HomeMy WebLinkAboutPEDERSEN TOYOTA EXPANSION - FDP - FDP180007 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE REPORT
FOR
Pedersen Toyota Expansion
Prepared by:
Interwest Consulting Group
1218 West Ash, Suite A
Windsor, Colorado 80550
Phone: 970.674.3300
Fax: 970.674.3303
Prepared for:
Architecture Workshop
280 S. Pennsylvania Street
Denver, Colorado 80209
Office: 303.788.1717
February 21, 2018
Job Number 1180-027-00
1218 W. ASH, STE. A, WINDSOR, COLORADO 80550
TEL. 970.674.3300 – FAX 970.674.3303
February 21, 2018
Mr. Wes Lamarque
Fort Collins Utilities
700 Wood Street
Fort Collins, CO 80522
RE: Pedersen Toyota Expansion – Final Drainage Report
Dear Wes,
We are pleased to submit for your review, the Final Drainage Report for the Pedersen Toyota
Expansion project. This report describes the drainage design and to be in accordance with the
criteria in the City of Fort Collins Storm Drainage Manual.
We appreciate your time and consideration in reviewing this submittal. Please call if you have
any questions.
Sincerely,
Jason T. Claeys, P.E., LEED AP
Interwest Consulting Group
Page i
TABLE OF CONTENTS
Table of Contents ............................................................................................................................. i
Engineer’s Certification Block ........................................................................................................ ii
General Description and Location .................................................................................................. 1
Site Description and Location ..................................................................................................... 1
Site Soils ...................................................................................................................................... 1
Existing Conditions ..................................................................................................................... 2
Storm Drainage Criteria .................................................................................................................. 3
Hydrologic Criteria ...................................................................................................................... 3
Hydraulic Criteria ........................................................................................................................ 3
Drainage Basins .............................................................................................................................. 4
Drainage Facility Design ................................................................................................................. 6
Drainage Conveyance Design ...................................................................................................... 6
Detention/Water Quality Pond Design ........................................................................................ 6
Low Impact Development ............................................................................................................... 7
Stormwater Pollution Prevention .................................................................................................... 9
Conclusions ................................................................................................................................... 10
References ..................................................................................................................................... 11
Appendix ....................................................................................................................................... 12
Appendix A – Site Descriptions, Characteristics, & References ................................................ A
Appendix B – Rational Calculations ........................................................................................... B
Appendix C – Detention Pond Calculations ................................................................................ C
Appendix D – Conveyance Element Sizing ............................................................................... D
Appendix E – Low Impact Development Calculations ............................................................... E
Page ii
ENGINEER’S CERTIFICATION BLOCK
I hereby certify that this Final Drainage Report for Pedersen Toyota Expansion was prepared by
me (or under my direct supervision) for the owners thereof and meets or exceeds the criteria of
the City of Fort Collins Stormwater Design Standards.
________________________________________
Jason T. Claeys, PE
Registered Professional Engineer
State of Colorado No. 42122
Page 1
GENERAL DESCRIPTION AND LOCATION
SITE DESCRIPTION AND LOCATION
The land encompassing the Pedersen Toyota Expansion is described as Being a Replat of Lot 1
Of Pedersen Toyota-Volvo-Saab P.U.D. and All of Mini-U-Storage P.U.D., Situate in the
Southeast Quarter of Section 35, Township 7 North, Range 69 West of the 6th P.M., City of Fort
Collins, County of Larimer, State of Colorado. More so, Pedersen Toyota Expansion is located at
the northwest corner of S. College Ave. (Hwy 287) and Kensington Dr., east of S. Mason St., and
south of the current Target retail store.
The project site is approximately 4.84 acres and is currently a car dealership and previously a
self-storage business. The self-storage buildings were recently removed and the site pavement
remains with temporary concrete slabs over the prior building pads.
The proposed project will consist of redevelopment of the self-storage site and of the Pedersen
Toyota site to expand the car dealership showroom and service center. Ultimately the project will
consist of additional vehicle inventory storage, an expansion of the showroom, offices, and
service center. The project will be completed in one phase.
The site drains to existing storm drainage facilities along the north and east sides of the site.
Runoff is conveyed to Mail Creek, then the Cache La Poudre River, ultimately to the South Platte
River.
The project is not located is a City or FEMA floodplain. The site is located on the unprinted
FIRM panel 08069C1000F.
SITE SOILS
The Pedersen Toyota site consists of Altvan-Satanta loam and Nunn clay loam and are classified
as Type B and C hydrologic groups, respectively. According to USDA/Natural Resource
Conservation Group, Type B soils have 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 textures, these soils have a moderate rate of
water transmission. Type C soils have a slow infiltration rate when thoroughly wet. These soils
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.
Per the “Subsurface Exploration Report – Pedersen Toyota Dealership Addition & Renovation”,
prepared be Earth Engineering Consultants (EEC), dated February 13, 2014:
Page 2
In summary, existing asphalt pavement and aggregate base course was encountered at the
surface of each boring and was underlain by apparent fill and/or native sandy lean clay subsoils,
granular sands and gravels, and sandstone bedrock. The in-situ cohesive materials were
generally classified as sandy lean clay, were soft to medium stiff, and exhibited low swell
potential, as measured in laboratory testing at current in-situ moisture contents and dry
densities. The granular soils were generally medium dense and the bedrock consisted of highly
weathered sandstone that became less weathered and more competent with depth.
Groundwater was also observed during the subsurface soil exploration:
Groundwater was encountered in four of the borings at depths ranging from approximately
fifteen (15) to twenty (20) feet during the initial drilling operations. The borings were backfilled
upon completion of the drilling operations; therefore subsequent groundwater measurements
were not obtained.
EXISTING CONDITIONS
Both the existing self-storage and Pedersen Toyota site have existing stormwater management
infrastructure onsite controlling the stormwater release rates.
The self-storage site utilizes a combination of detention ponds and parking lot surface ponding as
runoff storage with an orifice plate installed within an inlet to control the release rate. The self-storage
site was designed with a release rate of 0.88 cfs and a detention volume of 20,200 cu-ft (0.46 ac-ft).
The drainage outfall for the site is the existing 18” storm drain located north of the site. The existing
site is currently 82% impervious.
The existing Pedersen Toyota site utilizes parking lot surface ponding as runoff storage with an
orifice plate installed within an inlet to control the release rate. The Pedersen Toyota site was
designed with a release rate of 1.38 cfs and a required detention volume of 20,866 cu-ft (0.48 ac-ft).
The drainage outfall for the site is the existing 36” storm drain located east of the site along S. College
Avenue. The existing site is currently 87% impervious.
The historical release rates, stated above, are referenced for the stormwater release rates for the
proposed improvements. All calculations and exhibits are attached, including the previous grading &
drainage plans for the Mini-U-Storage and Pedersen Toyota sites.
Supporting figures can be found in the Appendix.
Page 3
STORM DRAINAGE CRITERIA
This final drainage report was prepared to meet or exceed the City of Fort Collins storm water
criteria. The City of Fort Collin’s Storm Drainage Design Criteria and amendments to the Urban
Drainage Flood Control District’s (UDFCD) Drainage Criteria Manual (USDCM) Volumes 1, 2
and 3 were referenced as guidelines for this design.
HYDROLOGIC CRITERIA
The rational method was performed to calculate the peak runoff rates for each basin. Percent
impervious were estimated based on land use and the associated runoff coefficients were
calculated. The time of concentration was calculated using USDCM Equation 6-5 and the
intensity was calculated using the corresponding storm rainfall depth and USDCM Equation 4-3.
To account for the City of Fort Collins’ IDF Curve, Coefficient 3 of the UDFCD’s intensity
formula was adjusted to 0.7867. The City of Fort Collins area has 1-hr rainfall depths for the 2-
yr of 0.82 inches, 5-yr of 1.14 inches, 10-yr of 1.40 inches, and a 100-yr of 2.86 inches. These
depths do account for the 1997 adjusted rainfall depths.
HYDRAULIC CRITERIA
The storm drain system throughout the Pedersen Toyota Expansion site have been designed to
convey the 100-yr storm event. The storm drains were modeled using Hydraflow Storm Sewers
Extension for Autodesk AutoCAD Civil 3D. The 100-yr peak runoff rates calculated from the
rational method calculations and routed through the storm drain system. Flow velocities from the
storm drain are reviewed and used to size the outlet soil reinforcements.
Inlets are provided for the overflow of the permeable paver areas. Due to the expanse of the
paver areas, the capture capacities were not calculated.
All swale and pipe outlets will be protected with riprap or suitable erosion protection methods.
Storm sewer pipe outlets will be protected using the requirements set by the USDCM for the
protection downstream of culverts.
All supporting calculations can be found in the Appendix.
Page 4
DRAINAGE BASINS
The proposed project will consist of redevelopment of the self-storage site and of the Pedersen
Toyota site to expanding the car dealership showroom and service center. Ultimately the project
will consist of additional vehicle inventory storage, and expansion of the showroom, offices, and
service center.
The site is broken into 8 drainage basins for analysis. There are 2 major basins within the project
site with the remaining basins being the adjacent public rights-of-way. Below are descriptions of
each basin:
Basin D1:
The major basin D1 is separated into 2 sub-basins, one for the roof drainage from the
building addition, and one being the site surrounding this portion of the addition.
Sub-basin D1A consists of 0.61 acres of the western drive isles, parking/inventory storage
and drainage facilities. A detention and water quality pond is located in the northwest corner
of this basin. The basin is approximately 50.2% impervious with a 100-yr peak runoff rate of
4.30 cfs.
Sub-basin D1B consists of 1.08 acres of building proposed building addition. The building
addition plumbing is to be such that there is one roof drain outlet along the north side of the
addition. This basin is assumed to be 90% impervious with a 100-yr peak runoff rate of
10.47 cfs.
Basin D2:
The major basin D2 is separated into 2 sub-basins, one for the parking area in the northeast
corner of the site, and one for the parking area in the southeast corner of the site.
Sub-basin D2A consists of 1.84 acres and includes a portion of the existing building,
parking/inventory storage, and drainage facilities. This basin includes a large portion of
permeable pavers that provides detention and water quality enhancement. The basin is
approximately 77.4% impervious with a 100-yr peak runoff rate of 17.41 cfs.
Sub-basin D2B consists of 0.91 acres and includes a portion of the existing building,
parkin/inventory storage, and drainage facilities. The basin includes a portion of permeable
pavers that provides detention and water quality enhancement. The basin is approximately
78.2% impervious with a 100-yr runoff rate of 8.85 cfs.
Basin D3 consists of 0.52 acres, approximately 59.9% impervious, along the east half of S.
Mason St. Historically this basin consisted of 0.34 acres and approximately 92.8% impervious.
This project is required to implement the Midtown Plan, requiring dedication of additional right-
Page 5
of-way and detached sidewalks. The basin will have an increase of runoff from 2.62 cfs to 3.57
cfs, a 0.95 cfs increase. Runoff is conveyed north along the curb line to an existing inlet located
near the northwest corner of the Pedersen Toyota site.
Basin D4 consists of 0.50 acres, approximately 67.4% impervious, along the north half of
Kensington Dr. Historically this basin consisted of 0.33 acres and approximately 83.5%
impervious. This project is required to implement the Midtown Plan, requiring dedication of
additional right-of-way and detached sidewalks. The basin will have an increase of runoff from
2.62 cfs to 4.22 cfs, a 1.60 cfs increase. Runoff is conveyed east along the curb line to S. College
Ave. to a sump inlet located along the west side of S. College Ave.
Basin D5 consists of 0.92 acres, approximately 68.6% impervious, along the west half of S.
College Ave. (Hwy 287). Historically this basin consisted of 0.83 acres and approximately 74.6%
impervious. This project is requiring dedication of additional right-of-way and detached
sidewalks. The basin will have an increase of runoff from 5.74 cfs to 7.32 cfs, a 1.58 cfs
increase. Runoff is conveyed south along the curb line to a sump inlet.
Basin D6 consists of 0.06 acres of landscape area along the north side of the site. This basin
historically drained offsite. The previous basin is estimated to be 0.18 acres, 39.8% impervious,
with a 100-yr runoff rate of 0.86 cfs. The proposed improvements will reduce the 100-yr runoff
rate to 0.19 cfs.
All supporting calculations can be found in the Appendix.
Page 6
DRAINAGE FACILITY DESIGN
DRAINAGE CONVEYANCE DESIGN
Surface drainage and storm drains will convey runoff proposed detention pond and permeable
paver/detention areas. Storm water detention and water quality enhancement will be achieved
through the use of an extended detention basin, parking lot detention, and permeable pavers.
DETENTION/WATER QUALITY POND DESIGN
The required detention volumes were calculated using the FAA Method and the water quality
capture volume is calculated using Urban Drainage’s criteria. There are 2 proposed detention
and water quality enhancement systems proposed and described below:
Drainage Basin D1:
Drainage Basin D1 is proposed to provide detention and water quality enhancement through the
use of an extended detention basin (EDB) and permeable pavers. The outfall for this basin is the
existing storm drain that provided service to the previous self-storage site and has an allowed
release rate of 0.88 cfs. Basin D1 has an estimated 100-yr peak runoff rate of 14.77 cfs, requiring
0.369 acre-ft of detention storage. The water quality capture volume (WQCV) is calculated to be
0.051 acre-ft. Combined the detention storage and WQCV, this basin required a total of 0.420
acre-ft of storage. The storage volume is provided in a combination of ponding volume and
storage within the paver aggregates. The EDB provides 0.398 acre-ft of storage with an
additional 0.022 acre-ft provided in the paver aggregate, achieving a total of 0.420 acre-ft of
storage
Drainage Basin D2:
Drainage Basin D2 is proposed to provide detention and water quality enhancement through the
use of parking lot detention and permeable pavers. The outfall for this basin the existing storm
drain that currently provides service for the Pedersen Toyota site and has an allowed release rate
of 1.38 cfs. Basin D2 has an estimated 100-yr peak runoff rate of 26.26 cfs, requiring 0.642 acre-
ft of detention storage. 100% of the redeveloped site is draining to and being treated by
permeable pavers. It is assumed that no addition water quality capture volume is required. The
detention volume is provided in a combination of parking lot ponding and storage within the
aggregates of three separate permeable paver areas. The parking lot ponding provides 0.149
acre-ft of storage with an additional 0.493 acre-ft provided in the paver aggregates, achieving a
total of 0.642 acres of storage.
All supporting calculations can be found in the Appendix.
Page 7
LOW IMPACT DEVELOPMENT
The City of Fort Collins updated the Low Impact Development ordinance in 2016 (Ordinance
No. 007, 2016) to require:
• Treat at least 75% of any newly developed or redeveloped area using one or a
combination of LID techniques, or
• Treat at least 50% of any newly developed or redeveloped area using one or a
combination of LID techniques when 25% of private drivable surfaces are permeable.
To satisfy the required implementation of Low Impact Development (LID) techniques, the
Pedersen Toyota Expansion project will utilize permeable pavers. 25.7% of private drivable
surfaces are proposed to be permeable pavers, treating 57.3% of the proposed new impervious
area. The permeable pavers will also be utilized to provide the detention volume required. The
volumes have been calculated within the #2 aggregates only. Per Urban Drainage, CDOT No. 57
and No. 67 aggregates has a porosity of 40%. Due to potential inconsistencies in delivered
aggregates the detention volumes were only calculated for the #2 aggregates. We found
references that AASHTO #3 has between 53 -54% void ratio and it is assumed that the ratio
increases for a #2 aggregate, thus assuming a 40% ratio should be considered conservative.
Below is a description of the 4 step process for selecting structural BMPs:
Urban Drainage and Flood Control District (UDFCD) recommends a Four Step Process for
receiving water protection that focuses on reducing runoff volumes, treating the water quality
capture volume (WQCV), stabilizing drainageways and implementing long-term source controls.
The Four Step Process applies to the management of smaller, frequently occurring events.
Step 1: Employ Runoff Reduction Practices
To reduce runoff peaks, volumes, and pollutant loads from urbanizing areas, implement Low
Impact Development (LID) strategies, including Minimizing Directly Connected Impervious
Areas (MDCIA).
Majority parking lot runoff, assumed to be the most contaminated runoff, is routed to permeable
paver areas with will slow runoff, promote infiltration, and filter runoff prior to being released
into the adjacent storm drain system.
Step 2: Implement BMPs that Provide a Water Quality Capture Volume with Slow Release
The permeable paver areas are designed to provide water quality enhancement by filtration
through the aggregates.
Page 8
Step 3: Stabilize Drainageways
Natural Drainageways are subject to bed and bank erosion due to increases in frequency,
duration, rate and volume of runoff during and following development. Because the site will
drain to an existing storm system, bank stabilization is unnecessary with this project.
Step 4: Implement Site Specific and Other Source Control BMPs
Proactively controlling pollutants at their source by preventing pollution rather than removing
contaminants once they have entered the stormwater system or receiving waters is important
when protecting storm systems and receiving waters. This can be accomplished through site
specific needs such as construction site runoff control, post-construction runoff control and
pollution prevention / good housekeeping. It will be the responsibility of the contractor to
develop a procedural best management practice for the site.
All calculations are attached for reference.
Page 9
STORMWATER POLLUTION PREVENTION
Erosion and sedimentation will be controlled on-site by use of sediment control logs, inlet
protection, a gravel construction entrance, seeding, mulch, and turf. The measures are designed
to limit the overall sediment yield increase due to construction as required by the City of Fort
Collins. During overlot and final grading the soil will be roughened and furrowed perpendicular
to the prevailing winds.
During the performance of the work required by these specifications or any operations
appurtenant thereto, whether on right-of-way provided by the City or elsewhere, the contractor
shall furnish all labor, equipment, materials, and means required. The Contractor shall carry out
proper efficient measures wherever and as necessary to reduce dust nuisance, and to prevent dust
nuisance that has originated from his operations from damaging crops, orchards, cultivated fields,
and dwellings, or causing naissance to persons. The Contractor will be held liable for any
damage resulting from dust originating from his operations under these specifications on right-
of-way or elsewhere.
It is unlawful to track or cause to be tracked mud or other debris onto city streets or rights-of-
way. Wherever construction vehicles access routes or intersect paved public roads, previsions
must be made to minimize the transport of sediment by runoff or vehicles tracking onto the
paved surface. Stabilized construction entrances are required with base material consisting of 6”
coarse aggregate. The contractor will be responsible for clearing mud tracked onto city streets on
a daily basis.
All temporary and permanent erosion and sediment control practices must be maintained and
repaired as needed to assure continued performance of their intended function. Silt fence and
sediment control logs will require periodic replacement. Maintenance is the responsibility of the
contractor.
All disturbed areas must be seeded and mulched within 30 days of project start. Vegetation shall
not be considered established until a ground cover is achieved which is demonstrated to be
mature enough to control soil erosion to the satisfaction of the City Inspector and to survive
severe weather condition.
Page 10
CONCLUSIONS
This Final Drainage Report for Pedersen Toyota Expansion has been prepared to comply with the
storm water criteria set by the City of Fort Collins. The proposed drainage system presented in
this report is designed to convey the developed peak storm water runoff through the site to the
existing storm drain system and to the development’s LID features, detention and water quality
facilities. Storm drains will be sized to adequately convey runoff form the 100-yr storm event,
and adequately convey the released runoff from the detention areas. This preliminary drainage
report anticipates the implementation of best management practices for erosion control,
temporary and permanent, and on-site construction facilities that will be further designed and
details in the Final Drainage Report.
It can therefore be concluded that development of Pedersen Toyota Expansion complies with the
storm water jurisdictional criteria and will not adversely affect the adjacent properties, streets,
storm drain system and/or detention/water quality facilities.
Page 11
REFERENCES
1. Urban Storm Drainage Criteria Manual (Volumes 1, 2, and 3), Urban Drainage and Flood
Control District, June 2001, Revised November 2010.
2. Storm Drainage Criteria Manual and Construction Standards, City of Fort Collins Storm
Water Utility, City of Fort Collins, Colorado, Updated January, 1997 with 2012
amendments.
3. Fort Collins Stormwater Criterial Manual (Draft for Council), Fort Collins Utilities, City
of Fort Collins, Colorado, Dated November 2017 [Anticipated to be adopted by City
Council in 2017]
4. “Hydrologic Group Rating for Larimer County Area, Colorado”, USDA-Natural
Resources Conservation Service, National Cooperative Soil Survey. Web Soil Survey
URL: http://websoilsurvey.nrcs.usda.gov. [2/20/2018]
5. “Subsurface Exploration Report – Pedersen Toyota Dealership Addition & Renovation”,
prepared by Earth Engineering Consultants, LLC, Dated February 13, 2014
Page 12
APPENDIX
Appendix A – Site Descriptions, Characteristics, & References
Appendix B – Rational Calculations
Appendix C – Detention Pond Calculations
Appendix D – Conveyance Element Sizing
Appendix E – Low Impact Development Calculations
Appendix A
APPENDIX A – SITE DESCRIPTIONS, CHARACTERISTICS, & REFERENCES
CITY OF FORT COLLINS BENCHMARK #48-01
APPROXIMATELY 1/2 MILE SOUTH OF HORSETOOTH ROAD, WEST OF
COLLEGE AVENUE AT THE ENTRANCE TO BARNES AND NOBLE BOOKSTORE,
IN THE NORTHEAST CORNER OF THEIR PARKING LOT, ON A CONCRETE CURB.
PROJECT DATUM - ELEV=5033.57 NGVD 29 (UNADJUSTED)
NAVD 88 = NGVD 29 (UNADJUSTED) + 3.19 = 5036.76
CITY OF FORT COLLINS BENCHMARK #15-94
ON THE NORTH SIDE OF WEST HARMONY RD, 450 FEET EAST OF HINSDALE
DR., ON THE CONCRETE RING OF AN ELECTRIC MANHOLE NEAR THE NORTH
RIGHT OF WAY FENCE.
PROJECT DATUM - ELEV=5051.59 NGVD 29 (UNADJUSTED)
NAVD 88 = NGVD 29 (UNADJUSTED) + 3.20 = 5054.79
BASIS OF BEARINGS AND LINEAL UNIT DEFINITION
ASSUMING THE EAST LINE OF THE SOUTHEAST QUARTER OF SECTION 35,
715 :$6%($5,1*1257+
:(67%(,1*$*5,'%($5,1*2)
THE COLORADO STATE PLANE COORDINATE SYSTEM, NORTH ZONE, NORTH
AMERICAN DATUM 1983/2007, A DISTANCE OF 2645.98 FEET WITH ALL
OTHER BEARINGS CONTAINED HEREIN RELATIVE THERETO.
THE LINEAL DIMENSIONS AS CONTAINED HEREIN ARE BASED UPON THE "U.S.
SURVEY FOOT."
vicinity map
Scale: 1" = 1000'
Hydrologic Soil Group—Larimer County Area, Colorado
(Pedersen Toyota)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/20/2018
Page 1 of 4
4486030 4486050 4486070 4486090 4486110 4486130 4486150 4486170 4486190
4486030 4486050 4486070 4486090 4486110 4486130 4486150 4486170 4486190
493230 493250 493270 493290 493310 493330 493350 493370 493390 493410 493430 493450 493470 493490
493230 493250 493270 493290 493310 493330 493350 493370 493390 493410 493430 493450 493470 493490
40° 31' 35'' N
105° 4' 47'' W
40° 31' 35'' N
105° 4' 36'' W
40° 31' 29'' N
105° 4' 47'' W
40° 31' 29'' N
105° 4' 36'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 50 100 200 300
Feet
0 15 30 60 90
Meters
Map Scale: 1:1,230 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Lines
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Points
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
3 Altvan-Satanta loams, 0
to 3 percent slopes
B 1.1 17.3%
4 Altvan-Satanta loams, 3
to 9 percent slopes
B 3.9 63.0%
74 Nunn clay loam, 1 to 3
percent slopes
C 1.2 19.7%
Totals for Area of Interest 6.2 100.0%
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.
Hydrologic Soil Group—Larimer County Area, Colorado Pedersen Toyota
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/20/2018
Page 3 of 4
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—Larimer County Area, Colorado Pedersen Toyota
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/20/2018
Page 4 of 4
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
Intensity (in/hr)
City of Fort Collins
Rainfall Intensity-Duration-Frequency Curve
2-yr (FTC)
10-yr (FTC)
100-yr (FTC)
2-yr (UD)
10-yr (UD)
100-yr (UD)
100-yr
10-yr
0.0
1.0
2.0
3.0
4.0
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0 65.0
Duration (min)
2-yr
10-yr
Duration
(minutes)
2-yr
Intensity
(in/hr)
10-yr
Intensity
(in/hr)
100-yr
Intensity
(in/hr)
Duration
(minutes)
2-yr
Intensity
(in/hr)
10-yr
Intensity
(in/hr)
100-yr
Intensity
(in/hr)
5 2.85 4.87 9.95 33 1.22 2.08 4.24
6 2.67 4.56 9.31 34 1.19 2.04 4.16
7 2.52 4.31 8.80 35 1.17 2.00 4.08
8 2.40 4.10 8.38 36 1.15 1.96 4.01
9 2.30 3.93 8.03 37 1.13 1.93 3.93
10 2.21 3.78 7.72 38 1.11 1.89 3.87
11 2.13 3.63 7.42 39 1.09 1.86 3.80
12 2.05 3.50 7.16 40 1.07 1.83 3.74
13 1.98 3.39 6.92 41 1.05 1.80 3.68
14 1.92 3.29 6.71 42 1.04 1.77 3.62
15 1.87 3.19 6.52 43 1.02 1.74 3.56
16 1.81 3.08 6.30 44 1.01 1.72 3.51
17 1.75 2.99 6.10 45 0.99 1.69 3.46
18 1.70 2.90 5.92 46 0.98 1.67 3.41
19 1.65 2.82 5.75 47 0.96 1.64 3.36
20 1.61 2.74 5.60 48 0.95 1.62 3.31
21 1.56 2.67 5.46 49 0.94 1.60 3.27
22 1.53 2.61 5.32 50 0.92 1.58 3.23
23 1.49 2.55 5.20 51 0.91 1.56 3.18
24 1.46 2.49 5.09 52 0.90 1.54 3.14
25 1.43 2.44 4.98 53 0.89 1.52 3.10
26 1.40 2.39 4.87 54 0.88 1.50 3.07
27 1.37 2.34 4.78 55 0.87 1.48 3.03
28 1.34 2.29 4.69 56 0.86 1.47 2.99
29 1.32 2.25 4.60 57 0.85 1.45 2.96
30 1.30 2.21 4.52 58 0.84 1.43 2.92
31 1.27 2.16 4.42 59 0.83 1.42 2.89
32 1.24 2.12 4.33 60 0.82 1.40 2.86
Figure 3-1a
City of Fort Collins
Rainfall Intensity-Duration-Frequency Table
for using the Rational Method
Duration 2-yr 10-yr 100-yr 2-yr ∆∆∆∆ 10-yr ∆∆∆∆ 100-yr ∆∆∆∆
5 2.85 4.87 9.95 2.78 -0.07 4.74 -0.13 9.68 -0.27
6 2.67 4.56 9.31 2.64 -0.03 4.51 -0.05 9.20 -0.11
7 2.52 4.31 8.80 2.52 0.00 4.30 -0.01 8.78 -0.02
8 2.40 4.10 8.38 2.41 0.01 4.11 0.01 8.39 0.01
9 2.30 3.93 8.03 2.31 0.01 3.94 0.01 8.04 0.01
10 2.21 3.78 7.72 2.21 0.00 3.78 0.00 7.72 0.00
11 2.13 3.63 7.42 2.13 0.00 3.64 0.01 7.43 0.01 2-yr 0.82
12 2.05 3.50 7.16 2.05 0.00 3.51 0.01 7.16 0.00 10-yr 1.40
13 1.98 3.39 6.92 1.98 0.00 3.39 0.00 6.92 0.00 100-yr 2.86
14 1.92 3.29 6.71 1.92 0.00 3.28 -0.01 6.69 -0.02
15 1.87 3.19 6.52 1.86 -0.01 3.17 -0.02 6.48 -0.04
16 1.81 3.08 6.30 1.80 -0.01 3.08 0.00 6.28 -0.02 C 1 28.5
17 1.75 2.99 6.10 1.75 0.00 2.99 0.00 6.10 0.00 C 2 10
18 1.70 2.90 5.92 1.70 0.00 2.90 0.00 5.93 0.01 C 3 0.786651
19 1.65 2.82 5.75 1.65 0.00 2.82 0.00 5.77 0.02
20 1.61 2.74 5.60 1.61 0.00 2.75 0.01 5.61 0.01
21 1.56 2.67 5.46 1.57 0.01 2.68 0.01 5.47 0.01
22 1.53 2.61 5.32 1.53 0.00 2.61 0.00 5.34 0.02
23 1.49 2.55 5.20 1.49 0.00 2.55 0.00 5.21 0.01
24 1.46 2.49 5.09 1.46 0.00 2.49 0.00 5.09 0.00
25 1.43 2.44 4.98 1.43 0.00 2.43 -0.01 4.97 -0.01
26 1.40 2.39 4.87 1.39 -0.01 2.38 -0.01 4.86 -0.01
27 1.37 2.34 4.78 1.36 -0.01 2.33 -0.01 4.76 -0.02
28 1.34 2.29 4.69 1.34 0.00 2.28 -0.01 4.66 -0.03
29 1.32 2.25 4.60 1.31 -0.01 2.24 -0.01 4.57 -0.03
30 1.30 2.21 4.52 1.28 -0.02 2.19 -0.02 4.48 -0.04
31 1.27 2.16 4.42 1.26 -0.01 2.15 -0.01 4.39 -0.03
32 1.24 2.12 4.33 1.24 0.00 2.11 -0.01 4.31 -0.02
33 1.22 2.08 4.24 1.21 -0.01 2.07 -0.01 4.23 -0.01
34 1.19 2.04 4.16 1.19 0.00 2.03 -0.01 4.15 -0.01
Coefficients
Intensity (in/hr)
Urban Drainage
Intensity (in/hr)
City of Fort Collins
Urban Drainage
Inputs
Urban Drainage Intensity Equation
1-hr Rainfall Depths (P 1 )
City of Fort Collins
Rainfall Intensity-Duration-Frequency Table
Use of Urban Drainage Intensity Equation for CoFC IDF Values
This cell was determined
using Solver to best match
intensities given from the
Fort Collins IDF values.
C 3
2
1 1
( c )
C t
C P
I
+
=
34 1.19 2.04 4.16 1.19 0.00 2.03 -0.01 4.15 -0.01
35 1.17 2.00 4.08 1.17 0.00 2.00 0.00 4.08 0.00
36 1.15 1.96 4.01 1.15 0.00 1.96 0.00 4.01 0.00
37 1.13 1.93 3.93 1.13 0.00 1.93 0.00 3.94 0.01
2-year 5-yr 10-yr 25-yr 50-yr 100-yr
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
City of Fort Collins
Design Storms
for using SWMM
Figure 3-1c
Time
(min)
Intensity (in/hr)
These are the 1-hour storm
2-year 5-yr 10-yr 25-yr 50-yr 100-yr
1-hr 0.82 1.14 1.40 1.81 2.27 2.86
2-hr 0.98 1.36 1.71 2.31 2.91 3.67
Storm
Duration
Rainfall Depth (in)
Note: The City of Fort Collins SWWM input hyetopgrah is used to calculate the
1-hr and 2-hr storm rainfall depths for the different storm events.
These are the 1-hour storm
depths that are used in the
Urban Drainage intensity
equation, derived from the CoFC
Hyetograph.
20 Beaver Road│Suite 104│Wethersfield, CT│06109│Toll Free 888-892-2694│Fax 866-328-8401 │www.stormtech.com
PPoorroossiittyy
ooff SSttrruucc
ttuurraall BBaac
ckkffiillll Tech Sheet # 1
Rev. 12/20/05
General:
StormTech advises that a porosity of 40% is appropriate to use for the storage capacity
of structural aggregate used in the bedding and embedment zones around StormTech
chambers. This memo provides technical support for the use of a porosity of 40%. The major
points of the memo are:
• 40% porosity is appropriate for the washed, open graded, angular aggregate material
StormTech recommends for foundation and embedment.
• Most of the porosity data available is based on a compacted condition. StormTech
requires compaction of the foundation (bedding) and allows dumped aggregate
embedment around the chambers.
• Test data indicates that although the porosity of the compacted foundation is
approximately 39%, the porosity of the dumped backfill in the embedment zone is
typically greater than 40% and the calculated weighted average porosity exceeds 40%
for typical StormTech systems.
• Porosity is protected from soils migration by a non-woven geotextile that surrounds the
entire system.
Terms:
Porosity (n) is defined as the volume voids over the total volume expressed as a
percent: n = (Vv / Vt ) x 100%. Other terms commonly used to describe porosity include; “voids”
and “void space”. .A related term that should not be confused with porosity is void ratio (e)
which is the volume of voids over the volume of solids expressed as a decimal: e = Vv / Vs.
Compilation of Known Test Data:
Sample Data Source Porosity Bulk Density Test / Description
AASHTO # 4 StormTech lab 39.9% 94.3 lbs/ft3 dumped, corrected1
AASHTO # 57 StormTech lab 45.4% 87.2 lbs/ft3 dumped, corrected1
AASHTO # 4 StormTech lab 37.4% 103.0 lbs/ft3 jiggled - tamped, corrected1
AASHTO # 57 StormTech lab 38.7% 97.7 lbs/ft3 jiggled - tamped, corrected1
AASHTO # 57 NTH lab 50 - 51% tapped & agitated, dried2
AASHTO # 57 NTH lab 50 - 52 % tapped & agitated, dried2
AASHTO # 3 NTH lab 53 - 54% tapped & agitated, dried2
-1 ½” Anderson Eng. Cons. 41.9% 96.8 lbs/ft3 jiggled - tamped, C293
-1 ½” Anderson Eng. Cons. 35.3% 101.7 lbs/ft3 jiggled - tamped, C293
-1 ½” Anderson Eng. Cons. 37.8% 98.6 lbs/ft3 jiggled - tamped, C293
-1 ½” Anderson Eng. Cons. 41.3% 93.6 lbs/ft3 jiggled - tamped, C293
-1 ½” Anderson Eng. Cons. 38.2% 98.7 lbs/ft3 jiggled - tamped, C293
-3/4” Anderson Eng. Cons. 38.5% 100.3 lbs/ft3 jiggled - tamped, C293
-3/4” Anderson Eng. Cons. 38.9% 97.9 lbs/ft3 jiggled - tamped, C293
20 Beaver Road│Suite 104│Wethersfield, CT│06109│Toll Free 888-892-2694│Fax 866-328-8401 │www.stormtech.com
Compilation of Known Test Data (continued):
Sample Data Source Porosity Bulk Density Test / Description
AASHTO # 4 Universal Eng. Serv. 44.3% 78.6 lbs/ft3 rodded - tamped, C294
AASHTO # 57 Universal Eng. Serv. 43.2% 79.8 lbs/ft3 rodded - tamped, C294
AASHTO # 4 Universal Eng. Serv. 46.1% 70.8 lbs/ft3 rodded - tamped, C295
AASHTO # 57 Universal Eng. Serv. 42.8% 74.8 lbs/ft3 rodded - tamped, C295
1 Testing was conducted by StormTech in Oct of 2003 using aggregate from Connecticut.
Water was used to fill voids and a correction factor that reduced porosities by 3 to 16%
was calculated and applied to correct for wall effects of the test container.
2 Testing was conducted by NTH Consultants, Exton, PA in Dec 2002 for ADS. This was
dry testing in accordance with the “Civil Engineering Reference Manual, Sixth Edition” by
Michael R. Lindburg, PE.
3 Testing was conducted by Anderson Engineering Consultants, Inc., Little Rock, AR in
February, 2000 for 7 different aggregate samples from four suppliers in Arkansas.
4 The material tested was lime rock from central Florida. Testing was conducted by
Universal Engineering Sciences in Orlando, FL in November, 2005.
5 The material tested was recycled, crushed concrete from central Florida. Testing was
conducted by Universal Engineering Sciences in Orlando, FL in November, 2005.
ASTM C29 is the “Standard Test Method for Bulk Density (“Unit Weight”) and Voids in
Aggregate”.
Porosity References:
• “Urban Runoff Quality Management” WEF MOP 23 / ASCE MOP 87. Table 5.12
lists uniform sized gravel at 40%.
• “Controlling Urban Runoff:” by Thomas R. Schueler, July 1987 describes storage
volume of the void space in the trench at 40% of the excavated trench volume.
• “On-site Stormwater Management: Applications for Landscape and Engineering”
Second Edition by Bruce Ferguson and Thomas Debo states that open graded
crushed stone has 40% void space.
DUMPED EMBEDMENT
EXCEEDS 40% POROSITY
12" MIN. TYP. COMPACTED BEDDING
DEPTH OF STONE
TO BE DETERMINED
BY DESIGN ENGINEER
6" MIN.*
¾ - 2 INCH WASHED,
CRUSHED, ANGULAR STONE
AASHTO M288 CLASS 2
NON-WOVEN GEOTEXTILE
6"
MIN.
6" MIN.
Appendix B
APPENDIX B – RATIONAL CALCULATIONS
Pedersen Toyota
DRAINAGE SUMMARY
Design Engineer:
Design Firm:
Project Number:
Date:
IMPERVIOUS SUMMARY:
Description
%
Impervious
Existing 82.8%
Proposed 73.1%
Difference -9.7%
DRAINAGE SUMMARY:
Area (acres)
%
Imprevious
100-yr Peak
Runoff (cfs) Area (acres)
%
Imprevious
100-yr Peak
Runoff (cfs)
H1/D1 2.08 82.3% 14.41 1.69 75.6% 14.77 0.36 Ex Mini-U-Storage
H2/D2 2.68 87.2% 22.21 2.76 78.2% 26.27 4.06 Ex Pedersen Toyota
H3/D3 0.34 92.8% 2.62 0.52 59.9% 3.57 0.95 S. Mason Street
H4/D4 0.33 83.5% 2.62 0.50 67.4% 4.22 1.60 Kensington Drive
H5/D5 0.83 74.6% 5.74 0.92 68.6% 7.32 1.58 S. College Avenue
H6/D6 0.18 39.8% 0.86 0.06 0.0% 0.19 -0.68 North Offiste
Totals 6.44 82.8% 48.46 6.44 73.1% 56.33 7.88
H4&H5/D4&D5 1.16 77.1% 8.36 1.42 68.1% 11.54 3.18 College & Kensington
Basins
Historical Proposed Hist vs. Dev
Peak Runoff
Difference Notes
J.Claeys
Interwest Consulting Group
1180-027-00
February 19, 2018
1180-027-00 Rational Calcs (FC).xlsx Page 1 of 1 Interwest Consulting Group
SOUTH COLLEGE AVENUE (HWY 287)
KENSINGTON DRIVE
SOUTH MASON STREET
1218 W. Ash, Suite C
Windsor , Colorado 80550
Phone: (970) 674-3300
Fax: (970) 674-3303
I N T E R W E S T C O N S U L T I N G G R O U P
PREPARED FOR
PROJ. NO.
DATE:
SCALE (H):
SCALE (V):
CHECKED BY:
DESIGNED BY:
PROJECT NAME
PEDERSEN TOYOTA
EXISTING DRAINAGE EXHIBIT
02/21/18
1"=60'
N/A
JTC
RA
1180-027-00
1 of 1
SCALE 1" =
0
60'
30 60
LEGEND
BASIN LABEL
DESIGN POINT
BASIN BOUNDARY
FLOW PATH
Design Engineer:
Design Firm:
Project Number:
Date:
%
Impervious
Runoff
Coefficient C
Return
Period
Frequency
Adjustment
Factor (Cf)
100% 0.95
2-year to
10-year
1.00
90% 0.95 100-year 1.25
90% 0.95
40% 0.50
0% 0.25
C2 to C10 C100
H1 90,711 2.08 37,981 40,789 0 0 11,941 82.3% 0.86 1.00
H2 116,796 2.68 79,480 24,481 422 0 12,414 87.2% 0.88 1.00
H3 14,677 0.34 13,626 0 0 0 1,051 92.8% 0.90 1.00
H4 14,428 0.33 12,054 0 0 0 2,374 83.5% 0.83 1.00
H5 36,307 0.83 24,523 0 2,836 0 8,948 74.6% 0.78 0.97
H4 & H5 50,735 1.16 36,577 0 2,836 0 8,948 77.1% 0.78 0.98
H6 7,818 0.18 0 3,457 0 0 4,361 39.8% 0.56 0.70
Overall 280,737 6.44 167,664 68,726 3,257 0 41,089 82.8% 0.85 1.00
Lawns
(Heavy, 2-7% Slope)
J.Claeys
Interwest Consulting Group
1180-027-00
February 19, 2018
Runoff Coefficients and Frequency Adjustment Factors for City of Fort Collins - Storm Water Criteria Manual
Land Use
Paved
Roof
Walks/RAP
Gravel/Pavers
Apavers
(sq feet)
Alawn
(sq feet)
Weighted %
Impervious
COMPOSITE
Pedersen Toyota
EXISTING IMPERVIOUS AREA CALCULATION
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
DESIGN CRITERIA:
BASINS:
% Impervious values from Table RO-3 in the Urban Storm Drainage Criteria Manual
Sub-basin
Designation
Atotal
(sq feet)
Atotal
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS:
-Equation 6-2 -Equation 6-4 -Urbanized Check Equation 6-5
- CoFC Overland Flow
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition
500 ft - Overland flow shall not exceed for undeveloped condition
Final t c = minimum of t i + t t and urbanized basin check
recommended minimum t c = 5 min for urbanized basins
Time of Concentration (2-yr to 10-yr)
Type of Travel
Surface
Cv
1 H1 82.3% 0.86 2.082 120 0.0164 4.21 477 0.0071 Paved Areas 20 1.69 4.72 8.93 0.0090 8.96 8.93
2 H2 87.2% 0.88 2.681 176 0.0203 4.40 176 0.0192 Paved Areas 20 2.77 1.06 5.45 0.0197 6.18 5.45
3 H3 92.8% 0.90 0.337 49 0.0170 2.20 451 0.0042 Paved Areas 20 1.29 5.81 8.01 0.0055 7.37 7.37
4 H4 83.5% 0.83 0.331 49 0.0247 2.57 427 0.0159 Paved Areas 20 2.52 2.82 5.39 0.0168 7.38 5.39
5 H5 74.6% 0.78 0.833 44 0.0133 3.65 295 0.0061 Paved Areas 20 1.56 3.15 6.81 0.0070 9.07 6.81
6 H6 39.8% 0.56 0.179 137 0.0446 7.18 47 0.0268 Paved Areas 20 3.27 0.24 7.42 0.0400 12.74 7.42
tt
(min)
OVERALL SLOPE
(ft/ft)
tc
(min)
SLOPE
(ft/ft)
ti
(min)
LENGTH
(ft)
SLOPE
(ft/ft)
Table RO-2 VELOCITY
(ft/s)
LENGTH
(ft)
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
Overland Flow Equations for City of Fort Collins - Storm Water Criteria Manual
SUB-BASIN DATA
INITIAL/OVERLAND TIME
(ti
)
TRAVEL TIME (tt
)
tc
=ti
+tt
(min)
Urban Check Final
tc
(min)
DESIGN
POINT
Sub-basin
%
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS:
-Equation 6-2 -Equation 6-4 -Urbanized Check Equation 6-5
- CoFC Overland Flow
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition
500 ft - Overland flow shall not exceed for undeveloped condition
Final t c = minimum of t i + t t and urbanized basin check
recommended minimum t c = 5 min for urbanized basins
Time of Concentration (100-yr)
Type of Travel
Surface
Cv
1 H1 82.3% 0.86 2.082 120 0.0164 4.21 477 0.0071 Paved Areas 20 1.69 4.72 8.93 0.0090 8.96 8.93
2 H2 87.2% 0.88 2.681 176 0.0203 4.40 176 0.0192 Paved Areas 20 2.77 1.06 5.45 0.0197 6.18 5.45
3 H3 92.8% 0.90 0.337 49 0.0170 2.20 451 0.0042 Paved Areas 20 1.29 5.81 8.01 0.0055 7.37 7.37
4 H4 83.5% 0.83 0.331 49 0.0247 2.57 427 0.0159 Paved Areas 20 2.52 2.82 5.39 0.0168 7.38 5.39
5 H5 74.6% 0.78 0.833 44 0.0133 3.65 295 0.0061 Paved Areas 20 1.56 3.15 6.81 0.0070 9.07 6.81
6 H6 39.8% 0.56 0.179 137 0.0446 7.18 47 0.0268 Paved Areas 20 3.27 0.24 7.42 0.0400 12.74 7.42
tt
(min)
OVERALL SLOPE
(ft/ft)
tc
(min)
SLOPE
(ft/ft)
ti
(min)
LENGTH
(ft)
SLOPE
(ft/ft)
Table RO-2 VELOCITY
(ft/s)
LENGTH
(ft)
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
Overland Flow Equations for City of Fort Collins - Storm Water Criteria Manual
SUB-BASIN DATA
INITIAL/OVERLAND TIME
(ti
)
TRAVEL TIME (tt
)
tc
=ti
+tt
(min)
Urban Check Final
tc
(min)
DESIGN
POINT
Sub-basin
%
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS: I = rainfall intensity (in/hr)
Q n = n -yr peak discharge (cfs) P 1 = one-hour point rainfall depth (in)
C n = n -yr runoff coefficient t c = time of concentration (min)
I n = n -yr rainfall intensity (in/hr) P 1-5yr = 1.14 in
A n = Basin drainage area (ac) P 1-10yr = 1.40 in
P 1-100yr = 2.86 in
BASIN SUMMARY:
tc (min)
Runoff Coeff
(C5)
C(A) (acres)
Intensity
(in/hr)
Q (ft3/s) tc (min)
Runoff Coeff.
(C10)
C(A) (acres)
Intensity
(in/hr)
Q (ft3/s) tc (min)
Runoff Coeff.
(C100)
C(A) (acres)
Intensity
(in/hr)
Q (ft3/s)
1 H1 2.082 8.93 0.86 1.79 3.21 5.74 8.93 0.86 1.79 3.95 7.05 8.93 0.86 1.79 8.06 14.41
2 H2 2.681 5.45 0.88 2.35 3.77 8.85 5.45 0.88 2.35 4.63 10.87 5.45 0.88 2.35 9.46 22.21
3 H3 0.337 7.37 0.90 0.30 3.44 1.04 7.37 0.90 0.30 4.22 1.28 7.37 0.90 0.30 8.63 2.62
4 H4 0.331 5.39 0.83 0.28 3.78 1.05 5.39 0.83 0.28 4.65 1.28 5.39 0.83 0.28 9.49 2.62
5 H5 0.833 6.81 0.78 0.65 3.53 2.29 6.81 0.78 0.65 4.33 2.81 6.81 0.78 0.65 8.86 5.74
6 H6 0.179 7.42 0.56 0.10 3.43 0.34 7.42 0.56 0.10 4.21 0.42 7.42 0.56 0.10 8.61 0.86
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised August 2006)
Design
Point
Sub-basin Area (acres)
5-yr Peak Runoff 10-yr Peak Runoff 100-yr Peak Runoff
February 19, 2018
Pedersen Toyota
HISTORIC PEAK RUNOFF
J.Claeys
Interwest Consulting Group
1180-027-00
Q n = C n I n A n
0.786651)
1
( 10 )
28 . 5
t c
P
I
+
=
1180-027-00 Rational Calcs (FC).xlsx Page 4 of 4 Interwest Consulting Group
Design Engineer:
Design Firm:
Project Number:
Date:
%
Impervious
Runoff
Coefficient C
Return
Period
Frequency
Adjustment
Factor (Cf)
100% 0.95
2-year to
10-year
1.00
90% 0.95 100-year 1.25
90% 0.95
40% 0.50
0% 0.25
C2 to C10 C100
D1A 26,605 0.61 12,256 0 704 1,192 12,453 50.2% 0.60 0.75
D1B 47,112 1.08 0 47,112 0 0 0 90.0% 0.95 1.00
D1 Total 73,717 1.69 12,256 47,112 704 1,192 12,453 75.6% 0.82 1.00
D2A 80,231 1.84 40,660 15,368 435 18,064 5,703 77.4% 0.80 1.00
D2B 39,832 0.91 18,862 11,075 713 5,841 3,341 79.9% 0.83 1.00
D2 Total 120,062 2.76 59,521 26,444 1,149 23,905 9,044 78.2% 0.81 1.00
D3 22,584 0.52 11,290 0 2,486 0 8,808 59.9% 0.68 0.85
D4 21,682 0.50 11,425 0 3,536 0 6,720 67.4% 0.73 0.92
D5 39,974 0.92 23,606 0 4,222 0 12,147 68.6% 0.74 0.92
D4 & D5 61,656 1.42 35,031 0 7,759 0 18,867 68.1% 0.74 0.92
D6 2,704 0.06 0 0 0 0 2,704 0.0% 0.25 0.31
Overall 280,724 6.44 118,098 73,556 12,097 25,097 51,876 73.1% 0.78 0.98
Weighted %
Impervious
Apaved COMPOSITE
(sq feet)
Aroof
(sq feet)
Awalk
(sq feet)
Agravel/pavers
(sq feet)
Alawn
(sq feet)
Gravel/Pavers
Lawns
(Heavy, 2-7% Slope)
Sub-basin
Designation
Atotal
(sq feet)
Atotal
(acres)
Land Use
Paved
Roof
Walks
Runoff Coefficients and Frequency Adjustment Factors for City of Fort Collins - Storm Water Criteria Manual
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS:
-Equation 6-2 -Equation 6-4 -Urbanized Check Equation 6-5
- CoFC Overland Flow
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition
500 ft - Overland flow shall not exceed for undeveloped condition
Final t c = minimum of t i + t t and urbanized basin check
recommended minimum t c = 5 min for urbanized basins
Time of Concentration (2-yr to 10-yr)
Type of Travel
Surface
Cv
1A D1A 50.2% 0.60 0.611 67 0.0410 4.76 202 0.0324 Paved Areas 20 3.60 0.93 5.69 0.0346 11.47 5.69
1B D1B 90.0% 0.95 1.082 55 0.0100 2.08 266 0.0100 Paved Areas 20 2.00 2.22 5.00 0.0100 6.09 5.00
2A D2A 77.4% 0.80 1.842 65 0.0293 3.17 303 0.0124 Paved Areas 20 2.23 2.27 5.44 0.0154 8.01 5.44
2B D2B 79.9% 0.83 0.914 93 0.0434 3.03 158 0.0167 Paved Areas 20 2.58 1.02 5.00 0.0265 6.85 5.00
3 D3 59.9% 0.68 0.518 46 0.0278 3.81 433 0.0054 Paved Areas 20 1.46 4.92 8.73 0.0075 12.50 8.73
4 D4 67.4% 0.73 0.498 60 0.0371 3.42 384 0.0169 Paved Areas 20 2.60 2.46 5.88 0.0196 9.77 5.88
5 D5 68.6% 0.74 0.918 37 0.0146 3.63 301 0.0047 Paved Areas 20 1.37 3.66 7.30 0.0058 10.32 7.30
6 D6 0.0% 0.25 0.062 8 0.1000 2.09 0 0.0000 Paved Areas 20 0.06 0.00 5.00 0.1000 18.04 5.00
tt
(min)
OVERALL SLOPE
(ft/ft)
tc
(min)
SLOPE
(ft/ft)
ti
(min)
LENGTH
(ft)
SLOPE
(ft/ft)
Table RO-2 VELOCITY
(ft/s)
LENGTH
(ft)
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
Overland Flow Equations for City of Fort Collins - Storm Water Criteria Manual
SUB-BASIN DATA
INITIAL/OVERLAND TIME
(ti
)
TRAVEL TIME (tt
)
tc
=ti
+tt
(min)
Urban Check Final
tc
(min)
DESIGN
POINT
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS:
-Equation 6-2 -Equation 6-4 -Urbanized Check Equation 6-5
- CoFC Overland Flow
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition
500 ft - Overland flow shall not exceed for undeveloped condition
Final t c = minimum of t i + t t and urbanized basin check
recommended minimum t c = 5 min for urbanized basins
Time of Concentration (100-yr)
Type of Travel
Surface
Cv
1A D1A 50.2% 0.75 0.611 67 0.0410 3.32 202 0.0324 Paved Areas 20 3.60 0.93 5.00 0.0346 11.47 5.00
1B D1B 90.0% 1.00 1.082 55 0.0100 1.38 266 0.0100 Paved Areas 20 2.00 2.22 5.00 0.0100 6.09 5.00
2A D2A 77.4% 1.00 1.842 65 0.0293 1.07 303 0.0124 Paved Areas 20 2.23 2.27 5.00 0.0154 8.01 5.00
2B D2B 79.9% 1.00 0.914 93 0.0434 1.10 158 0.0167 Paved Areas 20 2.58 1.02 5.00 0.0265 6.85 5.00
3 D3 59.9% 0.85 0.518 46 0.0278 2.28 433 0.0054 Paved Areas 20 1.46 4.92 7.21 0.0075 12.50 7.21
4 D4 67.4% 0.92 0.498 60 0.0371 1.71 384 0.0169 Paved Areas 20 2.60 2.46 5.00 0.0196 9.77 5.00
5 D5 68.6% 0.92 0.918 37 0.0146 1.79 301 0.0047 Paved Areas 20 1.37 3.66 5.45 0.0058 10.32 5.45
6 D6 0.0% 0.31 0.062 8 0.1000 1.93 0 0.0000 Paved Areas 20 0.06 0.00 5.00 0.1000 18.04 5.00
tt
(min)
OVERALL SLOPE
(ft/ft)
tc
(min)
SLOPE
(ft/ft)
ti
(min)
LENGTH
(ft)
SLOPE
(ft/ft)
Table RO-2 VELOCITY
(ft/s)
LENGTH
(ft)
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
Overland Flow Equations for City of Fort Collins - Storm Water Criteria Manual
SUB-BASIN DATA
INITIAL/OVERLAND TIME
(ti
)
TRAVEL TIME (tt
)
tc
=ti
+tt
(min)
Urban Check Final
tc
(min)
DESIGN
POINT
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS: I = rainfall intensity (in/hr)
Q n = n -yr peak discharge (cfs) P 1 = one-hour point rainfall depth (in)
C n = n -yr runoff coefficient t c = time of concentration (min)
I n = n -yr rainfall intensity (in/hr) P 1-5yr = 1.14 in
A n = Basin drainage area (ac) P 1-10yr = 1.40 in
P 1-100yr = 2.86 in
BASIN SUMMARY:
tc (min)
Runoff Coeff
(C5)
C(A) (acres)
Intensity
(in/hr)
Q (ft3/s) tc (min)
Runoff Coeff.
(C10)
C(A) (acres)
Intensity
(in/hr)
Q (ft3/s) tc (min)
Runoff Coeff.
(C100)
C(A) (acres)
Intensity
(in/hr)
Q (ft3/s)
1A D1A 0.611 5.69 0.60 0.37 3.72 1.37 5.69 0.60 0.37 4.57 1.68 5.00 0.75 0.46 9.35 4.30
1B D1B 1.082 5.00 0.95 1.03 3.86 3.97 5.00 0.95 1.03 4.74 4.87 5.00 1.00 1.08 9.68 10.47
2A D2A 1.842 5.44 0.80 1.47 3.77 5.55 5.44 0.80 1.47 4.63 6.82 5.00 1.00 1.84 9.47 17.41
2B D2B 0.914 5.00 0.83 0.75 3.86 2.91 5.00 0.83 0.75 4.74 3.58 5.00 1.00 0.91 9.68 8.85
3 D3 0.518 8.73 0.68 0.35 3.24 1.14 8.73 0.68 0.35 3.98 1.40 7.21 0.85 0.44 8.13 3.57
4 D4 0.498 5.88 0.73 0.36 3.69 1.35 5.88 0.73 0.36 4.53 1.65 5.00 0.92 0.46 9.26 4.22
5 D5 0.918 7.30 0.74 0.68 3.45 2.33 7.30 0.74 0.68 4.24 2.87 5.45 0.92 0.85 8.66 7.32
6 D6 0.062 5.00 0.25 0.02 3.86 0.06 5.00 0.25 0.02 4.74 0.07 5.00 0.31 0.02 9.68 0.19
5-yr Peak Runoff 10-yr Peak Runoff 100-yr Peak Runoff
Pedersen Toyota
DEVELOPED PEAK RUNOFF
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised August 2006)
DESIGN CRITERIA:
Design
Point
Sub-basin Area (acres)
J.Claeys
Interwest Consulting Group
1180-027-00
February 19, 2018
Q n = C n I n A n
0.786651)
1
( 10 )
28 . 5
t c
P
I
+
=
Appendix C
APPENDIX C – DETENTION POND CALCULATIONS
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
Detention Volume Calculation
0.82
1.25
1.00 ft3 acre-ft
1.69 acres 16,053 0.369
0.88 cfs
Time
(min)
100-yr
Intensity
(I , in/hr)
Q100
(cfs)
Accumulative
Runoff Volume
(ft3)
Release
Volume
(ft3)
Detained
Volume
(ft3)
Detained
Volume
(acre-ft)
0 0.00 0.00 0.00 0.00 0.00 0.000
5 9.95 16.82 5,044.65 264.00 4,780.65 0.110
10 7.72 13.05 7,828.08 528.00 7,300.08 0.168
15 6.52 11.02 9,916.92 792.00 9,124.92 0.209
20 5.60 9.46 11,356.80 1,056.00 10,300.80 0.236
25 4.98 8.42 12,624.30 1,320.00 11,304.30 0.260
30 4.52 7.64 13,749.84 1,584.00 12,165.84 0.279
35 4.08 6.90 14,479.92 1,848.00 12,631.92 0.290
40 3.74 6.32 15,169.44 2,112.00 13,057.44 0.300
45 3.46 5.85 15,787.98 2,376.00 13,411.98 0.308
50 3.23 5.46 16,376.10 2,640.00 13,736.10 0.315
55 3.03 5.12 16,898.31 2,904.00 13,994.31 0.321
60 2.86 4.83 17,400.24 3,168.00 14,232.24 0.327
65 2.72 4.60 17,927.52 3,432.00 14,495.52 0.333
70 2.59 4.38 18,383.82 3,696.00 14,687.82 0.337
75 2.48 4.19 18,860.40 3,960.00 14,900.40 0.342
80 2.38 4.02 19,306.56 4,224.00 15,082.56 0.346
85 2.29 3.87 19,737.51 4,488.00 15,249.51 0.350
90 2.21 3.73 20,168.46 4,752.00 15,416.46 0.354
95 2.13 3.60 20,518.29 5,016.00 15,502.29 0.356
100 2.06 3.48 20,888.40 5,280.00 15,608.40 0.358
105 2.00 3.38 21,294.00 5,544.00 15,750.00 0.362
110 1.94 3.28 21,638.76 5,808.00 15,830.76 0.363
115 1.89 3.19 22,039.29 6,072.00 15,967.29 0.367
120 1.84 3.11 22,389.12 6,336.00 16,053.12 0.369
Adjusted Runoff Coefficient (CC f )
Area (A )
Allowed Release Rate
Required Detention
Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, June 2001 (Revised April 2008)
Pedersen Toyota
Pond Summary (Basin D1)
Design Engineer:
Design Firm:
Project Number:
Date:
Pond Summary Table
0.051
5030.46
14.77
3 13/16
0.88
0.398
5033.74
0.420
J.Claeys
Interwest Consulting Group
1180-027-00
February 19, 2018
100-yr Detention Volume (acre-ft)
100-yr Water Surface Elev. (ft)
Detention Pond Summary Table
Water Quality Capture Volume (acre-ft)
WQCV Water Surface Elev. (ft)
100-yr Pond Max Inflow (cfs)
100-yr Site Release Rate (cfs)
Outlet Orifice Size (in)
Total Pond Storage (acre-ft)
1180-027-00 PondCalcs (Basin D1).xls Page 1 of 5 Interwest Consulting Group
Pedersen Toyota
Water Quality Pond and Outlet Sizing (Basin D1)
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
REQUIRED WATER QUALITY CAPTURE VOLUME (WQCV):
Tributary Area, A 1.69 acres
Composite. Imperviousness, I 75.6%
WQCV (watershed inches) 0.303 inches 40-Hour Drain Time (Fig SQ-2)
Required WQCV 0.051 acre-feet Including 20% for Sedimentation
WATER QUALITY OUTLET SIZING (Per USDCM, Volume 3):
Design Water Quality Depth, DWQ
1.56 ft
Determine K40
K40
= 0.013DWQ
2
+ 0.22DWQ
- 0.10 0.274
Maximum Area per Row, a a = WQCV / K40
0.186 square inches
Number of Rows, nr 4 rows
Number of Columns, nc (See Table 6a-1 for Max.) 1 columns
Choose Hole Diameter 3/8 inches
Use USDCM Volume 3, Figure 5 0.375 inches
Total Area per Row, Ao
0.11 square inches
Total Outlet Area, Aot
0.44 square inches
Does design work? Yes
Minimum Steel Plate Thickness 1/4 inch
(Not Used)
Number of Rows, nr 2 rows
Choose Rectangular Hole Width (w/ 2" Height) 0 inches
Use USDCM Volume 3, Figure 5 0.000 inches
Total Outlet Area, Aot
0.00 square inches
Does design work? Yes
Minimum Steel Plate Thickness 1/4 inch
Urban Storm Drainage Criteria Manual (USDCM) Volume III, Urban Drainage and Flood Control District, June 2001 (Updated November 2010)
Circular Perforation Sizing
Rectangular Perforation Sizing
J.Claeys
Interwest Consulting Group
1180-027-00
February 19, 2018
* * 1 . 2
12
Area
WQCV
Volume
=
1180-027-00 PondCalcs (Basin D1).xls Page 2 of 5 Interwest Consulting Group
Pedersen Toyota
Water Quality Pond and Outlet Sizing (Basin D1)
Design Engineer:
Design Firm:
Project Number:
Date:
J.Claeys
Interwest Consulting Group
1180-027-00
February 19, 2018
WATER QUALITY TRASH RACK SIZING (Per USDCM, Volume 3)
Required Open Area, At
At
=0.5*[77(e
-0.124D
)]*Aot
16 square inches
Min. Distance between Columns, Sc
2 inches
Width of Trash Rack and Concrete Opening per Column 3 inches
Use USDCM Volume 3, Table 6a-1
Total Width, Wconc
3 inches
Height of Trash Rack Screen, Htr
18 11/16 inches Check - Larger than Required
Type of Screen S.S. #93 VEE Wire (US Filter)
Screen Opening Slot Dimension 0.139" (US Filter)
Support Rod Type (See Table 6a-2)
Spacing of Support Rod (O.C.) 3/4 inches O.C.
Total Screen Thickness (See Table 6a-2) 0.31 inches
Carbon Steel Frame Type (See Table 6a-2)
(Not Used)
Required Open Area, At
(including 50% clogging)
At
=0.5*[77(e
-0.124D
)]*Aot
0 square inches
Width of Trash Rack Opening, Wopening
1 inches
Use USDCM Volume 3, Table 6b-1
Width of Concrete Opening, Wconc
12 inches
Min Height of Trash Rack Screen, Htr
(including 2' 4" below lowest openings) 28.00 inches
Type of Screen Kelmp KRP Series Aluminum Bar Gate (or Equal)
Screen Opening Slot Dimension 3/16" Bars on 1-3/16" Centers
Minimum Bearing Bar Size (See Table 6b-2)
Rectangular Perforation Trash Rack Sizing
1 in x 3/16 in
#156 VEE
3/8in x 1.0in flat bar
Circular Perforation Trash Rack Sizing
1180-027-00 PondCalcs (Basin D1).xls Page 3 of 5 Interwest Consulting Group
Pedersen Toyota
Circular Orifice Plate Sizing (Basin D1)
Design Engineer:
Design Firm:
Project Number:
Date:
Orifice Equation
where: C = Orifice Discharge Coefficient
A o
= Orifice Area (ft
2
)
g = Gravity (32.2 ft/s
2
)
∆h = Difference in Elevation Head (ft)
D o
= Orifice Diameter (in)
Calculations
100-yr Orifice Sizing 100-yr Orifice Rating Table
Knowns: 100-yr Release Rate 0.88 cfs
100-yr WSEL 5033.74 ft 5028.90 0.00 0.000
5029.00 0.00 0.000
Pond Outlet Invert 5028.80 ft 5030.00 0.36 0.021
5031.00 0.55 0.087
Discharge Coefficient 0.65 5032.00 0.69 0.178
5033.00 0.80 0.293
Tailwater Elevation 5029.24 ft 5033.74 0.88 0.398
Orifice Diameter 3 13/16 in
Orifice Area 0.079 ft
2
Centroid Elevation 5028.96 ft
Actual Release Rate 0.88 cfs
Pond Volume
(ac-ft)
J.Claeys
Interwest Consulting Group
1180-027-00
February 19, 2018
Elevation
(ft)
Discharge
(cfs)
C g h
Q
QCA o g h A o ∆
= ∆ ⇒ =
2
2
π
o
o
A
D
= 576
1180-027-00 PondCalcs (Basin D1).xls Page 4 of 5 Interwest Consulting Group
Pedersen Toyota
Critical Pond Elevations (Basin D1)
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, June 2001 (Revised April 2008)
Stage Storage
Volume (pond volume calculated using the prismoidal formula):
CONTOUR (FT) AREA (FT2) AREA (ACRE)
VOLUME
(ACRE-FT)
DEPTH (FT)
CUMULATIVE VOLUME
(ACRE-FT)
5028.90 0.000 0.000 0.00 0.000
5029.0 25 0.001 0.000 0.10 0.000
5030.0 2426 0.056 0.021 1.10 0.021
5031.0 3401 0.078 0.067 2.10 0.087
5032.0 4489 0.103 0.090 3.10 0.178
5033.0 5609 0.129 0.116 4.10 0.293
5034.0 6711 0.154 0.141 5.10 0.434
0.051 acre-ft 5030.46 ft
Required 100-yr Detention Volume =
0.369 acre-ft
0.022 acre-ft
0.398 acre-ft 5033.74 ft
0.420 acre-ft
40% Aggregate Void (w/in CDOT #2)
Storage Area Depth Min Bottom Elev
Paver 1 1,192 sqft 2.00 ft 953.6 cu-ft 0.022 acre-ft 5031.74 ft
Paver Storage
Required Water Quality Capture Volume =
100-yr Detention Volume
February 19, 2018
Total Storage Provided including WQCV
Paver Storage
Detention Volume
J.Claeys
Interwest Consulting Group
1180-027-00
Interpolates to an Elev. of
Interpolates to an Elev. of
( )
3
AAAADepth 1 2 1 2
V
+ +
=
1180-027-00 PondCalcs (Basin D1).xls Page 5 of 5 Interwest Consulting Group
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
Detention Volume Calculation
0.82
1.00
0.82 ft3 acre-ft
2.86 acres 3,004 0.069
1.38 cfs
Time
(min)
2-yr
Intensity
(I , in/hr)
Q100
(cfs)
Accumulative
Runoff Volume
(ft3)
Release
Volume
(ft3)
Detained
Volume
(ft3)
Detained
Volume
(acre-ft)
0 0.00 0.00 0.00 0.00 0.00 0.000
5 2.85 6.68 2,005.15 414.00 1,591.15 0.037
10 2.21 5.18 3,109.74 828.00 2,281.74 0.052
15 1.87 4.39 3,946.97 1,242.00 2,704.97 0.062
20 1.61 3.78 4,530.93 1,656.00 2,874.93 0.066
25 1.43 3.35 5,030.45 2,070.00 2,960.45 0.068
30 1.30 3.05 5,487.77 2,484.00 3,003.77 0.069
35 1.17 2.74 5,762.16 2,898.00 2,864.16 0.066
40 1.07 2.51 6,022.47 3,312.00 2,710.47 0.062
45 0.99 2.32 6,268.72 3,726.00 2,542.72 0.058
50 0.92 2.16 6,472.75 4,140.00 2,332.75 0.054
55 0.87 2.04 6,733.07 4,554.00 2,179.07 0.050
60 0.82 1.92 6,923.03 4,968.00 1,955.03 0.045
65 0.77 1.81 7,042.64 5,382.00 1,660.64 0.038
70 0.73 1.71 7,190.38 5,796.00 1,394.38 0.032
75 0.69 1.62 7,281.85 6,210.00 1,071.85 0.025
80 0.66 1.55 7,429.59 6,624.00 805.59 0.018
85 0.63 1.48 7,535.13 7,038.00 497.13 0.011
90 0.61 1.43 7,725.09 7,452.00 273.09 0.006
95 0.58 1.36 7,753.23 7,866.00 -112.77 -0.003
100 0.56 1.31 7,879.87 8,280.00 -400.13 -0.009
105 0.54 1.27 7,978.37 8,694.00 -715.63 -0.016
110 0.52 1.22 8,048.73 9,108.00 -1,059.27 -0.024
115 0.51 1.20 8,252.76 9,522.00 -1,269.24 -0.029
120 0.49 1.15 8,273.87 9,936.00 -1,662.13 -0.038
February 19, 2018
Pedersen Toyota
2-yr Detention Volume - FAA Method (Basin D2)
J.Claeys
Interwest Consulting
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
Detention Volume Calculation
0.82
1.00
0.82 ft3 acre-ft
2.86 acres 6,988 0.160
1.38 cfs
Time
(min)
10-yr
Intensity
(I , in/hr)
Q100
(cfs)
Accumulative
Runoff Volume
(ft3)
Release
Volume
(ft3)
Detained
Volume
(ft3)
Detained
Volume
(acre-ft)
0 0.00 0.00 0.00 0.00 0.00 0.000
5 4.87 11.42 3,426.34 414.00 3,012.34 0.069
10 3.78 8.86 5,318.91 828.00 4,490.91 0.103
15 3.19 7.48 6,733.07 1,242.00 5,491.07 0.126
20 2.74 6.43 7,711.02 1,656.00 6,055.02 0.139
25 2.44 5.72 8,583.43 2,070.00 6,513.43 0.150
30 2.21 5.18 9,329.21 2,484.00 6,845.21 0.157
35 2.00 4.69 9,849.84 2,898.00 6,951.84 0.160
40 1.83 4.29 10,300.12 3,312.00 6,988.12 0.160
45 1.69 3.96 10,701.15 3,726.00 6,975.15 0.160
50 1.58 3.71 11,116.25 4,140.00 6,976.25 0.160
55 1.48 3.47 11,453.96 4,554.00 6,899.96 0.158
60 1.40 3.28 11,819.81 4,968.00 6,851.81 0.157
65 1.32 3.10 12,073.09 5,382.00 6,691.09 0.154
70 1.25 2.93 12,312.30 5,796.00 6,516.30 0.150
75 1.19 2.79 12,558.55 6,210.00 6,348.55 0.146
80 1.14 2.67 12,832.93 6,624.00 6,208.93 0.143
85 1.09 2.56 13,036.97 7,038.00 5,998.97 0.138
90 1.05 2.46 13,297.28 7,452.00 5,845.28 0.134
95 1.01 2.37 13,501.32 7,866.00 5,635.32 0.129
100 0.97 2.27 13,649.06 8,280.00 5,369.06 0.123
105 0.94 2.20 13,888.27 8,694.00 5,194.27 0.119
110 0.91 2.13 14,085.27 9,108.00 4,977.27 0.114
115 0.88 2.06 14,240.05 9,522.00 4,718.05 0.108
120 0.86 2.02 14,521.48 9,936.00 4,585.48 0.105
February 19, 2018
Pedersen Toyota
10-yr Detention Volume - FAA Method (Basin D2)
J.Claeys
Interwest Consulting
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
Detention Volume Calculation
0.82
1.25
1.00 ft3 acre-ft
2.86 acres 27,953 0.642
1.38 cfs
Time
(min)
100-yr
Intensity
(I , in/hr)
Q100
(cfs)
Accumulative
Runoff Volume
(ft3)
Accumulative
Release
Volume
(ft3)
Detained
Volume
(ft3)
Detained
Volume
(acre-ft)
0 0.00 0.00 0.00 0.00 0.00 0.000
5 9.95 28.46 8,537.10 414.00 8,123.10 0.186
10 7.72 22.08 13,247.52 828.00 12,419.52 0.285
15 6.52 18.65 16,782.48 1,242.00 15,540.48 0.357
20 5.60 16.02 19,219.20 1,656.00 17,563.20 0.403
25 4.98 14.24 21,364.20 2,070.00 19,294.20 0.443
30 4.52 12.93 23,268.96 2,484.00 20,784.96 0.477
35 4.08 11.67 24,504.48 2,898.00 21,606.48 0.496
40 3.74 10.70 25,671.36 3,312.00 22,359.36 0.513
45 3.46 9.90 26,718.12 3,726.00 22,992.12 0.528
50 3.23 9.24 27,713.40 4,140.00 23,573.40 0.541
55 3.03 8.67 28,597.14 4,554.00 24,043.14 0.552
60 2.86 8.18 29,446.56 4,968.00 24,478.56 0.562
65 2.72 7.78 30,338.88 5,382.00 24,956.88 0.573
70 2.59 7.41 31,111.08 5,796.00 25,315.08 0.581
75 2.48 7.09 31,917.60 6,210.00 25,707.60 0.590
80 2.38 6.81 32,672.64 6,624.00 26,048.64 0.598
85 2.29 6.55 33,401.94 7,038.00 26,363.94 0.605
90 2.21 6.32 34,131.24 7,452.00 26,679.24 0.612
95 2.13 6.09 34,723.26 7,866.00 26,857.26 0.617
100 2.06 5.89 35,349.60 8,280.00 27,069.60 0.621
105 2.00 5.72 36,036.00 8,694.00 27,342.00 0.628
110 1.94 5.55 36,619.44 9,108.00 27,511.44 0.632
115 1.89 5.41 37,297.26 9,522.00 27,775.26 0.638
120 1.84 5.26 37,889.28 9,936.00 27,953.28 0.642
February 19, 2018
Pedersen Toyota
100-yr Detention Volume - FAA Method (Basin D2)
J.Claeys
Pedersen Toyota
Pond Summary (Basin D2)
Design Engineer:
Design Firm:
Project Number:
Date:
Pond Summary Table
26.27
4 1/16
1.38
0.493
0.149
0.642
5031.50
100-yr Site Release Rate (cfs)
Outlet Orifice Size (in)
100-yr Surface Detention Volume (acre-ft)
100-yr Total Detention Volume (acre-ft)
J.Claeys
Interwest Consulting Group
1180-027-00
February 19, 2018
100-yr Paver Detention Volume (acre-ft)
100-yr Water Surface Elev. (ft)
Detention Pond Summary Table
100-yr Pond Max Inflow (cfs)
1180-027-00 PondCalcs (Basin D2).xls Page 1 of 3 Interwest Consulting Group
Pedersen Toyota
Circular Orifice Plate Sizing (Basin D2)
Design Engineer:
Design Firm:
Project Number:
Date:
Orifice Equation
where: C = Orifice Discharge Coefficient
A o
= Orifice Area (ft
2
)
g = Gravity (32.2 ft/s
2
)
∆h = Difference in Elevation Head (ft)
D o
= Orifice Diameter (in)
Calculations
100-yr Orifice Sizing 100-yr Orifice Rating Table
Knowns: 100-yr Release Rate 1.38 cfs
100-yr WSEL 5031.50 ft 5030.48 1.30 0.000
5031.00 1.34 0.026
Pond Outlet Invert 5022.25 ft 5031.50 1.38 0.151
5032.00 1.42 0.379
Discharge Coefficient 0.65
Tailwater Elevation 5022.66 ft
Orifice Diameter 4 1/16 in
Orifice Area 0.089 ft
2
Centroid Elevation 5022.42 ft
Actual Release Rate 1.38 cfs
Pond Volume
(ac-ft)
J.Claeys
Interwest Consulting Group
1180-027-00
February 19, 2018
Elevation
(ft)
Discharge
(cfs)
C g h
Q
QCA o g h A o ∆
= ∆ ⇒ =
2
2
π
o
o
A
D
= 576
1180-027-00 PondCalcs (Basin D2).xls Page 2 of 3 Interwest Consulting Group
Pedersen Toyota
Critical Pond Elevations (Basin D2)
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, June 2001 (Revised April 2008)
Stage Storage
Parking Lot Volume (pond volume calculated using the prismoidal formula):
CONTOUR (FT) AREA (FT2) AREA (ACRE)
VOLUME
(ACRE-FT)
DEPTH (FT)
CUMULATIVE VOLUME
(ACRE-FT)
5030.48 0.000 0.000 0.00 0.000
5031.0 6620 0.152 0.026 0.52 0.026
5031.5 15707 0.361 0.124 1.02 0.151
5032.0 24423 0.561 0.228 1.52 0.379
Required 100-yr Detention Volume =
0.493 acre-ft
0.149 acre-ft 5031.50 ft
0.642 acre-ft
40% Aggregate Void (w/in CDOT #2)
Storage Area Depth Min Bottom Elev
Paver 2 2,008 sqft 0.00 ft 0.0 cu-ft 0.000 acre-ft N/A
Paver 3 11,731 sqft 3.75 ft 17,595.9 cu-ft 0.404 acre-ft 5025.90 ft
Paver 4 3,868 sqft 1.00 ft 1,547.1 cu-ft 0.036 acre-ft 5030.5 ft
Paver 5 5,841 sqft 1.00 ft 2,336.4 cu-ft 0.054 acre-ft 5030.5 ft
21,479.4 cu-ft 0.493 acre-ft
Estimated Ponding Depth in Parking Lot per Storm
Detention
Volume
(ac-ft)
Surface
Volume
(ac-ft)
Surface
Depth
(ft)
0.069 0.000 0.0
0.160 0.000 0.0
0.642 0.149 1.0
Storm
(% chance of annual
occurance)
2-yr Storm (50%)
10-yr Storm (10%)
100-yr Storm (1%)
J.Claeys
Interwest Consulting Group
1180-027-00
Surface Storage WSEL
Paver Storage
Total Required Storage
Detention Volume
February 19, 2018
Paver Storage
( )
Appendix D
APPENDIX D – CONVEYANCE ELEMENT SIZING
Assume a full pipe
Min TW = 5026.3 + 1.5 = 5027.8
Assume WQCV WSEL as
Min TW = 5030.46
Assume a full pipe
Min TW = 5019.2 + 3.0 = 5022.2
Q100 = 8.85 cfs
Q100 = 1.38 cfs
Q100 = 17.41 cfs
(modeled w/ full
100-yr)
Q100 = 10.47 cfs
Q100 = 0.88 cfs
SD-01
SD-02
SD-03
SD-04
Appendix E
APPENDIX E – LOW IMPACT DEVELOPMENT CALCULATIONS
1000-GAL
UP
UP
SOUTH COLLEGE AVENUE (HWY 287)
SOUTH MASON STREET
1218 W. Ash, Suite A
Windsor , Colorado 80550
Phone: (970) 674-3300
Fax: (970) 674-3303
I N T E R W E S T C O N S U L T I N G G R O U P
PREPARED FOR
PROJ. NO.
DATE:
SCALE (H):
SCALE (V):
CHECKED BY:
DESIGNED BY:
PROJECT NAME
LOW IMPACT DEVELOPMENT
PERMEABLE PAVER DRAINAGE AREAS
PEDERSEN TOYOTA
02/21/18
1"=60'
N/A
JTC
RA
1180-027-00
1 of 1
SCALE 1" =
0
60'
30 60
LEGEND
Pedersen Toyota
Low Impact Development
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
Low Impact Development Summary
Pavement Area Summary
96,895 sqft
24,916 sqft
25.7%
Paver Area Add Area Treated Ratio
Paver 1 1,192 sqft 2,496 sqft 2.09
Paver 2 2,008 sqft 5,491 sqft 2.73
Paver 3 11,550 sqft 33,038 sqft 2.86
Paver 4 4,325 sqft 2,131 sqft 0.49
Paver 5 5,841 sqft 18,852 sqft 3.23
24,916 sqft 62,008 sqft
Developed Area Summary
151,828 sqft
Total Area required for Treatment (50%): 75,914 sqft
24,916 sqft
62,008 sqft
86,924 sqft
0 sqft
86,924 sqft
57.3%
Impervious Area Treated by Rain Garden:
Proposed Area of Pavers:
Additional Area Treated by Pavers:
Total Area Treated by Pavers:
Total Area Treated by LID:
Percent Site Area Treated by LID:
Total New Paved Area:
Proposed Permeable Paver Area:
Percent Pavement Area as Permeable Pavers:
City of Fort Collins - Ordinance No. 007, 2016
- Treat at least 75% of any newly developed or redeveloped impervious area using one or a
combination of LID techniques, or
- Treat at least 50% of any newly developed or redeveloped impervious area using one or a
combination of LID techniques when 25% of private driveable surfaces are permeable.
Total New Impervious Area:
J.Claeys
Interwest Consulting Group
1180-027-00
February 19, 2018
Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, January 2010
1180-027-00 LID Tabulation.xlsx Page 1 of 1 Interwest Consulting Group
3
AAAADepth 1 2 1 2
V
+ +
=
1180-027-00 PondCalcs (Basin D2).xls Page 3 of 3 Interwest Consulting Group
Interwest Consulting
1180-027-00
Area (A )
Allowed Release Rate
Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, June 2001 (Revised April 2008)
City of Fort Collins - Storm Water Criteria Manual
Runoff Coefficient (C )
Frequency Factor (C f ) Required Detention
Adjusted Runoff Coefficient (CC f )
1180-027-00 Detention (FAA).xlsx Page 3 of 3 Interwest Consulting Group
1180-027-00
Area (A )
Allowed Release Rate
Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, June 2001 (Revised April 2008)
City of Fort Collins - Storm Water Criteria Manual
Runoff Coefficient (C )
Frequency Factor (C f ) Required Detention
Adjusted Runoff Coefficient (CC f )
1180-027-00 Detention (FAA).xlsx Page 2 of 3 Interwest Consulting Group
1180-027-00
Area (A )
Allowed Release Rate
Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, June 2001 (Revised April 2008)
City of Fort Collins - Storm Water Criteria Manual
Runoff Coefficient (C )
Frequency Factor (C f ) Required Detention
Adjusted Runoff Coefficient (CC f )
1180-027-00 Detention (FAA).xlsx Page 1 of 3 Interwest Consulting Group
City of Fort Collins - Storm Water Criteria Manual
February 19, 2018
Runoff Coefficient (C )
Frequency Factor (C f )
100-yr Detention Volume - FAA Method (Basin D1)
Pedersen Toyota
J.Claeys
Interwest Consulting
1180-027-00
1180-027-00 Detention (FAA).xlsx Page 1 of 1 Interwest Consulting Group
1180-027-00 Rational Calcs (FC).xlsx Page 4 of 4 Interwest Consulting Group
Sub-basin
%
Impervious
C100
AREA
(acres)
February 19, 2018
Pedersen Toyota
DEVELOPED TIME OF CONCENTRATION
J.Claeys
Interwest Consulting Group
1180-027-00
t c = t i + t t 0 . 5
V = C v S w
V
L
tt 60
=
��
= 18 − 15� +
�
60 24� + 12 �
��
=
1.87(1.1 − ��
��
) �
� �
1180-027-00 Rational Calcs (FC).xlsx Page 3 of 4 Interwest Consulting Group
Sub-basin
%
Impervious
C2-10
AREA
(acres)
February 19, 2018
Pedersen Toyota
DEVELOPED TIME OF CONCENTRATION
J.Claeys
Interwest Consulting Group
1180-027-00
t c = t i + t t 0 . 5
V = C v S w
V
L
tt 60
=
��
= 18 − 15� +
�
60 24� + 12 �
��
=
1.87(1.1 − ��
��
) �
� �
1180-027-00 Rational Calcs (FC).xlsx Page 2 of 4 Interwest Consulting Group
% Impervious values from Table RO-3 in the Urban Storm Drainage Criteria Manual
J.Claeys
Interwest Consulting Group
1180-027-00
February 19, 2018
Pedersen Toyota
DEVELOPED IMPERVIOUS AREA CALCULATION
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
BASINS:
1180-027-00 Rational Calcs (FC).xlsx Page 1 of 4 Interwest Consulting Group
Impervious
C100
AREA
(acres)
February 19, 2018
Pedersen Toyota
HISTORIC TIME OF CONCENTRATION
J.Claeys
Interwest Consulting Group
1180-027-00
t c = t i + t t 0 . 5
V = C v S w
V
L
tt 60
=
��
= 18 − 15� +
�
60 24� + 12 �
��
=
1.87(1.1 − ��
��
) �
� �
1180-027-00 Rational Calcs (FC).xlsx Page 3 of 4 Interwest Consulting Group
Impervious
C2-10
AREA
(acres)
February 19, 2018
Pedersen Toyota
HISTORIC TIME OF CONCENTRATION
J.Claeys
Interwest Consulting Group
1180-027-00
t c = t i + t t 0 . 5
V = C v S w
V
L
tt 60
=
��
= 18 − 15� +
�
60 24� + 12 �
��
=
1.87(1.1 − ��
��
) �
� �
1180-027-00 Rational Calcs (FC).xlsx Page 2 of 4 Interwest Consulting Group
(acres)
Apaved
(sq feet)
Aroof
(sq feet)
Awalk
(sq feet)
1180-027-00 Rational Calcs (FC).xlsx Page 1 of 4 Interwest Consulting Group
38 1.11 1.89 3.87 1.11 0.00 1.90 0.01 3.88 0.01
39 1.09 1.86 3.80 1.09 0.00 1.87 0.01 3.82 0.02
40 1.07 1.83 3.74 1.08 0.01 1.84 0.01 3.76 0.02
41 1.05 1.80 3.68 1.06 0.01 1.81 0.01 3.70 0.02
42 1.04 1.77 3.62 1.04 0.00 1.78 0.01 3.64 0.02
43 1.02 1.74 3.56 1.03 0.01 1.76 0.02 3.59 0.03
44 1.01 1.72 3.51 1.01 0.00 1.73 0.01 3.54 0.03
45 0.99 1.69 3.46 1.00 0.01 1.71 0.02 3.48 0.02
46 0.98 1.67 3.41 0.99 0.01 1.68 0.01 3.44 0.03
47 0.96 1.64 3.36 0.97 0.01 1.66 0.02 3.39 0.03
48 0.95 1.62 3.31 0.96 0.01 1.64 0.02 3.34 0.03
49 0.94 1.60 3.27 0.95 0.01 1.61 0.01 3.30 0.03
50 0.92 1.58 3.23 0.93 0.01 1.59 0.01 3.25 0.02
51 0.91 1.56 3.18 0.92 0.01 1.57 0.01 3.21 0.03
52 0.90 1.54 3.14 0.91 0.01 1.55 0.01 3.17 0.03
53 0.89 1.52 3.10 0.90 0.01 1.53 0.01 3.13 0.03
54 0.88 1.50 3.07 0.89 0.01 1.51 0.01 3.09 0.02
55 0.87 1.48 3.03 0.88 0.01 1.50 0.02 3.06 0.03
56 0.86 1.47 2.99 0.87 0.01 1.48 0.01 3.02 0.03
57 0.85 1.45 2.96 0.86 0.01 1.46 0.01 2.98 0.02
58 0.84 1.43 2.92 0.85 0.01 1.44 0.01 2.95 0.03
59 0.83 1.42 2.89 0.84 0.01 1.43 0.01 2.92 0.03
60 0.82 1.40 2.86 0.83 0.01 1.41 0.01 2.88 0.02
0.00 -0.02 0.00
C 3
2
1 1
( c )
C t
C P
I
+
=
of the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Survey Area Data: Version 12, Oct 10, 2017
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Mar 20, 2015—Oct
15, 2016
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Hydrologic Soil Group—Larimer County Area, Colorado
(Pedersen Toyota)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/20/2018
Page 2 of 4