HomeMy WebLinkAboutVILLAGE ON REDWOOD (FORT COLLINS HOUSING AUTHORITY) - FDP - FDP150036 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORTFINAL DRAINAGE REPORT
FOR
Village on Redwood
Prepared by:
Interwest Consulting Group
1218 West Ash, Suite A
Windsor, Colorado 80550
Phone: 970.674.3300
Fax: 970.674.3303
Prepared for:
Fort Collins Housing Authority
1715 West Mountain Ave.
Fort Collins, Colorado 80521
Phone: 970.416.2910
November 25, 2015
Job Number 1237-112-00
November 25, 2015
Mr. Wes Lamarque
Fort Collins Utilities
700 Wood Street
Fort Collins, CO 80522
RE: Final Drainage Report for Village on Redwood
Dear Wes,
We are pleased to submit for your review and approval, this Final Drainage Report for the
Village on Redwood low-income housing development. I certify that this report for the drainage
design was prepared in accordance with the criteria in the City of Fort Collins Storm Drainage
Manual.
I 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
1218 W. ASH, STE. A, WINDSOR, COLORADO 80550
TEL. 970.674.3300 – FAX 970.674.3303
TABLE OF CONTENTS
1. INTRODUCTION ................................................................................................................................................. 1
2. EXISTING CONDITIONS .................................................................................................................................... 1
3. DEVELOPED CONDITIONS ............................................................................................................................... 2
4. LOW IMPACT DEVELOPMENT TECHNIQUES .............................................................................................. 3
5. CONCLUSION ...................................................................................................................................................... 3
6. REFERENCES ...................................................................................................................................................... 4
APPENDIX A — SITE DESCRIPTIONS, CHARACTERISTICS & REFERENCES ........................................ A
APPENDIX B — RATIONAL CALCULATIONS .................................................................................................. B
APPENDIX C — STORM CONVEYANCE SIZING ............................................................................................. C
APPENDIX D — DETENTION POND CALCULATIONS ................................................................................... D
APPENDIX E — LOW IMPACT DEVELOPMENT CALCULATIONS ............................................................ E
1
1. INTRODUCTION
The project site currently is an undeveloped infill site located north of Nokomis Ct and
west of Redwood St. The site is 9.61 acres with approximately 3.0± acres being an
existing detention pond and approximately 6.6± acres of developable land. The property
will be subdivided into two lots, one containing the existing detention pond and the other
being the developed portion for low income housing. The project will consist of
constructing 12 low income housing buildings, a community clubhouse, and associated
pedestrian and vehicle accesses. This project will be completed in one phase of
construction.
2. EXISTING CONDITIONS
The project site is bound by Redwood St to the east and surrounded by previously
developed properties on the north, south, and west. The site is currently undeveloped and
appears to be vegetated with native grasses and wetland plants surrounding the existing
detention pond. The existing detention pond encompasses the western portion of the site.
Based on research of the site, it appears that this detention pond was constructed
sometime after 1975. The site is within the Dry Creek basin and within the basin limits
of the Northeast College Corridor Outfall (NECCO) improvements. The existing site is
approximately 2.7% impervious, including the west half of Redwood St. The existing
100-yr peak runoff rate to Redwood St (Basin H1) and to the existing detention pond
(Basin H2) is 14.10 cfs and 11.45 cfs, respectively. The runoff directed to Redwood St is
conveyed to and collected by an existing 15’ Type R inlet located near the southeast
corner of the site.
Upon further research of the surrounding storm drainage infrastructure, the design
drawings and calculations were found. Referencing the “Redwood Street Improvements”
plan set, dated September 1996 and prepared by Stewart & Associates, the existing storm
drain within Redwood Street was sized and constructed to convey the 100-yr developed
runoff from the proposed Village on Redwood site. The storm drain was anticipated to
capture and convey 33.5 cfs from the site during a 100-yr storm event. Since this site is
within the NECCO area plan, the site is constrained to matching the existing runoff rates
for the developed condition.
The existing runoff rates, stated above, are referenced for the stormwater release rates for
2
the proposed improvements. All calculations and exhibits are attached.
3. DEVELOPED CONDITIONS
The project proposes to develop this infill site with 12 low income housing buildings
(with a total of 72 units), a community clubhouse and associated infrastructure and
site/building pedestrian and vehicle access. The property will be subdivided into 2 lots,
one containing the existing detention pond and the remaining containing the proposed
low income housing development.
The project is required to detain the developed 100-yr runoff to the existing 100-yr runoff
rate. The detention requirements will be provided through the use of a detention pond in
the southeast corner of the site. Water quality capture volume and associated
infrastructure is not required as part of this project, though implementation of Low
Impact Development (LID) techniques for water quality enhancement are required and
proposed with this project.
Similar to the existing conditions, the proposed project is divided into two major basins,
one basin draining undetained to the existing detention pond to the west (Basin D7), and
the remaining basin draining towards Redwood St (Basins D1 thru D6). In general, the
basin limits are maintained for the areas draining to the existing detention pond and
towards Redwood Street. This causes a slight increase to the existing pond and is
considered negligible. Runoff from Basins D1 thru D5 are conveyed to the proposed
detention pond in the southeast corner of the site, with the outfall being the connection to
the existing storm drain within Redwood St. The undetained developed portion (Basin
D6) drains to the existing inlet within Redwood St. Under the developed condition, the
100-yr peak runoff rates to the existing detention pond and Redwood Street are estimated
to be 12.33 cfs and 26.57 cfs, respectively. Detaining the developed runoff to the
existing 100-yr runoff rate for the basin draining towards Redwood Street, in addition to
accounting for the undetained portions that drain directly to Redwood, requires a
detention volume of 0.402 acre-ft. The undetained portion has a runoff rate of 7.14 cfs,
combined with detention pond release rate of 6.96 cfs, has a peak 100-yr runoff rate of
14.10 cfs, equal to the existing 100-yr runoff rate.
The storm drain pipe sizes were determined utilizing Hydraflow. The storm drain system
has been designed to convey the 100-yr storm through a combination of the pipe and
overland flow. The grading design is such that when the hydraulic grade line exceeds the
3
pipe capacities at the inlets, the runoff will overtop the adjacent high point and convey
overland ultimately to the proposed detention pond.
The detention pond spillway will be a combination of overland and pipe emergency
overflow. The pond outlet structure and pipe are sized to handle majority of the 100-yr
runoff rate in the event that the 100-yr orifice plate was compromised with the remaining
runoff surface flowing to Redwood Street.
All calculations and exhibits are attached for reference.
4. LOW IMPACT DEVELOPMENT TECHNIQUES
In reference to the code requirements for implementation of Low Impact Development
(LID) techniques, the use of permeable pavers and a sand filter are necessary to satisfy
these requirements. The main LID being proposed to be implemented on site are
permeable pavers located in sections of the north and south drives. The remaining
developed area will be treated by a sand filter located near the southeast corner of the site
within the detention pond. The sand filter is designed to detain and infiltrate the required
water quality capture volume and directly spill into the detention area for events beyond
the capacity of the sand filter. The sand filter water quality capture volume is designed to
have a depth of 12 inches. Underdrains are not required with a full infiltration design.
Percolation test was performed and is provided in the appendix. Based on the average
percolation rate of 8.6 minutes per inch, it is estimated that the water quality capture
volume will infiltrate within 2 hrs of filling. A Standard Operations Procedure will be
provided to assist in ensuring that these BMPs will adequately perform over time.
All calculations are attached for reference.
5. CONCLUSION
All computations that have been completed within this report are in compliance with the
CoFC Stormwater Criteria Manual, and Urban Drainage and Flood Control District
requirements and standards. The proposed drainage concepts presented in this report and
on the construction plans adequately provide for stormwater quantity and quality
treatment of proposed impervious areas. Conveyance elements have been designed to
pass required flows and to minimize future maintenance.
4
If, at the time of construction, groundwater is encountered, a Colorado Department of
Health Construction Dewatering Permit will be required.
6. REFERENCES
1. Urban Storm Drainage Criteria Manual (Volumes 1, 2, and 3), Urban Drainage
and Flood Control District, June 2001, Revised April 2008.
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. “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. [03/28/2014]
APPENDIX A — SITE DESCRIPTIONS, CHARACTERISTICS & REFERENCES
vicinity map
PROJECT DATUM: NAVD88
CITY OF FORT COLLINS BENCHMARK #42-97
ON TOP OF A STORM INLET STRUCTURE ON THE EAST SIDE
OF REDWOOD ST., 400 FEET SOUTH OF WILLOX LANE.
ELEV= 4969.93
CITY OF FORT COLLINS BENCHMARK #43-97
ON THE SOUTH END OF THE WEST HEADWALL OF THE
LAKE CANAL BRIDGE AT NORTH LEMAY AVE., 200 FEET
SOUTH OF THE INTERSECTION OF LEMAY AVE. AND CONIFER ST.
ELEV= 4960.11
PLEASE NOTE: THIS PLAN SET IS USING NAVD88 FOR A VERTICAL
DATUM. SURROUNDING DEVELOPMENTS HAVE USED NGVD29
UNADJUSTED FOR THEIR VERTICAL DATUMS.
IF NGVD29 UNADJUSTED DATUM IS REQUIRED FOR ANY PURPOSE,
THE FOLLOWING EQUATIONS SHOULD BE USED:
NGVD29 UNADJUSTED = 4969.93 (NAVD88) - 3.18 = 4966.75
NGVD29 UNADJUSTED = 4960.11 (NAVD88) - 3.17 = 4956.94
Hydrologic Soil Group—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/14/2015
Page 1 of 4
4494910 4494940 4494970 4495000 4495030 4495060 4495090
4494910 4494940 4494970 4495000 4495030 4495060 4495090
494040 494070 494100 494130 494160 494190 494220 494250 494280 494310 494340
494040 494070 494100 494130 494160 494190 494220 494250 494280 494310 494340
40° 36' 24'' N
105° 4' 14'' W
40° 36' 24'' N
105° 4' 0'' W
40° 36' 17'' N
105° 4' 14'' W
40° 36' 17'' N
105° 4' 0'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 50 100 200 300
Feet
0 20 40 80 120
Meters
Map Scale: 1:1,470 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
64 Loveland clay loam, 0 to
1 percent slopes
C 3.3 32.5%
73 Nunn clay loam, 0 to 1
percent slopes
C 7.0 67.5%
Totals for Area of Interest 10.3 100.0%
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.
Rating Options
Aggregation Method: Dominant Condition
Hydrologic Soil Group—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/14/2015
Page 3 of 4
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/14/2015
Page 4 of 4
Storm drain sized for 100 yr
(33.5 cfs) developed flows from
Village on Redwood site
Assumed developed flows from
Village on Redwood site, referenced
for existing storm drain sizing
(100-yr = 33.5cfs)
B
APPENDIX B — RATIONAL CALCULATIONS
FCHA - Villages on Redwood
DRAINAGE SUMMARY
Design Engineer:
Design Firm:
Project Number:
Date:
DRAINAGE SUMMARY:
Area (acres)
%
Imprevious
100-yr Peak
Runoff (cfs) Area (acres)
%
Imprevious
100-yr Peak
Runoff (cfs)
To Redwood 6.217 4.4% 14.10 5.983 46.7% 26.57 H1 compared to D1+...D6
To Existing Pond 3.785 0.0% 11.45 4.020 1.4% 12.33 H2+OF1 compared to D7+OF1
Totals 10.002 2.7% 25.56 10.002 29.6% 38.90
T.Alva
Interwest Consulting Group
1237-112-00
November 25, 2015
Basins Notes
Historical Developed
FCHA - Villages on Redwood
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 August 2006)
BASINS:
%
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 270,830 6.217 11,888 0 0 0 258,941 4.4% 0.28 0.35
H2 162,764 3.737 0 0 0 0 162,764 0.0% 0.25 0.31
OF1 2,110 0.048 0 0 0 0 2,110 0.0% 0.25 0.31
Total 435,704 10.002 11,888 0 0 0 423,816 2.7% 0.27 0.34
Pavers
Walks
Apaved
(sq feet)
Lawns (Heavy, 2-7%
Slope)
Weighted % COMPOSITE
Impervious
1237-112-00
Interwest Consulting Group
T.Alva
November 25, 2015
Sub-basin
Designation
Atotal
(sq feet)
Atotal
(acres)
% Impervious values from Table RO-3 in the Urban Storm Drainage Criteria Manual
Runoff Coefficients and Frequency Adjustment Factors for City of Fort Collins - Storm Water Criteria Manual
Land Use
Paved
Roof
Alawn
(sq feet)
Apavers
FCHA - Villages on Redwood
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 August 2006)
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 t c
= 5 min for urbanized basins
BASINS:
Type of Travel
Surface
Cv
H1 H1 0.28 6.217 419 0.0043 40.72 495 0.0059 Paved Areas 20 1.54 5.37 46.09 15.08 15.08
H2 H2 0.25 3.737 32 0.2582 3.00 0 0.0001 Tilage/Field 5 0.05 0.00 5.00 10.18 5.00 All Overland Flow
OF1 OF1 0.25 0.048 15 0.0802 3.06 38 0.0251 Tilage/Field 5 0.79 0.81 5.00 10.30 5.00
SUB-BASIN DATA
INITIAL/OVERLAND
TIME (ti
)
T.Alva
Interwest Consulting Group
1237-112-00
November 25, 2015
DESIGN
POINT
Sub-basin C5
AREA
(acres)
LENGTH
(ft)
SLOPE
(ft/ft)
ti (min)
LENGTH Table RO-2
(ft)
TRAVEL TIME (tt
)
REMARKS
tc Urban
Check
Final tc
(min)
tc=ti+tt
SLOPE (min)
(ft/ft)
VEL.
(ft/s)
tt (min)
FCHA - Villages on Redwood
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 August 2006)
EQUATIONS:
Q n = n -yr peak discharge (cfs) I = rainfall intensity (in/hr) P 1-5yr = 1.14 in
C n = n -yr runoff coefficient P 1 = one-hour point rainfall depth (in) P 1-100yr = 2.86 in
I n = n -yr rainfall intensity (in/hr) t c = time of concentration (min) P 1-10yr = 1.40 in
A n = Basin drainage area (ac)
BASINS:
Runoff Coeff.
(C5
)
C(A)
(acres)
Intensity
(in/hr)
Q (ft
3
/s)
Runoff Coeff.
(C5
)
C(A)
(acres)
Intensity
(in/hr)
Q (ft
3
/s)
Runoff Coeff.
(C100
)
C(A) (acres)
Intensity
(in/hr)
Q (ft
3
/s)
H1 H1 6.217 15.08 0.28 1.75 2.58 4.50 0.28 1.75 6.46 11.28 0.35 2.18 6.46 14.10
H2 H2 3.737 5.00 0.25 0.93 3.86 3.61 0.25 0.93 9.68 9.05 0.31 1.17 9.68 11.31
OF1 OF1 0.048 5.00 0.25 0.01 3.86 0.05 0.25 0.01 9.68 0.12 0.31 0.02 9.68 0.15
5-yr Peak Runoff 10-yr Peak Runoff 100-yr Peak Runoff
T.Alva
Interwest Consulting Group
1237-112-00
November 25, 2015
City of Fort Collins - Storm Water Criteria Manual (1997)
Design
Point
Sub-basin Area (acres) tc
(min)
Q n = C n I n A n 0.786651)
1
( 10 )
28 . 5
FCHA - Villages on Redwood
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 August 2006)
BASINS:
%
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
D1 54,800 1.258 12,356 11,432 7,959 2,091 20,963 55.9% 0.67 0.83
D2 29,959 0.688 5,389 6,849 4,140 4,825 8,755 57.4% 0.67 0.84
D3 45,346 1.041 0 8,831 5,683 0 30,833 28.8% 0.47 0.59
D4 48,207 1.107 15,311 7,420 5,959 4,349 15,167 60.3% 0.69 0.86
D5 36,006 0.827 3,656 5,478 1,714 0 25,158 28.1% 0.46 0.58
D6 46,296 1.063 16,675 3,690 7,155 0 18,777 57.1% 0.67 0.83
D7 174,015 3.995 0 2,185 523 0 171,307 1.4% 0.26 0.33
OF1 1,076 0.025 0 0 0 0 1,076 0.0% 0.25 0.31
Total 435,704 10.002 53,386 45,884 33,133 11,265 292,036 29.6% 0.47 0.59
Headwall (D1+D2+D3) 130,104 2.987 17,745 27,112 17,782 6,915 60,551 46.8% 0.60 0.75
Inlet 01 (D1+D2+D3+D4) 178,311 4.093 33,056 34,532 23,741 11,265 75,718 50.5% 0.62 0.78
To Detention Outlet (D1+�.D5) 214,317 4.920 36,711 40,010 25,456 11,265 100,876 46.7% 0.60 0.75
To Redwood 260,614 5.983 53,386 43,699 32,610 11,265 119,653 48.6% 0.61 0.76
% Impervious values from Table RO-3 in the Urban Storm Drainage Criteria Manual
Runoff Coefficients and Frequency Adjustment Factors for City of Fort Collins - Storm Water Criteria Manual
T.Alva
Interwest Consulting Group
1237-112-00
November 25, 2015
Weighted %
Impervious
COMPOSITE
Roof
Apaved
(sq feet)
Aroof
(sq feet)
Awalk
(sq feet)
Apavers
(sq feet)
Alawn
(sq feet)
FCHA - Villages on Redwood
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 August 2006)
EQUATIONS:
-Equation RO-2 -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 t c = 5 min for urbanized basins
BASINS:
Type of Travel
Surface
Cv
D1 D1 0.67 1.258 31 0.0370 2.87 521 0.0069 Paved Areas 20 1.67 5.21 8.08 13.07 8.08
D2 D2 0.67 0.688 78 0.0239 5.16 156 0.0079 Paved Areas 20 1.77 1.47 6.62 11.30 6.62
D3 D3 0.47 1.041 101 0.0297 8.02 159 0.0253 Paved Areas 20 3.18 0.84 8.85 11.45 8.85
D4 D4 0.69 1.107 42 0.0191 3.93 246 0.0109 Paved Areas 20 2.09 1.97 5.90 11.60 5.90
D5 D5 0.46 0.827 97 0.0264 8.37 37 0.0083 Paved Areas 20 1.82 0.34 8.71 10.75 8.71
D6 D6 0.67 1.063 12 0.0651 1.50 563 0.0040 Paved Areas 20 1.26 7.42 8.92 13.20 8.92
D7 D7 0.26 3.995 37 0.0513 5.44 0 0.0001 Paved Areas 20 0.20 0.00 5.44 10.21 5.44 All Overland Flow
OF1 OF1 0.25 0.025 6 0.1371 1.66 0 0.0001 Paved Areas 20 0.20 0.00 5.00 10.04 5.00 All Overland Flow
TRAVEL TIME (tt)
REMARKS
tc
Urban
Check
Final tc
(min)
tc
=ti
+tt
SLOPE (min)
(ft/ft)
VEL.
(ft/s)
tt
(min)
T.Alva
Interwest Consulting Group
1237-112-00
November 25, 2015
SLOPE
(ft/ft)
ti
(min)
LENGTH Table RO-2
(ft)
SUB-BASIN DATA
INITIAL/OVERLAND
TIME (ti)
DESIGN
POINT
Sub-basin C5
FCHA - Villages on Redwood
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 August 2006)
EQUATIONS:
Q n = n -yr peak discharge (cfs) I = rainfall intensity (in/hr) P 1-5yr = 1.14 in
C n = n -yr runoff coefficient P 1 = one-hour point rainfall depth (in) P 1-10yr = 1.40 in
I n = n -yr rainfall intensity (in/hr) t c = time of concentration (min) P 1-100yr = 2.86 in
A n = Basin drainage area (ac)
BASIN SUMMARY:
Runoff Coeff.
(C5)
C(A)
(acres)
Intensity
(in/hr)
Q (ft3/s)
Runoff Coeff.
(C5)
C(A)
(acres)
Intensity
(in/hr)
Q (ft3/s)
Runoff Coeff.
(C100)
C(A)
(acres)
Intensity
(in/hr)
Q (ft3/s)
D1 D1 1.258 8.08 0.67 0.84 3.33 2.79 0.67 0.84 4.09 3.42 0.83 1.05 8.36 8.74
D2 D2 0.688 6.62 0.67 0.46 3.56 1.65 0.67 0.46 4.37 2.02 0.84 0.58 8.93 5.17
D3 D3 1.041 8.85 0.47 0.49 3.22 1.59 0.47 0.49 3.96 1.95 0.59 0.62 8.09 4.99
D4 D4 1.107 5.90 0.69 0.76 3.69 2.81 0.69 0.76 4.53 3.45 0.86 0.95 9.25 8.82
D5 D5 0.827 8.71 0.46 0.38 3.24 1.24 0.46 0.38 3.98 1.52 0.58 0.48 8.14 3.87
D6 D6 1.063 8.92 0.67 0.71 3.22 2.28 0.67 0.71 3.95 2.80 0.83 0.88 8.07 7.14
D7 D7 3.995 5.44 0.26 1.04 3.77 3.93 0.26 1.04 4.63 4.83 0.33 1.30 9.47 12.33
OF1 OF1 0.025 5.00 0.25 0.01 3.86 0.02 0.25 0.01 4.74 0.03 0.31 0.01 9.68 0.07
100-yr Peak Runoff
T.Alva
Interwest Consulting Group
1237-112-00
November 25, 2015
Design
Point
Sub-basin Area (acres) tc (min)
5-yr Peak Runoff 10-yr Peak Runoff
City of Fort Collins - Storm Water Criteria Manual (1997)
Q n = C n I n A n 0.786651)
1
( 10 )
28 . 5
t c
P
I
FCHA - Villages at Redwood
Attenuated Flows for Pipe Sizing
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001
EQUATIONS:
-Equation RO-2 -Equation RO-4
-Equation RO-3
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition Final t c = minimum of t i + t t and urbanized basin check
500 ft - Overland flow shall not exceed for undeveloped condition recommended minimum t c = 5 min for urbanized basins
Qn = n -yr peak discharge (cfs) I = rainfall intensity (in/hr)
Cn = n -yr runoff coefficient P1 = one-hour point rainfall depth (in)
In = n -yr rainfall intensity (in/hr) tc = time of concentration (min)
A = drainage area (ac) P1-5yr = 1.14 in.
P1-10yr = 1.40 in.
P1-100yr = 2.86 in.
BASINS:
UD-Sewer - DP/Manhole Headwall
Contributing Basins D1+D2+D3
Contributing Area (acres) 2.99
C2 to C10 C100
Runoff Coefficients 0.60 0.75
Overland Flow Time
Length (ft) 31
Slope (ft/ft) 0.03
ti
(min) 3.46
Travel Time
Length (ft) Slope (%)
Type of Travel
Surface Cv Velocity (ft/s) tt (min)
529 0.68% Paved Areas 20 1.65 5.33
147 1.80% Paved Areas 20 2.69 0.91
Total Time 6.24
Final Time of Concentration - tc (min)
tc
(min) 9.70
Intensities (in/hr)
5-yr 10-yr 100-yr
3.11 3.83 7.81
Discharge (cfs)
5-yr 10-yr 100-yr
5.58 6.86 17.51
T.Alva
Interwest Consulting Group
1237-112-00
November 25, 2015
City of Fort Collins - Storm Water Criteria Manual (1997)
Q n = C n I n A
t c = t i + t t 0 . 5
V = C v S w
V
L
tt 60
( ) =
0 .33
FCHA - Villages at Redwood
Attenuated Flows for Pipe Sizing
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001
EQUATIONS:
-Equation RO-2 -Equation RO-4
-Equation RO-3
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition Final t c = minimum of t i + t t and urbanized basin check
500 ft - Overland flow shall not exceed for undeveloped condition recommended minimum t c = 5 min for urbanized basins
Qn = n -yr peak discharge (cfs) I = rainfall intensity (in/hr)
Cn = n -yr runoff coefficient P1 = one-hour point rainfall depth (in)
In = n -yr rainfall intensity (in/hr) tc = time of concentration (min)
A = drainage area (ac) P1-5yr = 1.14 in.
P1-10yr = 1.40 in.
P1-100yr = 2.86 in.
BASINS:
UD-Sewer - DP/Manhole Inlet 01
Contributing Basins D1+D2+D3+D4
Contributing Area (acres) 4.09
C2 to C10 C100
Runoff Coefficients 0.62 0.78
Overland Flow Time
Length (ft) 21
Slope (ft/ft) 0.05
ti
(min) 2.38
Travel Time
Length (ft) Slope (%)
Type of Travel
Surface Cv Velocity (ft/s) tt (min)
529 0.68% Paved Areas 20 1.65 5.33
147 1.80% Paved Areas 20 2.69 0.91
76 0.26% Paved Areas 20 1.02 1.24
56 0.25% Paved Areas 20 1.00 0.93
Total Time 8.42
Final Time of Concentration - tc (min)
tc
(min) 10.79
Intensities (in/hr)
5-yr 10-yr 100-yr
2.99 3.67 7.49
Discharge (cfs)
5-yr 10-yr 100-yr
7.63 9.37 23.93
T.Alva
Interwest Consulting Group
1237-112-00
11/25/2015
City of Fort Collins - Storm Water Criteria Manual (1997)
Q n = C n I n A
t c = t i + t t 0 . 5
V = C v S w
V
L
tt 60
FCHA - Villages at Redwood
Attenuated Flows for Pipe Sizing
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001
EQUATIONS:
-Equation RO-2 -Equation RO-4
-Equation RO-3
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition Final t c = minimum of t i + t t and urbanized basin check
500 ft - Overland flow shall not exceed for undeveloped condition recommended minimum t c = 5 min for urbanized basins
Qn = n -yr peak discharge (cfs) I = rainfall intensity (in/hr)
Cn = n -yr runoff coefficient P1 = one-hour point rainfall depth (in)
In = n -yr rainfall intensity (in/hr) tc = time of concentration (min)
A = drainage area (ac) P1-5yr = 1.14 in.
P1-10yr = 1.40 in.
P1-100yr = 2.86 in.
BASINS:
UD-Sewer - DP/Manhole To Redwood
Contributing Basins D1+D2+D3+D4+D5
Contributing Area (acres) 4.92
C2 to C10 C100
Runoff Coefficients 0.60 0.75
Overland Flow Time
Length (ft) 21
Slope (ft/ft) 0.05
ti
(min) 2.51
Travel Time
Length (ft) Slope (%)
Type of Travel
Surface Cv Velocity (ft/s) tt (min)
529 0.68% Paved Areas 20 1.65 5.33
147 1.80% Paved Areas 20 2.69 0.91
76 0.26% Paved Areas 20 1.02 1.24
56 0.25% Paved Areas 20 1.00 0.93
97 1.05% Paved Areas 20 2.05 0.79 pan from fes to headwall
Total Time 9.20
Final Time of Concentration - tc (min)
tc
(min) 11.72
Intensities (in/hr)
5-yr 10-yr 100-yr
2.89 3.54 7.24
Discharge (cfs)
5-yr 10-yr 100-yr
8.47 10.40 26.57
T.Alva
Interwest Consulting Group
1237-112-00
November 25, 2015
City of Fort Collins - Storm Water Criteria Manual (1997)
Q n = C n I n A
t c = t i + t t 0 . 5
V = C v S w
V
L
C
APPENDIX C — STORM CONVEYANCE SIZING
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Wednesday, Nov 25 2015
Basin D1 Swale
Trapezoidal
Bottom Width (ft) = 2.00
Side Slopes (z:1) = 4.00, 4.00
Total Depth (ft) = 1.25
Invert Elev (ft) = 100.00
Slope (%) = 0.60
N-Value = 0.015
Calculations
Compute by: Known Q
Known Q (cfs) = 8.74
Highlighted
Depth (ft) = 0.55
Q (cfs) = 8.740
Area (sqft) = 2.31
Velocity (ft/s) = 3.78
Wetted Perim (ft) = 6.54
Crit Depth, Yc (ft) = 0.59
Top Width (ft) = 6.40
EGL (ft) = 0.77
0 2 4 6 8 10 12 14 16
Elev (ft) Depth (ft)
Section
99.50 -0.50
100.00 0.00
100.50 0.50
101.00 1.00
101.50 1.50
102.00 2.00
Reach (ft)
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Wednesday, Nov 25 2015
Basin D2 Swale
Trapezoidal
Bottom Width (ft) = 2.00
Side Slopes (z:1) = 4.00, 4.00
Total Depth (ft) = 1.25
Invert Elev (ft) = 100.00
Slope (%) = 1.00
N-Value = 0.015
Calculations
Compute by: Known Q
Known Q (cfs) = 5.17
Highlighted
Depth (ft) = 0.38
Q (cfs) = 5.170
Area (sqft) = 1.34
Velocity (ft/s) = 3.87
Wetted Perim (ft) = 5.13
Crit Depth, Yc (ft) = 0.45
Top Width (ft) = 5.04
EGL (ft) = 0.61
0 2 4 6 8 10 12 14 16
Elev (ft) Depth (ft)
Section
99.50 -0.50
100.00 0.00
100.50 0.50
101.00 1.00
101.50 1.50
102.00 2.00
Reach (ft)
D
APPENDIX D — DETENTION POND CALCULATIONS
100 Year
This is to convert % imp. to a C value
100-year (must insert % imp. and C pervious).
ft3 acre-ft.
'C' value 0.6 17493.8 0.402
'C' * 1.25 0.75
Area 4.92 acres Modified Modified
Release Rate 6.96 M. FATER D. JUDISH C. LI
5/95 Nov-97 Nov-98
TIME TIME INTENSITY Q 100 Runoff Release Required Required
cum 100 year Volume Cum total Detention Detention
(mins) (secs) (in/hr) (cfs) (ft^3) (ft^3) (ft^3) (ac-ft)
0 0 0 0.00 0 0.0 0.0 0.0000
5 300 9.950 36.72 11014.65 2088.0 8926.7 0.2049
10 600 7.720 28.49 17092.08 4176.0 12916.1 0.2965
15 900 6.520 24.06 21652.92 6264.0 15388.9 0.3533
20 1200 5.600 20.66 24796.8 8352.0 16444.8 0.3775
25 1500 4.980 18.38 27564.3 10440.0 17124.3 0.3931
30 1800 4.520 16.68 30021.84 12528.0 17493.8 0.4016
35 2100 4.080 15.06 31615.92 14616.0 16999.9 0.3903
40 2400 3.740 13.80 33121.44 16704.0 16417.4 0.3769
45 2700 3.460 12.77 34471.98 18792.0 15680.0 0.3600
50 3000 3.230 11.92 35756.1 20880.0 14876.1 0.3415
55 3300 3.030 11.18 36896.31 22968.0 13928.3 0.3198
60 3600 2.860 10.55 37992.24 25056.0 12936.2 0.2970
65 3900 2.720 10.04 39143.52 27144.0 11999.5 0.2755
70 4200 2.590 9.56 40139.82 29232.0 10907.8 0.2504
75 4500 2.480 9.15 41180.4 31320.0 9860.4 0.2264
80 4800 2.380 8.78 42154.56 33408.0 8746.6 0.2008
85 5100 2.290 8.45 43095.51 35496.0 7599.5 0.1745
90 5400 2.210 8.15 44036.46 37584.0 6452.5 0.1481
95 5700 2.130 7.86 44800.29 39672.0 5128.3 0.1177
100 6000 2.060 7.60 45608.4 41760.0 3848.4 0.0883
105 6300 2.000 7.38 46494 43848.0 2646.0 0.0607
110 6600 1.940 7.16 47246.76 45936.0 1310.8 0.0301
115 6900 1.890 6.97 48121.29 48024.0 97.3 0.0022
120 7200 1.840 6.79 48885.12 50112.0 -1226.9 -0.0282
125 7500 1.790 6.61 49538.25 52200.0 -2661.8 -0.0611
130 7800 1.750 6.46 50368.5 54288.0 -3919.5 -0.0900
135 8100 1.710 6.31 51110.19 56376.0 -5265.8 -0.1209
140 8400 1.670 6.16 51763.32 58464.0 -6700.7 -0.1538
145 8700 1.630 6.01 52327.89 60552.0 -8224.1 -0.1888
150 9000 1.600 5.90 53136 62640.0 -9504.0 -0.2182
155 9300 1.570 5.79 53877.69 64728.0 -10850.3 -0.2491
160 9600 1.540 5.68 54552.96 66816.0 -12263.0 -0.2815
165 9900 1.510 5.57 55161.81 68904.0 -13742.2 -0.3155
170 10200 1.480 5.46 55704.24 70992.0 -15287.8 -0.3510
175 10500 1.450 5.35 56180.25 73080.0 -16899.8 -0.3880
180 10800 1.420 5.24 56589.84 75168.0 -18578.2 -0.4265
185 11100 1.400 5.17 57342.6 77256.0 -19913.4 -0.4571
190 11400 1.380 5.09 58051.08 79344.0 -21292.9 -0.4888
195 11700 1.360 5.02 58715.28 81432.0 -22716.7 -0.5215
200 12000 1.340 4.94 59335.2 83520.0 -24184.8 -0.5552
205 12300 1.320 4.87 59910.84 85608.0 -25697.2 -0.5899
210 12600 1.300 4.80 60442.2 87696.0 -27253.8 -0.6257
215 12900 1.280 4.72 60929.28 89784.0 -28854.7 -0.6624
220 13200 1.260 4.65 61372.08 91872.0 -30499.9 -0.7002
225 13500 1.240 4.58 61770.6 93960.0 -32189.4 -0.7390
230 13800 1.220 4.50 62124.84 96048.0 -33923.2 -0.7788
235 14100 1.210 4.46 62955.09 98136.0 -35180.9 -0.8076
Village on Redwood
Critical Pond Elevations
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)
4962.33 0 0.000 0.000 0.00 0.000
4963.0 2061 0.047 0.011 0.67 0.011
4964.0 6214 0.143 0.091 1.67 0.101
4965.0 9583 0.220 0.191 2.67 0.293
4966.0 15126 0.347 0.281 3.67 0.574
0.402 4965.39 ft
T.Alva
Interwest Consulting Group
1237-112-00
Acre-Ft Interpolates to an Elev. of
Required 100-yr Detention Volume (including WQCV) =
November 25, 2015
4962.00
4962.50
4963.00
4963.50
4964.00
4964.50
4965.00
4965.50
4966.00
4966.50
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
ELEVATION (FT)
DETENTION POND VOLUME (AC-FT)
DETENTION POND VOLUME
VERSUS ELEVATION
( )
3
AAAADepth 1 2 1 2
V
+ +
=
1237-112-00 PondCalcs.xls - Pond Stage Storage Page 1 of 2 Interwest Consulting Group
Village on Redwood
Circular Orifice Plate Sizing
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 6.96 cfs
100-yr WSEL 4965.39 ft 4962.33 0.00 0.000
4964.00 4.50 0.101
Pond Outlet Invert 4962.33 ft 4965.00 6.37 0.293
4966.00 7.80 0.574
Discharge Coefficient 0.65
Tailwater Elevation 4963.00 ft
Orifice Diameter 12 9/16 in
Orifice Area 0.863 ft
2
Centroid Elevation 4962.85 ft
Actual Release Rate 6.96 cfs
Pond Volume
(ac-ft)
T.Alva
Interwest Consulting Group
1237-112-00
November 25, 2015
Elevation
(ft)
Discharge
(cfs)
C g h
Q
QCA o g h A o ∆
= ∆ ⇒ =
2
2
π
o
o
A
D
= 576
1237-112-00 PondCalcs.xls - Outlet Orifice Plate Sizing Page 2 of 2 Interwest Consulting Group
E
APPENDIX E — LOW IMPACT DEVELOPMENT CALCULATIONS
FCHA - Villages on Redwood
Low Impact Development
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
Low Impact Development Summary
Pavement Area Summary
43,661 sqft
11,265 sqft
25.8%
Newly Added Impervious Area Summary
115,390 sqft
11,265 sqft
30,431 sqft
41,696 sqft
15,999 sqft
57,695 sqft
50.0%
Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, January 2010
Total Paved Area:
Permeable Paver Area:
Total Site Impervious Area:
Proposed Area of Pavers:
Additional Area Treated by Pavers:
Total Area Treated by Pavers:
Area to be Treated by Sand Filter:
Total Area Treated by LID:
Percent Impervious Area Treated by LID:
Percent Pavement Area as Permeable Pavers:
City of Fort Collins - Ordinance No. 152
- No less than 25% of any newly added pavement areas must be treated using a permeable pavement
technology that is considered an LID Technique, and
- No less than 50% of any newly added impervious area must be treated using one or a combination of LID
techniques
T.Alva
Interwest Consulting Group
1237-112-00
November 25, 2015
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 100.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 1.000
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.40 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 16,000 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = 0.43 in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER = 533.3 cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum) DWQCV = 12 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin = 356 sq ft
D) Actual Flat Surface Area AActual = 359 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 707 sq ft
F) Rain Garden Total Volume VT= 533 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
4. Underdrain System
A) Are underdrains provided?
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y = N/A ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft
iii) Orifice Diameter, 3/8" Minimum DO = N/A in
Design Procedure Form: Rain Garden (RG)
J. Claeys
Interwest Consulting Group
November 25, 2015
Villages at Redwood
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
1237-112-00 UD-BMP_v3.03.xlsm, RG 11/25/2015, 4:36 AM
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is an impermeable liner provided due to proximity
of structures or groundwater contamination?
6. Inlet / Outlet Control
A) Inlet Control
7. Vegetation
8. Irrigation
A) Will the rain garden be irrigated?
Notes:
Design Procedure Form: Rain Garden (RG)
J. Claeys
Interwest Consulting Group
November 25, 2015
Villages at Redwood
Choose One
Choose One
Choose One
Sheet Flow- No Energy Dissipation Required
Concentrated Flow- Energy Dissipation Provided
Plantings
Seed (Plan for frequent weed control)
Sand Grown or Other High Infiltration Sod
Choose One
YES
NO
YES
NO
1237-112-00 UD-BMP_v3.03.xlsm, RG 11/25/2015, 4:36 AM
Percolation Test Results
DEPTH DEPTH PERC
PERC MINUTES START END CHANGE RATE
HOLE (INCHES) (INCHES) (INCHES) (MPI)
1 10 22.88 24.75 1.88 5.3
10 24.75 26.25 1.50 6.7
10 26.25 27.50 1.25 8.0
10 27.50 28.63 1.13 8.9
10 28.63 29.75 1.13 8.9
10 29.75 30.88 1.13 8.9
10 20.50 22.38 1.88 5.3
10 22.38 24.13 1.75 5.7
2* 10 19.38 19.38 0.00 >80
10 19.38 19.50 0.13 80.0
10 19.50 19.50 0.00 >80
10 19.50 19.63 0.13 80.0
10 19.63 19.75 0.13 80.0
10 19.75 19.75 0.00 >80
10 19.75 19.88 0.13 80.0
10 19.88 20.00 0.13 80.0
3 10 20.25 22.00 1.75 5.7
10 22.00 23.63 1.63 6.2
10 23.63 25.25 1.63 6.2
10 25.25 26.63 1.38 7.3
10 26.63 27.88 1.25 8.0
10 27.88 29.25 1.38 7.3
10 29.25 30.13 0.88 11.4
10 30.13 31.00 0.88 11.4
4 10 17.25 18.63 1.38 7.3
10 18.63 19.88 1.25 8.0
10 19.78 21.00 1.22 8.2
10 21.00 22.00 1.00 10.0
10 22.00 23.13 1.13 8.9
10 23.13 24.00 0.88 11.4
10 24.00 24.88 0.88 11.4
10 16.88 18.00 1.13 8.9
5 10 22.00 24.25 2.25 4.4
10 24.25 26.38 2.13 4.7
10 26.38 28.25 1.88 5.3
10 28.25 29.88 1.63 6.2
10 29.88 31.25 1.38 7.3
10 31.25 32.63 1.38 7.3
10 32.63 33.88 1.25 8.0
10 33.88 35.13 1.25 8.0
6 10 22.88 31.25 8.38 1.2
10 31.25 38.00 6.75 1.5
10 28.25 35.25 7.00 1.4
10 35.25 41.75 6.50 1.5
10 41.75 45.00 3.25 3.1
10 21.75 30.50 8.75 1.1
10 30.50 37.63 7.13 1.4
10 37.63 41.63 4.00 2.5
Average Percolation Rate (mpi): 8.6
*Perc hole 2 was neglected for our average percolation rate
INTERWEST CONSULTING GROUP
FCHA REDWOOD DEVELOPMENT
CTL | T PROJECT NO. FC06667.001-130 FIGURE 3
240 14400 1.200 4.43 63763.2 100224.0 -36460.8 -0.8370
Required detention
DETENTION POND SIZING
Page 1
tt 60
( ) =
0 .33
0 . 395 1 . 1 5
S
C L
ti
−
=
0.786651)
1
( 10 )
28 . 5
t c
P
I
+
=
( ) =
0 .33
0 . 395 1 . 1 5
S
C L
ti
−
=
0.786651)
1
( 10 )
28 . 5
t c
P
I
+
=
0 . 395 1 . 1 5
S
C L
ti
−
=
0.786651)
1
( 10 )
28 . 5
t c
P
I
+
=
+
=
AREA
(acres)
LENGTH
(ft)
( )
0 .33
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
=
Sub-basin
Designation
Paved
Pavers
Land Use
Atotal
(sq feet)
Atotal
(acres)
Walks
Lawns (Heavy, 2-7%
Slope)
t c
P
I
+
=
( )
0 .33
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
=
(sq feet)
Awalk
(sq feet)
Aroof
(sq feet)
Survey Area Data: Version 9, Sep 22, 2014
Soil map units are labeled (as space allows) for map scales 1:50,000
or larger.
Date(s) aerial images were photographed: Apr 22, 2011—Apr 28,
2011
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor shifting
of map unit boundaries may be evident.
Hydrologic Soil Group—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/14/2015
Page 2 of 4