HomeMy WebLinkAboutVILLAGE ON HORSETOOTH (AFFORDABLE HOUSING) - PDP - PDP160025 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPRELIMINARY DRAINAGE AND
EROSION CONTROL REPORT
FOR
VILLAGE ON HORSETOOTH
AT
1506 W. HORSETOOTH ROAD
FORT COLLINS, CO 80526
PREPARED FOR
FORT COLLINS HOUSING AUTHORITY
Fort Collins, CO 80521
AUGUST 17, 2016
Fort Collins Housing Authority - Village on Horsetooth
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TABLE OF CONTENTS
SITE LOCATION AND DESCRIPTION ......................................................................................... 4
DRAINAGE BASINS AND HISTORIC RUNOFF ............................................................................. 5
HISTORIC DRAINAGE ......................................................................................................... 5
DRAINAGE DESIGN CRITERIA ................................................................................................ 5
HYDROLOGIC METHOD AND DESIGN STORM FREQUENCIES ................................................... 5
HYDRAULIC CRITERIA ........................................................................................................ 5
VARIANCES FROM THE CRITERIA ............................................................................................ 6
DRAINAGE FACILITY DESIGN ................................................................................................. 6
GENERAL CONCEPT ......................................................................................................... 6
PROPOSED DEVELOPED SUBBASINS .................................................................................... 6
PROPOSED DETENTION POND ........................................................................................... 8
HISTORIC/DEVELOPED BASIN COMPARISON ....................................................................... 9
STORMWATER POLLUTION PREVENTION/EROSION CONTROL .................................................... 9
TEMPORARY EROSION CONTROL ....................................................................................... 9
PERMANENT EROSION CONTROL ....................................................................................... 9
STORMWATER MANAGEMENT CONTROLS ............................................................................ 10
SEQUENCE OF CONSTRUCTION ACTIVITIES ............................................................................ 12
CONCLUSIONS .................................................................................................................. 13
REFERENCES ...................................................................................................................... 14
LIST OF TABLES
TABLE 1. HISTORIC SWMM BASIN PROPERTIES AND FLOWS ........................................................ 5
TABLE 2. DEVELOPED SWMM SUBBASIN PROPERTIES, FLOWS, AND RUNOFF COEFFICIENTS ............ 8
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APPENDICES
Appendix A – Figures
1. Site Vicinity Map
2. Historic Drainage Map
3. Developed Drainage Map
Appendix B – Hydraulic/Hydrologic Computations
1. Historic C, Tc, and Runoff Calculations
2. Developed C, Tc, and Runoff Calculations
3. WQCV Calculations
4. Pond Volume Calculations
Appendix C – Referenced Documents
1. FEMA FIRM Map
2. Geotechnical Report – Summary of Conclusions by CTL Thompson INC
3. USDA NRCS Web Soil Survey Map and Soil Description
4. USDA National Wetlands Inventory Wetlands Map
5. City of Fort Collins Foothills Basin Master Plan WQ Conceptual
Alternatives Map
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ENGINEER’S STATEMENT:
“I hereby certify that this report (plan) for the Preliminary Drainage Design for the Fort Collins
Housing Authority Village on Horsetooth was prepared by me (or under my direct supervision) in
accordance with the provisions of the City of Fort Collins Standards for the Responsible Parties
thereof. I understand that the City of Fort Collins does not and shall not assume liability for
drainage facilities designed by others.”
______________________________
Charles R. Hager, IV, P.E.
Registered Professional Engineer
State of Colorado No. 37146
Fort Collins Housing Authority - Village on Horsetooth
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SITE LOCATION AND DESCRIPTION
The Village on Horsetooth (site) is being developed by the Fort Collins Housing Authority and is
located in Southeast Quarter of Section 27, Township 7 North, Range 69 West of the 6
th
Principal
Meridian, in Larimer County, Fort Collins, Colorado. Refer to Appendix A, Figure 1, for the site
vicinity map. Horsetooth Road (Horsetooth) to the south, Pleasant Valley and Lake Canal (Canal)
to the east, and residential subdivisions to the north and west border the property. There is open
space and residential housing to the west. The site is located in the Foothills Stormwater Basin.
The Foothill basin drains west to east through open channels and storm sewer that discharges into
the Fossil Creek Reservoir Inlet Ditch. The Foothills Basin Master Plan Water Quality Conceptual
Alternatives Map, provided by the City of Fort Collins, shows that the site is required to provide
flood control and water quality; the map is attached in Appendix C.
The current site is approximately 8.3 acres of partially developed land with an existing house and
horse stable, arena and grazing open space area with a total percent impervious of 14.9%. The site
historically generally drains to the east towards and into the Canal via overland flow with slopes
ranging from 0.2% to 8.0%. The north half of Horsetooth bordering the site drains to the north
onto the site and into the Canal. From the geotechnical report dated July 19, 2016, the soil is
mainly sandy clay and clayey sand with no bedrock encountered in the borings. Ground water was
located 19 to 22 feet below ground surface and did not drastically change several days after
drilling. A soil map created using the USDA Natural Resources Conservation Service Web Soil
Survey identifies the site’s soil as Altvan-Satanta Loams, which is in the hydrologic soil group B
with infiltration rates ranging from 0.6 to 2 inches/hour. A summary of the conclusions of the
geotechnical report and the web soil survey results are provided in Appendix C.
According to the FEMA Flood Insurance Rate Map Panel Number 08069C0986G dated
05/02/2012, the site is located outside of the 100-year floodplain area. The map panel is attached
in Appendix C.
The proposed site construction includes the demolition of the existing home, horse stables and
arena, gravel roadway and the construction of 9 new multi-unit residential buildings and clubhouse
building with surrounding asphalt parking areas, playground and grass fields, sidewalks, water
quality controls and detention pond. The site development will increase the overall percent
impervious to 51.1%. The proposed developed cannot drain or discharge into the Canal and must
tie into the City of Fort Collins (City) storm sewer system located in Horsetooth which eventually
drains to Fossil Creek Reservoir Inlet Ditch. Storm valley gutters, area inlets, under drains, curb
cuts, chases, channels and culverts are located throughout the site to capture and convey runoff to
the detention pond.
The main purpose of this study is to analyze the existing and developed drainage patterns in order
to convey stormwater into the Horsetooth storm sewer system without causing adverse effects to
the site and surrounding and downstream properties. The proposed scope of work will include
new storm piping, valley gutters, curb cuts, and site grading to accommodate an infiltration basin,
on-site water quality and detention pond, and piping to the existing Horsetooth storm system. An
outlet structure and pipe with a restrictor plate will be installed in the pond to control the water
quality release rate and the 100-year storm outflow rate to the calculated 2-year historical runoff
Fort Collins Housing Authority - Village on Horsetooth
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rate. A spillway is located along the southeast edge of the pond and will direct flow onto
Horsetooth if the outlet structure is ever clogged or not performing correctly.
DRAINAGE BASINS AND HISTORIC RUNOFF
HISTORIC DRAINAGE
The site historically drains to the east towards and into the Pleasant Valley and Lake Canal via
overland flow with slopes ranging from 0.2% to 8.0%. Runoff from the north half of Horsetooth
bordering the site drains north onto the site and into the Canal. The site consists of a gravel
roadway, house, horse stables, arena, and grazing area which have an overall percent impervious
of 14.9%. The peak 2-year and 100-year runoff rates are 2.24 cfs and 31.07 cfs, respectively.
The historic drainage is outlined below. Design flow calculations and the historical drainage map
are provided in Appendix A.
Table 1. Historic SWMM Basin Properties and Flows
Drainage
Basin
Design
Point
Area
(acre)
%
Impervious
Q-2
(cfs)
Q-100
(cfs)
Runoff
Coefficient
H1 1 8.68 14.9% 2.24 31.07 0.53
Total 8.68 14.9% 2.24 31.07 0.53
DRAINAGE DESIGN CRITERIA
HYDROLOGIC METHOD AND DESIGN STORM FREQUENCIES
The drainage for the site was designed to meet or exceed the City of Fort Collin’s Standards and
Specifications, including the Stormwater Criterial Manual which incorporates most of the Urban
Drainage and Flood Control District Criteria Manual (USDCM). The site’s basin percent
impervious values were calculated using impervious values from Table 6-3 in the USDCM. The
values for the 100-year event rainfall intensity duration for 0 to 60 minutes were taken from Table
RA-7 in the City of Fort Collins’ Stormwater Criteria Manual. Equation 5.30 from the USDCM
was used to calculate intensities for the 60 to 180 minute time steps. The runoff coefficients were
calculated using USDCM’s Table 6-4 equations.
HYDRAULIC CRITERIA
The proposed drainage facility has been designed to comply with the City of Fort Collins
Stormwater Criteria Manual, the Foothills Basin Master Plan design, and UDFCD’s Drainage
Criteria Manual. The Foothills Basin Master Plan requires best management practices to have
both flood control and water quality. Sizing for inlets and pipes has not been completed at this
time, but UD-Inlet Version 3.14, Hydraflow, and Flowmaster will be used for calculations.
Preliminary drainage plans are included in the construction documents. The pond volume was
calculated using the modified FAA method and includes the 100-year runoff volume plus 100%
Fort Collins Housing Authority - Village on Horsetooth
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of the WQCV and an additional 20% of the 100-year volume as per the City’s stormwater criteria
manual. Pond volume and runoff calculations are attached in Appendix B.
VARIANCES FROM THE CRITERIA
As per the City’s comments dated May 9, 2016, the site is required to discharge the 100-year event
at the historical 2-year rate. There is no micropool in the detention basin and due to volume
requirements there are no forebays in the pond, but there is an infiltration basin and riprap aprons
for velocity dissipation as concentrated runoff enters the pond.
DRAINAGE FACILITY DESIGN
GENERAL CONCEPT
As per the Foothills Basin Master Plan design, the site was graded in an attempt to capture all site
runoff to be treated and detained in the extended detention basin located along the east side of the
site. The pond has an outlet structure that ties into the City’s existing storm sewer system on the
south side of Horsetooth. This connection restricted the design of the site’s detention. Only a
portion of the site, 16.5%, was not able to be captured and treated onsite. Furthermore, 84.6% of
the site’s modified and added impervious area is captured and treated on site. The offsite flow will
drain onto Horsetooth Road and follow existing drainage pathways to the east. There is a small
area on the east side of the crushed rock path that represents the west bank and berm of the Pleasant
Valley and Lake Canal that will flow to the east, into the Canal, as it does in the historic flow
pattern. The open space area in the center of the site will capture most of the runoff from the
building roofs via two area inlets and a perforated underdrain pipe/bioswale, then discharge to the
detention pond. Due to the site’s soil infiltration rate ranging from 0.6 to 2.0 inches/hour,
infiltration is expected to occur within the center area and in the detention pond. Another
infiltration basin is located downstream of the north emergency access road culvert. This
infiltration basin will treat runoff before it enters the pond through a weir structure. Around the
exterior of the buildings, drainage flows away from the buildings and into the parking lot. The
parking lot has been designed with curb and gutter, concrete pans, channels, and chases to direct
flow to the east and into the detention pond through two curb cuts. The parking lot also acts as
part of the detention pond for larger storm events. Vertical curb and gutter will be installed along
Horsetooth road to convey flows east along the road, similar to what is occurring to the west and
east along Horsetooth.
PROPOSED DEVELOPED SUBBASINS
The site was delineated into seventeen subbasins, A1-A6, B and R1-R10. Basins A1-A6 and R1-
R10 will be captured and treated in the detention basin. Basin B is the offsite basin and will not
be treated. Basin A1 will flow through a culvert to the north infiltration pond in basin A6 and then
to the detention pond in Basin A5. Basins A2 and A3 will convey flow through the parking lot
and become treated in the detention pond through a curb cut and sidewalk chase. Drainage in basin
A4 will be collected in inlets and piped to the detention pond. The roof drain basins R1-R6 are
assumed to drain into basin A4. Roof drain R7 is assumed to be connected to the storm sewer
from A4 to convey to the pond. The basins R8-R10 are to drain North into A3 and then to the
detention pond. The developed drainage map is provided in Appendix A.
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SUBBASIN DESCRIPTIONS:
• Subbasin A1 contains the area to the north west contained mostly landscaped area and a
small bike parking area. This area flows around to the east and through a culvert
underneath the emergency access to Basin A6.
• Subbasin A2 contains the north and east section of the parking lots and the sidewalks and
landscape area along the north of the north buildings and east along the east buildings. It
also contains the swale between roof basins R2 and R4 and the swale around roof basin
R7. Runoff flows around the parking lot with the help of curb and gutter and concrete
channel to a curb cut to the detention pond.
• Subbasin A3 contains the south and most of the west portions of the parking lot and
sidewalk and landscape along the buildings. It also contains the north portion of the access
drive from Horsetooth. The basin drains through concrete pans and curb and gutter to the
sidewalk chase that flows to the detention pond.
• Subbasin A4 contains sidewalk, landscape, playground, and gravel grill areas at the inside
of the site. The runoff is collected in two area drains and piped to the detention pond to
the south east.
• Subbasin A5 contains the landscaped detention pond and the crushed rock path on the east
of the site. The runoff is directed to the middle concrete pan which directs flow to the
outlet structure. The flow from the outlet structure connects to an existing storm system to
the south of Horsetooth.
• Subbasin A6 contains the north infiltration pond, a section of crushed rock path, and a
section of the emergency access road from Birmingham Drive. The runoff is into the
infiltration pond and can overflow to the east into the detention pond.
• Subbasin B contains the north half of West Horsetooth Road, sidewalks, landscape areas,
and areas to the east of the crushed rock path. The subbasins runoff flow is the only basin
that is not captured on-site, and is directed to the east along Horsetooth to an existing inlet
and to the east towards the Pleasant Valley and Lake Canal.
• Roof Drain Subbasins R1, R2, R3, R4, R5 and R6 are assumed at this time that they will
outfall into basin A4 and collected into the area inlets.
• Roof Drain Subbasin R7 contains the south east building that is north of the parking lot.
This flow is piped into the storm drain system that flows from Subbasin A4 to the detention
pond.
• Roof Subbasins R8, R9, and R10 contain the south buildings. This flow is assumed to
outfall to the north into subbasin A3 and eventually to the detention pond.
Fort Collins Housing Authority - Village on Horsetooth
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Table 2. Developed SWMM Subbasin Properties, Flows, and Runoff Coefficients
Drainage
Basin
Design
Point
Area
(acre)
%
Impervious
Q-2
(cfs)
Q-100
(cfs)
Runoff
Coeff's
C100
A1 1 0.35 6.4% 0.04 1.20 0.49
A2 2 1.48 74.1% 1.90 8.22 0.82
A3 3 1.48 70.6% 1.94 8.63 0.80
A4 4 1.10 17.8% 0.37 4.42 0.54
A5 5 1.29 9.2% 0.21 4.51 0.50
A6 6 0.10 17.1% 0.03 0.39 0.54
B 7 1.43 44.6% 1.12 6.61 0.67
R1 8 0.18 90.0% 0.40 1.56 0.90
R2 9 0.18 90.0% 0.40 1.56 0.90
R3 10 0.18 90.0% 0.40 1.56 0.90
R4 11 0.18 90.0% 0.40 1.56 0.90
R5 12 0.11 90.0% 0.24 0.96 0.90
R6 13 0.07 90.0% 0.15 0.60 0.90
R7 14 0.11 90.0% 0.26 1.02 0.90
R8 15 0.18 90.0% 0.40 1.56 0.90
R9 16 0.18 90.0% 0.40 1.56 0.90
R10 17 0.11 90.0% 0.24 0.96 0.90
Total 8.68 51.1% 8.92 46.89 0.70
Total to Pond (No
Basin B)
7.25 52.4% 7.81 40.28 0.71
PROPOSED DETENTION POND
The detention pond has been designed to capture the 100-year runoff volume, plus 100% of the
WQCV and an additional 20% of the 100-year volume and discharge into City’s existing storm
sewer system on the south side of Horsetooth Road. Due to the existing grade of the site, of the
entire site only 16.5% of the sites area and runoff was not captured and conveyed through sites
drainage system and detention pond. A total of 86.4% of the modified and added impervious
surface is captured and treated on site. As per the City’s requirement, the 100-year outflow rate
from the pond into the City’s system was restricted to the existing 2-year flow rate of 2.24 cfs by
the use of a restrictor plate on the outlet pipe. The bottom of the pond is at an elevation of 5105.30
feet and is 3.95 feet deep with a total volume of 3.702 acre-ft. The pond’s overflow spillway is
located on the southern edge of the pond and will discharge to Horsetooth if the outlet structure of
the pond is ever clogged or malfunctioning. The spillway will be designed to be able to discharge
the peak 100-year runoff rate of 40.28 cfs. Access to the pond and outlet can be achieved by
entering the pond from the south from Horsetooth along the emergency spillway.
The detention pond will act as both flood and water quality control. For the 100-year storm event,
the pond will have a maximum water surface elevation of 5108.26 feet, which is a pond volume
of approximately 1.80 acre-feet. This allows for 0.99 feet of freeboard to the emergency spillway
at an elevation of 5109.25 feet. The maximum pond outflow rate is 2.24 cfs. The outlet pipe will
Fort Collins Housing Authority - Village on Horsetooth
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be a 15 inch reinforce concrete pipe with a restrictor plate placed 0.35 feet above the pipe invert.
The WQCV will be treated in two locations within the pond. There is an infiltration basin located
on the north portion of the pond and receive water from the drainage swale along the north and
west side of the site that treats 752 cf of the WQCV. The infiltration basin will consist of existing
soils having an infiltration rate ranging from 0.6-2 inches/hr. Once the infiltration basin fills above
an elevation of 5108.0 feet, the water will spill over a concrete weir into the main area of the pond.
The remaining required WQCV, 7129 cf, will be achieved in the detention pond. An orifice plate
will be installed on the outlet structure to provide a 40hr drawdown time for the WQCV. The
water surface elevation of the WQCV is 5106.51 feet and is also the outlet structure rim elevation.
HISTORIC/DEVELOPED BASIN COMPARISON
The site contains one historical basin that drains to the east into the Pleasant Valley and Lake
Canal. The developed site still drains primarily to the east, but instead of draining into the Canal,
the runoff is collected and discharged into the Horsetooth storm sewer system. A very small
portion of the sites detention pond berm will drain into the Canal. There is also a portion of the
site that will drain south onto Horsetooth and not be captured and treated on site. The total peak
100-year offsite runoff rate is 6.61 cfs with the majority draining onto Horsetooth. The existing
site has a peak 100-year runoff rate of 31.07 cfs. As required by the City, the pond has a discharge
rate of 2.24 cfs into the Horsetooth system, which is equivalent to the historical 2-year peak runoff
rate. In the event that the detention ponds outlet pipe is clogged, the pond’s overflow spillway
will safely convey flow onto Horsetooth at a peak rate of 40.28 cfs.
STORMWATER POLLUTION PREVENTION/EROSION CONTROL
TEMPORARY EROSION CONTROL
A temporary erosion control plan is to be implemented for the site during construction. Temporary
erosion control measures include, but are not limited to, slope and swale protection provided by
the use of erosion control wattles/sediment control logs, inlet protection, vehicle tracking control
at access points to the site. All temporary erosion control measures are to be removed after they
are deemed unnecessary. Refer to the Erosion Control Plan and Details for the Village on
Horsetooth for additional detailed information.
PERMANENT EROSION CONTROL
Chapter 2 of the Urban Drainage and Flood Control District’s Urban Storm Drainage Criteria
Manual Volume 3 (USDCM) provides guidelines for the selection of appropriate permanent
structural BMPs for a site that is to be developed or redeveloped. The Village on Horsetooth is
best characterized as a “conventional redevelopment” with over 1 acre of impervious area on the
project site. The BMP decision tree for such sites is provided in Figure 2-2 of the USDCM. As
previously stated, the site and surrounding vicinity is comprised of hydrologic soil group Type B
soils, per the NRCS soil survey, with a depth to bedrock of greater than 5 feet.
Permanent erosion control measures include, but are not limited to, the constructed detention
ponds, riprap pads placed for culvert and flared end section outlet protection, seeding and mulch
placed to enable and established vegetative growth, etc. Long-term maintenance of these erosion
control measures shall be the responsibility of the owner of the property. A general erosion control
plan has been provided in the construction documents.
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STORMWATER MANAGEMENT CONTROLS
The Stormwater Management Plan (SWMP) administrator is to be determined.
According to the CDPHE Stormwater Fact Sheet – Construction, construction activities produce
many different kinds of pollutants which may cause stormwater contamination problems. The main
pollutant of concern at construction sites is sediment. Grading activities remove grass, rocks,
pavement, and other protective ground covers, resulting in the exposure of underlying soil to the
elements. The soil is then easily picked up by wind and/or washed away by rain or snowmelt.
In addition, construction activities often require the use of toxic or hazardous materials such as
fuel, fertilizers, pesticides, and herbicides, and building materials such as asphalt, sealants, and
concrete, which may also pollute stormwater. These materials can be harmful to humans, plants,
and aquatic life.
There are no known potential pollution sources. However, this condition should be confirmed by
the owner/operator or SWMP administrator. Other pollution sources that could be present include:
runoff from vehicle washing, vehicle maintenance and/or fueling, There are no known existing
non-stormwater components of discharge (i.e., springs, landscape irrigation return flow, etc.), or
any anticipated during construction.
1. All Disturbed and Stored Soil:
The total disturbed area will be approximately 8.3 acres. Soil stockpiles should be kept
below the locally mandated maximum height of 10 feet and surrounded with sediment
control devices. If the storage of these soils occurs over a period greater than 30 days,
then consider temporarily seeding the soil to minimize soil loss to wind and water
erosion.
2. Vehicle Tracking of Sediments:
The majority of the existing site is unpaved. A temporary stabilized stone pad (Vehicle
Tracking Control pad, VTC) will be provided at points of ingress and egress onto the
unpaved area. The VTC is designed to reduce the amount of mud transported onto the
public roads by construction traffic. If the site is extraordinarily muddy, then consider
designating an area to wash construction vehicles before they leave the site and enter
the public right-of-way. A BMP such as this is a good way to avoid the costs associated
with street cleaning or accidentally discharging large amounts of sediment into other
storm drain systems.
When in doubt, choose methods that prevent pollution rather than ones that force
clean-up at the downstream end just before the stormwater enters the receiving
waters. In other words, the most efficient construction site BMPs are those that
prevent erosion from happening.
3. Inlet Protection (IP): gravel inlet protection will be used on all inlets to prevent
sediment and debris from entering the storm drain system.
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4. Street sweeping will be conducted as necessary to remove sediment tracked on to
pavement and adjacent streets.
5. Management of Contaminated Soils:
There are no known contaminated soils on site. If contaminated soils are found, the
contractor shall report to the SWMP administrator.
6. Loading and Unloading Operations:
Loading/unloading activities will occur within the paved area of the site or a
temporary gravel staging area will be provided.
7. Outdoor Storage Activities:
Materials storage, waste disposal, and vehicle maintenance and fueling can occur
within an enclosed and secure area.
8. Vehicle and Equipment Maintenance and Fueling:
Materials should be stored and handled in covered areas to prevent contact with
stormwater, and chemicals should be stored within berms or secondary containment
devices to prevent leaks and spills from entering stormwater runoff.
Spill Management
In general, spill prevention and response should include the following:
a) Notification procedures to be used in the event of an accident. At the very
least, the SWMP Administrator should be notified. Depending on the nature
of the spill and the material involved, the Colorado Department of Health,
downstream water users, or other agencies may also need to be notified.
b) Instructions for clean-up procedures.
c) Provisions for absorbents are to be made available for use in fuel areas, and
for containers to be available for used absorbents.
d) Procedures for properly washing out concrete trucks and other equipment in a
manner and location so that the materials and wash water cannot discharge
from the site, and never into a storm drain system or stream.
9. Significant Dust or Particulate Generating Processes:
Disturbed areas not yet ready to be seeded, landscaped, paved, or otherwise stabilized
shall be watered, or ripped as necessary to preclude visible dust emissions. Contractor
shall make every effort to minimize particulate emissions from vehicles performing the
work, including but not limited to regular maintenance of construction equipment.
10. Routine Maintenance Activates Involving Fertilizer, Pesticides, Detergents, Fuels,
Solvents, Oils, Etc:
Materials should be stored and handled in covered areas to prevent contact with
stormwater, and chemicals should be stored within berms or secondary containment
devices to prevent leaks and spills from entering stormwater runoff.
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11. On-site Waste Management Practices (Waste Piles, Liquid Wastes, Dumpsters, etc):
Materials storage, waste disposal, and vehicle maintenance and fueling can occur
within an enclosed and secure area. The area can be enclosed with temporary fencing
and accessed through a gate with a lock.
12. Concrete Truck/Equipment Washing:
A concrete washout facility will be provided onsite. Properly wash out concrete trucks
and other equipment in a manner and location (a minimum of 50 feet away from any
inlet structures) so that the materials and wash water cannot discharge from the site,
and never into a storm drain system or stream.
13. Dedicated Asphalt and Concrete Batch Plants:
There will be no dedicated batch plant on site.
14. Non-Industrial Waste Source Such as Workers Trash And Portable Toilets:
Garbage cans shall be located at break areas and portable toilets shall be provided if
onsite bathroom facilities cannot be used. Locate dumpsters and portable toilets away
from drainage courses (minimum 50 feet from any inlet structures) and stake down
toilets to prevent tipping.
15. Other Areas or Procedures where Potential Spills can Occur:
Records of spills, leaks, or overflows that result in the discharge of pollutants must be
documented and maintained. Record all spills that are responded to, even if they do
not result in a discharge of pollutants. Information that should be recorded for all
occurrences includes the time and date, weather conditions, reasons for the spill, etc.
Some spills may need to be reported to immediately. Specifically, a release of any
chemical, oil, petroleum product, sewage, etc., which may enter waters of the State of
Colorado (which include surface water, ground water and dry gullies or storm sewers
leading to surface water) must be reported. More guidance is available on the web at
www.colorado.gov. The Division’s toll-free 24-hour number for environmental
hazards and chemical spills and releases is 1-877-518-5608.
SEQUENCE OF CONSTRUCTION ACTIVITIES
Construction Start Date (This is the day you expect to begin disturbing soils, including grubbing,
stockpiling, excavating, demolition, and grading activities): January 2017
Final Stabilization Date (this is when the site is finally stabilized. This means that all disturbed
areas have been either built on, paved, or a uniform vegetative cover reaching over 70% of the
initial vegetative density has been established.) Even if you are doing one part of the project, the
estimated completion date must be for the overall project: June 2018
Construction Sequencing: (Detailed construction sequencing to be determined by the contractor)
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1. Installation of temporary erosion and sediment control measures.
This includes all sediment control logs, and inlet protection where land disturbing activities
will occur.
2. Sequence of all land disturbing activity.
Overlot grading in preparation for pouring of new sidewalks and building foundations will
occur early in the construction schedule. Additional land disturbance will occur around the
site for utility installation and the construction of the new driveway approach and sidewalk.
3. Drainage facility construction.
Construction of the detention pond, storm inlets and piping will occur early in the schedule.
4. Sediment basins, temporary channel stabilization.
Sediment control logs or erosion control blankets will be installed on the banks of the
vegetated detention pond and swale on the east side of the site.
5. Seeding
All disturbed areas will be seeded upon completing of finish grading. Refer to the landscape
plans for detailed planting and seeding schedule.
6. Mulching.
Spread straw mulch uniformly over seeded areas at a rate of 90 lbs per 1000 square feet of
ground. No more than 25% of the ground should be visible. Crimp or pinch mulch into
soil 2-4 inches by using either a mulch anchoring tool, a farm disk operating on the contour
of the slope, or by cleating with bulldozer tracks operating up and down the slopes (to
prevent tracks from forming gullies).
7. Required maintenance activities (e.g. after-storm checks of all BMPs, etc.).
All temporary sediment control BMPs shall be inspected after each rain event to ensure
proper protection and to determine if cleaning is necessary. Final cleaning of all storm
facilities shall be provided upon final stabilization of site.
CONCLUSIONS
This Preliminary Drainage and Erosion Control Report for the Fort Collins Housing Authority
Village on Horsetooth has been prepared to comply with the stormwater criteria set by the UDFCD
and the City of Fort Collins.
The proposed drainage system presented in this report is designed to convey the 100-year peak
stormwater runoff through the site to the proposed detention pond. Through calculations and
review of the proposed storm drain system, there appears to be adequate capacity to convey the
proposed flows. This report also proposes best management practices for erosion control,
permanent landscaping, riprap, and on-site construction facilities.
It can therefore be concluded that development of the detention pond complies with all of the
stormwater jurisdictional criteria and will not adversely affect the existing streets, storm drain
system and/or detention/water quality facilities.
Fort Collins Housing Authority - Village on Horsetooth
Page 14 of 14
REFERENCES
1. Urban Storm Drainage Criteria Manual (Volumes 1, 2, and 3), Urban Drainage and Flood
Control District, June 2001, January 2016.
2. City of Fort Collins Stormwater Criteria Manual, City of Fort Collins, December 2013.
3. “Geotechnical Investigation FCHA Village At Horsetooth 1506 West Horsetooth Road
Fort Collins, Colorado”, CTL Thompson Incorporated, Dated July 19, 2016.
4. City of Fort Collins Foothills Basin Master Plan, Retrieved from http://www.fcgov.com/
utilities/what-we-do/stormwater/drainage-basins/foothills-basin on August 8, 2016.
APPENDIX A – FIGURES
1. Site Vicinity Map
2. Historic Drainage Map
3. Developed Drainage Map
S. TAFT HILL RD
S. SHIELDS STREET
W. DRAKE RD
W. HORSETOOTH RD
HARMONY RD
JVA, Incorporated
25 Old Town Square
Suite 200
Fort Collins, CO 80524
Phone: 970.225.9099
Fax: 970.225.6963
E-mail: info@jvajva.com
CONSULTING ENGINEERS
VILLAGE ON HORSETOOTH
PROJECT
SHEET NUMBER
C JVA, INC
DATE:
JOB NUMBER:
CHECKED BY:
DRAWN BY:
DESIGNED BY:
NO. DATE DRAWN DESIGNED REVISION / ISSUE DESCRIPTION
JVA, Incorporated 25 Old Town Square
Suite 200 Fort Collins, CO 80524
E-mail: info@jvajva.com
Phone: 970.225.9099 Fax: 970.225.6963
CONSULTING ENGINEERS
FCHA - VILLAGE ON HORSETOOTH
2595c
08/17/2016
HISTORIC DRAINAGE MAP
EJK
EJK
CRH
FIG 2
SHEET NUMBER
C JVA, INC
DATE:
JOB NUMBER:
CHECKED BY:
DRAWN BY:
DESIGNED BY:
NO. DATE DRAWN DESIGNED REVISION / ISSUE DESCRIPTION
JVA, Incorporated 25 Old Town Square
Suite 200 Fort Collins, CO 80524
E-mail: info@jvajva.com
Phone: 970.225.9099 Fax: 970.225.6963
CONSULTING ENGINEERS
VILLAGE ON HORSETOOTH
2595c
08/17/2016
DEVELOPED DRAINAGE MAP
EJK
EJK
CRH
FIG 3
APPENDIX B – HYDRAULIC/HYDROLOGIC
COMPUTATIONS
1. Historic C, Tc, and Runoff Calculations
2. Developed C, Tc, and Runoff Calculations
3. WQCV Calculations
4. Pond Volume Calculations
JVA Incorporated JVA Office:
25 Old Town Square, S 200 Fort Collins
Fort Collins, CO 80524
Ph: (970) 225 9099
Version 2016_XT: 6/30/2016
Project Information:
Job Name: Village On Horsetooth
Job Number: 2595c
Date: 8/17/2016
Designed by: EJK/LAT
Municipality : Fort_Collins Soil Type: B
Runoff Calculations:
Minor Design Storm: 2 year
Major Design Storm: 100 year
Detention Calculations:
Minor Storm Detention: 2 year plus 100 % WQCV
Major Storm Detention: 100 year plus 100 % WQCV
Detention Volume by: ≤5ac FAA >5ac FAA+20% Enter WQCV : 7,881 cf
(GB, PP, PLD, SFB, EDB,etc.)
Allowable Release Rates (if applicable):
Max release rate 1 cfs / acre? No Site Area: 8.68 acres
Enter Offsite flows to bypass site (these will be added to the allowable release rates)
Q2 = 0.00 cfs (bypass flows) Q2allow= 2.24 cfs
Q100 = 0.00 cfs (bypass flows) Q100allow = 2.24 cfs
Rainfall Data Information:
Enter City, Town, or County: Fort_Collins
Frequency of Design
Event
Do you need to Calc P1? No
2 yr 0.82 in
5 yr 1.14 in
10 yr 1.40 in
100 yr 2.86 in
Runoff Coefficient Calculations:
Use UDFCD Equations? Yes
Intensity Duration Values:
I-D-F FortCollinsIDF
One Hour Point Rainfall P1
2595c - Rational Calculations.xlsx INTRO Page 1 of 1
JVA Incorporated Job Name: Village On Horsetooth
25 Old Town Square, S 200 Job Number: 2595c
Fort Collins, CO 80524 Date: 8/17/16
Ph: (970) 225 9099 By: EJK/LAT
Village On Horsetooth
Historic Runoff Coefficient & Time of Concentration Calculations
Location: Fort_Collins
Minor Design Storm: 2
Major Design Storm: 100
Soil Type: B
Basin Design Data
I (%) = 100% 90% 90% 40% 25% 25% 2% 2% I (%) tc Comp
tc
Final
Basin
Name
Design
Point
Apaved
streets
(sf)
Adrives/co
nc (sf)
Aroof
(sf)
Agravel
(sf)
Aplygnd
(sf)
Aart. turf
(sf)
Alscape (B
soil)
(sf)
Alscape
(C/D soil)
(sf)
ATotal
(sf)
ATotal
(ac)
Imp
(%)
C2 C5 C10 C100
Upper
most
Length
(ft)
Slope
(%)
ti
(min)
Length
(ft)
Slope
(%)
Type of Land Surface K
Velocity
(fps)
tt
JVA Incorporated Job Name: Village On Horsetooth
25 Old Town Square, S 200 Job Number: 2595c
Fort Collins, CO 80524 Date: 8/17/16
Ph: (970) 225 9099 By: EJK/LAT
Village On Horsetooth
Composite Runoff Coefficient Calculations
Location: Fort_Collins
Minor Design Storm: 2
Major Design Storm: 100
Soil Type: B
C Value calculated from UDFCDCM Chapter 6
Basin Design Data
I (%) = 100% 90% 90% 40% 25% 25% 2% 2% I (%)
Basin
Name
Design
Point
Apaved
streets
(sf)
Adrives/c
onc (sf)
Aroof
(sf)
Agravel
(sf)
Aplygnd
(sf)
Aart. turf
(sf)
Alscape (B
soil)
(sf)
Alscape
(C/D soil)
(sf)
ATotal
(sf)
ATotal
(ac)
Imp
(%)
C2 C5 C10 C100
A1 1 766 14,465 15,231 0.35 6.4% 0.06 0.06 0.18 0.49
A2 2 32,708 16,154 633 14,973 64,468 1.48 74.1% 0.66 0.69 0.73 0.82
A3 3 28,329 18,726 17,446 64,501 1.48 70.6% 0.63 0.66 0.70 0.80
A4 4 7,835 1,804 38,340 47,979 1.10 17.8% 0.16 0.17 0.27 0.54
A5 5 3,281 3,082 49,937 56,300 1.29 9.2% 0.08 0.09 0.20 0.50
A6 6 496 557 3,237 4,290 0.10 17.1% 0.15 0.16 0.26 0.54
B 7 20,961 6,663 110 34,340 62,074 1.43 44.6% 0.40 0.41 0.49 0.67
R1 8 7,641 7,641 0.18 90.0% 0.80 0.84 0.85 0.90
R2 9 7,641 7,641 0.18 90.0% 0.80 0.84 0.85 0.90
R3 10 7,641 7,641 0.18 90.0% 0.80 0.84 0.85 0.90
R4 11 7,641 7,641 0.18 90.0% 0.80 0.84 0.85 0.90
R5 12 4,673 4,673 0.11 90.0% 0.80 0.84 0.85 0.90
R6 13 2,917 2,917 0.07 90.0% 0.80 0.84 0.85 0.90
R7 14 4,987 4,987 0.11 90.0% 0.80 0.84 0.85 0.90
R8 15 7,641 7,641 0.18 90.0% 0.80 0.84 0.85 0.90
R9 16 7,641 7,641 0.18 90.0% 0.80 0.84 0.85 0.90
R10 17 4,673 4,673 0.11 90.0% 0.80 0.84 0.85 0.90
JVA Incorporated Job Name: Village On Horsetooth
25 Old Town Square, S 200 Job Number: 2595c
Fort Collins, CO 80524 Date: 8/17/16
Ph: (970) 225 9099 By: EJK/LAT
Village On Horsetooth
Time of Concentration Calculations
Location: Fort_Collins
Minor Design Storm: 2
Major Design Storm: 100
Soil Type: B
Sub-Basin Data tc
Comp
tc
Final
Basin
Name
Design
Point
ATotal
(ac)
C5
Upper
most
Length
(ft)
Slope
(%)
ti
(min)
Length
(ft)
Slope (%) Type of Land Surface Cv
Velocity
(fps)
tt
(min)
Time of
Conc
ti
+ tt
= tc
Total
Length
(ft)
tc
=(L/180)+
10 (min)
Min
tc
A1 1 0.35 0.06 160 1.3% 22.1 275 0.9% Grassed waterway 15 1.4 3.2 25.4 435 12.4 12.4
A2 2 1.48 0.69 59 3.0% 4.0 843 0.5%
Paved areas & shallow
paved swales
20 1.5 9.6 13.6 902 15.0 13.6
A3 3 1.48 0.66 40 4.6% 3.1 701 0.5%
Paved areas & shallow
paved swales
20 1.4 8.4 11.5 741 14.1 11.5
A4 4 1.10 0.17 89 1.9% 13.0 97 1.9% Grassed waterway 15 2.0 0.8 13.8 186 11.0 11.0
A5 5 1.29 0.09 60 1.2% 13.6 430 0.5%
JVA Incorporated Job Name: Village On Horsetooth
25 Old Town Square, S 200 Job Number: 2595c
Fort Collins, CO 80524 Date: 8/17/16
Ph: (970) 225 9099 By: EJK/LAT
Village On Horsetooth Developed Storm Runoff Calculations
Design Storm : 100 Year Point Hour Rainfall (P1) : 2.86
Basin Name
Design Point
Area (ac)
Runoff Coeff
tc (min)
C*A (ac)
I (in/hr)
Q (cfs)
Total tc (min)
ΣC*A (ac)
I (in/hr)
Q (cfs)
Inlet Type
Q intercepted
Q carryover
Q bypass
Pipe Size (in)
or equivalent
Pipe Material
Slope (%)
Pipe Flow
(cfs)
Max Pipe
Capacity (cfs)
Length (ft)
Velocity (fps)
tt (min)
Total Time
(min)
Notes
A1 1 0.35 0.49 12.40 0.17 7.06 1.20 12.40 0.17 7.06 1.20
A2 2 1.48 0.82 13.60 1.21 6.79 8.22 13.60 1.21 6.79 8.22
A3 3 1.48 0.80 11.50 1.18 7.29 8.63 11.50 1.18 7.29 8.63
A4 4 1.10 0.54 11.00 0.60 7.42 4.42 11.00 0.60 7.42 4.42
A5 5 1.29 0.50 12.70 0.65 6.99 4.51 12.70 0.65 6.99 4.51
A6 6 0.10 0.54 11.00 0.05 7.42 0.39 11.00 0.05 7.42 0.39
B 7 1.43 0.67 13.10 0.96 6.90 6.61 13.10 0.96 6.90 6.61
R1 8 0.18 0.90 5.00 0.16 9.95 1.56 5.00 0.16 9.95 1.56
R2 9 0.18 0.90 5.00 0.16 9.95 1.56 5.00 0.16 9.95 1.56
R3 10 0.18 0.90 5.00 0.16 9.95 1.56 5.00 0.16 9.95 1.56
R4 11 0.18 0.90 5.00 0.16 9.95 1.56 5.00 0.16 9.95 1.56
R5 12 0.11 0.90 5.00 0.10 9.95 0.96 5.00 0.10 9.95 0.96
R6 13 0.07 0.90 5.00 0.06 9.95 0.60 5.00 0.06 9.95 0.60
R7 14 0.11 0.90 5.00 0.10 9.95 1.02 5.00 0.10 9.95 1.02
R8 15 0.18 0.90 5.00 0.16 9.95 1.56 5.00 0.16 9.95 1.56
R9 16 0.18 0.90 5.00 0.16 9.95 1.56 5.00 0.16 9.95 1.56
R10 17 0.11 0.90 5.00 0.10 9.95 0.96 5.00 0.10 9.95 0.96
Direct Runoff Total Runoff Inlets Pipe Pipe/Swale Travel Time
2595c - Rational Calculations.xlsx Q100 Page 1 of 1
JVA Incorporated Job Name: Village On Horsetooth
25 Old Town Square, S 200 Job Number: 2595c
Fort Collins, CO 80524 Date: 8/17/16
Ph: (970) 225 9099 By: EJK/LAT
Village On Horsetooth Developed Storm Runoff Calculations
Design Storm : 2 Year Point Hour Rainfall (P1) : 0.82
Basin Name
Design Point
Area (ac)
Runoff Coeff
tc (min)
C*A (ac)
I (in/hr)
Q (cfs)
Total tc (min)
ΣC*A (ac)
I (in/hr)
Q (cfs)
Inlet Type
Q intercepted
Q carryover
Q bypass
Pipe Size (in)
or equivalent
Pipe Material
Slope (%)
Pipe Flow
(cfs)
Max Pipe
Capacity (cfs)
Length (ft)
Velocity (fps)
tt (min)
Total Time
(min)
Notes
A1 1 0.35 0.06 12.40 0.02 2.02 0.04 12.40 0.02 2.02 0.04
A2 2 1.48 0.66 13.60 0.98 1.94 1.90 13.60 0.98 1.94 1.90
A3 3 1.48 0.63 11.50 0.93 2.09 1.94 11.50 0.93 2.09 1.94
A4 4 1.10 0.16 11.00 0.17 2.13 0.37 11.00 0.17 2.13 0.37
A5 5 1.29 0.08 12.70 0.11 2.00 0.21 12.70 0.11 2.00 0.21
A6 6 0.10 0.15 11.00 0.01 2.13 0.03 11.00 0.01 2.13 0.03
B 7 1.43 0.40 13.10 0.57 1.97 1.12 13.10 0.57 1.97 1.12
R1 8 0.18 0.80 5.00 0.14 2.85 0.40 5.00 0.14 2.85 0.40
R2 9 0.18 0.80 5.00 0.14 2.85 0.40 5.00 0.14 2.85 0.40
R3 10 0.18 0.80 5.00 0.14 2.85 0.40 5.00 0.14 2.85 0.40
R4 11 0.18 0.80 5.00 0.14 2.85 0.40 5.00 0.14 2.85 0.40
R5 12 0.11 0.80 5.00 0.09 2.85 0.24 5.00 0.09 2.85 0.24
R6 13 0.07 0.80 5.00 0.05 2.85 0.15 5.00 0.05 2.85 0.15
R7 14 0.11 0.80 5.00 0.09 2.85 0.26 5.00 0.09 2.85 0.26
R8 15 0.18 0.80 5.00 0.14 2.85 0.40 5.00 0.14 2.85 0.40
R9 16 0.18 0.80 5.00 0.14 2.85 0.40 5.00 0.14 2.85 0.40
R10 17 0.11 0.80 5.00 0.09 2.85 0.24 5.00 0.09 2.85 0.24
Direct Runoff Total Runoff Inlets Pipe Pipe/Swale Travel Time
2595c - Rational Calculations.xlsx Q Minor Page 1 of 1
JVA Incorporated Job Name: Village On Horsetooth
25 Old Town Square, S 200 Job Number: 2595c
Fort Collins, CO 80524 Date: 42599
Ph: (970) 225 9099 By: EJK/LAT
Village On Horsetooth
Water Quality Capture Volume (WQCV) Calculations (UDFCD Volume 3 Chapter 3)
Infiltration Rate and Volume
Location: Fort_Collins
Major Design Storm: 100
Soil Type: B
WQCV=a((0.91I3)-(1.19I2)+(0.78I))
Where:
WQCV = Water Quality Capture Volume (watershed inches)
a = Drain Time Coefficient (see table below )
I = Imperviousness (%/100)
Drainage Time (hrs) Coefficient, a
12 0.8
24 0.9
40 1.00
WQCV North Basin: Max Rate: 2 in/hr
a= 1.00 Min Rate: 0.6 in/hr
I= 0.511 %/100 Depth in Pond: 1.21 ft
WQCV= 0.209 watershed inches WQCV Area in Pond at Depth: 5,912 ft2
Drawdown time: 40 hr
Vrequired=1.2*(WQCV/12)*A*43560 WQCV in EDB*: 7,129 ft3
MIN Infiltration in WQCV Area per hour: 296 ft3/hr
WQCV= 0.209 watershed inches MIN Infiltration in WQCV Area during DD time: 11,823 ft3
A = 8.68 acre *752 ft3 in North Infiltration Basin
Vrequired = 7881 cf
Vrequired = 0.181 acre-ft
Infiltration Rate from Websoil Survey Report
Soil can infiltrate all of WQCV in 40 hour
drawdown time
JVA Incorporated Job Name: Village On Horsetooth
25 Old Town Square, S 200 Job Number: 2595c
Fort Collins, CO 80524 Date: 8/17/16
Ph: (970) 225 9099 By: EJK/LAT
Village On Horsetooth
Detention Pond Volume Calculations: FAA Procedure
Based on FAA Procedure, per Federal Aviation Agency "Airport Drainage" Manual
Drainage Basin A
Design Storm 2 year
Composite "C" Factor 0.47
Time of Concentration Tc 13.30 min
Basin Size 7.25 acre
Release Rate Calculations
Allowable Release Rate for Site 2.24 cfs (Historic Flows for Basin H1)
Less Undetained Offsite Flows - 0.00 cfs
Allowable Release Rate for Pond 2.24 cfs
Rainfall Intensity Calculations
Point Hour Rainfall (P1) : 0.82 C1= 28.5
Rainfall Intensity: FortCollinsIDF C2= 10
I= C1*P1/(C2+T0)^C3 C3= 0.789
Volume Calculations
Inflow Volume = C * I * A * time (sec)
Outflow Volume = Alowable Release Rate * time (sec)
Storage Volume = Inflow Volume - Outflow Volume
Time
t
(min)
Intensity
I
(in/hr)
Inflow
Vin
(ft3)
Outflow
Adjustment
Factor m
Average
Outflow
(cfs)
Outflow
Vout
(ft3)
Storage
Vstor
(ft3)
5.0 2.85 2,892 1.00 2.24 672 2,220
10.0 2.21 4,485 1.00 2.24 1,344 3,141
15.0 1.87 5,693 0.94 2.11 1,902 3,791
20.0 1.61 6,535 0.83 1.87 2,238 4,297
25.0 1.43 7,256 0.77 1.72 2,574 4,681
30.0 1.30 7,915 0.72 1.62 2,910 5,005
35.0 1.17 8,325 0.69 1.55 3,246 5,079
40.0 1.07 8,703 0.67 1.49 3,582 5,120
45.0 0.99 9,060 0.65 1.45 3,919 5,141
50.0 0.92 9,356 0.63 1.42 4,255 5,101
55.0 0.87 9,722 0.62 1.39 4,591 5,132
60.0 0.82 9,985 0.61 1.37 4,927 5,059
65.0 0.77 10,222 0.60 1.35 5,263 4,959 Intensity Equation
70.0 0.74 10,462 0.60 1.33 5,599 4,863
75.0 0.70 10,686 0.59 1.32 5,935 4,751
JVA Incorporated Job Name: Village On Horsetooth
25 Old Town Square, S 200 Job Number: 2595c
Fort Collins, CO 80524 Date: 8/17/16
Ph: (970) 225 9099 By: EJK/LAT
Village On Horsetooth
Detention Pond Volume Calculations: FAA Procedure
Based on FAA Procedure, per Federal Aviation Agency "Airport Drainage" Manual
Drainage Basin A
Design Storm 100 year
Composite "C" Factor 0.71
Time of Concentration Tc 13.30 min
Basin Size 7.25 acre
Release Rate Calculations
Allowable Release Rate for Site 2.24 cfs (Historic Flows for Basin H1)
Less Undetained Offsite Flows - 0.00 cfs
Allowable Release Rate for Pond 2.24 cfs
Rainfall Intensity Calculations
Point Hour Rainfall (P1) : 2.86 C1= 28.5
Rainfall Intensity: FortCollinsIDF C2= 10
I= C1*P1/(C2+T0)^C3 C3= 0.789
Volume Calculations
Inflow Volume = C * I * A * time (sec)
Outflow Volume = Alowable Release Rate * time (sec)
Storage Volume = Inflow Volume - Outflow Volume
Time
t
(min)
Intensity
I
(in/hr)
Inflow
Vin
(ft3)
Outflow
Adjustment
Factor m
Average
Outflow
(cfs)
Outflow
Vout
(ft3)
Storage
Vstor
(ft3)
5.0 9.95 15,386 1.00 2.24 672 14,714
10.0 7.72 23,875 1.00 2.24 1,344 22,531
15.0 6.52 30,246 0.94 2.11 1,902 28,344
20.0 5.60 34,637 0.83 1.87 2,238 32,399
25.0 4.98 38,503 0.77 1.72 2,574 35,929
30.0 4.52 41,936 0.72 1.62 2,910 39,026
35.0 4.09 44,249 0.69 1.55 3,246 41,003
40.0 3.75 46,340 0.67 1.49 3,582 42,757
45.0 3.47 48,222 0.65 1.45 3,919 44,303
50.0 3.23 50,008 0.63 1.42 4,255 45,753
55.0 3.03 51,607 0.62 1.39 4,591 47,016
60.0 2.86 53,069 0.61 1.37 4,927 48,143
65.0 2.70 54,328 0.60 1.35 5,263 49,066 Intensity Equation
70.0 2.57 55,603 0.60 1.33 5,599 50,004
75.0 2.45 56,792 0.59 1.32 5,935 50,857
JVA Incorporated Job Name: Village On Horsetooth
25 Old Town Square, S 200 Job Number: 2595c
Fort Collins, CO 80524 Date: 8/17/16
Ph: (970) 225 9099 By: EJK/LAT
POND VOLUME CALCULATIONS - STAGE / STORAGE
Pond Volume = Prismoidal Formula
Volume Equation = (A1+A2+SQRT(A1*A2)*D/3
WEIGHTED INCREMENTAL CUMMULATIVE
ELEVATION DEPTH (D) AREA (A1) AVG AREA (A2) VOLUME VOLUME
ft ft ft
2
ft
2
ft
3
ft
3
5105.3 146 0
5105.5 0.2 587 367 68 68
5106.0 0.5 7,191 3,889 1,639 1,707
5106.5 0.5 14,358 10,775 5,285 6,992
5107.0 0.5 32,759 23,559 11,467 18,460
5107.5 0.5 41,632 37,196 18,553 37,013
5108.0 0.5 56,078 48,855 24,338 61,351
5108.5 0.5 74,177 65,128 32,458 93,810
5109.0 0.5 95,777 84,977 42,374 136,183
5109.25 0.3 104,838 100,308 25,068 161,252
Top of Pond
5109.25 3.95 161,252 cf 3.702 ac-ft
Required
Volume (ft
3
)
Required
Volume (ac-ft)
Water Surface
Elevation Water Depth
WQCV 7,129 cf 0.164 ac-ft 5106.51 ft 1.21 ft
V2 + 100% WQCV 13,299 cf 0.305 ac-ft 5106.77 ft 1.47 ft
V100 + 100% WQCV 78,246 cf 1.796 ac-ft 5108.26 ft 2.96 ft
V2 + 100% WQCV V100 + 100% WQCV
Vol Elev Vol Elev Vol Elev
6992.16 5106.50 6992.16 5106.50 61351.11 5108.00
7129.46 5106.51 13298.95 5106.77 78245.76 5108.26
18459.60 5107.00 18459.60 5107.00 93809.57 5108.50
North Infiltration Basin
WEIGHTED INCREMENTAL CUMMULATIVE
ELEVATION DEPTH (D) AREA (A1) AVG AREA (A2) VOLUME VOLUME
ft ft ft
2
ft
2
ft
3
ft
3
5107.0 65 0
5107.25 0.25 337 201 46 46
5107.50 0.25 729 533 130 176
5107.75 0.25 1,151 940 233 409
JVA Incorporated Job Name: Village On Horsetooth
25 Old Town Square, S 200 Job Number: 2595c
Fort Collins, CO 80524 Date: 8/17/16
Ph: (970) 225 9099 By: EJK/LAT
0
Top of Pond
161,252 cf
5109.25
WQCV
7,129 cf
5106.51 ft
V2 + 100% WQCV
13,299 cf
5106.77 ft
V100 + 100% WQCV
78,246 cf
5108.26 ft
5105.0
5105.5
5106.0
5106.5
5107.0
5107.5
5108.0
5108.5
5109.0
5109.5
0 20,000 40,000 60,000 80,000 100,000 120,000 140,000 160,000 180,000
WATER SURFACE ELEVATION
(FEET ABOVE MSL)
POND VOLUME (CF)
STAGE VS. STORAGE
Water Quality Detention Pond
2595c - Rational Calculations.xlsx Vol Pond Page 2 of 2
JVA Incorporated Job Name: Village On Horsetooth
25 Old Town Square, S 200 Job Number: 2595c
Fort Collins, CO 80524 Date: 8/17/16
Ph: (970) 225 9099 By: EJK/LAT
ORIFICE PLATE AT OUTLET PIPE WORKSHEET
Orifice Plate using Headwater above opening and
Q=cA(2gH)^.5 C= 0.65 QMAJOR
allowable release rate: 2.24 cfs
Summary of Available Pipe Releases 100-yr Water Surface Elev: 5108.26 ft
Pipe Dia Area Head H Q Inv Elev at Outlet Struct: 5105.20 ft
Outfall Pipe at centroid avail out Outlet Pipe at Structure: 15 in
(in) (sf) (ft) (cfs)
12 0.79 2.56 6.55
15 1.23 2.44 9.98
18 1.77 2.31 14.00
24 3.14 2.06 23.51
30 4.91 1.81 34.43
36 7.07 1.56 46.03
Q=cA(2gH)^.5 C= 0.65
Iteration process
Q 2.24 cfs
c 0.65
Hhead
2.44 ft
Needed Area 0.28 sf
Using Area- determine
Ao 0.28 sf
Apipe 1.23 sf
theta 4.056 rad
Ao-calced 0.28 sf
m -0.28 ft distance above(+) or below(-) center
H 0.35 ft Height above pipe invert
+
APPENDIX C – REFERENCED DOCUMENTS
1. FEMA FIRM Map
2. Geotechnical Report – Summary of Conclusions by CTL Thompson INC
3. USDA NRCS Web Soil Survey Map and Soil Description
4. USDA National Wetlands Inventory Wetlands Map
5. City of Fort Collins Foothills Basin Master Plan WQ Conceptual Alternatives Map
400 North Link Lane | Fort Collins, Colorado 80524
Telephone: 970-206-9455 Fax: 970-206-9441
GEOTECHNICAL INVESTIGATION
FCHA VILLAGE AT HORSETOOTH
1506 WEST HORESTOOTH ROAD
FORT COLLINS, COLORADO
FORT COLLINS HOUSING AUTHORITY
1715 West Mountain Avenue
Fort Collins, Colorado 80521
Attention: Kristin Fritz, AICP
Project No. FC07464-120
July 19, 2016
FORT COLLINS HOUSING AUTHORITY
VILLAGE AT HORSETOOTH
CTL | T PROJECT NO. FC07464-120
1
SCOPE
This report presents the results of our Geotechnical Investigation for the
proposed FCHA Village at Horsetooth in Fort Collins, Colorado. The purpose of
the investigation was to evaluate the subsurface conditions and provide founda-
tion recommendations and geotechnical design criteria for the project.
The report was prepared from data developed during field exploration, la-
boratory testing, engineering analysis and experience with similar conditions.
The report includes a description of subsurface conditions found in our explorato-
ry borings and discussions of site development as influenced by geotechnical
considerations. Our opinions and recommendations regarding design criteria
and construction details for site development, foundations, floor systems, slabs-
on-grade, lateral earth loads, pavements and drainage are provided. If the pro-
posed construction changes, we should be requested to review our recommen-
dations. Our conclusions are summarized in the following paragraphs.
SUMMARY OF CONCLUSIONS
1. Soils encountered in our borings consisted of interlayered sandy
clay and clayey sand to the depths explored. Based on laboratory
testing, the soils are generally non-expansive to low-swelling. No
bedrock was encountered in our borings.
2. Groundwater was encountered at depths of 19 to 23 feet during
drilling and was measured several days after drilling at depths of 19
to 22 feet. Existing groundwater levels are not expected to signifi-
cantly affect the proposed construction.
3. We believe the proposed structures can be constructed on a
spread footing foundation placed on natural, undisturbed soil and/or
properly compacted fill. Foundation design and construction rec-
ommendations are presented in this report.
FORT COLLINS HOUSING AUTHORITY
VILLAGE AT HORSETOOTH
CTL | T PROJECT NO. FC07464-120
2
4. We believe slab-on-grade floors are appropriate for this site. Some
movement of slab-on-grade floors should be anticipated. We ex-
pect movements will be minor, on the order of 1 inch or less. If
movement cannot be tolerated, structural floors should be consid-
ered.
5. Pavement subgrade at this site will generally consist of A-4 and A-
2-4 materials according to AASHTO criteria, with expected poor to
good subgrade support. Recommended section thicknesses and
pavement materials are provided in this report.
SITE CONDITIONS AND PROPOSED CONSTRUCTION
The area of proposed development is on the north side of Horsetooth
Road east of Big Ben Drive in Fort Collins, Colorado. An existing residence with
horse stalls and associated pasture areas were located on site at the time of our
investigation. The ground surface is generally flat; vegetation consisted of natural
grasses, weeds and trees. A ditch runs along the eastern boundary of the proper-
ty.
We understand that the proposed construction will consist of nine apart-
ment buildings having 96 units, a club house, and associated paved parking are-
as and access drives. No below grade areas are planned.
INVESTIGATION
Subsurface conditions were investigated by drilling thirteen exploratory
borings to depths of approximately 20 to 30 feet. Our representative observed
drilling operations, logged the soil found in the borings, and obtained samples.
Groundwater measurements were taken during and several days after drilling.
Summary logs of the borings, including results of field penetration resistance
tests, are presented on Figures 2 and 3.
Soil Map—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
8/11/2016
Page 1 of 3
4487500 4487530 4487560 4487590 4487620 4487650 4487680 4487710
4487500 4487530 4487560 4487590 4487620 4487650 4487680 4487710
490980 491010 491040 491070 491100 491130 491160 491190 491220 491250 491280 491310
490980 491010 491040 491070 491100 491130 491160 491190 491220 491250 491280 491310
40° 32' 24'' N
105° 6' 23'' W
40° 32' 24'' N
105° 6' 8'' W
40° 32' 17'' N
105° 6' 23'' W
40° 32' 17'' N
105° 6' 8'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 50 100 200 300
Feet
0 20 40 80 120
Meters
Map Scale: 1:1,610 if printed on A landscape (11" x 8.5") sheet.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Map Unit Polygons
Soil Map Unit Lines
Soil Map Unit Points
Special Point Features
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
Gravelly Spot
Landfill
Lava Flow
Marsh or swamp
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
Sodic Spot
Spoil Area
Stony Spot
Very Stony Spot
Wet Spot
Other
Special Line Features
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: http://websoilsurvey.nrcs.usda.gov
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
Map Unit Legend
Larimer County Area, Colorado (CO644)
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
3 Altvan-Satanta loams, 0 to 3
percent slopes
8.2 100.0%
Totals for Area of Interest 8.2 100.0%
Soil Map—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
8/11/2016
Page 3 of 3
Larimer County Area, Colorado
3—Altvan-Satanta loams, 0 to 3 percent slopes
Map Unit Setting
National map unit symbol: jpw2
Elevation: 5,200 to 6,200 feet
Mean annual precipitation: 13 to 15 inches
Mean annual air temperature: 48 to 50 degrees F
Frost-free period: 135 to 150 days
Farmland classification: Prime farmland if irrigated
Map Unit Composition
Altvan and similar soils: 45 percent
Satanta and similar soils: 30 percent
Minor components: 25 percent
Estimates are based on observations, descriptions, and transects of the
mapunit.
Description of Altvan
Setting
Landform: Benches, terraces
Landform position (three-dimensional): Side slope, tread
Down-slope shape: Linear
Across-slope shape: Linear
Parent material: Mixed alluvium
Typical profile
H1 - 0 to 10 inches: loam
H2 - 10 to 18 inches: clay loam, loam, sandy clay loam
H2 - 10 to 18 inches: loam, fine sandy loam, silt loam
H2 - 10 to 18 inches: gravelly sand, gravelly coarse sand, coarse
sand
H3 - 18 to 30 inches:
H3 - 18 to 30 inches:
H3 - 18 to 30 inches:
H4 - 30 to 60 inches:
H4 - 30 to 60 inches:
H4 - 30 to 60 inches:
Properties and qualities
Slope: 0 to 3 percent
Depth to restrictive feature: More than 80 inches
Natural drainage class: Well drained
Runoff class: Low
Capacity of the most limiting layer to transmit water (Ksat):
Moderately high to high (0.60 to 2.00 in/hr)
Depth to water table: More than 80 inches
Frequency of flooding: None
Frequency of ponding: None
Calcium carbonate, maximum in profile: 10 percent
Map Unit Description: Altvan-Satanta loams, 0 to 3 percent slopes---Larimer County Area,
Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
8/11/2016
Page 1 of 3
Available water storage in profile: Very high (about 13.2 inches)
Interpretive groups
Land capability classification (irrigated): 3e
Land capability classification (nonirrigated): 3e
Hydrologic Soil Group: B
Description of Satanta
Setting
Landform: Structural benches, terraces
Landform position (three-dimensional): Side slope, tread
Down-slope shape: Linear
Across-slope shape: Linear
Parent material: Mixed alluvium and/or eolian deposits
Typical profile
H1 - 0 to 9 inches: loam
H2 - 9 to 18 inches: loam, clay loam, sandy clay loam
H2 - 9 to 18 inches: loam, clay loam, fine sandy loam
H2 - 9 to 18 inches:
H3 - 18 to 60 inches:
H3 - 18 to 60 inches:
H3 - 18 to 60 inches:
Properties and qualities
Slope: 0 to 1 percent
Depth to restrictive feature: More than 80 inches
Natural drainage class: Well drained
Runoff class: Low
Capacity of the most limiting layer to transmit water (Ksat):
Moderately high to high (0.60 to 2.00 in/hr)
Depth to water table: More than 80 inches
Frequency of flooding: None
Frequency of ponding: None
Calcium carbonate, maximum in profile: 10 percent
Available water storage in profile: Very high (about 27.4 inches)
Interpretive groups
Land capability classification (irrigated): 1
Land capability classification (nonirrigated): 3c
Hydrologic Soil Group: B
Minor Components
Nunn
Percent of map unit: 10 percent
Larim
Percent of map unit: 10 percent
Map Unit Description: Altvan-Satanta loams, 0 to 3 percent slopes---Larimer County Area,
Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
8/11/2016
Page 2 of 3
Stoneham
Percent of map unit: 5 percent
Data Source Information
Soil Survey Area: Larimer County Area, Colorado
Survey Area Data: Version 10, Sep 22, 2015
Map Unit Description: Altvan-Satanta loams, 0 to 3 percent slopes---Larimer County Area,
Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
8/11/2016
Page 3 of 3
Village On Horsetooth - Wetlands Map
Source: DS,Airbus USDA, Esri, USGS, DigitalGlobe, AEX, Getmapping, GeoEye, Earthstar Aerogrid, Geographics, IGN, IGP, swisstopo, CNES/and
Estuarine and Marine Deepwater
Estuarine and Marine Wetland
Freshwater Emergent Wetland
Freshwater Forested/Shrub Wetland
Freshwater Pond
Lake
Other
Riverine
August 11, 2016
0 0.130325 0.065 0.mi
0 0.05 0.1 0.2 km
1:4,058
This page National was produced Wetlands by the Inventory NWI mapper (NWI)
This Service map is is not for responsible general reference for the accuracy only. The or US currentness Fish and Wildlife of the
base be used data in shown accordance on this with map. the All layer wetlands metadata related found data on should the
Wetlands Mapper web site.
#*
#*
#*
#*
#*
W PROSPECT RD
W DRAKE RD
W HARMONY RD
W HORSETOOTH RD
S TAFT HILL RD
S SHIELDS ST
S COLLEGE AVE
S LEMAY AVE
S TIMBERLINE RD
ZIEGLER RD
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Fort HCSollins
EleBmeaetntiteary
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S TIMBERLINE RD
E LEMAY AVE
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UP RAILROAD
Warren
Troutman
SCteawsaert
Westfield
FOOTHILLS Water Quality Master Concepetual Plan BASIN Alternatives
Fort ● Retrofit Collins Existing High School Pond to Pond
accommodate Volume Water Quality
Collindale ●Pond Retrofit Existing PUD Pond to
accommodate Volume Water Quality
Warren ● Water Lake Quality Treatment
provided Lake in Existing Warren
Southmoor ● Retrofit Existing Village Pond Pond to
accommodate Volume Water Quality
Lake ● Water Sherwood Quality Treatment
provided Sherwood in Existing Lake
Parkwood ● Retrofit Existing East Pond Pond to
accommodate Volume Water Quality
Proposed Restoration Stream
Improvement
0 500000 1,000 2,[
Feet
NAIP Image - 2009
Proposed BMP Basin Type
Foothills Basin Boundary
Flood Control Only
Water Quality Only
Flood Control and Water Quality
Proposed Improvements
None
Proposed Proposed WaterConceptual Quality Alternatives
Undeveloped Area
Water
Stream - Canal
Parks
Proposed andRestoration Habitat Stream Improvements
#* Proposed Water Quality Pond
the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Survey Area Data: Version 10, Sep 22, 2015
Soil map units are labeled (as space allows) for map scales 1:50,000
or larger.
Date(s) aerial images were photographed: Apr 22, 2011—Apr 28,
2011
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.
Soil Map—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
8/11/2016
Page 2 of 3
−
=
2
* cos
2
sin
2
2 θ θ
π
π θ
A o A pipe r r
=
2
cos θ
m r
H = r + m
2595c - Rational Calculations.xlsx Major Orifice Page 1 of 1
5108.00 0.25 1,603 1,377 343 752
5108.0 1.0 TOTAL VOLUME 752 cf 0.017 ac-ft
Top of Pond- North Infiltration Basin
Stage / Storage Input Table
TOTAL VOLUME
Pond Volume Summary Table
Volume Interpolation Calculations
WQCV
2595c - Rational Calculations.xlsx Vol Pond Page 1 of 2
80.0 2.34 57,907 0.58 1.31 6,271 51,636
85.0 2.24 58,957 0.58 1.30 6,607 52,350
90.0 2.15 59,949 0.57 1.29 6,943 53,006
95.0 2.07 60,890 0.57 1.28 7,279 53,610
100.0 2.00 61,784 0.57 1.27 7,615 54,169
105.0 1.93 62,638 0.56 1.26 7,951 54,686
110.0 1.87 63,454 0.56 1.26 8,287 55,166
115.0 1.81 64,235 0.56 1.25 8,623 55,612
120.0 1.75 64,986 0.56 1.24 8,960 56,026
125.0 1.70 65,707 0.55 1.24 9,296 56,412
130.0 1.65 66,403 0.55 1.23 9,632 56,771
135.0 1.61 67,074 0.55 1.23 9,968 57,106
140.0 1.56 67,722 0.55 1.23 10,304 57,418
145.0 1.52 68,349 0.55 1.22 10,640 57,709
150.0 1.49 68,957 0.54 1.22 10,976 57,981
155.0 1.45 69,546 0.54 1.22 11,312 58,234
160.0 1.42 70,119 0.54 1.21 11,648 58,471
165.0 1.39 70,675 0.54 1.21 11,984 58,691
170.0 1.35 71,216 0.54 1.21 12,320 58,896
175.0 1.33 71,743 0.54 1.21 12,656 59,086
180.0 1.30 72,256 0.54 1.20 12,992 59,264 Max from FoCo CM
Maximum Volume (ft3) 59,264
Max Volume + 20% of Max Volume 71,116 ft3
100% WQCV 7,881 ft3
Required 100Yr Volume 78,997 ft3
Detention Storage Calculations
2595c - Rational Calculations.xlsx Modified FAA-100-yr Page 1 of 1
80.0 0.67 10,895 0.58 1.31 6,271 4,624
85.0 0.64 11,093 0.58 1.30 6,607 4,486
90.0 0.62 11,280 0.57 1.29 6,943 4,336
95.0 0.59 11,457 0.57 1.28 7,279 4,177
100.0 0.57 11,625 0.57 1.27 7,615 4,010
105.0 0.55 11,786 0.56 1.26 7,951 3,834
110.0 0.53 11,939 0.56 1.26 8,287 3,652
115.0 0.52 12,086 0.56 1.25 8,623 3,463
120.0 0.50 12,227 0.56 1.24 8,960 3,268
125.0 0.49 12,363 0.55 1.24 9,296 3,068
130.0 0.47 12,494 0.55 1.23 9,632 2,862
135.0 0.46 12,620 0.55 1.23 9,968 2,652
140.0 0.45 12,742 0.55 1.23 10,304 2,438
145.0 0.44 12,860 0.55 1.22 10,640 2,220
150.0 0.43 12,975 0.54 1.22 10,976 1,999
155.0 0.42 13,085 0.54 1.22 11,312 1,773
160.0 0.41 13,193 0.54 1.21 11,648 1,545
165.0 0.40 13,298 0.54 1.21 11,984 1,314
170.0 0.39 13,400 0.54 1.21 12,320 1,079
175.0 0.38 13,499 0.54 1.21 12,656 842
180.0 0.37 13,595 0.54 1.20 12,992 603 Max from FoCo CM
Maximum Volume (ft3) 5,141
Max Volume + 20% of Max Volume 6,169 ft3
100% WQCV 7,881 ft3
Required 2Yr Volume 14,051 ft3
Detention Storage Calculations
2595c - Rational Calculations.xlsx Modified FAA-2-yr Page 1 of 1
Paved areas & shallow
paved swales
20 1.4 5.2 18.8 490 12.7 12.7
A6 6 0.10 0.16 56 3.8% 8.3 120 0.3% Grassed waterway 15 0.8 2.7 11.0 176 11.0 11.0
B 7 1.43 0.41 118 1.4% 12.3 445 0.4%
Paved areas & shallow
paved swales
20 1.3 5.6 17.9 563 13.1 13.1
R1 8 0.18 0.84 60 2.0% 3.0
Paved areas & shallow
paved swales
20 0.0 0.0 3.0 60 10.3 5.0
R2 9 0.18 0.84 60 2.0% 3.0
Paved areas & shallow
paved swales
20 0.0 0.0 3.0 60 10.3 5.0
R3 10 0.18 0.84 60 2.0% 3.0
Paved areas & shallow
paved swales
20 0.0 0.0 3.0 60 10.3 5.0
R4 11 0.18 0.84 60 2.0% 3.0
Paved areas & shallow
paved swales
20 0.0 0.0 3.0 60 10.3 5.0
R5 12 0.11 0.84 60 2.0% 3.0
Paved areas & shallow
paved swales
20 0.0 0.0 3.0 60 10.3 5.0
R6 13 0.07 0.84 45 2.0% 2.6
Paved areas & shallow
paved swales
20 0.0 0.0 2.6 45 10.3 5.0
R7 14 0.11 0.84 60 2.0% 3.0
Paved areas & shallow
paved swales
20 0.0 0.0 3.0 60 10.3 5.0
R8 15 0.18 0.84 60 2.0% 3.0
Paved areas & shallow
paved swales
20 0.0 0.0 3.0 60 10.3 5.0
R9 16 0.18 0.84 60 2.0% 3.0
Paved areas & shallow
paved swales
20 0.0 0.0 3.0 60 10.3 5.0
R10 17 0.11 0.84 60 2.0% 3.0
Paved areas & shallow
paved swales
20 0.0 0.0 3.0 60 10.3 5.0
Initial Overland Time (ti
)
Travel Time (tt
)
tt
=Length/(Velocity x 60)
tc Urbanized Check
ON
2595c - Rational Calculations.xlsx Developed Tc Page 1 of 1
TOTAL SITE 81,998 53,921 63,096 6,186 0 0 172,738 0 377,939 8.68 51.1% 0.46 0.48 0.54 0.70
61,037 47,258 63,096 6,076 0 0 138,398 0 315,865 7.25 52.4% 0.47 0.49 0.55 0.71
Runoff Coeff's
Total To Pond (No
Basin B)
2595c - Rational Calculations.xlsx Developed C Page 1 of 1
(min)
Time of
Conc
ti + tt = tc
Total
Length
(ft)
tc=(L/180)+
10 (min.)
Min
tc
H1 1 17,418 530 8,896 61,800 289,292 377,936 8.68 14.9% 0.13 0.14 0.25 0.53 500 1.3% 36.0 150 0.8%
Paved areas & shallow
paved swales
20 1.8 1.4 37.4 650 13.6 13.6
TOTAL SITE 17,418 530 8,896 61,800 0 0 289,292 0 377,936 8.68 14.9% 0.13 0.14 0.25 0.53
Basin
Name
Design
Point
Time of
Conc
(tc)
C2 C5 C10 C100 2 5 10 100 ATotal (sf)
ATotal
(ac)
Q2 Q5 Q10 Q100
H1 1 13.6 0.13 0.14 0.25 0.53 1.94 0.00 3.33 6.79 377,936 8.68 2.24 0.00 7.10 31.07
TOTAL SITE 377,936 8.68 2.24 0.00 7.10 31.07
Initial Overland Time (ti)
Travel Time (tt) tt=Length/(Velocity
x 60)
tc Urbanized Check
ON
Runoff Coeff's Rainfall Intensities (in/hr) Area Flow Rates (cfs)
Runoff Coeff's
2595c - Rational Calculations.xlsx Historic Page 1 of 1