.84 1.00 2.85 2.85 9.95 1.16 1.16 4.82
os2 OS2 1.80 9.3 9.3 0.91 1.00 2.30 2.30 8.03 3.77 3.77 14.45
os3 OS3 0.87 5.0 5.0 0.86 1.00 2.85 2.85 9.95 2.14 2.14 8.69
Tc100
(min)
Intensity,
i2
(in/hr)
Intensity,
i100
(in/hr)
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
Intensity,
i10
(in/hr)
Flow,
Q10
(cfs)
()()()AiCCQf=
NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE QUARRY BY WATERMARK
FORT COLLINS | GREELEY APPENDIX
APPENDIX B
HYDRAULIC COMPUTATIONS
NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE QUARRY BY WATERMARK
FORT COLLINS | GREELEY APPENDIX
B.1 – Detention Ponds
Pond Stage-Storage Curve
Pond: 1
Project: 1791-001
By: CLU
Date: 10/18/21
Stage
(FT)
Contour Area
(SF)
Volume
(CU.FT.)
Volume
(AC-FT)
5006.80 2.47 0.00 0.00
5007.00 540.42 38.63 0.00
5007.20 1682.33 250.38 0.01
5007.40 3357.73 744.83 0.02
5007.60 5668.22 1637.40 0.04
5007.80 8663.48 3060.02 0.07
5008.00 12229.92 5139.14 0.12
5008.20 15000.13 7857.43 0.18
5008.40 17067.89 11062.01 0.25
5008.60 18482.35 14616.10 0.34
5008.80 19183.36 18382.45 0.42
5009.00 19807.07 22281.33 0.51
5009.20 20413.20 26303.20 0.60
5009.40 20996.32 30444.02 0.70
5009.60 21565.35 34700.06 0.80
5009.80 22114.54 39067.93 0.90
5010.00 22630.95 43542.38 1.00
5010.20 23367.81 48142.06 1.11
5010.40 24489.98 52927.40 1.22
5010.60 25657.31 57941.67 1.33
5010.80 26634.08 63170.51 1.45
5011.00 27443.71 68578.09 1.57
5011.20 27992.41 74121.61 1.70
5011.40 28545.43 79775.30 1.83 100-YR WSEL
5011.60 29101.90 85539.94 1.96
5011.80 29662.54 91416.30 2.10
Pond Stage-Storage Curve
Pond: 2
Project: 1791-001
By: CLU
Date: 10/18/21
Stage
(FT)
Contour Area
(SF)
Volume
(CU.FT.)
Volume
(AC-FT)
5011.00 13.48 0.00 0.00
5011.20 266.06 22.63 0.00
5011.40 722.70 117.78 0.00
5011.60 1641.13 347.97 0.01
5011.80 2919.21 797.91 0.02
5012.00 4473.39 1531.67 0.04
5012.20 5816.26 2557.70 0.06 WQ Elevation
5012.40 6984.68 3836.01 0.09
5012.60 8060.75 5339.27 0.12
5012.80 9055.19 7049.90 0.16
5013.00 10006.64 8955.29 0.21
5013.20 10893.75 11044.70 0.25
5013.40 11658.44 13299.48 0.31
5013.60 12380.18 15702.99 0.36
5013.80 13121.41 18252.79 0.42
5014.00 13883.39 20952.91 0.48
5014.20 14668.97 23807.78 0.55
5014.40 15484.34 26822.75 0.62
5014.60 16402.04 30010.94 0.69
5014.80 17338.60 33384.57 0.77
5015.00 18403.47 36958.20 0.85
5015.20 20897.84 40885.74 0.94
5015.40 23715.17 45344.08 1.04
100-YR WSEL
Quarry by Watermark
ORIFICE RATING CURVE
Pond 1
100-yr Orifice
Project:Quarry by Watermark
Date:10/18/2021
By:C. Ungerman
100-yr WSEL=5011.37
Orifice Plate
Outflow Q 1 cfs
Orifice Coefficient Cd 0.65
Gravity Constant g 32.2 ft/s^2
100-year head H 4.62 ft
Orifice Area Ao 0.09 ft^2
Orifice Area Ao 12.84 in^2
Radius r 2.0 in
Diameter d 4.0 in
Orifice Curve
Stage (ft)H (ft) Q (cfs) SWMM Stage Note
5006.75 0.00 0.00 0.00 Pond Invert
5006.95 0.20 0.21 0.20
5007.15 0.40 0.29 0.40
5007.35 0.60 0.36 0.60
5007.55 0.80 0.42 0.80
5007.75 1.00 0.47 1.00
5007.95 1.20 0.51 1.20
5008.15 1.40 0.55 1.40
5008.35 1.60 0.59 1.60
5008.55 1.80 0.62 1.80
5008.75 2.00 0.66 2.00
5008.95 2.20 0.69 2.20
5009.15 2.40 0.72 2.40
5009.35 2.60 0.75 2.60
5009.55 2.80 0.78 2.80
5009.75 3.00 0.81 3.00
5009.95 3.20 0.83 3.20
5010.15 3.40 0.86 3.40
5010.35 3.60 0.88 3.60
5010.55 3.80 0.91 3.80
5010.75 4.00 0.93 4.00
5010.95 4.20 0.95 4.20
5011.15 4.40 0.98 4.40
5011.35 4.60 1.00 4.60
5011.37 4.62 1.00 4.62 100-yr WSEL
10/18/2021 1:15 PM P:\1791-001\Drainage\Detention\1791-001_Pond 1 100-yr Restrictor\Orifice Size
Quarry by Watermark
ORIFICE RATING CURVE
Pond 2
100-yr Orifice
Project:Quarry by Watermark
Date:10/18/2021
By:C. Ungerman
100-yr WSEL=5014.91
Orifice Plate
Outflow Q 5.4 cfs
Orifice Coefficient Cd 0.65
Gravity Constant g 32.2 ft/s^2
100-year head H 4.00 ft
Orifice Area Ao 0.52 ft^2
Orifice Area Ao 74.54 in^2
Radius r 4.9 in
Diameter d 9.7 in
Orifice Curve
Stage (ft)H (ft) Q (cfs) SWMM Stage Note
5010.91 0.00 0.00 0.00 Pond Invert
5011.11 0.20 1.21 0.20
5011.31 0.40 1.71 0.40
5011.51 0.60 2.09 0.60
5011.71 0.80 2.41 0.80
5011.91 1.00 2.70 1.00
5012.11 1.20 2.96 1.20
5012.31 1.40 3.19 1.40
5012.51 1.60 3.42 1.60
5012.71 1.80 3.62 1.80
5012.91 2.00 3.82 2.00
5013.11 2.20 4.00 2.20
5013.31 2.40 4.18 2.40
5013.51 2.60 4.35 2.60
5013.71 2.80 4.52 2.80
5013.91 3.00 4.68 3.00
5014.11 3.20 4.83 3.20
5014.31 3.40 4.98 3.40
5014.51 3.60 5.12 3.60
5014.71 3.80 5.26 3.80
5014.91 4.00 5.40 4.00 100-yr WSEL
10/18/2021 1:16 PM P:\1791-001\Drainage\Detention\1791-001_Pond 2 100-yr Restrictor\Orifice Size
NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE QUARRY BY WATERMARK
FORT COLLINS | GREELEY APPENDIX
B.2 – Water Quality
Project:
Basin ID:
Depth Increment = 0.20 ft
Watershed Information Top of Micropool -- 0.00 -- -- -- 13 0.000
Selected BMP Type =EDB Note: L / W Ratio > 8 -- 0.20 -- -- -- 266 0.006 28 0.001
Watershed Area = 6.45 acres L / W Ratio = 12.19 -- 0.40 -- -- -- 723 0.017 127 0.003
Watershed Length = 1,850 ft -- 0.60 -- -- -- 1,641 0.038 363 0.008
Watershed Length to Centroid = 925 ft -- 0.80 -- -- -- 2,919 0.067 819 0.019
Watershed Slope = 0.011 ft/ft -- 1.00 -- -- -- 4,473 0.103 1,558 0.036
Watershed Imperviousness = 79.00% percent -- 1.20 -- -- -- 5,816 0.134 2,587 0.059
Percentage Hydrologic Soil Group A = 7.5% percent -- 1.40 -- -- -- 6,985 0.160 3,867 0.089
Percentage Hydrologic Soil Group B = 69.8% percent -- 1.60 -- -- -- 8,061 0.185 5,372 0.123
Percentage Hydrologic Soil Groups C/D = 22.7% percent -- 1.80 -- -- -- 9,055 0.208 7,084 0.163
Target WQCV Drain Time = 40.0 hours -- 2.00 -- -- -- 10,007 0.230 8,990 0.206
Location for 1-hr Rainfall Depths = Denver - Capitol Building -- 2.20 -- -- -- 10,894 0.250 11,080 0.254
-- 2.40 -- -- -- 11,658 0.268 13,335 0.306
-- 2.60 -- -- -- 12,380 0.284 15,739 0.361
Optional User Overrides -- 2.80 -- -- -- 13,121 0.301 18,289 0.420
Water Quality Capture Volume (WQCV) =0.208 acre-feet 0.208 acre-feet -- 3.00 -- -- -- 13,883 0.319 20,990 0.482
Excess Urban Runoff Volume (EURV) =0.558 acre-feet 0.558 acre-feet -- 3.20 -- -- -- 14,669 0.337 23,845 0.547
2-yr Runoff Volume (P1 = 0.82 in.) = 0.327 acre-feet 0.82 inches -- 3.40 -- -- -- 15,484 0.355 26,860 0.617
5-yr Runoff Volume (P1 = 1.14 in.) = 0.481 acre-feet 1.14 inches -- 3.60 -- -- -- 16,402 0.377 30,049 0.690
10-yr Runoff Volume (P1 = 1.4 in.) = 0.619 acre-feet 1.40 inches -- 3.80 -- -- -- 17,339 0.398 33,423 0.767
25-yr Runoff Volume (P1 = 1.81 in.) = 0.861 acre-feet 1.81 inches -- 4.00 -- -- -- 18,403 0.422 36,997 0.849
50-yr Runoff Volume (P1 = 2.27 in.) = 1.122 acre-feet 2.27 inches -- 4.20 -- -- -- 20,898 0.480 40,927 0.940
100-yr Runoff Volume (P1 = 2.86 in.) = 1.470 acre-feet 2.86 inches -- 4.40 -- -- -- 23,715 0.544 45,388 1.042
500-yr Runoff Volume (P1 = 4.39 in.) = 2.360 acre-feet 4.39 inches -- -- -- --
Approximate 2-yr Detention Volume = 0.308 acre-feet -- -- -- --
Approximate 5-yr Detention Volume = 0.452 acre-feet -- -- -- --
Approximate 10-yr Detention Volume = 0.579 acre-feet -- -- -- --
Approximate 25-yr Detention Volume = 0.706 acre-feet -- -- -- --
Approximate 50-yr Detention Volume = 0.818 acre-feet -- -- -- --
Approximate 100-yr Detention Volume = 0.974 acre-feet -- -- -- --
-- -- -- --
Define Zones and Basin Geometry -- -- -- --
Zone 1 Volume (WQCV) = 0.208 acre-feet -- -- -- --
Zone 2 Volume (EURV - Zone 1) = 0.350 acre-feet -- -- -- --
Zone 3 Volume (100-year - Zones 1 & 2) = 0.416 acre-feet -- -- -- --
Total Detention Basin Volume = 0.974 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 -- -- -- --
--------
--------
--------
--------
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)
The Quarry by Watermark
MHFD-Detention, Version 4.04 (February 2021)
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)
Quarry_MHFD-Detention_v4 04, Basin 10/18/2021, 1:19 PM
Project:
Basin ID:
Estimated Estimated
Stage (ft) Volume (ac-ft) Outlet Type
Zone 1 (WQCV) 2.01 0.208 Orifice Plate
Zone 2 (EURV) 3.24 0.350 Not Utilized
Zone 3 (100-year) 4.28 0.416 Circular Orifice
Total (all zones) 0.974
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 = 8.333E-04 ft2
Depth at top of Zone using Orifice Plate = 2.01 ft (relative to basin bottom at Stage = 0 ft) Elliptical Half-Width = N/A feet
Orifice Plate: Orifice Vertical Spacing = 8.00 inches Elliptical Slot Centroid = N/A feet
Orifice Plate: Orifice Area per Row = 0.12 sq. inches (diameter = 3/8 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 0.70 1.40
Orifice Area (sq. inches) 0.12 0.12 0.12
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
Zone 3 Circular Not Selected Zone 3 Circular Not Selected
Invert of Vertical Orifice = 3.24 N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Area = N/A ft2
Depth at top of Zone using Vertical Orifice = 4.28 N/A ft (relative to basin bottom at Stage = 0 ft) Vertical Orifice Centroid = N/A feet
Vertical Orifice Diameter = 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 Not Selected Not Selected Not Selected Not Selected
Overflow Weir Front Edge Height, Ho = N/A N/A ft (relative to basin bottom at Stage = 0 ft)Height of Grate Upper Edge, Ht =N/A N/A feet
Overflow Weir Front Edge Length = N/A N/A feet Overflow Weir Slope Length = N/A N/A feet
Overflow Weir Grate Slope = N/A N/A H:V Grate Open Area / 100-yr Orifice Area = N/A N/A
Horiz. Length of Weir Sides = N/A N/A feet Overflow Grate Open Area w/o Debris = N/A N/A ft2
Overflow Grate Type = N/A N/A Overflow Grate Open Area w/ Debris = N/A N/A ft2
Debris Clogging % = N/A 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
Not Selected Not Selected Not Selected Not Selected
Depth to Invert of Outlet Pipe = N/A N/A ft (distance below basin bottom at Stage = 0 ft)Outlet Orifice Area = N/A N/A ft2
Circular Orifice Diameter = N/A N/A inches Outlet Orifice Centroid = N/A N/A feet
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= ft (relative to basin bottom at Stage = 0 ft) Spillway Design Flow Depth= feet
Spillway Crest Length = feet Stage at Top of Freeboard = feet
Spillway End Slopes = H:V Basin Area at Top of Freeboard = acres
Freeboard above Max Water Surface = feet Basin Volume at Top of Freeboard = acre-ft
Max Ponding Depth of Target Storage Volume =4.40 feet Discharge at Top of Freeboard =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) =0.208 0.558 0.327 0.481 0.619 0.861 1.122 1.470 2.360
Inflow Hydrograph Volume (acre-ft) =N/A N/A 0.327 0.481 0.619 0.861 1.122 1.470 2.360
CUHP Predevelopment Peak Q (cfs) =N/A N/A 0.0 0.1 0.5 1.8 2.9 4.8 8.9
OPTIONAL Override Predevelopment Peak Q (cfs) =N/A N/A
Predevelopment Unit Peak Flow, q (cfs/acre) =N/A N/A 0.00 0.01 0.08 0.28 0.46 0.74 1.38
Peak Inflow Q (cfs) =N/A N/A 2.9 4.2 5.4 8.2 10.7 14.0 22.3
Peak Outflow Q (cfs) =0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Ratio Peak Outflow to Predevelopment Q =N/A N/A N/A 0.2 0.0 0.0 0.0 0.0 0.0
Structure Controlling Flow =Plate Plate Plate Plate Plate Plate N/A N/A N/A
Max Velocity through Grate 1 (fps) =N/A N/A N/A N/A N/A N/A N/A N/A N/A
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) =>120 >120 >120 >120 >120 >120 >120 >120 >120
Time to Drain 99% of Inflow Volume (hours) =>120 >120 >120 >120 >120 >120 >120 >120 >120
Maximum Ponding Depth (ft) =2.01 3.24 2.46 2.98 3.39 4.01 4.40 4.40 4.40
Area at Maximum Ponding Depth (acres) =0.23 0.34 0.27 0.32 0.35 0.43 0.54 0.54 0.54
Maximum Volume Stored (acre-ft) =0.209 0.561 0.322 0.475 0.613 0.854 1.042 1.042 1.042
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 4.04 (February 2021)
The Quarry by Watermark
Example Zone Configuration (Retention Pond)
Quarry_MHFD-Detention_v4 04, Outlet Structure 10/18/2021, 1:23 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 2 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)1 1 5yr, <72hr 0
Count_Weir1 = 0 0.29(diameter = 5/8 inch)>5yr, <120hr 0
Count_Weir2 = 0 0.36(diameter = 11/16 inch)Max Depth Row
Count_OutletPipe1 = 0 0.42(diameter = 3/4 inch)WQCV 202 Watershed Constraint Check
Count_OutletPipe2 = 0 0.50(diameter = 13/16 inch)2 Year 247 Slope 0.011
COUNTA_2 (Standard FSD Setup)= 0 0.58(diameter = 7/8 inch)EURV 325 Shape 6.00
Hidden Parameters & Calculations 0.67(diameter = 15/16 inch)5 Year 299
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 402
WQ Plate Flow at 100yr depth = 0.02 0.97(diameter = 1-1/8 inches)50 Year 441
CLOG #1= N/A 1.08(diameter = 1-3/16 inches)100 Year 441 1 Z1_Boolean
n*Cdw #1 = N/A 1.20(diameter = 1-1/4 inches)500 Year 441 1 Z2_Boolean
n*Cdo #1 = N/A 1.32(diameter = 1-5/16 inches)Zone3_Pulldown Message 0 Z3_Boolean
Overflow Weir #1 Angle = N/A 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
0
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 0 0 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 0 0 0 Freeboard
2.72(diameter = 1-7/8 inches)Outlet Pipe 2 0 0 0 Spillway
Count_User_Hydrographs 0 2.90(diameter = 1-15/16 inches)0 Spillway Length
CountA_3 (EURV & 100yr) = 0 3.09(diameter = 2 inches)FALSE Time Interval
CountA_4 (100yr Only) = 0 3.29(use rectangular openings)Button Visibility Boolean
COUNTA_5 (FSD Weir Only)= 0 0 WQCV Underdrain
COUNTA_6 (EURV Weir Only)= 0 1 WQCV Plate
0 EURV-WQCV Plate
Outlet1_Pulldown_Boolean 0 EURV-WQCV VertOriice
Outlet2_Pulldown_Boolean 0 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 50,000 10
S-A-V-D Chart Axis Override X-axis Left Y-Axis Right Y-Axis
minimum bound
maximum bound
MHFD-Detention, Version 4.04 (February 2021)
DETENTION BASIN OUTLET STRUCTURE DESIGN
0
5
10
15
20
25
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
0.5
1
1.5
2
2.5
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3.5
4
4.5
5
0.1 1 10 100PONDING DEPTH [ft]DRAIN TIME [hr]
500YR
100YR
50YR
25YR
10YR
5YR
2YR
EURV
WQCV
0
1
2
3
4
5
6
7
8
9
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0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
45,000
50,000
0.00 1.00 2.00 3.00 4.00 5.00 6.00 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]
Quarry_MHFD-Detention_v4 04, Outlet Structure 10/18/2021, 1:24 PM
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia =72.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100)i = 0.720
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.23 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 318,413 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 =7,243 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 =4585 sq ft
D) Actual Flat Surface Area AActual =6646 sq ft
E) Area at Design Depth (Top Surface Area)ATop =7973 sq ft
F) Rain Garden Total Volume VT=7,310 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)
C. Ungerman
October 18, 2021
The Quarry
Rain Garden A
UD-BMP (Version 3.07, March 2018)
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
Rain Garden A_UD-BMP_v3.07, RG 10/18/2021, 1:26 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)
C. Ungerman
October 18, 2021
The Quarry
Rain Garden A
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
Rain Garden A_UD-BMP_v3.07, RG 10/18/2021, 1:26 PM
Project Title Date:
Project Number Calcs By:
City
Basins
0.8
WQCV = Watershed inches of Runoff (inches)77%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100)0.248 in
A =1.75 ac
V = 0.0362 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
1894 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
The Quarry October 18, 2021
1791-001 C. Ungerman
Fort Collins
Stormtech Chambers 1 (A2)
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
00.10.20.30.40.50.60.70.80.91WQCV (watershed inches)Total Imperviousness Ratio (i = Iwq/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
()iii78.019.10.91aWQCV 23 +-=
()iii78.019.10.91aWQCV 23 +-=
AV*
12
WQCV
=
12 hr
Project Title Date:
Project Number Calcs By:
City
Basins
0.8
WQCV = Watershed inches of Runoff (inches)58%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100)0.184 in
A =1.87 ac
V = 0.0286 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
1496 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
The Quarry October 18, 2021
1791-001 C. Ungerman
Fort Collins
Stormtech Chambers 2 (D5, D6, D7)
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
00.10.20.30.40.50.60.70.80.91WQCV (watershed inches)Total Imperviousness Ratio (i = Iwq/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
()iii78.019.10.91aWQCV 23 +-=
()iii78.019.10.91aWQCV 23 +-=
AV*
12
WQCV
=
12 hr
Pond No :
A2
WQ
0.99
5.00 min 1313 ft3
1.75 acres 0.03 ac-ft
Max Release Rate =0.68 cfs
Time (min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
QWQ
(cfs)
Outflow Volume
(ft3)
Storage Volume
(ft3)
5 1.425 741 1.00 0.68 204 537
10 1.105 1149 1.00 0.68 408 741
15 0.935 1458 0.67 0.45 408 1050
20 0.805 1674 0.63 0.43 510 1164
25 0.715 1858 0.60 0.41 612 1246
30 0.650 2027 0.58 0.40 714 1313
35 0.585 2128 0.57 0.39 816 1312
40 0.535 2225 0.56 0.38 918 1307
45 0.495 2315 0.56 0.38 1020 1295
50 0.460 2391 0.55 0.37 1122 1269
55 0.435 2487 0.55 0.37 1224 1263
60 0.410 2557 0.54 0.37 1326 1231
65 0.385 2601 0.54 0.37 1428 1173
70 0.365 2656 0.54 0.36 1530 1126
75 0.345 2690 0.53 0.36 1632 1058
80 0.330 2744 0.53 0.36 1734 1010
85 0.315 2783 0.53 0.36 1836 947
90 0.305 2853 0.53 0.36 1938 915
95 0.290 2864 0.53 0.36 2040 824
100 0.280 2911 0.53 0.36 2142 769
105 0.270 2947 0.52 0.36 2244 703
110 0.260 2973 0.52 0.36 2346 627
115 0.255 3048 0.52 0.35 2448 600
120 0.245 3056 0.52 0.35 2550 506
*Note: Using the method described in FCSCM Chapter 6 Section 2.3
A =
Tc =
Project Location :
Design Point
C =
Design Storm
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
1791-001
The Quarry
Project Number :
Project Name :
Chambers 1
Page 3 of 7
1791-001 Chamber Summary
Pond No :
Basins D5, D6, D7
WQ
0.83
6.10 min 1155 ft3
1.87 acres 0.03 ac-ft
Max Release Rate =0.61 cfs
Time (min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
QWQ
(cfs)
Outflow Volume
(ft3)
Storage Volume
(ft3)
5 1.425 664 1.00 0.61 183 481
10 1.105 1029 1.00 0.61 366 663
15 0.935 1306 0.70 0.43 386 920
20 0.805 1499 0.65 0.40 478 1022
25 0.715 1665 0.62 0.38 569 1095
30 0.650 1816 0.60 0.37 661 1155
35 0.585 1907 0.59 0.36 752 1155
40 0.535 1993 0.58 0.35 844 1149
45 0.495 2074 0.57 0.35 935 1139
50 0.460 2142 0.56 0.34 1027 1115
55 0.435 2228 0.56 0.34 1118 1110
60 0.410 2291 0.55 0.34 1210 1081
65 0.385 2330 0.55 0.33 1301 1029
70 0.365 2379 0.54 0.33 1393 987
75 0.345 2410 0.54 0.33 1484 926
80 0.330 2459 0.54 0.33 1576 883
85 0.315 2493 0.54 0.33 1667 826
90 0.305 2556 0.53 0.33 1759 798
95 0.290 2566 0.53 0.32 1850 715
100 0.280 2608 0.53 0.32 1942 666
105 0.270 2640 0.53 0.32 2033 607
110 0.260 2663 0.53 0.32 2125 539
115 0.255 2731 0.53 0.32 2216 515
120 0.245 2738 0.53 0.32 2308 430
*Note: Using the method described in FCSCM Chapter 6 Section 2.3
C =
Tc =
A =
Chambers 2
Input Variables Results
Design Point
Design Storm Required Detention Volume
Project Location : Fort Collins, Colorado
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Project Number : 1791-001
Project Name : The Quarry
Page 4 of 7
1791-001 Chamber Summary
Vault IDTotal RequiredWQ Volume(cf)Flow,WQ(cfs)ChamberTypeChamber Release Ratea(cfs)ChamberVolumeb(cf)Installed Chamber w/ Aggregatec(cf)Mimimum No. of ChambersdTotal Release Ratee(cfs)Required Storage Volume by FAA Method(cf)Mimimum No. of ChambersfProvided Number of Chambers Provided Release Rate (cfs)Storage Provided within the Chambersg(cf)Total Installed System Volumeh(cf)Pond1 1894 1.97 SC-740 0.024 45.90 74.90 26 0.61 131329 29 0.681331 2172Pond2 1496 0.58 SC-740 0.024 45.90 74.90 20 0.47 115526 26 0.611193 1947a. Release rate per chamber, limited by flow through geotextile with accumulated sediment.b. Volume within chamber only, not accounting for void spaces in surrounding aggregate.c. Volume includes chamber and void spaces (40%) in surrounding aggregate, per chamber unit.d. Number of chambers required to provide full WQCV within total installed system, including aggregate.e. Release rate per chamber times number of chambers.f. Number of chambers required to provide required FAA storage volume stored within the chamber only (no aggregate storage).g. Volume provided in chambers only (no aggregate storage). This number must meet or exceed the required FAA storage volume.h. System volume includes total number of chambers, plus surrounding aggregate. This number must meet or exceed the required WQCV.Chamber Configuration SummaryP:\1791-001\Drainage\LID\1791-001 Chamber Summary
Chamber Dimensions SC-160 SC-310 SC-740 MC-3500 MC-4500
Width (in) 34.0 34.0 51.0 77.0 100.0
Length (in)85.4 85.4 85.4 90.0 52.0
Height (in)16.0 16.0 30.0 45.0 60.0
Floor Area (sf)20.2 20.2 30.2 48.1 36.1
Chamber Volume (cf)6.9 14.7 45.9 109.9 106.5
Chamber/Aggregate Volume (cf)29.3 29.3 74.9 175.0 162.6
Flow Rate* 0.35 gpm/sf
1 cf =7.48052 gal
1 gallon =0.133681 cf
1 GPM = 0.002228 cfs
*Flow rate based on 1/2 of Nov 07 QMAX in Figure 17 of UNH Testing Report
SC-160 SC-310 SC-740 MC-3500 MC-4500
Flow Rate/chamber (cfs)0.015724 0.015724 0.023586 0.037528 0.028159
end caps have a volume of 108.7 cu. ft.
StormTech Chamber Data
Chamber Flow Rate
Chamber Flow Rate Conversion (gpm/sf to cfs)
end caps have a volume of 45.1 cu. ft.
P:\1791-001\Drainage\LID\1791-001 Chamber Summary
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FORT COLLINS | GREELEY APPENDIX
B.3 – Storm Sewers