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OVERALL DRAINAGE REPORT FOR
STRAUSS LAKES
CITY OF FORT COLLINS
COUNTY OF LARIMER
STATE OF COLORADO
PREPARED FOR:
Cottonwood Land and Farms, LLC
PO Box 229
Boulder, CO 80306
PREPARED BY:
Civil Resources, LLC
8308 Colorado Blvd.
Suite 200
Firestone, Colorado 80504
PREPARED: NOVEMBER 2024
REVISED: SEPTEMBER 2025
Overall Drainage Report Strauss Lakes
Prepared: November 2024; Revised: September 2025 Page 2 of 11
Table of Contents
Page
1.0 BACKGROUND ..................................................................................................................................................... 5
1.1 General Location ........................................................................................................................................... 5
1.2 Existing Site Information................................................................................................................................ 5
1.3 Floodplain Information ................................................................................................................................... 5
1.4 Master Drainage Basin Description ............................................................................................................... 6
1.5 Previous Studies ........................................................................................................................................... 6
1.6 Project Description ........................................................................................................................................ 7
2.0 DRAINAGE DESIGN CRITERIA ............................................................................................................................ 7
2.1 Regulations ................................................................................................................................................... 7
2.2 Hydrologic & Hydraulic Criteria ..................................................................................................................... 7
3.0 PROPOSED DRAINAGE FACILITIES ................................................................................................................... 8
3.1 General Concept ........................................................................................................................................... 8
3.2 Drainage System Outfall ............................................................................................................................... 9
3.3 Low Impact Development (LID) ..................................................................................................................... 9
3.4 Municipal Separate Storm Sewer System (MS4) Permit ............................................................................. 10
3.5 Detention & Flood Control ........................................................................................................................... 10
4.0 CONCLUSIONS ................................................................................................................................................... 10
4.1 Compliance with Criteria ............................................................................................................................. 10
4.2 Drainage Concept ....................................................................................................................................... 11
5.0 REFERENCES .................................................................................................................................................... 11
Overall Drainage Report Strauss Lakes
Prepared: November 2024; Revised: September 2025 Page 3 of 11
List of Appendices
APPENDIX A FIGURES & TABLES
Project Vicinity Map
Hydrologic Soils Map & Table
Effective Flood Insurance Rate Map
Fort Collins Risk Map
Fort Collins Stormwater Criterial Manual (select pages)
APPENDIX B REFERENCE REPORTS
Fox Meadows Basin Selected Plan – Water Quality Improvements
Addendum to the Final Design Report for the Fossil Creek Reservoir Inlet Ditch Storm Water Overflow
Memorandum: Hydraulic Analysis of Fossil Creek Reservoir Inlet Ditch
Final Drainage and Erosion Control Report Rigden Farm – Filing Six
APPENDIX C HYDROLOGIC & HYDRAULIC COMPUTATIONS
East Horsetooth Road Historic Runoff Calculations
Historic SWMM Model
Preliminary Proposed SWMM Model
WQCV Calculations
Constructed Wetland Pond Calculations
Modified FAA Calculations
Hydraflow Express Output
APPENDIX D DRAINAGE PLANS
Historic Drainage Plan
Proposed Drainage Plan
Overall Drainage Report Strauss Lakes
Prepared: November 2024; Revised: September 2025 Page 4 of 11
ENGINEER’S CERTIFICATION OF DRAINAGE REPORT
“I hereby certify that this report for the overall drainage design of Strauss Lakes was prepared by me (or under my direct
supervision) in accordance with the provisions of the Fort Collins Stormwater Criteria Manual for the owners thereof.”
__________________________________________________________________________
Registered Professional Engineer
State of Colorado No. 40551
Overall Drainage Report Strauss Lakes
Prepared: November 2024; Revised: September 2025 Page 5 of 11
1.0 BACKGROUND
1.1 General Location
The Strauss Lakes project is located northeast of the intersection of Ziegler Road and East Horsetooth Road, and is
situated in Section 28, Township 7 North, Range 68 West of the 6th Principal Meridian, County of Larimer, State of
Colorado. The project area includes parcel 8728000003, located within the City of Fort Collins, and parcel 8728000009,
located in unincorporated Larimer County. The Site is bounded by Ziegler Road to the west, East Horsetooth Road to the
south, Great Western Railway to the north, and the Boxelder Ditch to the northeast. Refer to Appendix A for a Project
Vicinity Map.
The purpose of this report is to accompany an annexation and ODP application. The ODP establishes overall land uses
for the property, but does not propose specific layouts or design. This report serves to establish the overall drainage
objectives to be followed in future final drainage reports for each phase of development
1.2 Existing Site Information
The Strauss Lakes project Site is currently undeveloped with native grass land cover. The property slopes west to east
with grades generally ranging from 0.02% to 5.2%. Native, on-site soils can be classified as approximately 26% Hydrologic
Soil Group B, 29% Group C, and 45% Group D. Refer to Appendix A for soils map and classification table. A significant
portion of the Site has been filled using material removed from a gravel pit located north of the Great Western Railroad.
There are approximately 2.91 acres of existing wetlands and 12.42 acres of open water within the property boundary.
Refer to the Ecological Characterization Study – Strauss Lakes Residential Development, prepared by ERO Resources
Corporation.
The Fossil Creek Reservoir Inlet Ditch (FCRID) traverses the Site, separating the City parcel (8728000003) from the
unincorporated land (8728000009). The FCRID conveys irrigation flows diverted from the Cache la Poudre River, as well
as treated discharge from the Fort Collins wastewater treatment plant, to the Fossil Creek Reservoir. A spill structure for
the ditch is located along the south property line, just north of East Horsetooth Road. The spill structure is further described
in section 1.4. There is flow in the FCRID year-round, and some waters are used to support regional oil and gas activities.
The Boxelder Ditch is located within the north end of the Site and flows southeast along the eastern boundary of the Site.
The Boxelder Ditch diverts irrigation flows from the Cache la Poudre River, and conveys flows to various on-site and off-
site headgates downstream of the Site. A control structure for the ditch is located at the southeast corner of the Site.
The Foothills Channel Outfall (FCO) runs along the southern property line of the unincorporated parcel (8728000009),
along the north side of East Horsetooth Road. The FCO is an overflow channel for the FCRID, which conveys flows east
along East Horsetooth Road and discharges to the Cache la Poudre River. The FCO is normally dry, and only has flows
during significant wet weather events when the FCRID overflows to the FCO.
1.3 Floodplain Information
A portion of the Site, southwest of the Boxelder Ditch, lies within Zone X, of the Cache La Poudre River, per Federal
Emergency Management Agency (FEMA) Flood Insurance Rate Map (FIRM) number 08069C0992G. Zone X is defined
as the area of 0.2% annual chance flood (500-year floodplain). A portion of the Site north of the Boxelder Ditch is located
within Zone AE, the 1.0% annual chance flood (100-year floodplain). A copy of the effective FIRM is included in
Appendix A.
The floodplain in this area is currently being remapped by consultants for the Colorado Water Conservation Board and
FEMA. A copy of the preliminary map (Fort Collins Risk Map) is included in Appendix A. The preliminary mapping
indicates no portion of the Site will be located in the 100-year floodplain.
Overall Drainage Report Strauss Lakes
Prepared: November 2024; Revised: September 2025 Page 6 of 11
1.4 Master Drainage Basin Description
A portion of the Site is located within the Cache La Poudre River Master Drainage Basin and the remaining portion is
within the Fox Meadows Master Drainage Basin. The master drainage reports for both of these basins are in the process
of being updated.
1.4.1 Cache La Poudre Master Drainage Basin
The Cache La Poudre River Master Drainage Basin (Poudre Basin) was analyzed in the Cache La Poudre River Master
Drainageway Plan, prepared by Ayres Associates in August 2001.
This report discusses several problem drainage areas along the Cache la Poudre River, including sites upstream and
downstream of the subject Site, but none directly impacting the Site.
The Riverbend Ponds Area is located upstream of the subject Site, northwest of the City’s wastewater treatment plant.
The report identifies significant flooding and flood damage in this area. Several alternatives are presented in the report
including the construction of levees, modification of existing levees, and the construction of a weir. These improvements
have been completed.
1.4.2 Fox Meadows Drainage Basin
The Fox Meadows Drainage Basin was evaluated in the following master reports:
• Fox Meadows Basin Drainage Master Plan Update – 50-Year Alt. Plan, prepared by ICON Engineering, Inc. on
December 6th, 2002.
• Fox Meadows Basin Drainage Master Plan Update Phase A – Baseline Hydraulics and Problem Identification
Report, prepared by ICON Engineering, Inc. and revised February 2003.
• Fox Meadows Basin Drainage Master Plan Update Selected Plan Report, prepared by ICON Engineering, Inc.
and revised February 2003.
These reports state that much of the master basin has been developed, with little development potential remaining, and
identifies several drainage problems within the master basin including overtopping detention ponds, insufficient
freeboard of irrigation ditches, and conveyance channels and roadway overtopping. The subject Site is located on the
upstream end of the master basin, and the problems identified in these reports occur downstream of the Site. Several
mitigation efforts are proposed in the plans; however, it is unknown which, if any, of these solutions have been
implemented.
As indicated on the Fox Meadows Basin Selected Plan – Water Quality Improvements figure, the southwest corner of the
Site (8728000003) was considered as an potential location for a water quality pond to serve the Fox Meadows Drainage
Basin (see Appendix B for referenced figure). Per discussions between City staff and the Developer, the Strauss Lakes
development will not need to accommodate a water quality pond to treat off-site flows.
1.5 Previous Studies
The Site has been included in previous studies of the Fossil Creek Reservoir Inlet Ditch (FCRID), which traverses the
Site. The Foothills Channel Outfall (FCO) was first described in the Final Design Report for the Fossil Creek Reservoir
Inlet Ditch Storm Water Overflow prepared by Donohue & Associates, Inc. in February 1988. The FCO was designed to
convey excess flows from the FCRID to the Cache la Poudre River. Flow is diverted from the FCRID via a spill structure
located north of East Horsetooth Road. The FCRID was initially designed to convey the total 100-year peak flow to the
structure, which is 1,160 cfs. The Addendum to the Final Design Report for the Fossil Creek Reservoir Inlet Ditch Storm
Water Overflow prepared by Donohue & Associates, Inc. in September 1988, limits this flow to 860 cfs, which means the
Overall Drainage Report Strauss Lakes
Prepared: November 2024; Revised: September 2025 Page 7 of 11
control gate passes 300 cfs to the FCRID, south of East Horsetooth Road, during the 100-year peak storm.
The flow in the FCO was most recently analyzed by Anderson Consulting Engineers, Inc. in the April 30, 2020
memorandum Hydraulic Analysis of Fossil Creek Reservoir Inlet Ditch Between Cache la Poudre River and Harmony
Road for Future Strauss Lake Development. This study found that a maximum of 523 cfs flows through the FCO,
downstream of the FCRID spill structure. This results in an available capacity of 337 cfs in the FCO at this location.
The FCRID was also evaluated by Anderson Consulting Engineers, Inc. in the 2002 Hydraulic Analysis and Design of
the Fossil Creek Reservoir Inlet Ditch Controlled Spill System. The information in this report is superseded by the 2020
memorandum.
See Appendix B for relevant excerpts of the abovementioned reports.
1.6 Project Description
The Strauss Lakes Project proposes to develop the approximately 159-acre subject Site into a mixed-use neighborhood.
The neighborhood will consist of both residential units (townhomes, single-family homes, paired homes, and multi-family
homes) and commercial units (restaurant, retail, and neighborhood support services). This development will require both
annexation of the unincorporated parcel (8728000009) into the City, and rezoning of the Site to a combination of LMN
and MMN. The currently annexed parcel (8728000003) is zoned Low Density Mixed-Use Neighborhood District (LMN).
Related neighborhood infrastructure will include roadways, alleys, parks, trails, water quality improvements, on- and off-
site utilities, local flood control/detention measures, access points off of Ziegler Road and East Horsetooth Road, and
roadway improvements to East Horsetooth Road.
The development Site is adjacent to the Rigden Farm, Dakota Ridge, and Stone Ridge developments, located west of
Ziegler Road, Rigden reservoir to the east, Environmental Learning Center, Running Deer Natural Area, and Cache la
Poudre River to the north, and Topminnow Natural Area and unincorporated residential homes to the south.
2.0 DRAINAGE DESIGN CRITERIA
2.1 Regulations
The proposed drainage design will comply with the regulations set forth in the Fort Collins Stormwater Criteria Manual
(FCSCM), revised December 2018.
2.2 Hydrologic & Hydraulic Criteria
The hydrology of the Site and the hydraulic of the stormwater system will be analyzed per the methods outlined in Chapter
5 of the FCSCM. The following methods will be presented in the final drainage report.
• EPA Stormwater Management Model (SWMM) version 5.2 will be used to estimate the 2 and 100-year peak
developed runoff as the minor and major storm events, respectively. The input parameters listed in Table 4.1-1
and the intensity-duration-frequency values from Table 4.1-4 of the FCSCM will be used to model the
subcatchments and rain gauges.
• Impervious values for the Site will be determined by land use for conceptual design, per Table 4.1-2 in the
FCSCM, and will later be revised by surface type, per Table 4.1-3.
• Inlets will be sized to capture the peak flow rate from the minor 2-year storm (minus the allowable street capacity),
per chapter 12, section 1.4 of the FCSCM.
• The water quality capture volume (WQCV) will be calculated per equations 7-1 and 7-2 in the FCSCM.
• The on-site conveyance swale and emergency spillways will be sized using the Hydraflow Express extension for
Overall Drainage Report Strauss Lakes
Prepared: November 2024; Revised: September 2025 Page 8 of 11
Autodesk Civil 3D.
• The 100-year detention volumes will be determined using both the Modified FAA method, and EPA Stormwater
Management Model (SWMM) version 5.2. The subcatchment input parameters for SWMM were taken from Table
4.1-1 in the FCSCM.
3.0 PROPOSED DRAINAGE FACILITIES
3.1 General Concept
For the purposes of this Overall Drainage Report, the Site has been divided into three drainage basins: the West Site,
located west of the FCRID, the East Site, located east of the FCRID, and East Horsetooth Road. Furthermore, the East
Site has been subdivided into five (5) conceptual 20-acre sub-basins. The basin shapes are arbitrary, and not based on a
specific road layout or grading scenario, but were developed to estimate runoff in order to preliminarily size a drainage
swale parallel to the Boxelder Ditch.
The stormwater systems for the West Site and East Site will function independently of one another. See Appendix D for
the Overall Drainage Plan.
3.1.1 West Site
The West Site will generally maintain the historic drainage pattern by directing flow northeast, via paved conveyances,
inlets, and storm sewer. Captured runoff will be directed to a detention pond, located in the northern corner of the West
Site. This pond will be sized to detain the developed 100-year tributary flow, and discharge to the FCRID at a rate equal
to or below the 2-year historic discharge rate of 0.90 cfs. The drainage area of the West Site is approximately 12.08
acres. The layout and density of the West Site is unknown at this point; therefore the impervious value of the West Site
is conservatively assumed to be 90% (high density) per Table 4.1-2 of the FCSCM. The impervious value will be further
refined in subsequent drainage reports using Table 4.1-3. The configuration and grading of the West Site may also
require the detention volume be provided by two ponds, one located on the north portion of the Site, and the other along
the eastern portion. The 100-year developed runoff of the West Site is estimated to be 118.88 cfs, per SWMM. See
Appendix C for SWMM summary tables.
3.1.2 East Site
The East Site currently drains east towards the Boxelder Ditch. The Boxelder intercepts minor storms, and major events
either overtop the ditch and enter Rigden Reservoir, or enter the FCO. The proposed design will intercept runoff prior to
entering the Boxelder Ditch. The drainage area of the East Site is approximately 99.10 acres. The layout and density of
the East Site is unknown at this point; therefore the impervious value of the East Site is conservatively assumed to be
90% (high density) per Table 4.1-2 of the FCSCM. The impervious value will be further refined in subsequent drainage
reports using Table 4.1-3. The 100-year developed runoff of each subbasin of the East Site was calculated using SWMM
to be 133.77 cfs, for a total runoff of 668.85 cfs. See Appendix C for SWMM summary tables. Each drainage subbasin
will discharge to a conveyance swale located along the east property line, just west of the Boxelder Ditch. Forebays will
be provided at each inlet to this conveyance swale to provide energy dissipation, trash collection, and sediment control.
The conveyance swale will flow southeast to a constructed wetland pond (CWP), located at the southeast corner of the
East Site. The swale was preliminarily sized for the cumulative flow from each of the five conceptual 20-acre basins,
which resulted in a maximum top width of 62-feet. The Hydraflow Express analysis is included in Appendix C. The CWP
will provide water quality treatment (further described in section 3.2) and flood control for the 100-year major storm
event. Runoff from the major storm will be detained in the pond, and released to the Foothills Channel Outfall (FCO), via
an outlet structure. The detained runoff will be released at a rate equal to or below the available capacity of the FCO,
minus the discharge from the West Site and East Horsetooth Road. There will be an emergency spillway located on the
south side of the pond, which will be sized to pass the undetained 100-year runoff from the pond tributary area, per
section 3.2 of the FCSCM. The spillway will discharge south to the FCO.
Overall Drainage Report Strauss Lakes
Prepared: November 2024; Revised: September 2025 Page 9 of 11
3.1.3 East Horsetooth Road
The Site historically receives off-site flows from East Horsetooth Road, from the intersection with Ziegler Road to the
FCRID crossing. The development of the Strauss Lakes Site will require improving the roadway to a two-lane arterial
street, per Figure 7-3F of the Larimer County Urban Area Street Standards (LCUASS). Costs for this roadway
construction will be shared by the City and the developer. For a Site frontage of approximately 2,950 linear feet, this
results in an impervious area of 4.33 acres. The future impervious value of the roadway is assumed to be 95%, resulting
in a 100-year developed runoff of approximately 43.44 cfs, per SWMM. See Appendix C for SWMM summary tables.
The development will be responsible for providing water quality treatment of this new impervious area. The location of
the FCO creates a barrier to treating the roadway runoff on-site; therefore, it is proposed to treat the runoff from East
Horsetooth Road using an extended detention basin, located south of the road on City of Fort Collins property (parcel
8733231902). The exact location of this stormwater facility will need to be coordinated with the City. Developed runoff
will be captured in street inlets, and conveyed via storm sewer to the detention pond. The detention pond will be sized
for the WQCV and 100-year storage volume of the full-width roadway buildout, and will discharge to the FCO. The pond
outlet structure will be designed to discharge the 100-year developed runoff at or below the historic 2-year runoff rate of
2.34 cfs, as calculated using the Rational Method.
3.2 Drainage System Outfall
Per prior agreements between Cottonwood Land and the City of Fort Collins, developed runoff from the development will
be allowed to discharge to the Foothills Channel Outfall (FCO). As previously discussed, the FCO was most recently
studied by Anderson Consulting Engineers, Inc. in a memorandum dated April 30, 2020. This study determined that the
maximum overflow from the FCRID to the FCO was 523 cfs. Assuming the 100-year capacity of the channel is 860 cfs,
per the 1988 report, the maximum release rate from the Site is 337 cfs. For the purpose of this overall report, a reduction
factor of 25% was applied to this capacity, resulting in an allowable release rate of 252.75 cfs. The 100-year capacity will
need to be verified through hydraulic modeling of the FCO, and final design of the project may utilize the modeled excess
capacity of the FCO.
Developed runoff from the West Site will be detained in the detention pond and discharged to the FCRID at a rate equal
to or below the historic 2-year runoff rate of 0.90 cfs. The Horsetooth Road detention pond outlet structure will be designed
to release the 100-year developed runoff from the roadway at or below the historic 2-year runoff rate of 2.34 cfs. This
leaves 249.51 cfs of receiving capacity in the FCO. The outlet structure of the constructed wetland pond will be designed
to release the 100-year storage volume at or below this remaining capacity. To discharge at this high rate, the CWP outlet
structure will likely be constructed from a combination of orifices, weirs, and outflow channels.
All runoff discharged to the FCO will flow east along the north side of East Horsetooth Road, eventually discharging to the
Cache la Poudre River just east of Strauss Cabin Road.
3.3 Low Impact Development (LID)
The City of Fort Collins requires the implementation of Low Impact Development (LID) systems to treat 75% of newly
added or modified impervious areas. Several LID systems were evaluated for the East Site, including bioretention,
infiltration trenches, and constructed wetlands.
Bioretention rain gardens were preliminarily sized to treat the WQCV of the East Site. Per Mile High Flood District (MHFD)
design guidelines for Bioretention Systems (Fact Sheet T-3), the maximum WQCV depth is 1-foot, which results in a
required rain garden treatment area of approximately 3.6 acres. Fort Collins requires a minimum of 30 inches of filter
media and bedding material, which would total approximately 14,500 cubic yards of material for the treatment area.
Because of the size requirements and volume of bedding material required, rain gardens were determined to be impractical
for the East Site.
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Prepared: November 2024; Revised: September 2025 Page 10 of 11
Infiltration trenches cannot be implemented because of the high groundwater levels on the Site. Therefore, a constructed
wetland pond (CWP) is proposed to treat the WQCV of the East Site. The permanent pool volume was calculated per
equation RP/CWP-1 of the MHFD Fact Sheet T-7, and was determined to be 2.69 acre-feet. See Appendix C for
preliminary sizing calculations of the CWP. The permanent pool of the CWP will be maintained through exposed ground
water, which will require a pond well permit, as well as water rights. The estimated area of exposed groundwater is
approximately 3.78 acres, which includes the constructed wetland pond (2.91 acres) and the conveyance swale (0.87
acres). The 2.91 acres of permanent wetland will mitigate the effects of removing 0.14 acres of existing wetland on the
West Site, resulting in 2.77 acres of wetland available for stormwater mitigation.
Per discussion with City staff, LID will not be required to treat runoff from the East Horsetooth Road widening. The
impervious area of East Horsetooth Road will account for less than 25% of the entire Site, and therefore can be excluded.
LID for the West Site will be implemented locally through the use of grass buffers, grass swales, rain gardens, permeable
pavers, and other LID features, as needed, to meet the 75% requirement of the City. LID features will not be provided
within right-of-way, or within single-family private lots, per section 6.1 of the FCSCM.
3.4 Municipal Separate Storm Sewer System (MS4) Permit
Per the Colorado Department of Public Health and Environment’s (CDPHE) COR090000 Municipal Separate Storm
Sewer Systems (MS4) Permit, the Site must meet one of the post-construction base design standards. This Site will be
designed to meet the WQCV standard, by capturing and treating 100% of the WQCV for the applicable development site
(excluding up to 1 acre). This standard will be met through the use of a detention pond, as described in section 3.1.1,
and a constructed wetland pond, as described in section 3.1.2.
3.5 Detention & Flood Control
The 100-year runoff of the West Site will be detained in an extended detention pond and discharged to the FCRID via an
outlet structure. Per SWMM, the preliminary 100-year developed runoff from the West Site is 118.88 cfs, and the outlet
structure will be designed to release the 100-year developed runoff at a rate equal to or below the SWMM-calculated 2-
year historic runoff rate of 0.90 cfs. Per the Modified FAA Procedure, as described in section 2.3 of the FCSCM, the 100-
year storage volume is estimated to be 2.97 acre-feet.
The developed 100-year runoff from East Horsetooth Road will be detained in an extended detention basin, located south
of the road, on City property. The exact location of this pond will need to be coordinated with the City. The 100-year storage
volume was estimated to be 1.23 acre-feet, per the Modified FAA Procedure. The available pond working depth south of
East Horsetooth Road is estimated to be 4.5-feet, based on preliminary survey, and one-foot of freeboard is required,
which results in an available storage depth of 3.5 feet. The outlet structure of this pond will be designed to release the
100-year detention volume at or below the historic 2-year runoff rate of 2.34 cfs. Detained runoff will discharge to the FCO.
The 100-year runoff of the East Site will be detained in the constructed wetland pond, and will be released to the receiving
body (FCO) at a controlled rate, via an outlet structure. Preliminary sizing of the constructed wetland pond was performed
using SWMM, and the maximum storage volume was determined to be 469,407 cubic feet, or 10.78 acre-feet. For a
preliminary WQCV of 3.58 acre-feet, this results in a required 100-year storage volume of 7.20 acre-feet. A preliminary
pond with a footprint of approximately 5 acres was evaluated in SWMM. See Appendix C for SWMM summary tables. The
CWP outlet structure will be designed to release the 100-year volume at or below 249.51 cfs, which is equal to the capacity
of the FCO (252.75 cfs), minus the detained discharge from the West Site and East Horsetooth Road (3.24 cfs).
4.0 CONCLUSIONS
4.1 Compliance with Criteria
This overall drainage report is in compliance with the provisions outlined in the Fort Collins Stormwater Criteria Manual.
Overall Drainage Report Strauss Lakes
Prepared: November 2024; Revised: September 2025 Page 11 of 11
4.2 Drainage Concept
The proposed drainage system will improve Site drainage through the following methods:
• The 100-year developed runoff from the West Sites will be detained and released to the FCRID at XX
• The 100-year developed runoff from the East Site will be released to the Foothills Channel Outfall at a rate
equal to the remaining capacity of the channel.
• Low Impact Development systems will be implemented to treat a minimum of 75% of the new or modified
impervious area.
• 100% of the water quality capture volume of the applicable development site (excluding up to 1 acre) will be
treated, per CDPHE MS4 requirements.
The preliminary design of the drainage system is in accordance with applicable design standards and criteria, and is
therefore not anticipates to have an adverse impact on the existing drainage conditions of the Site nor its immediate
vicinity.
5.0 REFERENCES
• Cache la Poudre River Master Drainageway Plan. Ayres Associates, EDAW. August 2001.
• Final Design Report for the Fossil Creek Reservoir Inlet Ditch Storm Water Overflow. Donohue & Associates,
Inc. March 1988.
o Addendum to the Final Design Report for the Fossil Creek Reservoir Inlet Ditch Storm Water Overflow.
Donohue & Associates, Inc. September 1988.
• Final Drainage and Erosion Control Report Rigden Farm – Filing Six. JR Engineering. Revised February 8,
2002.
• Fort Collins Stormwater Criteria Manual. City of Fort Collins. December 2018.
• Fox Meadows Basin Drainage Master Plan Update – 50-Year Alt. Plan. ICON Engineering, Inc. December
6, 2002.
• Fox Meadows Basin Drainage Master Plan Update Phase A – Baseline Hydraulics and Problem Identification
Report. ICON Engineering, Inc. Revised February 2003.
• Fox Meadows Basin Drainage Master Plan Update Selected Plan Report. ICON Engineering, Inc. Revised
February 2003.
• Hydraulic Analysis of Fossil Creek Reservoir Inlet Ditch Between Cache la Poudre River and Harmony Road
for Future Strauss Lake Development. Anderson Consulting Engineers, Inc. April 30, 2020.
• Hydraulic Analysis of the Fossil Creek Reservoir Inlet Ditch Controlled Spill System. Anderson Consulting
Engineers, Inc. December 2, 2002.
• Urban Storm Drainage Criteria Manual. Mile High Flood District. Partially updated March 2024.
APPENDIX A
Figures & Tables
Hydrologic Soil Group—Larimer County Area, Colorado
(Strauss Lakes)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/12/2024
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1
'
2
3
'
'
W
40° 32' 11'' N
10
5
°
0
'
2
2
'
'
W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 450 900 1800 2700
Feet
0 100 200 400 600
Meters
Map Scale: 1:9,330 if printed on A portrait (8.5" x 11") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Lines
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Points
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Survey Area Data: Version 18, Aug 24, 2023
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Jul 2, 2021—Aug 25,
2021
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Hydrologic Soil Group—Larimer County Area, Colorado
(Strauss Lakes)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/12/2024
Page 2 of 4
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
22 Caruso clay loam, 0 to 1
percent slope
D 79.3 43.7%
35 Fort Collins loam, 0 to 3
percent slopes
C 22.1 12.2%
53 Kim loam, 1 to 3 percent
slopes
B 16.5 9.1%
62 Larimer-Stoneham
complex, 3 to 10
percent slopes
B 14.1 7.8%
64 Loveland clay loam, 0 to
1 percent slopes
C 0.0 0.0%
73 Nunn clay loam, 0 to 1
percent slopes
C 11.1 6.1%
74 Nunn clay loam, 1 to 3
percent slopes
C 0.3 0.1%
101 Stoneham loam, 1 to 3
percent slopes
B 10.8 6.0%
102 Stoneham loam, 3 to 5
percent slopes
C 3.5 1.9%
105 Table Mountain loam, 0
to 1 percent slopes
B 15.1 8.3%
136 Water 8.6 4.7%
Totals for Area of Interest 181.3 100.0%
Hydrologic Soil Group—Larimer County Area, Colorado Strauss Lakes
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/12/2024
Page 3 of 4
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive
precipitation from long-duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three dual classes (A/D, B/D, and C/D). The groups are defined as follows:
Group A. Soils having a high infiltration rate (low runoff potential) when
thoroughly wet. These consist mainly of deep, well drained to excessively
drained sands or gravelly sands. These soils have a high rate of water
transmission.
Group B. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well
drained soils that have moderately fine texture to moderately coarse texture.
These soils have a moderate rate of water transmission.
Group C. Soils having a slow infiltration rate when thoroughly wet. These consist
chiefly of soils having a layer that impedes the downward movement of water or
soils of moderately fine texture or fine texture. These soils have a slow rate of
water transmission.
Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink-swell
potential, soils that have a high water table, soils that have a claypan or clay
layer at or near the surface, and soils that are shallow over nearly impervious
material. These soils have a very slow rate of water transmission.
If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is
for drained areas and the second is for undrained areas. Only the soils that in
their natural condition are in group D are assigned to dual classes.
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—Larimer County Area, Colorado Strauss Lakes
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/12/2024
Page 4 of 4
Fort Collins Risk Map
This map is a user generated static output from the City of Fort Collins FCMaps
Internet mapping site and is for reference only. Data layers that appear on this
map may or may not be accurate, current, or otherwise reliable.
18,056
City of Fort Collins - GIS
0.6
1:
WGS_1984_Web_Mercator_Auxiliary_Sphere
Miles0.600.28
Notes
Legend
Growth Management Area
City Limits
Percent Annual Chance Grids
0.2%
> 0.2% - 1%
> 1% - 2%
> 2% - 4%
> 4% - 10%
Citations
FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5)
4.0 SWMM
4.1 Input Parameters
Page 10
4.0 SWMM
This section is for project sites that require the use of the Stormwater Management Model (SWMM) to
determine storm hydrograph routing and is the only method that is able to assess the overall
performance of multiple detention basins in parallel or in series in a particular project site or watershed.
Reference: The theory and methodology for reservoir routing is not covered in this Manual
as this subject is well described in many hydrology reference books. The EPA SWMM
Reference Manuals, dated January 2016, have been utilized in preparing the information in
this section of the Manual.
4.1 Input Parameters
Table 4.1-1 provides required input values to be used for SWMM modeling.
Basin and conveyance element parameters must be computed based on the physical characteristics of
the site.
Table 4.1-1. SWMM Input Parameters
Impervious Areas 0.1 inches
Pervious Areas 0.3 inches
Maximum 0.51 in/hr
Minimum 0.50 in/hr
Decay Rate
0.0018 in/sec or
6.48 in/hr
1%
Pervious Surfaces 0.250
Impervious Surfaces 0.016
For Overall Drainage Plan (ODP) and Project Development Plan (PDP) submittals, when surface types
may not yet be known, land uses may be used to estimate impervious percentages. Table 4.1-2 lists the
percent imperviousness for common types of land uses in the City.
FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5)
4.0 SWMM
4.1 Input Parameters
Page 11
Table 4.1-2. Land Use - Percent Impervious
Urban Estate 30
Low Density 50
Medium Density 70
High Density 90
Commercial 80
Industrial 90
Open Lands, Transition 20
Greenbelts, Agriculture 2
Offsite Flow Analysis (when
Land Use not defined) 45
Reference: For further guidance regarding zoning classifications, refer to the Land Use
Code, Article 4.
For Final Plan (FP) submittals, impervious values must be based on the proposed land surface types.
Refer to Table 4.1-3 for recommended percent impervious values.
Table 4.1-3. Surface Type – Percent Impervious
Asphalt, Concrete 100
Rooftop 90
Recycled Asphalt 80
Gravel 40
Pavers 40
Playgrounds 25
Lawns, Sandy soil 2
Lawns, Clayey soil 2
FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5)
4.0 SWMM
4.1 Input Parameters
Page 12
The composite imperviousness is obtained using the following formula:
( )
t
n
i
ii
A
xAI
I
∑
==1 Equation 5-6
Where: I = Composite Imperviousness, %
Ii = Imperviousness for Specific Area (Ai), %
Ai = Area of Surface with Imperviousness of Ii, acres or square feet
n = Number of different surfaces to be considered
At = Total Area over which I is applicable, acres or square feet
4.1.1 Intensity-Duration-Frequency Curves for SWMM
The hyetograph input option must be selected when creating SWMM input files. Hyetographs for the 2-
year, 5-year, 10-year, 25-year, 50-year, and 100-year Fort Collins rainfall events are provided in Table
4.1-4.
Table 4.1-4. IDF Table for SWMM
Duration 2-year 5-year
Intensity
10-year
Intensity
25-year
Intensity
50-year
Intensity
100-year
5 0.29 0.40 0.49 0.63 0.79 1.00
10 0.33 0.45 0.56 0.72 0.90 1.14
15 0.38 0.53 0.65 0.84 1.05 1.33
20 0.64 0.89 1.09 1.41 1.77 2.23
25 0.81 1.13 1.39 1.80 2.25 2.84
30 1.57 2.19 2.69 3.48 4.36 5.49
35 2.85 3.97 4.87 6.30 7.90 9.95
40 1.18 1.64 2.02 2.61 3.27 4.12
45 0.71 0.99 1.21 1.57 1.97 2.48
50 0.42 0.58 0.71 0.92 1.16 1.46
55 0.35 0.49 0.60 0.77 0.97 1.22
60 0.30 0.42 0.52 0.67 0.84 1.06
65 0.20 0.28 0.39 0.62 0.79 1.00
70 0.19 0.27 0.37 0.59 0.75 0.95
75 0.18 0.25 0.35 0.56 0.72 0.91
80 0.17 0.24 0.34 0.54 0.69 0.87
85 0.17 0.23 0.32 0.52 0.66 0.84
90 0.16 0.22 0.31 0.50 0.64 0.81
95 0.15 0.21 0.30 0.48 0.62 0.78
100 0.15 0.20 0.29 0.47 0.60 0.75
105 0.14 0.19 0.28 0.45 0.58 0.73
110 0.14 0.19 0.27 0.44 0.56 0.71
115 0.13 0.18 0.26 0.42 0.54 0.69
120 0.13 0.18 0.25 0.41 0.53 0.67
APPENDIX B
Reference Reports
!(
!(
!(
!(
!(
!(
!(
!(
E HARMONY RD
ZI
E
G
L
E
R
R
D
E HORSETOOTH RD
S
T
I
M
B
E
R
L
I
N
E
R
D
S
L
E
M
A
Y
A
V
E
CO RD 40
UN
I
O
N
P
A
C
I
F
I
C
R
A
I
L
R
O
A
D
Golden Meadow Pond• Retrofit Existing Pond to accommodate Water Quality Volume
Fox Meadows Pond• Retrofit Existing Pond to accommodate Water Quality Volume
FCRID Pond• New Pond to accommodate Water Quality Volume
Sunstone Village Regional Pond• Retrofit Existing Pond to accommodate Water Quality Volume
Hewlitt-Packard Ponds• Retrofit Existing Pond to accommodate Water Quality Volume
Woodland Park Pond• Retrofit Existing Pond to accommodate Water Quality Volume
Fos
s
i
l
C
r
e
e
k
R
e
s
e
r
v
o
i
r
I
n
l
e
t
D
i
t
c
h
(
F
C
R
I
D
)
Collindale Golf Course• Source Control BMP's (see report text)Alternate Locations Evaluated
Stone Ridge Pond• Alternative to FCRID location (EDBD)
K
I
F
C
B
A
H
Fox Meadows BasinSelected Plan - Water Quality Improvements .1 inch = 500 feet
0 500 1,000 1,500 2,000Feet
Fox Meadows Basin
Proposed BMP Basin Type
Flood Control Only
Water Quality Only
Flood Control and Water Quality
Proposed Improvements
Proposed Selected PlanWater Quality AlternativesProposed
FEB 25W
FINAL DRAINAGE AND
EROSION CONTROL REPORT
Rigden Farm - Filing Six
Prepared for:
Rigden Farm LLC
c/o Wheeler Commercial
1027 W. Horsetooth Road, Suite 200
Fort Collins, Colorado 80526
970)225-9305
Prepared by:
JR Engineering
2620 E. Prospect Road, Suite 190
Fort Collins, Colorado 80325
970)491-9888
Revised February 8, 2002
Revised December.5, 2001
Revised July 25, 2001
Revised March 28, 2001
December 13, 2000
Job Number 9164.12
0
0
Swale to Poudre River
Worksheet for Trapezoidal Channel
Project Description
Project File x:\3910000.all\3916412\drainage\filing6.fm2
Worksheet Swale to Poudre River
Flow Element Trapezoidal Channel
Method Manning's Formula
Solve For Channel Depth
Input Data
Mannings Coefficient 0.035
Channel Slope 0.003000 ft/ft
Left Side Slope 4.000000 H : V
Right Side Slope 4.000000 H : V
Bottom Width 15.00 ft
Discharge 134.00 cfs — Q top\
Results
Depth 1.97 ft
Flow Area 45.12 ft2
Wetted Perimeter 31.26 ft
Top Width 30.77 ft
Critical Depth 1.21 It
Critical Slope 0.018313 ft/ft
Velocity 2.97 ft/s
Velocity Head 0.14 ft
Specific Energy 2.11 ft
Froude Number 0.43
Flow is subcritical.
Notes:
Q = hB i Q100 from SWMM 9164-PRO.out CE 9 2-Vl
03/24/01 FlowMaster v5.15
03:56:27 PM Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 Page 1 of 1
Swale to Poudre River
Cross Section for Trapezoidal Channel
Project Description
Project File x:\3910000.all\3916412\drainage\filing6.fm2
Worksheet Swale to Poudre River
Flow Element Trapezoidal Channel
Method Manning's Formula
Solve For Channel Depth
Section Data
Mannings Coefficient 0.035
Channel Slope 0.003000 ft/ft
Depth 1.97 ft
Left Side Slope 4.000000 H : V
Right Side Slope 4.000000 H : V
Bottom Width 15.00 ft
Discharge 134.00 cfs - Q too
15.00 ft
1.97 ft
1
VD
H 1
NTS
Ol
03/24/01 FlowMaster v5.15
03:56:32 PM Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 Page 1 of 1
0
Swale to Poudre River
Worksheet for Trapezoidal Channel
Project Description
Project File x:\3910000.all\3916412\drainage\filing6.fm2
Worksheet Swale to Poudre River
Flow Element Trapezoidal Channel
Method Manning's Formula
Solve For Channel Depth
Input Data
Mannings Coefficient 0.035
Channel Slope 0.003000 ft/ft
Left Side Slope 4.000000 H : V
Right Side Slope 4.000000 H : V
Bottom Width 15.00 ft
Discharge 178.00 cfs — r33,/p o c(jOo6sgc
Results
Depth 2.29 ft
Flow Area 55.24 ft'
Wetted Perimeter 33.86 ft
Top Width 33.30 ft
Critical Depth 1.43 ft
Critical Slope 0.017490 ft/ft
Velocity 3.22 ft/s
Velocity Head 0.16 ft
Specific Energy 2.45 ft
Froude Number 0.44
Flow is subcritical.
Notes:
Q = 133% of Q100 from SWMM 9164-PRO.out CE-W Zl/(,
03/24/01 FlowMaster v5.15
03:52:53 PM Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 Page 1 of 1
Swale to Poudre River
Cross Section for Trapezoidal Channel
Project Description
Project File x:\3910000.all\3916412\drainage\filing6.fm2
Worksheet Swale to Poudre River
Flow Element Trapezoidal Channel
Method Manning's Formula
Solve For Channel Depth
Section Data
Mannings Coefficient 0.035
Channel Slope 0.003000 ft/ft
Depth 2.29 ft
Left Side Slope 4.000000 H : V
Right Side Slope 4.000000 H: V
Bottom Width 15.00 ft /
r / I Y( tslDischarge178.00 cfs—ISSOtp O Q too
2.29 ft
1
15.00 ft V
H 1
NTS
03/24/01 FlowMaster v5.15
03:53:16 PM Haeslad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 Page 1 of 1
APPENDIX C
Hydrologic & Hydraulic Computations
Prepared By:RJJ
Project:Strauss Lakes Date:07/26/24
Basin Description:
NRCS Hydrologic Soil Rating:D
Basin Area=5.61 [acres] =244,291 [sf]
Surface Characteristics1 Sub-Area Imp Runoff
[acres] [%]Coefficients1
asphalt, concrete 0.30 100.0 0.20
gravel 1.63 40.00 0.50
lawns, clayey soil, avg slope 2-7%3.69 2.00 0.25
1 City of Fort Collins "Stormwater Criteria Manual", Table 3.2-2
Weighted Percent Imperviousness :I [%] = 18.29 AI = 44,669.11 [sf]
Composite Runoff Coefficients:C =0.32
Frequency Adjustment Factors (Cf)2:
2-Year Cf = 1.00 10-Year Cf = 1.00 100-Year Cf = 1.25
C2 = 0.32 C10 = 0.32 C100
2 = 0.40
2 City of Fort Collins "Stormwater Criteria Manual", Table 3.2-3
Time of Concentration:
Overland Flow Time:Channelized Flow Time:
Li [ft] = 42 Lt1 [FT] = 1860 Lt2 [FT] = 0
Si [%] = 0.10 St1 [%] = 0.01 St2 [%] = 0.00
ti [min] = 20.13 Vt1 [fps]= 3.20 Vt2 [fps]= 0.00
tt1 [min] = 9.69 tt2 [min] = 0.00
tt [min] = 9.69
Time of Concentration:
tc=ti+tt [min] = 29.82
tc(minimum)= 5 min tc [min] = 29.8
Rainfall Intensity3
I2 [in/hr]= 1.30 I10 [in/hr]= 2.21 I100 [in/hr]= 4.52
3 City of Fort Collins "Stormwater Criteria Manual", Table 3.4-1
Runoff - Rational Method Equation4
Q2 [cfs]= 2.34 Q10 [cfs]= 3.97 Q100 [cfs]= 10.16
4 City of Fort Collins "Stormwater Criteria Manual", Equation 5-1
Rational Method Calculations
Horsetooth Road
Existing Conditions
East Horsetooth Road
J:\Cottonwood Land - 372\372.001.01 Strauss Lakes\Memos & Reports\Drainage\Spreadsheets\Rational Method Calcs.xlsx
06/28/2024 00:15:00
Historic SWMM Model
SWMM 5.2 Page 1
Subcatchment Runoff Summary
Total Total Total Total Imperv
Precip Runon Evap Infil Runoff
Subcatchment in in in in in
WestSite 0.98 0.00 0.00 0.94 0.02
EastSite 0.98 0.00 0.00 0.96 0.02
Historic SWMM Model
SWMM 5.2 Page 1
Subcatchment Runoff Summary
Perv Total Total Peak
Runoff Runoff Runoff Runoff Runoff
Subcatchment in in 10^6 gal CFS Coeff
WestSite 0.02 0.04 0.01 0.90 0.036
EastSite 0.00 0.02 0.05 4.92 0.018
Historic SWMM Model
SWMM 5.2 Page 2
06/28/2024 00:15:00
Preliminary Proposed SWMM Model
SWMM 5.2 Page 1
Subcatchment Runoff Summary
Total Total Total Total Imperv
Precip Runon Evap Infil Runoff
Subcatchment in in in in in
E-1 3.69 0.00 0.00 0.15 3.24
E-2 3.69 0.00 0.00 0.15 3.24
E-3 3.69 0.00 0.00 0.15 3.24
E-4 3.69 0.00 0.00 0.15 3.24
E-5 3.69 0.00 0.00 0.15 3.24
Preliminary Proposed SWMM Model
SWMM 5.2 Page 1
Subcatchment Runoff Summary
Perv Total Total Peak
Runoff Runoff Runoff Runoff Runoff
Subcatchment in in 10^6 gal CFS Coeff
E-1 0.22 3.46 1.88 133.77 0.937
E-2 0.22 3.46 1.88 133.77 0.937
E-3 0.22 3.46 1.88 133.77 0.937
E-4 0.22 3.46 1.88 133.77 0.937
E-5 0.22 3.46 1.88 133.77 0.937
Preliminary Proposed SWMM Model
SWMM 5.2 Page 2
Storage Volume Summary
Average Average Evaporation Exfiltration Maximum
Storage Volume Percent Loss Loss Volume
Unit 1000 ft³ Full % % 1000 ft³
CWP 229.665 46.6 0.0 0.0 469.407
Preliminary Proposed SWMM Model
SWMM 5.2 Page 1
Storage Volume Summary
Maximum Day of Hour of Maximum
Storage Percent Maximum Maximum Outflow
Unit Full Volume Volume CFS
CWP 95.3 0 01:35 129.20
Preliminary Proposed SWMM Model
SWMM 5.2 Page 2
Area 99.10 acres
α1 0.90 (24 hours, CWP)
Imperviousness 0.90 % as decimal
WQCV 0.36 wat-in
WQCV 3.58 ac-ft
155984 ft3
Area 12.08 acres
α1 1.00 (40 hours, WQCV Pond)
Imperviousness 0.90 % as decimal
WQCV 0.40 wat-in
WQCV 0.485 ac-ft
21127 ft3
Area 5.61 acres
α1 1.00 (40 hours, EDB)
Imperviousness 0.95 % as decimal
WQCV 0.45 wat-in
WQCV 0.25 ac-ft
10929 ft3
1Drain time coefficients from Table 5.4-1 of the FCSCM and Table 3-2 of the USDCM.
EAST SITE
WEST SITE
HORSETOOTH ROAD
WQCV Calculations
CV
1 0.75
WQCV 3.58 ac-ft
VP
2 2.69 ac-ft
116988 ft3
2Equation RP/CWP-1 from MHFD Fact Sheet T-7.
Permanent Pool
Constructed Wetland Pond
1Sizing coefficient from MHFD Fact Sheet T-7.
Area 12.08 AC 526205 SF
Impervious 90%
1Runoff Coefficient 0.85
QOUT 0.90 CFS
Storm Duration Rainfall Intensity Inflow Volume Outflow Volume Storage Volume
T 2 I 3 V I
4 V O
5 V S
(min) (in/hr)(ft3)(ft3)(ft3)
5 9.95 30650 270 30380
10 7.72 47561 540 47021
15 6.52 60253 810 59443
20 5.60 69001 1080 67921
25 4.98 76702 1350 75352
30 4.52 83540 1620 81920
35 4.08 87976 1890 86086
40 3.74 92166 2160 90006
45 3.46 95924 2430 93494
50 3.23 99497 2700 96797
55 3.03 102670 2970 99700
60 2.86 105719 3240 102479
65 2.71 108522 3510 105012
70 2.59 111695 3780 107915
75 2.48 114591 4050 110541
80 2.38 117302 4320 112982
85 2.29 119920 4590 115330
90 2.21 122538 4860 117678
95 2.13 124664 5130 119534
100 2.06 126912 5400 121512
105 2.00 129377 5670 123707
110 1.94 131471 5940 125531
115 1.88 133196 6210 126986
120 1.84 136030 6480 129550
129550 (ft3)
2.97 (ac-ft)
1Runoff coefficient from table 3.2.1 in Fort Collins Stormwater Criteria Manual (FCSCM).
2Intensity from Table 3.4.1 in FCSCM.
3Calculated per equation 6-1 in FCSCM.
3Calculated per equation 6-2 in FCSCM.
3Calculated per equation 6-3 in FCSCM.
Modified FAA Storage Volume
Modified FAA Storage Volume
West Site
Major Design Storm: 100-year
FAA Detention Sizing
Area 5.61 AC 244372 SF
Impervious 95%
1Runoff Coefficient 0.95
QOUT 2.34 CFS
Storm Duration Rainfall Intensity Inflow Volume Outflow Volume Storage Volume
T 2 I 3 V I
4 V O
5 V S
(min) (in/hr)(ft3)(ft3)(ft3)
5 9.95 15909 702 15207
10 7.72 24686 1404 23282
15 6.52 31274 2106 29168
20 5.60 35814 2808 33006
25 4.98 39811 3510 36301
30 4.52 43361 4212 39149
35 4.08 45663 4914 40749
40 3.74 47838 5616 42222
45 3.46 49788 6318 43470
50 3.23 51643 7020 44623
55 3.03 53290 7722 45568
60 2.86 54873 8424 46449
65 2.71 56327 9126 47201
70 2.59 57974 9828 48146
75 2.48 59477 10530 48947
80 2.38 60884 11232 49652
85 2.29 62243 11934 50309
90 2.21 63602 12636 50966
95 2.13 64705 13338 51367
100 2.06 65873 14040 51833
105 2.00 67152 14742 52410
110 1.94 68239 15444 52795
115 1.88 69134 16146 52988
120 1.84 70605 16848 53757
53757 (ft3)
1.23 (ac-ft)
1Runoff coefficient from table 3.2.1 in Fort Collins Stormwater Criteria Manual (FCSCM).
2Intensity from Table 3.4.1 in FCSCM.
3Calculated per equation 6-1 in FCSCM.
3Calculated per equation 6-2 in FCSCM.
3Calculated per equation 6-3 in FCSCM.
Modified FAA Storage Volume
Modified FAA Storage Volume
FAA Detention Sizing
Major Design Storm: 100-year
Horsetooth Road
Channel Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Monday, Jul 29 2024
Conveyance Swale (Basins 1)
User-defined
Invert Elev (ft) = 100.00
Slope (%) = 0.25
N-Value = 0.053
Calculations
Compute by: Known Q
Known Q (cfs) = 133.77
(Sta, El, n)-(Sta, El, n)...
( 0.00, 105.00)-(15.00, 102.00, 0.025)-(21.00, 100.00, 0.090)-(27.00, 102.00, 0.090)-(42.00, 105.00, 0.025)
Highlighted
Depth (ft) = 4.25
Q (cfs) = 133.77
Area (sqft) = 64.31
Velocity (ft/s) = 2.08
Wetted Perim (ft) = 35.59
Crit Depth, Yc (ft) = 2.64
Top Width (ft) = 34.50
EGL (ft) = 4.32
-5 0 5 10 15 20 25 30 35 40 45 50
Elev (ft)Depth (ft)Section
99.00 -1.00
100.00 0.00
101.00 1.00
102.00 2.00
103.00 3.00
104.00 4.00
105.00 5.00
106.00 6.00
Sta (ft)
Channel Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Monday, Jul 8 2024
Conveyance Swale (Basins 1-2)
User-defined
Invert Elev (ft) = 100.00
Slope (%) = 0.25
N-Value = 0.048
Calculations
Compute by: Known Q
Known Q (cfs) = 267.54
(Sta, El, n)-(Sta, El, n)...
( 0.00, 105.75)-(18.75, 102.00, 0.025)-(24.75, 100.00, 0.090)-(30.75, 102.00, 0.090)-(49.50, 105.75, 0.025)
Highlighted
Depth (ft) = 5.18
Q (cfs) = 267.54
Area (sqft) = 100.72
Velocity (ft/s) = 2.66
Wetted Perim (ft) = 45.08
Crit Depth, Yc (ft) = 3.41
Top Width (ft) = 43.80
EGL (ft) = 5.29
-5 0 5 10 15 20 25 30 35 40 45 50 55
Elev (ft)Depth (ft)Section
99.00 -1.00
100.00 0.00
101.00 1.00
102.00 2.00
103.00 3.00
104.00 4.00
105.00 5.00
106.00 6.00
Sta (ft)
Channel Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Monday, Jul 8 2024
Conveyance Swale (Basins 1-3)
User-defined
Invert Elev (ft) = 100.00
Slope (%) = 0.25
N-Value = 0.045
Calculations
Compute by: Known Q
Known Q (cfs) = 401.31
(Sta, El, n)-(Sta, El, n)...
( 0.00, 106.50)-(22.50, 102.00, 0.025)-(28.50, 100.00, 0.090)-(34.50, 102.00, 0.090)-(57.00, 106.50, 0.025)
Highlighted
Depth (ft) = 5.83
Q (cfs) = 401.31
Area (sqft) = 131.31
Velocity (ft/s) = 3.06
Wetted Perim (ft) = 51.71
Crit Depth, Yc (ft) = 3.94
Top Width (ft) = 50.30
EGL (ft) = 5.98
-5 0 5 10 15 20 25 30 35 40 45 50 55 60 65
Elev (ft)Depth (ft)Section
99.00 -1.00
100.00 0.00
101.00 1.00
102.00 2.00
103.00 3.00
104.00 4.00
105.00 5.00
106.00 6.00
107.00 7.00
Sta (ft)
Channel Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Monday, Jul 29 2024
Conveyance Swale (Basins 1-4)
User-defined
Invert Elev (ft) = 100.00
Slope (%) = 0.25
N-Value = 0.043
Calculations
Compute by: Known Q
Known Q (cfs) = 535.08
(Sta, El, n)-(Sta, El, n)...
( 0.00, 107.00)-(25.00, 102.00, 0.025)-(31.00, 100.00, 0.090)-(37.00, 102.00, 0.090)-(62.00, 107.00, 0.025)
Highlighted
Depth (ft) = 6.34
Q (cfs) = 535.08
Area (sqft) = 158.26
Velocity (ft/s) = 3.38
Wetted Perim (ft) = 56.91
Crit Depth, Yc (ft) = 4.37
Top Width (ft) = 55.40
EGL (ft) = 6.52
-5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70
Elev (ft)Depth (ft)Section
99.00 -1.00
100.00 0.00
101.00 1.00
102.00 2.00
103.00 3.00
104.00 4.00
105.00 5.00
106.00 6.00
107.00 7.00
108.00 8.00
Sta (ft)
APPENDIX D
Drainage Plans
ZIEGLER ROAD
FOS
S
I
L
C
R
E
E
K
R
E
S
E
R
V
O
I
R
I
N
L
E
T
D
I
T
C
H
(IR
R
I
G
A
T
I
O
N
)
BOXEL
D
E
R
D
I
T
C
H
(IRRIG
A
T
I
O
N
)
GRE
A
T
W
E
S
T
E
R
N
R
A
I
L
W
A
Y
RIGDEN RESERVOIR
CA
C
H
E
L
A
P
O
U
D
R
E
R
I
V
E
R
RIGDEN FARM
POND 216
WI
L
L
I
A
M
N
E
A
L
PA
R
K
W
A
Y
PE
R
C
H
E
R
O
N
D
R
I
V
E
FLATIRONS POND
E
H
O
R
S
E
T
O
O
T
H
R
O
A
D
FO
O
T
H
I
L
L
S
C
H
A
N
N
E
L
O
U
T
F
A
L
L
0.90
CFS
12.08
AC.
WEST
SITE
4.92
CFS
100.84
AC.
EAST
SITE
2.34
CFS
5.61
AC.
HORSETOOTH
ROAD
RIG
D
E
N
F
A
R
M
S
O
U
T
F
A
L
L
C
H
A
N
N
E
L
REVISIONS
SCALE:
DATE:
SHEET:
DESIGNED BY:
DRAWN BY:
CHECKED BY:
JOB NO.:
DWG NAME:37200101HIST ODP
JAB
RJJ
RJJ 07/11/2024
LA
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ST
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A
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E
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372.001.01
1" = 200'
D-1
HISTORIC
DRAINAGE PLAN
(1"=200')
8308 COLORADO BLVD
SUITE 200
FIRESTONE, CO 80530
303.833.1416
WWW.CIVILRESOURCES.COM
J:
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P
PROPERTY LINE
MAJOR CONTOUR
MINOR CONTOUR
BARBED WIRE FENCE
CHAINLINK FENCE
GAS LINE
WATER LINE
STORM SEWER
TELECOM
UNDERGROUND ELECTRIC
OVERHEAD WIRES
SANITARY SEWER
RETAINING WALL
A
LEGEND
COTTONWOOD
LAND & FARMS, LLC
BILL MCDOWELL
MANAGING PARTNER
PO BOX 229
BOULDER, CO 80306
CHANNEL CENTERLINE
FLOW DIRECTION
SIGN
SANITARY MANHOLE
FLARED END SECTION
STORM MANHOLE
LIGHT POLE/UTILITY POLE
TREE
DRAINAGE BASIN BOUNDARY
DRAINAGE BASIN NAME
2-YEAR FLOW (CFS)
DRAINAGE AREA (ACRES)
LEGEND CONT.
NO.DESCRIPTION DATE
01 1ST REVIEW CITY COMMENTS07/28/25
ZIEGLER ROAD
FOSSIL CREEK RESERVOI
R
I
N
L
E
T
D
I
T
C
H
(IRRIGATION)
BOXEL
D
E
R
D
I
T
C
H
(IRRIG
A
T
I
O
N
)
GRE
A
T
W
E
S
T
E
R
N
R
A
I
L
W
A
Y
RIG
D
E
N
F
A
R
M
O
U
T
F
A
L
L
C
H
A
N
N
E
L
RIGDEN RESERVOIR
CA
C
H
E
L
A
P
O
U
D
R
E
R
I
V
E
R
118.88
CFS
12.08
AC.
WEST
SITE
133.77
CFS
20.68
AC.
E-1
133.77
CFS
19.90
AC.
E-5
133.77
CFS
20.35
AC.
E-2
133.77
CFS
20.28
AC.
E-3
133.77
CFS
19.64
AC.
E-4
RIGDEN FARM
POND 216
WI
L
L
I
A
M
N
E
A
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PA
R
K
W
A
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PE
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C
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D
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E
FLATIRONS POND
EAST SITE
APPROX. LOCATION OF DETENTION POND
AREA OF POND = TBD
WQCV = 0.48 AC-FT
MODIFIED FAA STORAGE VOLUME = 2.97 AC-FT
APPROX. AREA OF CONSTRUCTED
WETLAND POND = 4.91 AC
PERMANENT POOL = 2.69 AC-FT
WQCV = 3.58 AC-FT
100-YR VOL. = 7.20 AC-FT
TOTAL STORAGE VOL. = 10.78 AC-FT
APPROX. LOCATION OF
POND DISCHARGE TO FCO
APPROX. LOCATION OF
POND DISCHARGE TO FCRID
E
H
O
R
S
E
T
O
O
T
H
R
O
A
D
APPROX. AREA OF
DETENTION POND = 0.76 AC
WQCV = 0.25 AC-FT
MODIFIED FAA STORAGE VOL. =
1.23 AC-FT
5.06
CFS
5.61
AC.
HORSETOOTH
ROAD
FO
O
T
H
I
L
L
S
C
H
A
N
N
E
L
O
U
T
F
A
L
L
APPROX. LOCATION OF
POND DISCHARGE TO FCO
62.0' MAXIMUM
SWALE TOP WIDTH
Q100 = 535.08 CFS
42.0' MINIMUM
SWALE TOP WIDTH
Q100 = 133.77 CFS
49.5' SWALE
TOP WIDTH
Q100 = 267.54 CFS
57.0' SWALE
TOP WIDTH
Q100 = 401.31 CFS
DP - W2
DP - E1
DP - E2
DP - E3
DP - E4
DP -
E
5
DP - E6
DP - H2
DP
-
H
1
NOTE:
LID WILL BE PROVIDED REGIONALLY
FOR THE EAST SITE VIA THE
CONSTRUCTED WETLAND POND.
NOTE:
LID WILL BE PROVIDED LOCALLY
FOR THE WEST SITE VIA RAIN
GARDENS, PERMEABLE PAVERS,
GRASS BUFFERS, ETC.
NOTE:
LID WILL NOT BE PROVIDED FOR
THE HORSETOOTH ROAD BASIN.
LID FOR ALL OTHER DRAINAGE
BASINS WILL ACCOUNT FOR THE
75% LID REQUIREMENT.
APPROX. LOCATION OF
POND DISCHARGE TO FCRID
APPROX. LOCATION OF
SECONDARY DETENTION POND
(IF REQUIRED)
DP - W1
REVISIONS
NO.DESCRIPTION DATE
SCALE:
DATE:
SHEET:
DESIGNED BY:
DRAWN BY:
CHECKED BY:
JOB NO.:
DWG NAME:37200101ODP
JAB
RJJ
RJJ 07/11/2024
LA
R
I
M
E
R
C
O
U
N
T
Y
,
C
O
L
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A
D
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Y
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F
F
O
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T
C
O
L
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I
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S
ST
R
A
U
S
S
L
A
K
E
S
372.001.01
1" = 200'
D-2
OVERALL
DRAINAGE PLAN
(1"=200')
8308 COLORADO BLVD
SUITE 200
FIRESTONE, CO 80530
303.833.1416
WWW.CIVILRESOURCES.COM
J:
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1
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K
E
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W
I
N
G
S
\
S
H
E
E
T
S
\
3
7
2
0
0
1
0
1
O
D
P
PROPERTY LINE
MAJOR CONTOUR
MINOR CONTOUR
BARBED WIRE FENCE
CHAINLINK FENCE
GAS LINE
WATER LINE
STORM SEWER
TELECOM
UNDERGROUND ELECTRIC
OVERHEAD WIRES
SANITARY SEWER
RETAINING WALL
CHANNEL CENTER LINE
FLOW DIRECTION
A
LEGEND
PROPOSED
LEGEND CONT.
PROPOSED
WATER QUALITY/
FLOOD CONTROL FACILITY
CONVEYANCE SWALE
SIGN
SANITARY MANHOLE
FLARED END SECTION
STORM MANHOLE
LIGHT POLE/UTILITY POLE
TREE
DRAINAGE BASIN BOUNDARY
DESIGN POINT
DRAINAGE BASIN NAME
100-YEAR FLOW (CFS)
DRAINAGE AREA (ACRES)
DP - #A
COTTONWOOD
LAND & FARMS, LLC
BILL MCDOWELL
MANAGING PARTNER
PO BOX 229
BOULDER, CO 80306
01 1ST REVIEW CITY COMMENTS07/28/25