HomeMy WebLinkAboutReports - Drainage - 11/01/2024 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
CIVIL 111110LJRCESLLC PREPARED: NOVEMBER 2024
Overall Drainage Report Strauss Lakes
Table of Contents
Paqe
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...........................................................................................................................................7
1.6 Project Description........................................................................................................................................7
2.0 DRAINAGE DESIGN CRITERIA............................................................................................................................7
2.1 Regulations...................................................................................................................................................7
2.2 Hydrologic& Hydraulic Criteria.....................................................................................................................8
3.0 PROPOSED DRAINAGE FACILITIES...................................................................................................................8
3.1 General Concept...........................................................................................................................................8
3.2 Drainage System Outfall...............................................................................................................................9
3.3 Low Impact Development(LID)...................................................................................................................10
3.4 Municipal Separate Storm Sewer System (MS4) Permit.............................................................................11
3.5 Detention & Flood Control...........................................................................................................................11
4.0 CONCLUSIONS...................................................................................................................................................12
4.1 Compliance with Criteria.............................................................................................................................12
4.2 Drainage Concept.......................................................................................................................................12
5.0 REFERENCES ....................................................................................................................................................12
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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
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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
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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 61h 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 PUD overlay application. The PUD 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 Existin_p 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 and 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). 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),just
north 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.
There is a drainage ditch, Rigden Farm Outfall Channel (RFOC), located along the northern property line, between the
railroad and existing access road.This ditch accepts discharge from the Rigden Farm water quality pond,located northeast
of East Drake Road,and west of the FCRID. Flow in the outfall channel travels southwest and discharges to the Cache la
Poudre River, east of Rigden Reservoir.
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
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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.The portion of the Site north of the Boxelder
Ditch will be within the 500-year floodplain. This portion of the Site will need to be filled to elevate it out of the 500-year
floodplain and to achieve more favorable drainage characteristics.
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 61h,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 alternative location for a water quality pond to serve the Fox Meadows Drainage
Basin (see Appendix B for referenced figure). The Strauss Lakes development does not accommodate a water quality
pond to treat off-site flows.
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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 FCO 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
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.
The design of the Rigden Farm Outfall Channel (RFOC)was detailed in the Final Drainage and Erosion Control Report
Rigden Farm—Filing Six, prepared by JR Engineering, last revised February 8, 2002.The RFOC was previously a
lateral of the Boxelder Ditch, and was repurposed to convey outflow from Pond 216 of the Rigden Farm development
(located west of the FCRID, adjacent to the northern portion of the Site)to the Cache la Poudre River. Per the report, the
100-year discharge from the Pond 216 siphon outlet structure is 134 cfs, and the channel capacity is 178 cfs.
See Appendix B for relevant excerpts of the abovementioned reports.
1.6 Proiect Description
The Strauss Lakes Project proposes to develop the approximately 188-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 Planned Unit
Development Overlay(PUD).The currently annexed parcel (8728000003) is zoned Low Density Mixed-Use
Neighborhood District(LMN),which will be the basis of the PUD development characteristics. 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 Re_- ulations
The proposed drainage design will comply with the regulations set forth in the Fort Collins Stormwater Criteria Manual
(FCSCM), revised December 2018.
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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
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 the West Site, located west of the FCRID,
the East Site, located east of the FCRID, and the North Site, located North of the Boxelder Ditch. Furthermore, the East
Site has been subdivided into five(5)conceptual 20-acre drainage 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 conceptually size a drainage
swale parallel to the Boxelder Ditch. The stormwater systems for the West Site, East Site, and North 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 curb and gutter, inlets,
and storm sewer. Captured runoff will be directed to a water quality pond located in teg eastern corner of the West Site.
This pond will treat the WQCV of the West Site, and will not provide flood control.The flows greater than the WQCV will
discharge east to the FCRID via a pipe and/or spillway. The 100-year flow will enter the FCO via the FCRID spill
structure.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 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
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entering the Boxelder Ditch. Each drainage basin will discharge to a conveyance swale located along the east property
line,just west of the Boxelder Ditch.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. 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.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.
3.1.3 North Site
The North Site will maintain the historic drainage pattern by directing developed runoff east, via surface flow,curb and
gutter, inlets, and storm sewer,to an extended detention basin (detention pond) located on the east side of the North
Site. The pond will intercept the developed runoff and redirect it north, discharging to the Rigden Farm Outfall Channel.
While the RFOC is not the historic discharge point of the North Site, redirecting the detained flow to the RFOC will
reduce the amount of runoff flowing east to the future community park. The detention pond will be sized to treat the
WQCV of the North Site, and temporarily store the 100-year developed runoff, releasing the detained flow at the
allowable remaining capacity in the RFOC.This varies from the FCSCM requirement which limits developed runoff to the
historic 2-year discharge for the Site. This variance from the standards is proposed because the detention pond will not
be discharging to the historic discharge point(the adjacent property to the east), and the RFOC is a direct outfall to the
Cache la Poudre River.The pond will have an emergency spillway located along the northeast side,which will be sized
to pass the undetained 100-year runoff from the North Site,and discharge to the RFOC. The drainage area of the North
Site is approximately 20 acres.The layout and density of the North Site is unknown at this point;therefore the
impervious value of the North 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 the North Site was estimated to be 127.26 cfs, per SWMM. See Appendix C for SWMM summary tables.
3.1.4 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 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 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 historic 2-year runoff of East Horsetooth
Road was estimated to be 2.34 cfs per the Rational Method.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. Developed runoff will be captured in street inlets,and conveyed via storm sewer to the detention pond.
3.2 Drainage System Outfall
Per prior agreements between Cottonwood Land and the City of Fort Collins, developed runoff from the West and East
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Sites, and East Horsetooth Road 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. Undetained 100-year runoff from the West Site will be discharged to
the FCRID at a rate of 118.88 cfs. During the 100-year event, the FCRID overflows to the FCO. The constructed wetland
pond outlet structure will be designed to release the 100-year runoff from the East Site at a rate of approximately 132.87
cfs. The detention pond outlet structure will be designed to release the 100-year runoff from East Horsetooth Road at a
rate of approximately 1 cfs. This results in a total 100-year discharge from the West and East Sites of 252.75 cfs, the
maximum allowable. 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.
Developed runoff from the North Site will discharge to the RFOC along the northeast property line. The RFOC receives
134 cfs of runoff from Rigden Farm Pond 216 during the 100-year storm event.The capacity of the RFOC is 178 cfs,which
means there is 44 cfs of remaining capacity in the channel.At the time of this report,the RFOC has not been hydraulically
modeled to verify the capacity of the channel; therefore, for the purpose of this overall report, a reduction factor of 25%
was applied to the original design capacity, resulting in an allowable capacity of 33 cfs. This reduction factor is a
conservative assumption, and the actual capacity of the RFOC will be verified through hydraulic modeling and discussed
in future drainage reports. The North Site and the future East Community Park (planned for the lot located east of the
North Site)will discharge developed flow to the RFOC. The allowable capacity of the channel was apportioned based on
the acreage of the North Site and the future park, 20.29 and 57.97 acres, respectively, resulting in an allowable 100-year
discharge of 9 cfs, for the North Site, and 24 cfs for the future park. See Appendix C for SWMM summary tables. The
outlet structure for the North Site detention pond will be designed to release the 100-year storage volume at or below 9
cfs. Runoff discharged to the RFOC will flow southeast and discharge to the Cache la Poudre River, east of Rigden
Reservoir.
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.
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.
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LID will not be implemented for 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 North and West Sites 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 water quality pond, as described in section 3.1.1,
a constructed wetland pond, as described in section 3.1.2, and an extended detention basin, as described in section
3.1.3.
3.5 Detention&Flood Control
The West Site will not have flood control, and will release the undetained 100-year runoff directly to the FCRID. During
the a 100-year event,the FCRID overflows to the FCO. Per SWMM,the preliminary 100-year runoff from the West Site is
118.88 cfs. This will be reduced to some degree with the runoff is routed through the water quality facilities, which will
provide some detention capacity.A detailed analysis of this will be included in future drainage reports.
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 455,107 cubic feet, or 10.45 acre-feet. For a
preliminary WQCV of 3.58 acre-feet, this results in a required 100-year storage volume of 6.87 acre-feet. A preliminary
pond with a footprint of approximately 5 acres was evaluated in SWMM. See Appendix C for SWMM summary tables. To
account for the undetained discharge from the West Site, the CWP outlet structure will be designed to release the 100-
year volume at a rate of approximately 132.87 cfs,which is equal to the capacity of the FCO(252.75 cfs), minus the direct
discharge from the West Site (118.88 cfs).
The 100-year runoff of the North Site will be detained in the extended detention basin, and released to the RFOC. The
detention pond was preliminarily sized using the Modified FAA Procedure,and the 100-year storage volume was estimated
to be 3.68 acre-feet. The WQCV of the North Site was calculated to be 0.80 acre-feet, resulting in a total storage volume
of 4.48 acre-feet. The pond outfall to the RFOC and the 1-foot freeboard requirement limits the storage depth of the pond
to approximately 1-foot,which will require fill of the Site. This results in an approximate pond footprint of 4.87 acres. This
footprint could be reduced by importing additional material to the Site. See Appendix C for preliminary Modified FAA
calculations.The detention pond outlet structure will be designed to release the 100-year volume at a rate of 9 cfs, based
on the allowable capacity in the channel, refer to section 3.2.
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 pond was preliminarily sized using the Modified FAA Method, and the 100-year storage
volume was estimated to be 1.46 acre-feet. The WQCV was estimated to be 0.25 acre-feet, resulting in a total required
storage volume of 1.71 acre-feet.The available pond working depth south of East Horsetooth Road is estimated to be 4.5-
feet, based on preliminary survey. With a one-foot of freeboard requirement, this results in a pond storage depth of 3.5
feet, and an approximate pond area of 0.75 acres.
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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.
4.2 Draina_pe Concept
The proposed drainage system will improve Site drainage through the following methods:
• The 100-year developed runoff of the North Site will be detained and released to the RFOC at a rate
proportional to the remaining capacity in the channel. This will reduce the amount runoff discharging to the
adjacent property to the east.
• The 100-year developed runoff from the East and West Sites 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 Creet Reservoir Inlet Ditch Storm Water Overflow. Donohue&Associates,
Inc. March 1988.
o Addendum to the Final Design Report for the Fossil Creet 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
Prepared:November 2024 Page 12 of 13
Overall Drainage Report Strauss Lakes
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.
Prepared:November 2024 Page 13 of 13
APPENDIX A
Figures & Tables
r
LL NIA go
.k
Strauss Lakes Vicinity Map
F -t Collins, CO
or
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Hydrologic Soil Group—Larimer County Area,Colorado R:
(Strauss Lakes)
0 o
qqq 498100 498300 498500 498700 498900 499100 499300
40°33'13"N — 40°33'13"N
S.
I �
d.
ei ffi
.. -.
ML
Soil Map may not be valid at this scal=.
40°32'11"N 40°32'11"N
498100 498300 498500 498700 498900 499100 499300
3 3
Map Scale:1:9,330 fi printed on A portrait(8.5"x 11")sheet. b
Meber N s °
0 100 200 400 600
Feet
0 450 900 1800 2700
Map projection:Web Mercator Comer coordinates:WGS84 Edge tics:11TM Zone 13N WGS84
USDA Natural Resources Web Soil Survey 7/12/2024
i Conservation Service National Cooperative Soil Survey Page 1 of 4
Hydrologic Soil Group—Larimer County Area,Colorado
(Strauss Lakes)
MAP LEGEND MAP INFORMATION
Area of Interest(AOI) 0 C The soil surveys that comprise your AOI were mapped at
Area of Interest(AOI) CID 1:24,000.
0
Soils ® D Warning:Soil Map may not be valid at this scale.
Soil Rating Polygons
A Not rated or not available Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
F—] AID Water Features line placement.The maps do not show the small areas of
Streams and Canals contrasting soils that could have been shown at a more detailed
0 B
scale.
Transportation
B/D
. Rails Please rely on the bar scale on each map sheet for map
0 C measurements.
� Interstate Highways
0 C/D US Routes Source of Map: Natural Resources Conservation Service
Web Soil Survey LIRL:
0 D Major Roads Coordinate System: Web Mercator(EPSG:3857)
0 Not rated or not available Local Roads
Maps from the Web Soil Survey are based on the Web Mercator
Soil Rating Lines Background projection,which preserves direction and shape but distorts
q distance and area.A projection that preserves area,such as the
Aerial Photography Albers equal-area conic projection,should be used if more
.-.. AID accurate calculations of distance or area are required.
++� B This product is generated from the USDA-NRCS certified data as
ti B/D of the version date(s)listed below.
C Soil Survey Area: Larimer County Area,Colorado
Survey Area Data: Version 18,Aug 24,2023
r.i CID
Soil map units are labeled(as space allows)for map scales
... D 1:50,000 or larger.
Not rated or not available Date(s)aerial images were photographed: Jul 2,2021—Aug 25,
Soil Rating Points 2021
p A The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
E3 AID imagery displayed on these maps.As a result,some minor
B shifting of map unit boundaries may be evident.
B/D
USDA Natural Resources Web Soil Survey 7/12/2024
Conservation Service National Cooperative Soil Survey Page 2 of 4
Hydrologic Soil Group—Larimer County Area,Colorado Strauss Lakes
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
22 Caruso clay loam,0 to 1 D 79.3 43.7%
percent slope
35 Fort Collins loam,0 to 3 C 22.1 12.2%
percent slopes
53 Kim loam, 1 to 3 percent B 16.5 9.1%
slopes
62 Larimer-Stoneham B 14.1 7.8%
complex,3 to 10
percent slopes
64 Loveland clay loam,0 to C 0.0 0.0%
1 percent slopes
73 Nunn clay loam,0 to 1 C 11.1 6.1%
percent slopes
74 Nunn clay loam, 1 to 3 C 0.31 0.1%
percent slopes
101 Stoneham loam, 1 to 3 B 10.8 6.0%
percent slopes
102 Stoneham loam,3 to 5 C 3.5 1.9%
percent slopes
105 Table Mountain loam,0 B 15.1 8.3%
to 1 percent slopes
136 Water 8.6 4.7%
Totals for Area of Interest 1+81.3 100.0%
USDA Natural Resources Web Soil Survey 7/12/2024
Conservation Service National Cooperative Soil Survey Page 3 of 4
Hydrologic Soil Group—Larimer County Area,Colorado Strauss Lakes
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
USDA Natural Resources Web Soil Survey 7/12/2024
Conservation Service National Cooperative Soil Survey Page 4 of 4
NOTES TO USERS Cache La LEGEND
This map is for use in administering the National Flood Insurance Program. It Poudre River SPECIAL FLOOD HAZARD AREAS (SFHAs) SUBJECT TO
does not necessarily identify all areas subject to flooding, particularly from local Split R Path INUNDATION BY THE 1% ANNUAL CHANCE FLOOD
drainage sources of small size. The community map repository should be 3135000 FT 1��4894 105,00,00.01, The 1% annual chance flood (100-year flood), also known as the base flood, is the flood
consulted for possible updated or additional flood hazard information. 105101'52�5" JOINS PANEL 0984 4013345.0" that has a 1% chance of being equaled or exceeded in any given year. The Special
40133'45.0"
..... . ....
........ .
..........
...................... Flood Hazard Area is the area subject to flooding by the 1% annual chance flood. Areas
To obtain more detailed information in areas where Base Flood Elevations RIVERBEND COURT-/ of Special Flood Hazard include Zones A, AE, AH, AO, AR, A99, V and VE. The Base
.............
LUN E:A:E
"'ISIS
......... ..
.................................... ..
.1-1:11111":....:,-.. - Flood Elevation is the water-surface elevation of the 1%annual chance flood.
(BFEs) and/or floodways have been determined, users are encouraged to consult ........ ...........: : ::: ii LARIMER COUNTY
I........................ :SISSISIS
.......................................
X-N.I.-N.,
the Flood Profiles and Floodway Data and/or Summary of Stillwater Elevations UNINCORPORATED AREAS ZONE A No Base Flood Elevations determined.
............. .. ............
tables contained within the Flood Insurance Study (FIS) report that accompanies Z
.................................... .. . . ............
OLLINS 080101
CITY OF FORT C
ZONEAE Base Flood Elevations determined.
...................................
this FIRM. Users should be aware that BFEs shown on the FIRM represent
".. .......I.".,.,.,.,.,."..'�..'-.,.,.,.,.:.."."..,::..".,.,.,.,..".,,.:.."..,.,..',..'-..'.-
080102 ZONEAH Flood depths of I to 3 feet (usually areas of ponding)- Base Flood
rounded whole-foot elevations. These BFEs are intended for flood insurance
..................
rating purposes only and should not be used as the sole source of flood Elevations determined.
P.RbFILE �.�: FLOODING EFFECTS:FROM 9 44 000M
elevation information. Accordingly, flood elevation data presented in the FIS 48 Boxelder Creek 1-25 Split 90 IN ZONEAO Flood depths of I to 3 feet (usually sheet flow on sloping terrain);
....... ....................... BASELINE
RIVER.
.. .... ............ .21
Sx,
report should be utilized in conjunction with the FIRM for purposes of AE PROFILE BASE LINE average depths determined. For areas of alluvial fan flooding, velocities
iij�iiijil Pitch�Diversio
SPLITL�PATR
also determined.
construction and/or floodplain management. ZONE AE
'/VP D
........ ...
ZONE AR Special Flood Hazard Area formerly protected from the 1% annual
.. . ... .... ... .. .......
Coastal Base Flood Elevations shown onthis map apply only landward
... . ... ... . ... ... .. . ....... .. chance flood by a flood control system that was subsequently
4D
of 0.0' North American Vertical Datum of 1988 (NAVD 88). Users of this ... decertified. Zone AR indicates that the former flood control system is
4905
S
being restored to provide protection from the 1% annual chance or
FIRM should be aware that coastal flood elevations are also provided in the 41893 greater flood.
Summary of Stillwater Elevations table in the Flood Insurance Study report
"'S
for this jurisdiction. Elevations shown in the Summary of Stillwater Elevations ZONE A99 Area to be protected from 1% annual chance flood by a Federal
C, MCLAUGHLIN LANE
table should be used for construction and/or floodplain management purposes to flood protection system under construction; no Base Flood Elevations
when they are higher than the elevations shown on this FIRM. --Boxelder Creek 1-25 determined.
NX ZONE V
..... ... Coastal flood zone with velocity hazard (wave action); no Base Flood
Boundaries of the floodways were computed at cross sections and interpolated Split Overflow
Elevations determined.
Boxelder Creek 4899
between cross sections. The floodways were based on hydraulic considerations ZONE VE
r-xx Coastal flood zone with velocity hazard (wave action); Base Flood
-T1
with regard to requirements of the National Flood Insurance Program. Floodway LL0488 A''t ....... Elevations determined.
X
vea
widths and other pertinent floodway data are provided in the Flood Insurance
. .. . ... ... . .... ... 21 4885
Study report for this jurisdiction.
FLOODWAY AREAS IN ZONE AE
.............
.. ... . ... .... ....... 18
...... 48821 6,
Certain areas not in Special Flood Hazard Areas may be protected by flood 11 1 5SS:
�:�NOTE;THIS AREA IS SHOWNA&BEING PPIOTECTED:� The floodway is the channel of a stream plus any adjacent floodplain areas that must be
control structures. Refer to Section 2.4 "Flood Protection Measures" of
:FROM THE1-PEPICENT-ANNUAL-CHANCE�OPI�GREATER
kept free of encroachment so that the 1% annual chance flood can be carried without
the Flood Insurance Study report for information on flood control structures FLOOD HAZARD BYW LEVEE:SYSTEM OVERTOPPING:::, substantial increases in flood heights.
......... ...................
... ......
for this jurisdiction. ::OR FAILURE OF�ANY.LEVEE SYSTEKIS�POSSIBLE. FOR
79
ADDITIONAL INFORMATION,:SEETHE"ACCREDITED
XN.N.
N OTHER FLOOD AREAS
K NOTES TO:USERS. ..............
The projection used in the preparation of this map was Colorado State
Plane north zone (FIPSZONE 0501).The horizontal datum was NAD83, ZONE X Areas of 0.2% annual chance flood; areas of 1% annual chance flood
..............
........ ... ........... ........
with average depths of less than I foot or with drainage areas less than
GRS1980 spheroid. Differences in datum, spheroid, projection or State Plane
..............
LARIMER:COUNTY:.::: ...... 0 1 square mile; and areas protected by levees from 1% annual chance
..........
. ......... ... ...
zones used in the production of FIRMs for adjacent jurisdictions may result in Cach flood.
..........
....UNINCORPORAT D AREAS-, .. 41
slight positional differences in map features across jurisdiction boundaries.
......... .... ......... ......
. ..........
....... ....
These differences do not affect the accuracy of the FIRM. :::�:080101:�� Lowflow.... Channel ZONE All= OTHER AREAS
..........
................
.......... .... .. IF
Flood elevations on this map are referenced to the North American Vertical ......... ......
..... .......
ZONE X Areas determined to be outside the 0.2% annual chance floodplain.
............
..........
...........Datum of 1988. These flood elevations must be compared to structure and
..................
------ ....
ZONE D Areas in which flood hazards are undetermined but possible.
ground elevations referenced to the same vertical datum. For information .........
................
...........
............. .......regarding conversion between the National Geodetic Vertical Datum of 1929 1445000 FT
COASTAL BARRIER RESOURCES SYSTEM (CBRS) AREAS
and the North American Vertical Datum of 1988, visit the National Geodetic .......
.............
CITY OFFORT COLLIINS:: .........
Survey website at http://www.ngs.noaa.gov/ or contact the National Geodetic ....... ........... .................................
............... .....................
Survey at the following address: ............................. ........ ............... ..........
.................
...............
....... ........ OTHERWISE PROTECTED AREAS (OPAs)
..........
NGS Information Services ................ .................. ........ .............. ....
............. ............ .........................
CBRS areas and OPAs are normally located within or adjacent to Special Flood Hazard Areas.
.......... ....NOAA, N/NGS12 ....................
ID
.................................... ...................................
National Geodetic Survey DRAKE ROA ..... ....... ..
D ....... ...... Floodplain boundary
. ...........................
LU .............. ........................ .................
...... .............
SSMC-3, #9202 > ....... ...... DRIVE:�...
..... .... ..
..............
............................. Floodway boundary
.............................................................
1315 East-West Highway .............. ------------------------------
......................
.. .... ... .......;................ .. ... Zone D boundary
DRIVE ...............
Silver Spring, MD 20910-3282 ....... .. .... 44 000M
...... . .... 89 IN CBRS and OPA boundary
..................
............
..................... ............................. ..................................
.......... .....................
. .... . . ..
..............
................... ...........................................
To obtain current elevation, description, and/or location information for bench marks 0 ........... ............
LL ......... 7.... .................
..........
shown on this map, please contact the Information Services Branch of the Boundary dividing Special Flood Hazard Areas of different
... . ........ .
............................. ...............
National Geodetic Survey at (301) 713-3242, or visit its website at 0 LIMON DRIV Base Flood Elevations, flood depths or flood velocities.
.... .... ...... ......................
..................
............ .
. . ........
http://www.ngs.noaa.gov/. 513 Base Flood Elevation line and value; elevation in feet*
............... .....
..........
Base map information on this FIRM was provided by the Larimer County GIS and .......... ...
(EL 987) Base Flood Elevation value where uniform within zone;
......... . ...
.............
Mapping Department. Additional input was provided by the City of Fort Collins
levation in feet*
e
LL0490 ..............
................................. ...........
Geographic Information Services Division. These data are current as of 2010. . .... Referenced to the North American Vertical Datum of 1988 (NAVD 88)
............
...........
..................................
Cross section line
This map reflects more detailed and up-to-date stream channel configurations
.................. -------- Transect line
than those shown on the previous FIRM for this jurisdiction. The floodplains 0 ..............
...........................
and floodways that were transferred from the previous FIRM may have been
..... ..... Geographic coordinates referenced to the North American
7-07'30",32-22'301,
adjusted to conform to these new stream channel configurations. As a 9
--------- --- --- Datum of 1983 (NAD 83)
result, the Flood Profiles and Floodway Data tables in the Flood Insurance
........... 1000-meter Universal Transverse Mercator grid ticks,zone 13
42
Study report (which contains authoritative hydraulic data) may reflect stream 75000mN
channel distances that differ from what is shown on this map.
.................................. 5000-foot grid ticks: Colorado State Plane coordinate
6000000 FT
system, north zone(FIPSZONE 0501),Lambert Conformal Conic
.............................. ...
Corporate limits shown on this map are based on the best data available 0 JOSEPH DR.
0
0
at the time of publication. Because changes due to annexations or de-annexations 0
A
may have occurred after this map was published, map users should contact ... ...
Bench mark (see explanation in Notes to Users section of
.........
............... ..... ......... . . ...... ......... DX551 0
...... LLI
appropriate community officials to verify current corporate limit locations. X this FIRM panel)
Lu AN ..........
........ ....... Z
.........
/S
Z <
... ............. M1.5
W.4,, ..............................
U)
.................. .........
Please refer to the separately printed Map Index for an overview map of the River Mile
county showing the layout of map panels;community map repository addresses; 0 M �,FLINGER DRIVE C)
0 Z
Z MAP REPOSITORIES
and a Listing of Communities table containing National Flood Insurance Program 0
.11. .........s
0 Refer to Map Repositories list on Map Index
dates for each community as well as a listing of the panels on which each ...... ....
community is located.
................
.........
EFFECTIVE DATE OF COUNTYWIDE
....... ......
CO, <
PARKWAY
FLOOD INSURANCE RATE MAP
For information and questions about this map, available products associated with this
December 19,2006
FIRM including historic versions of this FIRM, how to order products or the National
EFFECTIVE DATE(S)OF REVISION(S)TO THIS PANEL
Flood Insurance Program in general, please call the FEMA Map Information eXchange 29
. ...... ...
0)
May 2,2012-to change Special Flood Hazard Areas, to change floodway, to reflect updated
at l-,877-FEMA-MAP (1--877-336-2627) or visit the FEMA Map Service Center website
topographic information, to change Base Flood Elevations,and to incorporate previously issued
BANK DRIVE Letters of Map Revision.
at http://msc.fema.gov.Available products may include previously issued Letters of Map SLADE STREET
M <
Change, a Flood Insurance Study Report, and/or digital versions of this map. Many of
0 ......
...........
..............
these products can be ordered or obtained directly from the website. Usersmay
... . ......
determine the current map date for each FIRM panel by visiting the FEMA Map . . ... ..........
RED CLOUD COURT
Service Center website or by calling the FEMA Map Information eXchange.
For community map revision history prior to countywide mapping,refer to the Community
0
GO-
Map History table located in the Flood Insurance Study report for this jurisdiction.
..........
To determine if flood insurance is available in this community, contact your insurance
00
RED MOO
Accredited Levee Notes to Users: Check with your local communi
ty to obtain
MAROON C01jr,
agent or call the National Flood Insurance Program at 1-800-638-6620.
44 000M
more information, such as the estimated level of protection provided (which may
exc ... . ......
88 IN
COURT
rn
eed the I-percent-annual-chance level) and Emergency Action Plan, on the Fossil Creek Reservoir Inlet Canal
G
levee system(s) shown as providing protection for areas on this panel. To mitigate flood risk in residual risk areas, property owners and residents are DRIVF MAP SCALE 1 500'
encouraged to consider flood insurance and floodprocifing or other protective < 250 0 500
4863
0
1
measures. For more information on flood insurance, interested parties should
METERS
150 0 150 300
visit the FEMA Website at http://www.fema.gov/business/nfip/index.shtm.
3e\PJELSTONE COURT
.. ......11.:....:�.*
M
LU
........ .....
UJ
N
PANEL 0992G
01 .................................... .
...........
1440000 FT
us 0
C1.
DRIVE
FIRM
FLOOD INSURANCE RATE MAP
>
................
C11 UJ
DRIVE Z
0 E COURT BLACKSTO LARIMER COUNTY,
............
0
<
SETOO
HOR TH
'4858 AND INCORPORATED AREAS
LU ......
> ANTELOPE
ROAD
. .........
..........
............ ...........
cc
........ PANEL 992 OF 1420
U col/%,
OtA ...
............
.... . . .... . ..... . .. .. (SEE MAP INDEX FOR FIRM PANEL LAYOUT)
0
CONTAINS
...........
COURT 44/ Q - 34 COMMUNITY NUMBER PANEL SUFFIX
\Nr
NOTE: MAP AREA SHOWN ON THIS PANEL IS LOCATED ............. .......
0 MICHELLE LANE
LARIMER COUNTY 080101 0992 G
WITHIN TOWNSHIP 7 NORTH, RANGE 68 WEST.
.. ... . ... .. ... .. . FORT COLLINS,CITY OF 080102 0992 G
0 0
>
..........
...... ...........
. ....... .....
0 ......
0 ...... ........ ........
BISON rZ
cr
rn
32
<
Y DRIVE 33
CHARLIE
cc LARIMER COUNTY .. 44 000M
0 87 IN
WHITWORTH DRIVE DRIVE ........
Z UNINCORPORATED AREAS . . ... ...
W
CITY OF FORT COLLINS CITY OF FORT COLLINS
080101
080102 LJ 4
080102
"F-SA VERDE Notice to User: The Map Number shown below should be
DRIV
used when placing map orders; the Community Number shown
<
above should be used on insurance applications for the subject
> .... .
0 community.
Z ......
Z
LU 11IVE
0
Z
:D CANYON
S 08069CO992G
....... MAPNUMBER
sTRES1
.... . ... ...
pp,DDINGTON ROAD 40131'52.5"
T
77
40131'52.5,, r JOINS PANEL 0994 105'00'00.0" MAP REVISED
105101'52.5" 498000m E 4 99000m E ND 5 MAY 2, 2012
Federal Emergency Management Agency
�city. CoTns Fort Collins Risk Map
cis
Legend
•� �. a g
! "aEl Growth Management Area
a.� a4, •1 M+ �.. City Limits
Percent Annual Chance Grids
C >0.2%-1%
' 5 ~" >1%-2%
>2%-4%
� 'C ■ >4%-10%
Citations
kW y
w
� - S Efa O�+ Ct1
Ir'e rr.he Ir,o n r , t �•
,gona Ridge
r...........
�.:4
1: 18,056
oprionnow �. Notes
0.6 0 0.28 0.6 Miles
This map is a user generated static output from the City of Fort Collins FCMaps
WGS_1984_Web_Mercator_Auxiliary_Sphere Internet mapping site and is for reference only.Data layers that appear on this
City of Fort Collins-GIS
map may or may not be accurate,current,or otherwise reliable.
FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards(Ch. 5)
4.0 SWMM
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
Depth of Storage
Impervious Areas 0.1 inches
Pervious Areas 0.3 inches
Infiltration Parameters
Maximum 0.51 in/hr
Minimum 0.50 in/hr
0.0018 in/sec or
Decay Rate 6.48 in/hr
Zero Detention Depth 1%
Manning's"n"
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.
City of 4.1 Input Parameters
i'^Fort Collins Page 10
FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards(Ch. 5)
4.0 SWMM
Table 4.1-2. Land Use-Percent Impervious
Percent Impervious
Land Use N
Residential
Urban Estate 30
Low Density 50
Medium Density 70
High Density 90
Commercial
Commercial 80
Industrial 90
Undeveloped
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
Percent Impervious
Surface Type N
Hardscape or Hard Surface
Asphalt, Concrete 100
Rooftop 90
Recycled Asphalt 80
Gravel 40
Pavers 40
Landscape or Pervious Surface
Playgrounds 25
Lawns, Sandy soil 2
Lawns, Clayey soil 2
City of 4.1 Input Parameters
'^Fort Collins Page 11
FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards(Ch. 5)
4.0 SWMM
The composite imperviousness is obtained using the following formula:
n
I(I;xAj
I= `-1 A Equation 5-6
Where: I = Composite Imperviousness,
I; = Imperviousness for Specific Area (A),
A; =Area of Surface with Imperviousness of I;, 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
Intensity Intensity Intensity Intensity Intensity Intensity
Duration 2-year 5-year 10-year 25-year 50-year 100-year
min in/hr in/hr in/hr in/hr in/hr in/hr
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
Cjtyof 4.1 Input Parameters
F6rt Collins Page 12
APPENDIX B
Reference Reports
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Selected Plan = Water QualityImprovements1 inch = 500feetENGINEERING INC.
ihhlfi�: a
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fs Addendum
s, to
The Final Design Report
for
= �k The Fossil Creek Reservoir Inlet Ditch
' tiyf Storm Water Overflow
` a
September 198
{3. 8
fist.:•4 -- -i
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City of Fort Collins Storm Water Utility f �
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Donohue & Associates, Inc.
7 4 4730 South College Avenue
Fort Collins
: , Colorado 80525 J:
226-2323
K.`` k' �,i Project No. 272. 000
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SUMMARY
The review of the "Final Design Report for the Fossil Creek
Reservoir Inlet Ditch Storm Water Overflow" by the City of Fort
Collins and the other affected property and ditch owners
indicated several refinements to the design were desirable.
1 These design refinements include improvements in alignment,
hydraulics, operations and maintenance considerations, safety and
"- coordination with existing. facilities.
�a>
r
' The appropriate figures from the Final Design Report have been
modified to reflect the revised design concept and are included
4- in this addendum. The design as outlined in this addendum will
be used to prepare the construction documents and easement
descriptions for this project.
DESIGN REVISIONS
lti The basic channel design has been modified to occupy the smallest
amount of easement space possible while still meeting the City of
Fort Collins criteria for major drainage channels. The channel
design criteria is as follows:
`` . Design flow, 100-year recurrence interval 860 CFS
Maximum depth at 100-year flow 4 feet
Y; Friction factor (n) 0. 04
Side Slopes 4 : 1
Maximum desirable velocity 5 FPS
The channel is routed due east along the north side of County
<` Road 40 . The south side of the channel is 34 feet from the south
section line of Section 28 which is the centerline of County Road
4 40. The existing right-of-way (ROW) for County Road 40 is 30
feet either side of the section line. The additional four feet
.' of setback is for the anticipated ROW required for the City of
<<` Fort Collins standard 'collector street which will be constructed ,
in the future when the area is annexed.
The channel parallels County Road 40 to the east side of County
Road 7 where it turns south across the County Road 40 ROW making
a smooth confluence with the Poudre River. The basic channel ROW
requirements are an 80-foot wide ROW west of the Box Elder Ditch
and a 100-foot ROW east of the Box Elder Ditch. The channel
alignment utilizes a minimum of private property and county road
ROW.
x A seven percent grade section of channel in the first reach (Sta.
0+00 to Sta. 1+00 will cause a hydraulic um to occur in the
) Y jump
channel at approximately Sta. 0+80. The hydraulic jump will be
weak and submerged under most conditions. Riprap channel
protection will be provided from Sta. 0+00 to Sta. 1+20 to insure '
Y.
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MEMORANDUM N ANdtit5uN CUNSUIHNy EMIiNWO, 1011-
001 - ff&,P—Resouives • Fnr+i+o n e nlal
DATE: April 30, 2020 ACE PROJECT NO.: COCLF11
TO: Bill McDowell, Manger, Cottonwood Land and Farms
FROM: Brian Smith, Anderson Consulting Engineers, Inc.
Brad Anderson, Anderson Consulting Engineers, Inc.
Mike Turner, Anderson Consulting Engineers, Inc.
SUBJECT: Hydraulic Analysis of Fossil Creek Reservoir Inlet Ditch (FCRID) Between Cache la Poudre
River and Harmony Road for Future Strauss Lake Development
BACKGROUND INFORMATION AND PREVIOUS STUDIES:
In 2001 and 2002, Anderson Consulting Engineers, Inc. (ACE) completed a hydrologic and hydraulic
evaluation of the Fossil Creek Reservoir Inlet Ditch (FCRID) for Cottonwood Land and Farms. The
purpose of this study was two-fold: (1) assess flooding potential along the ditch from large magnitude
storms that enter the ditch from the Cache la Poudre River (Poudre River), the Foothills Regional
Channel, and local runoff from adjacent neighborhoods; and (2) investigate options for controlling the
flooding potential as it pertains to Cottonwood Land and Farms' future development site (Strauss Lake
Development) east of the ditch. Recommendations from the 2002 study resulted in the sizing and
construction of a bridge/culvert over the ditch at William Neal Parkway, which is located directly to the
west of the existing concrete batch plant. An orifice plate was installed on the upstream side of the
William Neal Parkway crossing to check flows in excess of the maximum irrigation flow to facilitate the
diversion of excess stormwater from the ditch. The 2002 study conceptually envisioned that a lateral
overtopping spill structure would be created to spill excess stormwater from the ditch that is being
checked by the orifice plate. The lateral overtopping spill would be created by the lowering of the
eastern bank of the ditch between the William Neal Parkway crossing and the upstream Environmental
Drive road crossing. It is noted that the lowering of the eastern bank of the ditch and installation of this
overtopping spillway has yet to be constructed. A vicinity map of FCRID, William Neal Parkway, the
conceptual lateral overtopping spill location from the 2002 study, and the study reach evaluated for this
study is illustrated in Figure 1.
In 2017 and 2018,ACE conducted a calibration study of FCRID between Horsetooth Road and the Great
Western Railroad (GWR) for the City of Fort Collins Utilities Department. The purpose of this study was
to develop a depth/discharge rating curve of the ditch at the upstream side of the Environmental Drive
Bridge crossing that would allow the City and the North Poudre Irrigation Company to estimate the
discharge in the ditch based on a water depth reading from a staff gage. Results of this study indicated
that the development of a rating curve was possible, but that the rating curve could shift dramatically
based on downstream tailwater conditions and roughness values of the ditch. This study also concluded
that under current ditch conditions,the maximum flow rate that can be conveyed within the ditch prior
to flow spilling over the lateral weir structure upstream of Horsetooth Road is approximately 120 cfs.
This maximum irrigation flow rate,and the roughness values determined as part of the calibration study,
were utilized as part of this study. It was also realized as part of the 2017/2018 study that the eastern
bank of the ditch, upstream of the GWR, was lowered in the early 1990s to create an emergency
overflow weir as part of the City's flood control project for the adjacent wastewater treatment plant.
The location of the existing low bank/overflow weir is also illustrated on Figure 1. It is noted that the
presence of this overflow weir was not incorporated into ACE's 2002 hydraulic evaluation of FCRID.
FCRID Hydraulic Evaluation Memo.docx Page 1 of 8 April 30,2020
MEMORANDUM ANdti(sury Curvsuhilv4 Eivtiilvttics, hu.
Civil Water Resources Environmental
Upstream Study Umltt
' � f e
Al 4 r
COFC Wastewater
Treatment
e
- Existing Low
a BsnklOverllow t1
Weir Location �•�
Concepti tal Lateral f
I' Spill Location From ®®
?era amrty
Futur®
William Nadi Pkayr
Park
� I Site
orifice Plats c ,
i. Cottonwood
La rite,and
Fossil Creek Fauns
Ron ervoirInlet
Ditch(FCRID)
Y,orsotoolki Rd
Radial Gate :� a
and Lateral k
Snlll Location \
fi
:•r
Ail -
Y�'�A�I 1 - ." F Dovlmatraam Sludy Llmlt
liarnh4ny Rd - _ - i�ew_.�.r•
0 750 1,500 3,000 m4fjd]4 `
FeetEk
--
2s
Figure 1.Vicinity Map.
FCRID Hydraulic Evaluation Memo.docx Page 2 of 8 April 30,2020
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F FEB 2 5 ?Ate
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ate 5IZCI) �Z
FINAL DRAINAGE AND
EROSION CONTROL REPORT
Rigden Farm - Filing Six
Prepared for:
Rigden Farm LLC
c/o Wheeler Commercial
1'027 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 80525
(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
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
Results
Depth 1.97 ft
Flow Area 45.12 ft2
Wetted Perimeter 31.26 ft
Top Width 30.77 ft
Critical Depth 1.21 ft
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 = ASINWQ100 from SWMM 9164-PRO.out CE 9�ZV--,
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:13910000.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 — too
1.97 ft
1
15.00 ft V
H 1
NITS
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
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 CC> Q�dO (!�L[C \
Results
Depth 2.29 ft
Flow Area 55.24 ftz
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 CEW Z1.�,
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:13910000.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 // �
Discharge 178.00 cfs — i3��lp (op C�'Y{C,FS
2.29 ft
1
15.00 ft V
H 1
NTS
03/24/01 FlowMaster v5.15
03'53:16 PM Haestad Methods, Inc. 37 Brookside Road Waterbury,CT 06708 (203)755-1686 Page 1 of 1
APPENDIX C
Hydrologic & Hydraulic Computations
Rational Method Calculations
Horsetooth Road
Existing Conditions
Prepared By: RJJ
Project: Strauss Lakes Date: 07/26/24
Basin Description: East Horsetooth Road
NRCS Hydrologic Soil Rating: D
Basin Area= 5.61 [acres]= 244,291 [sf]
Surface Characteristics' Sub-Area Imp Runoff
[acres] [%] Coefficients'
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 A,= 44,669.11 [sf]
Composite Runoff Coefficients: C= 0.32
Frequency Adjustment Factors(C,)z:
2-Year Cf= 1.00 10-Year Cf= 1.00 100-Year Cf= 1.25
Cz= 0.32 C10= 0.32 C1002
= 0.40
z City of Fort Collins"Stormwater Criteria Manual",Table 3.2-3
Time of Concentration:
Overland Flow Time: Channelized Flow Time:
L;[ft]= 42 Lt1[FT]= 1860 Lt2[FT]= 0
Si[%]= 0.10 St1[%]= 0.01 Ste[%]= 0.00
t;[min]= 20.13 Vt1[fps]= 3.20 V12[fps]= 0.00
tt1[min]= 9.69 tt2[min]= 0.00
tt[min]= 9.69
Time of Concentration:
t,=t;+tt[min]= 29.82
t,(minimum)= 5 min t,[min]
Rainfall Intensity3
IZ[in/hr]= 1.30 110[in/hr]= 2.21 1100[in/hr]= 4.52
3 City of Fort Collins"Stormwater Criteria Manual"Table 3.4-1
Runoff-Rational Method Equation
Q2[cfs]= 2.34 Q10[cfs]= 3.97 Q100[cfs]= 10.16
°City of Fort Collins"Stormwater Criteria Manual",Equation 5-1
J:\Cottonwood Land-372\372.001.01 Strauss Lakes\Memos&Reports\Drainage\Spreadsheets\Rational Method Calcs.xlsx i .a, R F s-,i_is c_
Historic SWM M Model
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SWMM a2 Page 1
Historic SWMM Model
Subcatchment Runoff Summary
Total Total Total Total hnpery Pery Total Total
Precip Runon Evap Infil Runoff Runoff Runoff Runoff
Subcatchment in in in in in in in 10^6 gal
WestSite 0.98 0.00 0.00 0.94 0.02 0.02 0.04 0.01
NorthSite 0.98 0.00 0.00 0.96 0.02 0.00 0.02 0.01
EastSite 0.98 0.00 0.00 0.96 0.02 0.00 0.02 0.05
SWMM 5.2 Page 1
Historic SWMM Model
Subcatchment Runoff Summary
Peak
Runoff Runoff
Subcatchment CFS Coeff
WestSite 0.90 0.036
NorthSite 1.16 0.020
EastSite 4.92 0.018
SWMM 5.2 Page 2
Preliminary Proposed SWMM Model
06/28/2024 00:15A0
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I 1:
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SWMM 5.2 Page 1
Preliminary Proposed SWMM Model
Subcatchment Runoff Summary
Total Total Total Total Impery Pery Total Total
Precip Runon Evap Infil Runoff Runoff Runoff Runoff
Subcatchment in in in in in in in 10^6 gal
E-1 3.69 0.00 0.00 0.15 3.24 0.22 3.46 1.88
E-2 3.69 0.00 0.00 0.15 3.24 0.22 3.46 1.88
E-3 3.69 0.00 0.00 0.15 3.24 0.22 3.46 1.88
E-4 3.69 0.00 0.00 0.15 3.24 0.22 3.46 1.88
E-5 3.69 0.00 0.00 0.15 3.24 0.22 3.46 1.88
WestSite 3.69 0.00 0.00 0.14 3.26 0.24 3.50 1.15
NorthSite 3.69 0.00 0.00 0.15 3.24 0.22 3.46 1.88
SWMM 5.2 Page 1
Preliminary Proposed SWMM Model
Subcatchment Runoff Summary
Peak
Runoff Runoff
Subcatchment CFS Coeff
E-1 133.77 0.937
E-2 133.77 0.937
E-3 133.77 0.937
E-4 133.77 0.937
E-5 133.77 0.937
WestSite 118.88 0.946
NorthSite 127.26 0.936
SWMM 5.2 Page 2
Preliminary Proposed SWMM Model
Storage Volume Summary
Average Average Evaporation Exfiltration Maximum Maximum Day of Hour of
Storage Volume Percent Loss Loss Volume Percent Maximum Maximum
Unit 1000 ft3 Full % % 1000 ft3 Full Volume Volume
CWP 231.070 46.9 0.0 0.0 473.224 96.1 0 01:38
WaterQualityP nd 19.605 92.1 0.0 0.0 21.281 100.0 0 00:32
SWMM 5.2 Page 1
Preliminary Proposed SWMM Model
Storage Volume Summary
Maximum
Storage Outflow
Unit CFS
CWP 122.83
WaterQualityP nd 0.08
SWMM 5.2 Page 2
WQCV Calculations
NORTH SITE
Area 20.00 acres
a' 1.00 (40 hours, EDB)
Imperviousness 0.90 % as decimal
WQCV 0.40 wat-in
WQCV 0.80 ac-ft
34978 ft
EAST SITE
Area 99.10 acres
a' 0.90 (24 hours, CWP)
Imperviousness 0.90 % as decimal
WQCV 0.36 wat-in
WQCV 3.58 ac-ft
155984 ft
WEST SITE
Area 12.08 acres
a' 1.00 (40 hours, WQCV Pond)
Imperviousness 0.90 % as decimal
WQCV 0.40 wat-in
WQCV 0.485 ac-ft
21127 ft
HORSETOOTH ROAD
Area 5.61 acres
a' 1.00 (40 hours, EDB)
Imperviousness 0.95 % as decimal
WQCV 0.45 wat-in
WQCV 0.25 ac-ft
10929 ft
'Drain time coefficients from Table 5.4-1 of the FCSCM and Table 3-2 of the USDCM.
Constructed Wetland Pond
Permanent Pool
Cv' 0.75
WQCV 3.58 ac-ft
VP2 2.69 ac-ft
116988 W
'Sizing coefficient from MHFD Fact Sheet T-7.
2Equation RP/CWP-1 from MHFD Fact Sheet T-7.
FAA Detention Sizing
Major Design Storm: 100-year
Horsetooth Road
Area 5.61 AC 244372 SF
Impervious 95%
'Runoff Coefficient 0.95
QouT 1 US
Storm Duration Rainfall Intensity Inflow Volume Outflow Volume Storage Volume
T 2/ 3V' 4Vo 5VS
(min) (in/hr) ft3 ft3 ft3
5 9.95 15909 300 15609
10 7.72 24686 600 24086
15 6.52 31274 900 30374
20 5.60 35814 1200 34614
25 4.98 39811 1500 38311
30 4.52 43361 1800 41561
35 4.08 45663 2100 43563
40 3.74 47838 2400 45438
45 3.46 49788 2700 47088
50 3.23 51643 3000 48643
55 3.03 53290 3300 49990
60 2.86 54873 3600 51273
65 2.71 56327 3900 52427
70 2.59 57974 4200 53774
75 2.48 59477 4500 54977
80 2.38 60884 4800 56084
85 2.29 62243 5100 57143
90 2.21 63602 5400 58202
95 2.13 64705 5700 59005
100 2.06 65873 6000 59873
105 2.00 67152 6300 60852
110 1.94 68239 6600 61639
115 1.88 69134 6900 62234
120 1.84 70605 7200 63405
Modified FAA Storage Volume 63405 ft3
Modified FAA Storage Volume 1.46 ac-ft
'Runoff 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.
FAA Detention Sizing
Major Design Storm: 100-year
North Site
Area 20.00 AC 871200 SF
Impervious 90%
'Runoff Coefficient 0.85
QouT 9 US
Storm Duration Rainfall Intensity Inflow Volume Outflow Volume Storage Volume
T 2/ 3V 4Vo 5vs
(min) (in/hr) ft3 ft3 ft3
5 9.95 50745 2700 48045
10 7.72 78744 5400 73344
15 6.52 99756 8100 91656
20 5.60 114240 10800 103440
25 4.98 126990 13500 113490
30 4.52 138312 16200 122112
35 4.08 145656 18900 126756
40 3.74 152592 21600 130992
45 3.46 158814 24300 134514
50 3.23 164730 27000 137730
55 3.03 169983 29700 140283
60 2.86 175032 32400 142632
65 2.71 179673 35100 144573
70 2.59 184926 37800 147126
75 2.48 189720 40500 149220
80 2.38 194208 43200 151008
85 2.29 198543 45900 152643
90 2.21 202878 48600 154278
95 2.13 206397 51300 155097
100 2.06 210120 54000 156120
105 2.00 214200 56700 157500
110 1.94 217668 59400 158268
115 1.88 220524 62100 158424
120 1.84 225216 64800 160416
Modified FAA Storage Volume 160416 ft3
Modified FAA Storage Volume 3.68 ac-ft
'Runoff 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.
Channel Report
Hydraflow Express Extension for Autodesk®Civil 3D®by Autodesk, Inc. Monday,Jul 29 2024
Conveyance Swale (Basins 1)
User-defined Highlighted
Invert Elev (ft) = 100.00 Depth (ft) = 4.25
Slope (%) = 0.25 Q (cfs) = 133.77
N-Value = 0.053 Area (sqft) = 64.31
Velocity (ft/s) = 2.08
Calculations Wetted Perim (ft) = 35.59
Compute by: Known Q Crit Depth, Yc (ft) = 2.64
Known Q (cfs) = 133.77 Top Width (ft) = 34.50
EGL (ft) = 4.32
(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)
Elev (ft) Section Depth (ft)
106.00 6.00
105.00 5.00
104.00 4.00
103.00 3.00
102.00 2.00
101.00 1.00
100.00 0.00
99.00 -1.00
-5 0 5 10 15 20 25 30 35 40 45 50
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 Highlighted
Invert Elev (ft) = 100.00 Depth (ft) = 5.18
Slope (%) = 0.25 Q (cfs) = 267.54
N-Value = 0.048 Area (sqft) = 100.72
Velocity (ft/s) = 2.66
Calculations Wetted Perim (ft) = 45.08
Compute by: Known Q Crit Depth, Yc (ft) = 3.41
Known Q (cfs) = 267.54 Top Width (ft) = 43.80
EGL (ft) = 5.29
(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)
Elev (ft) Section Depth (ft)
106.00 6.00
Nr
105.00 5.00
104.00 4.00
103.00 3.00
102.00 2.00
101.00 1.00
100.00 0.00
99.00 -1.00
-5 0 5 10 15 20 25 30 35 40 45 50 55
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 Highlighted
Invert Elev (ft) = 100.00 Depth (ft) = 5.83
Slope (%) = 0.25 Q (cfs) = 401.31
N-Value = 0.045 Area (sqft) = 131.31
Velocity (ft/s) = 3.06
Calculations Wetted Perim (ft) = 51.71
Compute by: Known Q Crit Depth, Yc (ft) = 3.94
Known Q (cfs) = 401.31 Top Width (ft) = 50.30
EGL (ft) = 5.98
(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)
Elev (ft) Section Depth (ft)
107.00 7.00
106.00 6.00
105.00 5.00
104.00 4.00
103.00 3.00
102.00 2.00
101.00 1.00
100.00 0.00
99.00 -1.00
-5 0 5 10 15 20 25 30 35 40 45 50 55 60 65
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 Highlighted
Invert Elev (ft) = 100.00 Depth (ft) = 6.34
Slope (%) = 0.25 Q (cfs) = 535.08
N-Value = 0.043 Area (sqft) = 158.26
Velocity (ft/s) = 3.38
Calculations Wetted Perim (ft) = 56.91
Compute by: Known Q Crit Depth, Yc (ft) = 4.37
Known Q (cfs) = 535.08 Top Width (ft) = 55.40
EGL (ft) = 6.52
(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)
Elev (ft) Section Depth (ft)
108.00 8.00
107.00 7.00
106.00 6.00
105.00 5.00
104.00 4.00
103.00 3.00
102.00 2.00
101.00 1.00
100.00 0.00
99.00 -1.00
-5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70
Sta (ft)
APPENDIX D
Drainage Plans
LEGEND LEGEND CO NT.
7
PROPERTY LINE CHANNEL CENTERLINE
CIVIL IZLS1)[ 1RGI S
MAJOR CONTOUR — — — —5740— - FLOW DIRECTION
MINOR CONTOUR — — -5736- SIGN 8308 COLORADO BLVD
SUITE 200
BARBED WIRE FENCE k: SANITARY MANHOLE FIRESTONE, CO 80530
303.833.1416
CHAINLINK FENCE FLARED END SECTION WWW.CIVILRESOURCES.COM
GAS LINE STORM MANHOLE /
WATER LINE LIGHT POLE/UTILITY POLE
X
STORM SEWERSTRUCT RE
/ I /
TREE BOXELDER DITCH I,
� I
TELECOM COTTONWOOD
UNDERGROUND ELECTRIC DRAINAGE BASIN BOUNDARY ■ �J I LAND & FARMS LLC
OVERHEAD WIRES off DRAINAGE BASIN NAME
SANITARY SEWER 2-YEAR FLOW CFS
( ) A XXX xxx � �� ��' I BILL MCDOWELL
ke'' MANAGING PARTNER
RETAINING WALL DRAINAGE AREA (ACRES) RIGDENRESERV O R I /! `\ I
/ 486 8 � PO BOX 229
50.0' DITCH BOULDER CO 80306
EASEMENT
f
r QBjw I
/ /
Q
- - W J
@MEN*, U
/ I
. I I �
30.o' EX UTitITr '.
HORSETOOTH
TOOTH
AD
r
%-� _ AG CFS
Q � O
DjTcH / / J ) 4875 II I Lu
BpX6�06ATroNi / I 1
_ � O
R
♦ _ - Iz Q Q
EXISTING GROUNDWATER
MONITORING WELL (TYP.) I
— /
�_ -
-
_ _ -- - EXISTING SPILL
EAST
/ �- / SITE J I REVISIONS
STRUCTURE TO FCO
00.8 4.92 f NO DESCRIPTION DATE
EXisTiCFS
NG Di�ERS10N-
/ STRUCTURE TO
- i - - - - - RIDGEN RESERVOIR /
6 J, -
/ - __ - EXISTING FCRID
FLOW CONTROL GATE
�1
f
NORTH' ��� i�%'� v \� � _ _ - � i / / /
a / SITE
p 20.291.16
O / / /� / AC. CFS
00*
711
Mu')
LLJ
ui
r �
r
/ ��� % / // I - - �- — �) — � �O /
4000"
Q(G� L 1 FLATIRONS POND _ _ DESIGNED BY: RJJ DATE: 07/11/2024
_ ��� _ WEST
- / / /
w �1G/ / C ' \\ / _ _ �� / / S TE J / DRAWN BY: RJJ SCALE: 1" = 200'
// / - ✓ - -- __ I ��� / �C a�� / - / / I CHECKED BY: JAB
�� - �� osCFS f
1z.
�� ti� / � AC.CFS
-- v u H JOB NO.: 372.001.01
% - - - -- _ �> - / 0 U `- i DWG NAME:37200101HIST ODP
- -
40
Ln
/ �! _ - —/ — \ :�1 - - — __ — J l J ✓ 'i IN FEET)
-- =_ -- -
C - � __ -- 1
o / / �- J
M !SO4t
Ne �� ,, _ HISTORIC
- - J - -- - - - - - - - - - � �-..A _� � -- - - - - - , - -- � _ -- �_� Win— ,
— — ---- --
- _ � DRAINAGE PLAN
4 �
0
A& _
oM RIGDE/V FAR Q SHEET:
InPOND 216 ti Know whats below.
,
k D - 1
Call before you dig.
LEGEND LEGEND CO NT.
PROPOSED EXISTING PROPOSED EXIXTIXG DESIGN POINT SUMMARY
Design Point Description Q 100 (cfs)
PROPERTY LINE - - WATER QUALITY/ DP-N1 flow to detention pond 127.26 �.
FLOOD CONTROL FACILITY discharge from detention C 7 I V I L R [ S l_1 R C: F S
MAJOR CONTOUR - - - -5740- - - - - - DP-N2 9
r r CONVEYANCE SWALE pond
- -5736- - - - - - r r r r DP-E1 flow to swale section 1 133.77
MINOR CONTOUR - 8308 COLORADO BLVD
ACCESS ROAD/TRAIL DP-E2 flow to Swale section 2 267.54 SUITE 200
BARBED WIRE FENCE FIRESTONE, CO 80530
SIGN DP-E3 flow to swale section 3 401.31 303.833.1416
CHAINLINK FENCE DP-E4 flow to swale section 4 535.08 WWW.CIVILRESOURCES.COM
SANITARY MANHOLE II surface flow to CWP 133.77
GAS LINE G FLARED END SECTION DP-E6 discharge from CWP 133.23
WATER LINE W ® % DP-W1 flow to water quality pond 118.88
Q� discharge from water
STORM MANHOLE g EXISTING CONTROL
J STORM SEWER ST - l DP-W2 0.08 STRUCTURE FOR
Q
LIGHT POLE/UTILITY POLE / quality pond aoXELDER DITCH /
TELECOM DP-H1 flow to detention and 5.06 ) I }�I I�
discharge from detention / > 111
p ' ��� �� �� �� APPROX. LOCATION OF COTTONWOOD
UNDERGROUND ELECTRIC TREE DP-H1 pond 1 �////l i POND DISCHARGE TO FCO LAND & FARMS, LLC
OVERHEAD WIRES off DRAINAGE BASIN BOUNDARY / X !
SANITARY SEWER pp _ #A DESIGN POINT / / o
0 j //� , � � BILL MCDOWELL
g867 I I �j , APPROX. AREA OF CONSTRUCTED MANAGING PARTNER
RETAINING WALL DRAINAGE BASIN NAME / r - WETLAND POND = 4.91 AC
RIGDENRESERI/OIR �/! /�� 4868 I II II PERMANENT POOL = 2.69 AC-FT PO BOX 229
50.0' DITCH f i, WQCV = 3.58 AC-FT BOULDER, CO 80306
CHANNEL CENTER LINE XX A xx 100-YEAR FLOW (CFS) EASEMENT i I 100-YR VOL. = 6.87 AC-FT
TOTAL STORAGE VOL = 10.45 AC-FT
FLOW DIRECTION DRAINAGE AREA (ACRES) / / � �869 � I � APPROX. LOCATION OF
/ I POND DISCHARGE TO FCO
62.0' MAXIMUM / / //i / _ DP - E4.
SWALE TOP WIDTH
Q100 = 535.08 CFS
i
/ _ I DP - H2 Q
57.0' SWALE �� Q
TOP WIDTH / �� / t / �p
Q100 = 401.31CFS i �_:� � DP - E3.
; U)
APPROXDETENTION
AREA OF
I 1 I DETENTION POND = 0.76 AC
A° j l I �: wgcv = 0.25 AC-FT
49.5' SWALE / - J - - - 30.0' EX UTILITY
/ � _ I� I � 100-YR VOL. = 1.48 AC-FT
/ j EASEMENT TOTAL STORAGE VOL. = 1.73 AC-FT
TOP WIDTH
Q100 = 267.54 CFS / // DP - E2 O
r �� �� I _ - -
LL
_
19.90 133.77 I � l�� �_ L.V U
AC. CFS I V HORR ADOTH O
5.615.06
LU
X 11 I
� / � j � � I I I I NOTE:
gO RjGA / _ / Jar I - - L _r I I I I LID WILL NOT BE PROVIDED FOR
_ _ J I THE HORSETOOTH ROAD BASIN.
20.0' SHARED �� / I II LID FOR ALL OTHER DRAINAGE
/ BASINS WILL ACCOUNT FOR THE
7r MAINTENANCE ROAD
/ //" - - - / E-4 \ I Q I 75/o LID REQUIREMENT.
&RECREATIONAL TRAIL / / - \- �D P - E 1 - - ��-' t� 7 19.64 133.77 � I V �O I
APPROX. LOCATION OF /j _ - - - Ac. cFs -
// POND DISCHARGE TO /� / Y - / I EAST SITE -I \ f v RIGDEN FARM OUTFALL CHANNEL 42.0' MINIMUM / / / r I - '�
SWALE TOP WIDTH //// - / NOTE.
Q100 - 133.77 CFS �_ // .� . / LID WILL BE PROVIDED REGIONALLYFOR THE EAST SITE VIA THE _ - 1
CONSTRUCTED WETLAND POND. '/
/ APPROX. AREA OF / /i/ jj /
L DP N2DETENTION POND _
P / / �„ ` I I
100-YR VOL. = 3.68 AC-FT /// / J� r EXISTING SPILL
WQCV /�i Jj rr , � - , - � _ / - - - - E-3 j � � � , \ 1 I I
/// / r - - - _ - - STRUCTURE TO FCO I REVISIONS
TOTAL STORAGE VOL. = 4.48 AC-FT / / / Q2O2. 133.77cFs / NO DESCRIPTION DATE
EXISTING 0114f RsioN
STRUCTURE TO I l
RIDGEN RESERVOIR
E-2
r
2036 133.77 - o r - - I I ? EXISTING FCRID
AC. CFS / W - ) /
/ / / �� / /1 J FLOW CONTROL GATE
/ DP - W2, APPROX. LOCATION OF
/ -j `r / / I / / / POND DISCHARGE TO FCRID
EXISTING GROUNDWATER
MONITORING WELL / �
NORTH \ \ - =
✓ y APPROX. AREA OF WATER
SITE % / / 1 I ���/' ; j G / / QUALITY POND = 0.29 AC
o / / / f zo.z9 1z7.z6 / ✓� ^\\ y� / \ / i 1 J o J_ \ _ - J 5(\�p�Q`^S WQCV = 0.485 AC-FT
Oo AC. CFS cA� �,''/ � \X \^ / / I ` / J 1 1 ` , \ - /.C�j�
r1l
/ IDTWILL BE PROVIDED LOCALLY `�8� / ' J / / `� / I ✓ X / / / j
V) / S. / �\ \ �
w /" FOR THE NORTH SITE VIA RAIN �� / / / \ - _ _ _ _ - _/ / I I ' �� / I / / / j I
LD / // / GARDENS,PERMEABLE PAVERS, / / / I I _ -. - �� - �� / '�, / /. I V 1J
� / ,(�'�// GRASS BUFFERS,ETC.
/ - _ - Q� / APPROX. LOCATION OF /
,%o STORM SEWER HEADER PIPE
I �` --/,/WEST /
-��� / SITE
- - - \ 1z.08 11a.as DESIGNED BY: RJJ DATE: 07/11/2024
FLATIRONS POND \ - - \� - - I \� � 1- - - _ r G�� / ////// j ��X AC. CFS
- - -
cn / / / ? j I j �� G' / -• \\ I DRAWN BY: RJJ SCALE: 1" = 200'
wI -
a
aJ NOTE: CHECKED BY: JAB
Y _ \ O Q' / / - LID WILL BE PROVIDED LOCALLY
/�/ / / / `- - r �_� _ _ r----- -1 e �>� - -�- � r\ \ �' ` / i / - FOR THE WEST SITE VIA RAIN
/ /.. l _ / / _ ..� •~ �X i ^ - _: - - - - _ / _ jp- �I ✓ i / / /- ,.�/ i j GARDENS,PERMEABLE PAVERS,
Q / G / v ` -> % / ✓ / % J ^ \ \ i- 7 i J - _ - - _ \ _- 1- - - - - , X"/ / /"/. / C) � GRASS BUFFERS,ETC. f/ I��URTH JOB N A 372.001.01
_ �1 i
-�� T- / - - _ I� �_ - -T-- - - �/ f/ i / ��;C' / 0 100 200 W NA
/� / � / - - - J X_ / // / / , D G ME:372001010DP
// /�--K
o j N / - \ / _ �_ �\ - - - - \- i'-- � � __= / l g �� / = \ IN FEET)
,
J
-=J/ (�r-zoo:
MN
1c=
- O VERA LL
LERROAD DRAINAGE PL
AN
-- _ -
•
k
'1L- # .
oRIGDEN FARM Q SHEET:
o
POND 216 D - 2
� � Know whit s below.
U
Call before you dig.