HomeMy WebLinkAboutPEDERSEN TOYOTA EXPANSION - PDP - PDP140007 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORTAugust 6, 2014
Mr. Wes Lamarque
Fort Collins Utilities – Stormwater
700 Wood Street
Fort Collins, CO 80522
Re: Pedersen Toyota – Preliminary Storm Drainage Report
Dear Wes,
Please accept the following letter report on behalf of the Heath Construction and Pedersen Toyota for
the Pedersen Toyota expansion and site redevelopment to demonstrate the site’s ability to comply
with the City’s stormwater requirements.
INTRODUCTION
The project site will consist of the existing Pedersen Toyota showroom and sales office located at the
northwest corner of S. College Avenue and Kensington Drive and the Mini-U-Storage site located at
the northeast corner of S. Mason Street and Kensington Drive. These two existing sites are bound by
S. Mason Street to the west, Kensington Drive to the south, S. College Avenue to the east, and the
existing Target retail store to the north. The proposed project will consist of demolition of the Mini-
U-Storage improvements and limited redevelopment of the Pedersen Toyota site to expand the
existing Toyota showroom and service center, and ultimately construct a parking garage for vehicle
inventory with vehicle detailing and retail shops. Potential phasing of the parking garage is being
considered but is not anticipated to affect the drainage design.
EXISTING CONDITIONS
Both the existing Mini-U-Storage and Pedersen Toyota site have existing stormwater management
infrastructure onsite controlling the stormwater release rates.
The Mini-U-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 Mini-U-
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.
Pedersen Toyota – Preliminary Storm Drainage Report
August 6, 2014
Page 2 of 5
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.
PROPOSED DEVELOPMENT
The project proposes to redevelop the existing Mini-U-Storage site and redevelop limited areas of the
Pedersen Toyota site to expand the showroom and service center and ultimately construct a parking
garage, with vehicle detailing and retail shops, to provide additional vehicle inventory storage. The
two properties will be re-platted into one lot.
The detention and water quality requirements will be provided through the use of a detention pond in
the northwest corner of the site and a combination of permeable paving area, parking lot surface
detention and underground detention within the northeast parking lot.
The northwest detention and water quality pond is proposed to be designed as an extended detention
basin per City of Fort Collins and Urban Drainage standards. All of the developed Basin D1 will
drain to this pond and will consist of the parking garage upper deck drainage, vehicle detailing and
retail shop roof drainage, and parking/access drainage. The pond is designed with a release rate
equal to the existing Mini-U-Storage release rate, 0.88 cfs, and utilizes the existing 18” storm drain
as the site’s drainage outfall. The developed percent impervious is 76% for Basin D1, which is a
reduction compared to the existing percent impervious. Basin D1 requires 0.32 acre-ft of storage for
detention and water quality.
The north side of the existing Pedersen Toyota site is going to be improved to accommodate the
expanded service center. The service center footprint absorbs some of the existing parking lot
detention area and requires the storm infrastructure to be adjusted. The existing parking lot detention
depth is 18” and the proposed improvements will reduce this ponding depth to be 12” during a 100-yr
storm event, to meet current standards. To be able to achieve the required detention volume, along
with the new rainfall data and the existing release rate, the necessary storage for Basin D2 will be
provided by the combination of storage within the drainage course of the permeable paver section
(limited to less than 25% of the required detention volume), parking lot surface detention, and
underground detention (requiring an engineering variance). Along with the detention volume, the
permeable pavers will also provide water quality enhancement and proposed to satisfy the Low
Impact Development (LID) techniques for this redevelopment site. The developed percent
impervious is 80%, which is a reduction in compared to the existing percent impervious. Basin D2
requires 22,909 cu-ft (0.53 acre-ft) of detention storage and is estimated to be achieved with 6,000
cu-ft of parking lot surface storage, 3,445 cu-ft of storage within the paver section, and 13,860 cu-ft
of underground storage within dual reinforced concrete boxes.
For the purposes of this preliminary drainage review, we analyzed underground detention through the
use of reinforced concrete box culverts. The project team is also considering other means such as
utilizing a Contech manifold system with perforated corrugated metal piping which would be placed
under the proposed permeable pavers and northeast parking area. Additional feasibility review will
occur during the final design to determine the most acceptable and efficient underground storage
system. The variance requesting approval for underground detention can be found further in the
letter.
Pedersen Toyota – Preliminary Storm Drainage Report
August 6, 2014
Page 3 of 5
The Midtown Plan requires improvements for the S. Mason Street, Kensington Drive, and S. College
Avenue with dedication of additional right-of-way and detached sidewalks. This dedication increased
the areas draining to the respected streets. Though the basin areas increased, there was a reduction in
the percent impervious due to the inclusion of a landscaped parkway associated with the detached
sidewalk along S. Mason Street and Kensington Drive. The basin area increased slightly along S.
College Avenue, and since a wider sidewalk is required, the percent impervious did increase.
Historically, the runoff associated with the adjacent right-of-ways drain to street inlets within S.
Mason Street and S. College Avenue. An analysis was completed to review the impacts of the
required dedication of right-of-way. Slight increases in runoff are anticipated and due to the limited
change in runoff rates, improvements or adjustments to the existing right-of-way storm drain
infrastructure is not anticipated.
During a 100-yr storm event, S. Mason Street has an increase of 0.28 cfs, which drains to the inlet on
the east side of Mason, just north of the existing Mini-U-Storage site. Basin D4, associated with
Kensington Drive, and Basin D5, associated with S. College Avenue, drain to the existing inlet on S.
College Avenue (Design Point D5), just east of the existing Pedersen Toyota showroom. In
reference to the attenuated flows from Basin D4 and D5, draining to Design Point D5, there is an
increase of 0.22 cfs. This is 3% increase in the 100-yr storm runoff rate and is considered negligible.
The current onsite drainage infrastructure was designed referencing the pre-1997 rainfall data and the
proposed improvements associated with the redevelopment of the Mini-U-Storage and Pedersen
Toyota site will improve the performance of the site drainage, including incorporation of the new
rainfall data, and should satisfy the City’s storm drainage criteria.
All calculations and exhibits are attached for reference.
DETENTION VARIANCE
This letter will constitute a request for variance of the current design criteria which discourages the
use of underground detention methods. The western portion of the site will be treated via an
Extended Detention Basin with a soft pond bottom to satisfy Low Impact Development criteria.
However, the eastern portion of the site will remain generally in its current developed site
configuration thus requiring the use of an underground detention system to provide stormwater
quantity measures.
The system proposed includes a combination of pervious paver storage, surface ponding, and a series
of underground chambers to provide the remainder of the required storage volume. The underground
portion of the system currently shown consists of 600 lineal feet of 4’x 6’ Reinforced Concrete Box
Culvert (RCBC). As noted in the narrative above, additional configurations and pipe sizes are being
evaluated and further detail will be provided with the final engineering documents.
There are several key design considerations to be evaluated when utilizing underground storage
systems:
• Access point(s) for maintenance at inlet and outlet structures
Pedersen Toyota – Preliminary Storm Drainage Report
August 6, 2014
Page 4 of 5
o The proposed system will include multiple manhole access locations for monitoring
and regular maintenance purposes
o Access openings may consist of a standard frame, grate and solid cover, or a
removable panel
o The minimum pipe diameter shall be 36 inches
• Systems shall be downstream of water quality BMPs (Pre-treatment required)
o The proposed system will incorporate inlets Snouts/Sumps to separate larger debris
and sediment particles and provide maintenance access locations
o A pervious paver system will be utilized upstream or in conjunction with the
underground system
• Regular maintenance of the system is required
o Standard Operating Procedures (SOPs) will be provided to define the regular and
long term maintenance considerations for the systems.
o Debris shall be removed from inlet and outlet structures
o Sediment accumulation shall be monitored regularly
o Sediment and floatable debris will be removed using catch basin cleaning equipment
(vacuum pumps, etc.)
o The system will be privately owned and maintained
o The system will be placed within a city recorded Drainage Easement
• Runoff Controls
o An orifice plate structure will be provided in the downstream end of the system to
control the release rate from the system
o An emergency spillway / control weir will be provided for events larger than the 100-
year design storm
LOW IMPACT DEVELOPMENT TECHNIQUES
In reference to the code requirements for implementation of Low Impact Development (LID)
techniques, we have looked at many options, along with the site redevelopment constraints, to satisfy
these requirements. An extended detention basin (EDB), which is considered “somewhat” of a LID
technique per Urban Drainage, is proposed to be located in the northwest corner of the site and will
treat and detain runoff from Basin D1. To enhance the LID characteristics of the EDB, it is proposed
to incorporate a soft bottom pond that will promote filtration through a drainage filter/growing media
section and ground infiltration. The runoff from Basin D2 is proposed to satisfy the LID
requirements through the use of permeable pavers and Snouts installed into each inlet contributing to
the underground detention structure. Underdrains, clean-outs, and a Standard Operations Procedure
will be provided at final design to assist in ensuring that these BMPs will adequately perform over
time.
EROSION CONTROL
Erosion and sedimentation will be controlled on-site by use of silt fences, culvert inlet protection, a
gravel construction entrance, and seeding and mulch. 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.
Pedersen Toyota – Preliminary Storm Drainage Report
August 6, 2014
Page 5 of 5
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 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.
Thank you in advance for your time and if you have any questions or comments please contact me at
(970) 674-3300 extension 8917.
Sincerely,
Jason T. Claeys, P.E., LEED AP
Interwest Consulting Group
Attachments
Site Descriptions,
Characteristics & References
Hydrologic Soil Group—Larimer County Area, Colorado
(Pedersen Toyota)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
3/27/2014
Page 1 of 4
4486030 4486050 4486070 4486090 4486110 4486130 4486150 4486170 4486190
4486030 4486050 4486070 4486090 4486110 4486130 4486150 4486170 4486190
493240 493260 493280 493300 493320 493340 493360 493380 493400 493420 493440 493460 493480
493240 493260 493280 493300 493320 493340 493360 493380 493400 493420 493440 493460 493480
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: 1:1,210 if printed on A landscape (11" x 8.5") sheet.
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: 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
the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Hydrologic Soil Group
Hydrologic Soil Group— Summary by Map Unit — Larimer County Area, Colorado (CO644)
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 18.7%
4 Altvan-Satanta loams, 3
to 9 percent slopes
B 3.8 62.9%
74 Nunn clay loam, 1 to 3
percent slopes
C 1.1 18.4%
Totals for Area of Interest 6.1 100.0%
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
3/27/2014
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
3/27/2014
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.
Pedersen Toyota
DRAINAGE SUMMARY
Design Engineer:
Design Firm:
Project Number:
Date:
IMPERVIOUS SUMMARY:
Description
%
Impervious
Existing 81.8%
Proposed 72.3%
Difference -9.4%
DRAINAGE SUMMARY:
Area
(acres)
%
Imprevious
100-yr Peak
Runoff (cfs)
Area
(acres)
%
Imprevious
100-yr Peak
Runoff (cfs)
H1/D1 2.08 82.3% 11.23 1.66 75.7% 9.22 -2.02 Ex Mini-U-Storage
H2/D2 2.68 87.2% 16.06 2.93 79.7% 16.70 0.63 Ex Pedersen Toyota
H3/D3 0.34 92.8% 2.33 0.54 58.4% 2.61 0.28 S. Mason Street
H4/D4 0.33 83.5% 2.25 0.42 72.4% 2.67 0.42 Kensington Drive
H5/D5 0.83 74.6% 4.91 0.84 77.1% 4.98 0.07 S. College Avenue
H6/D6 0.18 39.8% 0.81 0.04 0.0% 0.16 -0.64 North Offiste
Totals 6.44 81.8% 37.60 6.44 72.3% 36.34 -1.26
H4&H5/D4&D5 1.16 77.1% 7.10 1.27 75.5% 7.32 0.22 College & Kensington
Basins Notes
Historical Proposed Hist vs. Dev
Peak Runoff
Difference
J.Claeys
Interwest Consulting Group
1180-027-00
May 28, 2014
SOUTH COLLEGE AVENUE (HWY 287)
KENSINGTON DRIVE
SOUTH MASON STREET
PREPARED FOR
PROJ. NO.
DATE:
SCALE (H):
SCALE (V):
CHECKED BY:
DESIGNED BY:
PROJECT NAME
PEDERSEN TOYOTA
EXISTING DRAINAGE EXHIBIT
05/28/14
1"=60'
N/A
JTC
RA
1180-027-00
1 of 2
SCALE 1" =
0
60'
30 60
LEGEND
BASIN LABEL
DESIGN POINT
BASIN BOUNDARY
FLOW PATH
Pedersen Toyota
HISTORIC IMPERVIOUS AREA CALCULATION
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised April 2008)
BASINS:
C2 C5 C10 C100 C2 C5 C10 C100
0.89 0.90 0.92 0.96 0.89 0.90 0.92 0.96
0.71 0.73 0.75 0.81 0.73 0.75 0.77 0.83
0.71 0.73 0.75 0.81 0.73 0.75 0.77 0.83
0.23 0.30 0.36 0.50 0.28 0.35 0.42 0.58
0.02 0.08 0.15 0.35 0.04 0.15 0.25 0.50
C2 C5 C10 C100
H1 C 90,711 2.08 37,981 40,789 0 0 11,941 82.3% 0.62 0.65 0.69 0.76
H2 C 116,796 2.68 79,480 24,481 422 0 12,414 87.2% 0.69 0.71 0.74 0.81
H3 C 14,677 0.34 13,626 0 0 0 1,051 92.8% 0.77 0.78 0.81 0.87
H4 C 14,428 0.33 12,054 0 0 0 2,374 83.5% 0.64 0.66 0.70 0.77
H5 C 36,307 0.83 24,523 0 2,836 0 8,948 74.6% 0.54 0.57 0.61 0.71
H6 C 7,818 0.18 0 3,457 0 0 4,361 39.8% 0.28 0.35 0.42 0.58
Total - 280,737 6.44 167,664 68,726 3,257 0 41,089 81.8% 0.62 0.64 0.68 0.76
H4 & H5 C 50,735 1.16 36,577 0 2,836 0 11,322 77.1% 0.56 0.60 0.63 0.72
Pavers 40%
J.Claeys
Interwest Consulting Group
1180-027-00
May 28, 2014
% Impervious values from Table RO-3 in the Urban Storm Drainage Criteria Manual for Hydrologic Soil Classifications
Land Use % Impervious
Hydrologic Soil
Classification B
Runoff Coefficient
Hydrologic Soil
Classification C
Runoff Coefficient
Roof 90%
Walk 90%
Paved 100%
Lawns, clayey soil 0%
Sub-basin
Designation
Soil
Type
Atotal
(sq feet)
Atotal
(acres)
Apaved
(sq feet)
Aroof
(sq feet)
Awalk
(sq feet)
Apavers
(sq feet)
Alawn
(sq feet)
Weighted %
Pedersen Toyota
HISTORIC TIME OF CONCENTRATION
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised April 2008)
EQUATIONS:
-Equation RO-3 -Equation RO-4 -Urbanized Check Equation RO-5
-Equation RO-3
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 tc = 5 min for urbanized basins
BASINS:
Type of Travel
Surface
Cv
H1 H1 0.65 2.08 120 0.0288 6.35 477 0.0044 Paved Areas 20 1.33 6.00 12.34 13.32 12.34
H2 H2 0.71 2.68 176 0.0203 7.50 391 0.0086 Paved Areas 20 1.86 3.51 11.01 13.15 11.01
H3 H3 0.78 0.34 49 0.0170 3.40 451 0.0042 Paved Areas 20 1.29 5.81 9.21 12.78 9.21
H4 H4 0.66 0.33 49 0.0251 4.11 427 0.0158 Paved Areas 20 2.52 2.83 6.94 12.64 6.94
H5 H5 0.57 0.83 44 0.0225 4.92 295 0.0061 Paved Areas 20 1.56 3.15 8.08 11.89 8.08
H6 H6 0.35 0.18 137 0.0446 9.80 47 0.0268 Paved Areas 20 3.27 0.24 10.04 11.02 10.04
H5 H4 & H5 0.60 1.16 44 0.0225 4.70 295 0.0061 Paved Areas 20 1.56 3.15 7.85 11.89 7.85
REMARKS
tc Urban
Check
Final tc
(min)
tc=ti+tt
SLOPE (min)
(ft/ft)
VEL.
(ft/s)
tt (min)
SLOPE
(ft/ft)
ti (min)
LENGTH Table RO-2
(ft)
TRAVEL TIME (tt)
DESIGN
POINT
Sub-basin C5
AREA
(acres)
LENGTH
(ft)
SUB-BASIN DATA
INITIAL/OVERLAND
TIME (ti)
J.Claeys
Interwest Consulting Group
1180-027-00
May 28, 2014
( )
0 .33
Pedersen Toyota
HISTORIC PEAK RUNOFF
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised April 2008)
EQUATIONS:
Q n = n-yr peak discharge (cfs) I = rainfall intensity (in/hr)
C n = n -yr runoff coefficient P 1 = one-hour point rainfall depth (in)
I n = n -yr rainfall intensity (in/hr) t c = time of concentration (min)
A n = Basin drainage area (ac) P 1-2yr = 0.82 in
P 1-5yr = 1.14 in
P 1-10yr = 1.40 in
P 1-100yr = 2.86 in
BASINS:
Runoff Coeff.
(C2)
C(A)
(acres)
Intensity
(in/hr)
Q (ft3/s)
Runoff Coeff.
(C5)
C(A)
(acres)
Intensity
(in/hr)
Q (ft3/s)
Runoff Coeff.
(C10)
C(A)
(acres)
Intensity
(in/hr)
Q (ft3/s)
Runoff Coeff.
(C100)
C(A)
(acres)
Intensity
(in/hr)
Q (ft3/s)
H1 H1 2.08 12.34 0.62 1.30 2.03 2.63 0.65 1.36 2.82 3.82 0.69 1.43 3.46 4.94 0.76 1.59 7.08 11.23
H2 H2 2.68 11.01 0.69 1.84 2.13 3.92 0.71 1.90 2.96 5.63 0.74 1.98 3.64 7.21 0.81 2.16 7.43 16.06
H3 H3 0.34 9.21 0.77 0.26 2.29 0.59 0.78 0.26 3.18 0.84 0.81 0.27 3.90 1.07 0.87 0.29 7.97 2.33
H4 H4 0.33 6.94 0.64 0.21 2.52 0.53 0.66 0.22 3.51 0.77 0.70 0.23 4.31 1.00 0.77 0.26 8.80 2.25
H5 H5 0.83 8.08 0.54 0.45 2.40 1.07 0.57 0.48 3.33 1.59 0.61 0.51 4.09 2.09 0.71 0.59 8.36 4.91
H6 H6 0.18 10.04 0.28 0.05 2.21 0.11 0.35 0.06 3.07 0.19 0.42 0.07 3.77 0.28 0.58 0.10 7.71 0.81
Total 6.44 8.86 12.85 16.59 37.60
H5 H4 & H5 1.16 7.85 0.56 0.66 2.42 1.59 0.60 0.69 3.37 2.34 0.63 0.74 4.13 3.05 0.72 0.84 8.45 7.10
5-yr Peak Runoff 100-yr Peak Runoff
J.Claeys
Interwest Consulting Group
1180-027-00
May 28, 2014
Design
Point
SOUTH COLLEGE AVENUE (HWY 287)
KENSINGTON DRIVE
SOUTH MASON STREET
PREPARED FOR
PROJ. NO.
DATE:
SCALE (H):
SCALE (V):
CHECKED BY:
DESIGNED BY:
PROJECT NAME
PEDERSEN TOYOTA
PROPOSED DRAINAGE EXHIBIT
08/06/14
1"=60'
N/A
JTC
RA
1180-027-00
2 of 2
SCALE 1" =
0
60'
30 60
LEGEND
BASIN LABEL
DESIGN POINT
BASIN BOUNDARY
FLOW PATH
Pedersen Toyota
DEVELOPED IMPERVIOUS AREA CALCULATION
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised April 2008)
BASINS:
C2 C5 C10 C100 C2 C5 C10 C100
0.89 0.90 0.92 0.96 0.89 0.90 0.92 0.96
0.71 0.73 0.75 0.81 0.73 0.75 0.77 0.83
0.71 0.73 0.75 0.81 0.73 0.75 0.77 0.83
0.23 0.30 0.36 0.50 0.28 0.35 0.42 0.58
0.02 0.08 0.15 0.35 0.04 0.15 0.25 0.50
C2 C5 C10 C100
D1 C 72,461 1.66 11,744 47,266 634 0 12,817 75.7% 0.55 0.58 0.62 0.71
D2 C 127,738 2.93 61,837 37,158 953 14,053 13,737 79.7% 0.59 0.62 0.66 0.74
D3 C 23,708 0.54 11,498 0 2,613 0 9,596 58.4% 0.39 0.45 0.50 0.63
D4 C 18,447 0.42 11,677 0 1,857 0 4,913 72.4% 0.51 0.55 0.59 0.69
D5 C 36,762 0.84 24,628 0 4,114 0 8,020 77.1% 0.56 0.60 0.63 0.72
D6 C 1,604 0.04 0 0 0 0 1,604 0.0% 0.04 0.15 0.25 0.50
Total - 280,720 6.44 121,384 84,425 10,172 14,053 50,686 72.3% 0.51 0.55 0.59 0.69
D4 & D5 C 55,209 1.27 36,305 0 5,971 0 12,933 75.5% 0.55 0.58 0.62 0.71
J.Claeys
Interwest Consulting Group
1180-027-00
May 28, 2014
% Impervious values from Table RO-3 in the Urban Storm Drainage Criteria Manual for Hydrologic Soil Classifications
Sub-basin
Designation
Apaved
(sq feet)
Atotal
(acres)
Atotal
(sq feet)
Soil
Type
Land Use % Impervious
Hydrologic Soil
Classification B
Runoff Coefficient
Hydrologic Soil
Classification C
Runoff Coefficient
Paved 100%
Roof 90%
COMPOSITE
Weighted %
Impervious
Alawn
(sq feet)
Apavers
(sq feet)
Lawns, clayey soil
Awalk
(sq feet)
Aroof
(sq feet)
Pedersen Toyota
DEVELOPED TIME OF CONCENTRATION
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised April 2008)
EQUATIONS:
-Equation RO-3 -Equation RO-4 -Urbanized Check Equation RO-5
-Equation RO-3
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 tc = 5 min for urbanized basins
BASINS:
Type of Travel
Surface
Cv
D1 D1 0.58 1.66 50 0.0100 6.72 456 0.0150 Paved Areas 20 2.45 3.10 9.82 12.81 9.82
D2 D2 0.62 2.93 153 0.0432 6.65 418 0.0101 Paved Areas 20 2.01 3.47 10.12 13.17 10.12
D3 D3 0.45 0.54 45 0.0323 5.46 422 0.0053 Paved Areas 20 1.46 4.83 10.29 12.60 10.29
D4 D4 0.55 0.42 34 0.0474 3.49 408 0.0162 Paved Areas 20 2.55 2.67 6.16 12.46 6.16
D5 D5 0.60 0.84 37 0.0146 4.96 301 0.0048 Paved Areas 20 1.38 3.64 8.59 11.88 8.59
D6 D6 0.15 0.04 53 0.0638 6.86 52 0.0352 Paved Areas 20 3.75 0.23 7.09 10.58 7.09
D5 D4 & D5 0.58 1.27 37 0.0146 5.11 301 0.0048 Paved Areas 20 1.38 3.64 8.74 11.88 8.74
J.Claeys
Interwest Consulting Group
1180-027-00
May 28, 2014
SLOPE
(ft/ft)
ti (min)
LENGTH Table RO-2
(ft)
SUB-BASIN DATA
INITIAL/OVERLAND
TIME (ti)
DESIGN
POINT
Sub-basin C5
AREA
(acres)
LENGTH
(ft)
TRAVEL TIME (tt)
REMARKS
tc Urban
Check
Final tc
(min)
tc=ti+tt
SLOPE (min)
(ft/ft)
VEL.
(ft/s)
tt (min)
( )
0 .33
Pedersen Toyota
DEVELOPED PEAK RUNOFF
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised April 2008)
EQUATIONS:
Q n = n-yr peak discharge (cfs) I = rainfall intensity (in/hr)
C n = n -yr runoff coefficient P 1 = one-hour point rainfall depth (in)
I n = n -yr rainfall intensity (in/hr) t c = time of concentration (min)
A n = Basin drainage area (ac) P 1-2yr = 0.82 in
P 1-5yr = 1.14 in
P 1-10yr = 1.40 in
P 1-100yr = 2.86 in
BASINS:
Runoff Coeff.
(C2)
C(A)
(acres)
Intensity
(in/hr)
Q (ft3/s)
Runoff Coeff.
(C5)
C(A)
(acres)
Intensity
(in/hr)
Q (ft3/s)
Runoff Coeff.
(C10)
C(A)
(acres)
Intensity
(in/hr)
Q (ft3/s)
Runoff Coeff.
(C100)
C(A)
(acres)
Intensity
(in/hr)
Q (ft3/s)
D1 D1 1.66 9.82 0.55 0.91 2.23 2.03 0.58 0.97 3.10 3.00 0.62 1.03 3.81 3.94 0.71 1.19 7.78 9.22
D2 D2 2.93 10.12 0.59 1.73 2.20 3.82 0.62 1.82 3.06 5.59 0.66 1.93 3.76 7.26 0.74 2.17 7.69 16.70
D3 D3 0.54 10.29 0.39 0.21 2.19 0.47 0.45 0.24 3.04 0.74 0.50 0.27 3.74 1.02 0.63 0.34 7.64 2.61
D4 D4 0.42 6.16 0.51 0.22 2.62 0.57 0.55 0.23 3.64 0.85 0.59 0.25 4.47 1.12 0.69 0.29 9.13 2.67
D5 D5 0.84 8.59 0.56 0.47 2.34 1.11 0.60 0.50 3.26 1.64 0.63 0.53 4.00 2.14 0.72 0.61 8.18 4.98
D6 D6 0.04 7.09 0.04 0.00 2.51 0.00 0.15 0.01 3.48 0.02 0.25 0.01 4.28 0.04 0.50 0.02 8.74 0.16
Total 6.44 8.01 11.83 15.52 36.34
D5 D4 & D5 1.27 8.74 0.55 0.69 2.33 1.61 0.58 0.74 3.24 2.38 0.62 0.79 3.98 3.12 0.71 0.90 8.13 7.32
100-yr Peak Runoff
J.Claeys
Interwest Consulting Group
1180-027-00
May 28, 2014
10-yr Peak Runoff
Design
Detention Calculations
Pedersen Toyota
Pond Summary (Basin D1)
Design Engineer:
Design Firm:
Project Number:
Date:
Pond Summary Table
0.05
5030.04
16.74
4 3/16
0.88
0.32
5033.02
J.Claeys
Interwest Consulting Group
2598.1
May 28, 2014
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)
1180-027-00 PondCalcs.xls - Pond Summary Page 1 of 4 Interwest Consulting Group
Project:
Basin ID:
Design Information (Input): Design Information (Input):
Catchment Drainage Imperviousness Ia = 75.70 percent Catchment Drainage Imperviousness I
a = 75.70 percent
Catchment Drainage Area A = 1.660 acres Catchment Drainage Area A = 1.660 acres
Predevelopment NRCS Soil Group Type = C A, B, C, or D Predevelopment NRCS Soil Group Type = C A, B, C, or D
Return Period for Detention Control T = 2 years (2, 5, 10, 25, 50, or 100) Return Period for Detention Control T = 100 years (2, 5, 10, 25, 50, or 100)
Time of Concentration of Watershed Tc = 10 minutes Time of Concentration of Watershed Tc = 10 minutes
Allowable Unit Release Rate q = 0.53 cfs/acre Allowable Unit Release Rate q = 0.53 cfs/acre
One-hour Precipitation P1 = 0.82 inches One-hour Precipitation P
1 = 2.86 inches
Design Rainfall IDF Formula i = C1* P
1/(C2
+Tc)^C
3 Design Rainfall IDF Formula i = C1
* P1/(C
2+Tc
)^C3
Coefficient One C1 = 28.50 Coefficient One C
1 = 28.50
Coefficient Two C2 = 10 Coefficient Two C
2 = 10
Coefficient Three C3 = 0.787 Coefficient Three C
3 = 0.787
Determination of Average Outflow from the Basin (Calculated): Determination of Average Outflow from the Basin (Calculated):
Runoff Coefficient C = 0.55 Runoff Coefficient C = 0.71
Inflow Peak Runoff Qp-in = 2.04 cfs Inflow Peak Runoff Qp-in = 9.17 cfs
Allowable Peak Outflow Rate Qp-out = 0.88 cfs Allowable Peak Outflow Rate Qp-out = 0.88 cfs
Mod. FAA Minor Storage Volume = 1,060 cubic feet Mod. FAA Major Storage Volume = 11,743 cubic feet
Mod. FAA Minor Storage Volume = 0.024 acre-ft Mod. FAA Major Storage Volume = 0.270 acre-ft
15 <- Enter Rainfall Duration Incremental Increase Value Here (e.g. 5 for 5-Minutes)
Rainfall Rainfall Inflow Adjustment Average Outflow Storage Rainfall Rainfall Inflow Adjustment Average Outflow Storage
Duration Intensity Volume Factor Outflow Volume Volume Duration Intensity Volume Factor Outflow Volume Volume
minutes inches / hr acre-feet "m" cfs acre-feet acre-feet minutes inches / hr acre-feet "m" cfs acre-feet acre-feet
(input) (output) (output) (output) (output) (output) (output) (input) (output) (output) (output) (output) (output) (output)
5 2.78 0.017 1.00 0.88 0.006 0.011 5 9.68 0.079 1.00 0.88 0.006 0.073
20 1.61 0.040 0.75 0.66 0.018 0.022 20 5.61 0.182 0.75 0.66 0.018 0.164
35 1.17 0.051 0.64 0.56 0.027 0.024 35 4.08 0.232 0.64 0.56 0.027 0.205
50 0.93 0.059 0.60 0.53 0.036 0.022 50 3.25 0.264 0.60 0.53 0.036 0.228
65 0.78 0.064 0.58 0.51 0.045 0.019 65 2.73 0.288 0.58 0.51 0.045 0.243
80 0.68 0.068 0.56 0.49 0.054 0.014 80 2.37 0.307 0.56 0.49 0.054 0.253
95 0.60 0.072 0.55 0.49 0.064 0.008 95 2.10 0.323 0.55 0.49 0.064 0.260
110 0.54 0.075 0.54 0.48 0.073 0.002 110 1.89 0.337 0.54 0.48 0.073 0.264
125 0.49 0.077 0.54 0.47 0.082 -0.004 125 1.72 0.349 0.54 0.47 0.082 0.267
140 0.45 0.080 0.54 0.47 0.091 -0.011 140 1.58 0.360 0.54 0.47 0.091 0.269
155 0.42 0.082 0.53 0.47 0.100 -0.018 155 1.47 0.369 0.53 0.47 0.100 0.270
170 0.39 0.084 0.53 0.47 0.109 -0.025 170 1.37 0.378 0.53 0.47 0.109 0.269
185 0.37 0.086 0.53 0.46 0.118 -0.032 185 1.29 0.387 0.53 0.46 0.118 0.269
200 0.35 0.088 0.52 0.46 0.127 -0.040 200 1.21 0.394 0.52 0.46 0.127 0.267
215 0.33 0.089 0.52 0.46 0.136 -0.047 215 1.15 0.402 0.52 0.46 0.136 0.265
230 0.31 0.091 0.52 0.46 0.145 -0.055 230 1.09 0.408 0.52 0.46 0.145 0.263
245 0.30 0.092 0.52 0.46 0.154 -0.062 245 1.04 0.415 0.52 0.46 0.154 0.260
260 0.29 0.093 0.52 0.46 0.164 -0.070 260 1.00 0.421 0.52 0.46 0.164 0.257
275 0.27 0.095 0.52 0.46 0.173 -0.078 275 0.96 0.426 0.52 0.46 0.173 0.254
290 0.26 0.096 0.52 0.45 0.182 -0.086 290 0.92 0.432 0.52 0.45 0.182 0.250
305 0.25 0.097 0.52 0.45 0.191 -0.094 305 0.88 0.437 0.52 0.45 0.191 0.246
320 0.24 0.098 0.52 0.45 0.200 -0.102 320 0.85 0.442 0.52 0.45 0.200 0.242
335 0.24 0.099 0.51 0.45 0.209 -0.110 335 0.82 0.447 0.51 0.45 0.209 0.238
350 0.23 0.100 0.51 0.45 0.218 -0.118 350 0.79 0.452 0.51 0.45 0.218 0.234
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 1.66 acres
Composite. Imperviousness, I 75.7%
WQCV (watershed inches) 0.303 inches 40-Hour Drain Time (Fig SQ-2)
Required WQCV 0.050 acre-feet Including 20% for Sedimentation
WATER QUALITY OUTLET SIZING (Per USDCM, Volume 3):
Design Water Quality Depth, DWQ
1.29 ft
Determine K40
K40
= 0.013DWQ
2
+ 0.22DWQ
- 0.10 0.206
Maximum Area per Row, a a = WQCV / K40
0.245 square inches
Number of Rows, nr 3 rows
Number of Columns, nc (See Table 6a-1 for Max.) 1 columns
Choose Hole Diameter 1/2 inches
Use USDCM Volume 3, Figure 5 0.500 inches
Total Area per Row, Ao
0.20 square inches
Total Outlet Area, Aot
0.59 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
May 28, 2014
* * 1 . 2
12
Area
WQCV
Volume
=
1180-027-00 PondCalcs.xls - WQCV & Outlet Structure Page 2 of 4 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
May 28, 2014
WATER QUALITY TRASH RACK SIZING (Per USDCM, Volume 3)
Required Open Area, At
At
=0.5*[77(e
-0.124D
)]*Aot
21 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
15 8/16 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.xls - WQCV & Outlet Structure Page 3 of 4 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)
5028.75 0.000 0.000 0.00 0.000
5029.0 1546 0.035 0.003 0.25 0.003
5030.0 2382 0.055 0.045 1.25 0.048
5031.0 3338 0.077 0.065 2.25 0.113
5032.0 4418 0.101 0.089 3.25 0.202
5033.0 5670 0.130 0.115 4.25 0.317
5034.0 6518 0.150 0.140 5.25 0.457
0.05 5030.04 ft
0.32 5033.02 ft
J.Claeys
Interwest Consulting Group
1180-027-00
Acre-Ft Interpolates to an Elev. of
Acre-Ft Interpolates to an Elev. of
Required Water Quality Capture Volume =
Required 100-yr Detention Volume (including WQCV) =
May 28, 2014
5028.00
5029.00
5030.00
5031.00
5032.00
5033.00
5034.00
5035.00
0.0 0.1 0.2 0.3 0.4 0.5
ELEVATION (FT)
DETENTION POND VOLUME (AC-FT)
DETENTION POND VOLUME
VERSUS ELEVATION
( )
3
AAAADepth 1 2 1 2
V
+ +
=
1180-027-00 PondCalcs.xls - Pond Stage Storage Page 4 of 4 Interwest Consulting Group
Pedersen Toyota
Parking Lot Detention (Basin D2)
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, January 2010
Detention Volume
Required Detained Volume 22,909 cu-ft
Est Paver Detention 3,445 cu-ft 15% of Total Detention Volume
Est Parking lot Detention 6,000 cu-ft
Underground Detention (Dual RCB) 13,860 cu-ft
Total Detention Volume Supplied 23,305 cu-ft
Paver
Area 1
Paver
Area 2 RCB Height (ft) 4
Area (sqft) 2,829 4,071 RCB Width (ft) 6
Length (ft) 70.5 97 RCB Length (ft) 300
Width (ft) 40 40 RCB Slope 0.10%
Surface Longitudinal Slope 2.00% 2.00% Initial Invert Elevation (ft) 100
Subgrade Longitudinal Slope 0.50% 0.50% Final Invert Elevation (ft) 100.3
Initial Surface Elev (ft) 100 100 RCB Volume (cu-ft/pipe) 6,930
Initial Drainage Depth (ft) 1.5 1.5
Initial Drainage Elev (ft) 98.5 98.5
Final Surface Elev (ft) 101.41 101.94
Final Subgrade Elev (ft) 98.85 98.99
Final Drainage Depth (ft) 2.56 2.96
Drainage Voids 40% 40%
Detained Volume (cu-ft) 1,493 1,952
Total Paver Volume (cu-ft) 3,445
1180-027-00
August 6, 2014
Estimated Permeable Paver Detention Volume
Basin D2 Detention Volume Summary
Estimated Underground Detention Volume
J.Claeys
Interwest Consulting Group
Project:
Basin ID:
Design Information (Input): Design Information (Input):
Catchment Drainage Imperviousness Ia = 79.70 percent Catchment Drainage Imperviousness I
a = 79.70 percent
Catchment Drainage Area A = 2.930 acres Catchment Drainage Area A = 2.930 acres
Predevelopment NRCS Soil Group Type = C A, B, C, or D Predevelopment NRCS Soil Group Type = C A, B, C, or D
Return Period for Detention Control T = 2 years (2, 5, 10, 25, 50, or 100) Return Period for Detention Control T = 100 years (2, 5, 10, 25, 50, or 100)
Time of Concentration of Watershed Tc = 10 minutes Time of Concentration of Watershed Tc = 10 minutes
Allowable Unit Release Rate q = 0.47 cfs/acre Allowable Unit Release Rate q = 0.47 cfs/acre
One-hour Precipitation P1 = 0.82 inches One-hour Precipitation P
1 = 2.86 inches
Design Rainfall IDF Formula i = C1* P
1/(C2
+Tc)^C
3 Design Rainfall IDF Formula i = C1
* P1/(C
2+Tc
)^C3
Coefficient One C1 = 28.50 Coefficient One C
1 = 28.50
Coefficient Two C2 = 10 Coefficient Two C
2 = 10
Coefficient Three C3 = 0.787 Coefficient Three C
3 = 0.787
Determination of Average Outflow from the Basin (Calculated): Determination of Average Outflow from the Basin (Calculated):
Runoff Coefficient C = 0.59 Runoff Coefficient C = 0.74
Inflow Peak Runoff Qp-in = 3.81 cfs Inflow Peak Runoff Qp-in = 16.67 cfs
Allowable Peak Outflow Rate Qp-out = 1.38 cfs Allowable Peak Outflow Rate Qp-out = 1.38 cfs
Mod. FAA Minor Storage Volume = 2,379 cubic feet Mod. FAA Major Storage Volume = 22,909 cubic feet
Mod. FAA Minor Storage Volume = 0.055 acre-ft Mod. FAA Major Storage Volume = 0.526 acre-ft
15 <- Enter Rainfall Duration Incremental Increase Value Here (e.g. 5 for 5-Minutes)
Rainfall Rainfall Inflow Adjustment Average Outflow Storage Rainfall Rainfall Inflow Adjustment Average Outflow Storage
Duration Intensity Volume Factor Outflow Volume Volume Duration Intensity Volume Factor Outflow Volume Volume
minutes inches / hr acre-feet "m" cfs acre-feet acre-feet minutes inches / hr acre-feet "m" cfs acre-feet acre-feet
(input) (output) (output) (output) (output) (output) (output) (input) (output) (output) (output) (output) (output) (output)
5 2.78 0.033 1.00 1.38 0.010 0.024 5 9.68 0.145 1.00 1.38 0.010 0.135
20 1.61 0.077 0.75 1.04 0.029 0.048 20 5.61 0.335 0.75 1.04 0.029 0.307
35 1.17 0.098 0.64 0.89 0.043 0.055 35 4.08 0.427 0.64 0.89 0.043 0.384
50 0.93 0.111 0.60 0.83 0.057 0.054 50 3.25 0.486 0.60 0.83 0.057 0.429
65 0.78 0.121 0.58 0.80 0.071 0.050 65 2.73 0.530 0.58 0.80 0.071 0.459
80 0.68 0.129 0.56 0.78 0.086 0.044 80 2.37 0.565 0.56 0.78 0.086 0.479
95 0.60 0.136 0.55 0.76 0.100 0.036 95 2.10 0.594 0.55 0.76 0.100 0.495
110 0.54 0.142 0.55 0.75 0.114 0.027 110 1.89 0.620 0.55 0.75 0.114 0.506
125 0.49 0.147 0.54 0.75 0.128 0.018 125 1.72 0.642 0.54 0.75 0.128 0.513
140 0.45 0.151 0.54 0.74 0.143 0.009 140 1.58 0.662 0.54 0.74 0.143 0.519
155 0.42 0.155 0.53 0.74 0.157 -0.002 155 1.47 0.680 0.53 0.74 0.157 0.523
170 0.39 0.159 0.53 0.73 0.171 -0.012 170 1.37 0.696 0.53 0.73 0.171 0.525
185 0.37 0.163 0.53 0.73 0.185 -0.023 185 1.29 0.711 0.53 0.73 0.185 0.526
200 0.35 0.166 0.53 0.72 0.200 -0.034 200 1.21 0.725 0.53 0.72 0.200 0.526
215 0.33 0.169 0.52 0.72 0.214 -0.045 215 1.15 0.739 0.52 0.72 0.214 0.525
230 0.31 0.172 0.52 0.72 0.228 -0.057 230 1.09 0.751 0.52 0.72 0.228 0.523
245 0.30 0.174 0.52 0.72 0.242 -0.068 245 1.04 0.763 0.52 0.72 0.242 0.520
260 0.29 0.177 0.52 0.72 0.257 -0.080 260 1.00 0.774 0.52 0.72 0.257 0.517
275 0.27 0.179 0.52 0.72 0.271 -0.092 275 0.96 0.785 0.52 0.72 0.271 0.514
290 0.26 0.182 0.52 0.71 0.285 -0.104 290 0.92 0.795 0.52 0.71 0.285 0.509
305 0.25 0.184 0.52 0.71 0.300 -0.116 305 0.88 0.804 0.52 0.71 0.300 0.505
320 0.24 0.186 0.52 0.71 0.314 -0.128 320 0.85 0.813 0.52 0.71 0.314 0.500
335 0.24 0.188 0.52 0.71 0.328 -0.140 335 0.82 0.822 0.52 0.71 0.328 0.494
350 0.23 0.190 0.51 0.71 0.342 -0.152 350 0.79 0.831 0.51 0.71 0.342 0.489
SNOUT - TSS Removal
(for reference)
SUBJECT: SUSPENDED SOLIDS REMOVAL
The SNOUT system will have a positive impact on the reduction of suspended solids.
The total efficiency of removal will vary depending on the nature of the solids
found in the stormwater runoff and the size distribution of those solids as typified by the
native sediment and soils.
As is the case in all stormwater quality improvement designs,
the largest particles will be most easily removed and the smaller particles are more likely
to stay suspended. Without a detailed analysis of the type and size of the suspended
solids entrained in any
given storm flow, and the exact parameters of any given installation, the total percent
removal is difficult if not impossible to estimate.
However, according to generally accepted engineering practices, the range of theoretical
solids reductions will vary widely. For a single SNOUT equipped inlet with a deep sump
and proper maintenance, suspended solids removals from 30 to over 50 percent have
been shown. Given favorable site conditions, proper maintenance and a multiple
structure treatment train, up to 89.5 percent removals could be possible.
Please contact Best Management Products, Inc. if you have further questions.
MD Office: Ph. (800) 504-8008 Fax (410) 687-6757 ♦ CT Office: Ph. (860)
434-0277 Fax (860) 434-3195
www.bmpinc.com
Conservatively
estimating 40% TSS
removal
365 0.22 0.192 0.51 0.71 0.357 -0.165 365 0.77 0.839 0.51 0.71 0.357 0.483
380 0.21 0.194 0.51 0.71 0.371 -0.177 380 0.75 0.847 0.51 0.71 0.371 0.476
395 0.21 0.195 0.51 0.71 0.385 -0.190 395 0.72 0.855 0.51 0.71 0.385 0.470
410 0.20 0.197 0.51 0.71 0.399 -0.202 410 0.70 0.862 0.51 0.71 0.399 0.463
425 0.20 0.199 0.51 0.71 0.414 -0.215 425 0.68 0.869 0.51 0.71 0.414 0.456
440 0.19 0.200 0.51 0.71 0.428 -0.227 440 0.67 0.876 0.51 0.71 0.428 0.449
455 0.19 0.202 0.51 0.71 0.442 -0.240 455 0.65 0.883 0.51 0.71 0.442 0.441
470 0.18 0.203 0.51 0.70 0.456 -0.253 470 0.63 0.890 0.51 0.70 0.456 0.433
485 0.18 0.205 0.51 0.70 0.471 -0.266 485 0.62 0.896 0.51 0.70 0.471 0.426
500 0.17 0.206 0.51 0.70 0.485 -0.279 500 0.60 0.902 0.51 0.70 0.485 0.418
515 0.17 0.208 0.51 0.70 0.499 -0.291 515 0.59 0.909 0.51 0.70 0.499 0.409
530 0.17 0.209 0.51 0.70 0.513 -0.304 530 0.58 0.915 0.51 0.70 0.513 0.401
545 0.16 0.210 0.51 0.70 0.528 -0.317 545 0.57 0.920 0.51 0.70 0.528 0.393
560 0.16 0.212 0.51 0.70 0.542 -0.330 560 0.55 0.926 0.51 0.70 0.542 0.384
575 0.16 0.213 0.51 0.70 0.556 -0.343 575 0.54 0.932 0.51 0.70 0.556 0.376
590 0.15 0.214 0.51 0.70 0.570 -0.356 590 0.53 0.937 0.51 0.70 0.570 0.367
605 0.15 0.215 0.51 0.70 0.585 -0.369 605 0.52 0.942 0.51 0.70 0.585 0.358
620 0.15 0.217 0.51 0.70 0.599 -0.382 620 0.51 0.948 0.51 0.70 0.599 0.349
635 0.14 0.218 0.51 0.70 0.613 -0.395 635 0.50 0.953 0.51 0.70 0.613 0.340
650 0.14 0.219 0.51 0.70 0.627 -0.408 650 0.49 0.958 0.51 0.70 0.627 0.330
665 0.14 0.220 0.51 0.70 0.642 -0.422 665 0.48 0.963 0.51 0.70 0.642 0.321
680 0.14 0.221 0.51 0.70 0.656 -0.435 680 0.48 0.968 0.51 0.70 0.656 0.312
695 0.13 0.222 0.51 0.70 0.670 -0.448 695 0.47 0.972 0.51 0.70 0.670 0.302
710 0.13 0.223 0.51 0.70 0.684 -0.461 710 0.46 0.977 0.51 0.70 0.684 0.293
725 0.13 0.224 0.51 0.70 0.699 -0.474 725 0.45 0.982 0.51 0.70 0.699 0.283
740 0.13 0.225 0.51 0.70 0.713 -0.488 740 0.45 0.986 0.51 0.70 0.713 0.273
755 0.13 0.226 0.51 0.70 0.727 -0.501 755 0.44 0.991 0.51 0.70 0.727 0.263
770 0.12 0.227 0.51 0.70 0.741 -0.514 770 0.43 0.995 0.51 0.70 0.741 0.253
785 0.12 0.228 0.51 0.70 0.756 -0.527 785 0.43 0.999 0.51 0.70 0.756 0.244
800 0.12 0.229 0.51 0.70 0.770 -0.541 800 0.42 1.003 0.51 0.70 0.770 0.233
815 0.12 0.230 0.51 0.70 0.784 -0.554 815 0.41 1.008 0.51 0.70 0.784 0.223
830 0.12 0.231 0.51 0.70 0.798 -0.567 830 0.41 1.012 0.51 0.70 0.798 0.213
845 0.12 0.232 0.51 0.70 0.813 -0.581 845 0.40 1.016 0.51 0.70 0.813 0.203
860 0.11 0.233 0.51 0.70 0.827 -0.594 860 0.40 1.020 0.51 0.70 0.827 0.193
875 0.11 0.234 0.51 0.70 0.841 -0.607 875 0.39 1.024 0.51 0.70 0.841 0.182
890 0.11 0.235 0.51 0.70 0.856 -0.621 890 0.39 1.028 0.51 0.70 0.856 0.172
905 0.11 0.236 0.51 0.70 0.870 -0.634 905 0.38 1.031 0.51 0.70 0.870 0.162
Mod. FAA Minor Storage Volume (cubic ft.) = 2,379 Mod. FAA Major Storage Volume (cubic ft.) = 22,909
Mod. FAA Minor Storage Volume (acre-ft.) = 0.0546 Mod. FAA Major Storage Volume (acre-ft.) = 0.5259
Determination of MAJOR Detention Volume Using Modified FAA Method
(For catchments less than 160 acres only. For larger catchments, use hydrograph routing method)
(NOTE: for catchments larger than 90 acres, CUHP hydrograph and routing are recommended)
UDFCD DETENTION BASIN VOLUME ESTIMATING WORKBOOK Version 2.34, Released November 2013
Determination of MINOR Detention Volume Using Modified FAA Method
DETENTION VOLUME BY THE MODIFIED FAA METHOD
Petersen Toyota
D2
1180-027-00 Basin D2 Detention Volume - Existing Release Rate.xls, Modified FAA 5/27/2014, 8:19 PM
Existing Release Rate
Required Detention Volume
365 0.22 0.101 0.51 0.45 0.227 -0.126 365 0.77 0.456 0.51 0.45 0.227 0.229
380 0.21 0.102 0.51 0.45 0.236 -0.134 380 0.75 0.460 0.51 0.45 0.236 0.224
395 0.21 0.103 0.51 0.45 0.245 -0.142 395 0.72 0.465 0.51 0.45 0.245 0.219
410 0.20 0.104 0.51 0.45 0.254 -0.150 410 0.70 0.469 0.51 0.45 0.254 0.214
425 0.20 0.105 0.51 0.45 0.264 -0.159 425 0.68 0.473 0.51 0.45 0.264 0.209
440 0.19 0.106 0.51 0.45 0.273 -0.167 440 0.67 0.476 0.51 0.45 0.273 0.204
455 0.19 0.107 0.51 0.45 0.282 -0.175 455 0.65 0.480 0.51 0.45 0.282 0.198
470 0.18 0.107 0.51 0.45 0.291 -0.183 470 0.63 0.484 0.51 0.45 0.291 0.193
485 0.18 0.108 0.51 0.45 0.300 -0.192 485 0.62 0.487 0.51 0.45 0.300 0.187
500 0.17 0.109 0.51 0.45 0.309 -0.200 500 0.60 0.491 0.51 0.45 0.309 0.182
515 0.17 0.110 0.51 0.45 0.318 -0.208 515 0.59 0.494 0.51 0.45 0.318 0.176
530 0.17 0.110 0.51 0.45 0.327 -0.217 530 0.58 0.497 0.51 0.45 0.327 0.170
545 0.16 0.111 0.51 0.45 0.336 -0.225 545 0.57 0.500 0.51 0.45 0.336 0.164
560 0.16 0.112 0.51 0.45 0.345 -0.234 560 0.55 0.503 0.51 0.45 0.345 0.158
575 0.16 0.112 0.51 0.45 0.354 -0.242 575 0.54 0.506 0.51 0.45 0.354 0.152
590 0.15 0.113 0.51 0.45 0.364 -0.250 590 0.53 0.509 0.51 0.45 0.364 0.146
605 0.15 0.114 0.51 0.45 0.373 -0.259 605 0.52 0.512 0.51 0.45 0.373 0.140
620 0.15 0.114 0.51 0.45 0.382 -0.267 620 0.51 0.515 0.51 0.45 0.382 0.133
635 0.14 0.115 0.51 0.45 0.391 -0.276 635 0.50 0.518 0.51 0.45 0.391 0.127
650 0.14 0.116 0.51 0.45 0.400 -0.284 650 0.49 0.521 0.51 0.45 0.400 0.121
665 0.14 0.116 0.51 0.45 0.409 -0.293 665 0.48 0.523 0.51 0.45 0.409 0.114
680 0.14 0.117 0.51 0.45 0.418 -0.301 680 0.48 0.526 0.51 0.45 0.418 0.108
695 0.13 0.117 0.51 0.45 0.427 -0.310 695 0.47 0.529 0.51 0.45 0.427 0.101
710 0.13 0.118 0.51 0.45 0.436 -0.318 710 0.46 0.531 0.51 0.45 0.436 0.095
725 0.13 0.119 0.51 0.45 0.445 -0.327 725 0.45 0.534 0.51 0.45 0.445 0.088
740 0.13 0.119 0.51 0.45 0.454 -0.335 740 0.45 0.536 0.51 0.45 0.454 0.082
755 0.13 0.120 0.51 0.45 0.464 -0.344 755 0.44 0.538 0.51 0.45 0.464 0.075
770 0.12 0.120 0.51 0.45 0.473 -0.352 770 0.43 0.541 0.51 0.45 0.473 0.068
785 0.12 0.121 0.51 0.45 0.482 -0.361 785 0.43 0.543 0.51 0.45 0.482 0.061
800 0.12 0.121 0.51 0.45 0.491 -0.370 800 0.42 0.545 0.51 0.45 0.491 0.055
815 0.12 0.122 0.51 0.45 0.500 -0.378 815 0.41 0.548 0.51 0.45 0.500 0.048
830 0.12 0.122 0.51 0.45 0.509 -0.387 830 0.41 0.550 0.51 0.45 0.509 0.041
845 0.12 0.123 0.51 0.45 0.518 -0.395 845 0.40 0.552 0.51 0.45 0.518 0.034
860 0.11 0.123 0.51 0.45 0.527 -0.404 860 0.40 0.554 0.51 0.45 0.527 0.027
875 0.11 0.124 0.51 0.44 0.536 -0.413 875 0.39 0.556 0.51 0.44 0.536 0.020
890 0.11 0.124 0.51 0.44 0.545 -0.421 890 0.39 0.559 0.51 0.44 0.545 0.013
905 0.11 0.125 0.51 0.44 0.554 -0.430 905 0.38 0.561 0.51 0.44 0.554 0.006
Mod. FAA Minor Storage Volume (cubic ft.) = 1,060 Mod. FAA Major Storage Volume (cubic ft.) = 11,743
Mod. FAA Minor Storage Volume (acre-ft.) = 0.0243 Mod. FAA Major Storage Volume (acre-ft.) = 0.2696
Determination of MAJOR Detention Volume Using Modified FAA Method
(For catchments less than 160 acres only. For larger catchments, use hydrograph routing method)
(NOTE: for catchments larger than 90 acres, CUHP hydrograph and routing are recommended)
UDFCD DETENTION BASIN VOLUME ESTIMATING WORKBOOK Version 2.34, Released November 2013
Determination of MINOR Detention Volume Using Modified FAA Method
DETENTION VOLUME BY THE MODIFIED FAA METHOD
Petersen Toyota
D1
1180-027-00 Basin D1 Detention Volume - Existing Release Rate.xls, Modified FAA 5/27/2014, 8:20 PM
Existing Release Rate
Required Detention Volume
Point
Sub-basin Area (acres) tc (min)
2-yr Peak Runoff 5-yr Peak Runoff
Q n = C n I n A n
0.786
1
(10 )
28 . 5
t c
P
I
+
=
0 . 395 1 . 1 5
S
C L
ti
−
=
t c = t i + t t 0 . 5
V = C v S w 10
180
= +
L
tc
V
L
tt 60
=
0%
Pavers 40%
Walk 90%
Sub-basin Area (acres) tc (min)
2-yr Peak Runoff 10-yr Peak Runoff
Q n = C n I n A n
0.786
1
(10 )
28 . 5
t c
P
I
+
=
0 . 395 1 . 1 5
S
C L
ti
−
=
t c = t i + t t 0 . 5
V = C v S w 10
180
= +
L
tc
V
L
tt 60
=
Impervious
COMPOSITE
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
+
=
Survey Area Data: Version 8, Dec 23, 2013
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—Nov 18,
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.
Hydrologic Soil Group—Larimer County Area, Colorado
(Pedersen Toyota)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
3/27/2014
Page 2 of 4