DRAINAGE REPORT PARADIGM ODP FORT COLLINS, CO 80525 Prepared For: Paradigm Properties, LLC 2186 Knoll Drive Ventura, CA 93003 Prepared By Coffey Engineering & Surveying 4045 St. Cloud Drive, Suite 180 Loveland, CO 80538 970-622-2095 Project No. 2276.00 October 17, 2017
Paradigm ODP ODP DRAINAGE REPORT ENGINEER S CERTIFICATION I hereby certify that this Overall Development Plan Drainage Report for the design of stormwater management facilities for the Paradigm ODP was prepared by me, or under my direct supervision, in accordance with the provisions of the City of Fort Collins Stormwater Criteria Manual for the owners thereof. Troy Campbell, PE Registered Professional Engineer State of Colorado No. 41159 PAGE 1
I. Table of Contents I. GENERAL LOCATION AND EXISTING SITE INFORMATION... 3 II. MAJOR DRAINAGE BASIN INFORMATION... 4 III. Floodplain information... 4 IV. Proposed drainage facilities... 4 V. REFERENCES... 5 VI. APPENDICES A. Hydrologic Computations FEMA Firm Panel 08069C1003E NRSC Soil Map Fort Collins Rainfall Intensity Curve Fort Collins Rainfall Intensity Table Table 3.2-1 Zoning Classification - Runoff Coefficients Table 4.1-2 Land Use - Percent Impervious Rational Method Calculated Composite C Tables Rational Method Calculated Imperviousness Rational Method Calculated Flows B. Hydraulic Computations Preliminary Modified FAA Method C. Map Pocket Drainage Plan PAGE 2
I. GENERAL LOCATION AND EXISTING SITE INFORMATION The Overall Development Plan Drainage Report serves as the summary of the hydrologic design for parcels 8722200013 and 8722200025. The site is located in the NW 1/4 Section 22 Township 07N Range 68W of the 6 th Principal Meridian in the City of Fort Collins, Larimer County, Colorado. More specifically the site is bound by the I-25 exit ramp to the west, Prospect Road to the north, and I-25 Frontage Road to the south and east. The site is currently used for agricultural purposes, but is zoned as General Commercial. An existing recreational vehicle dealership is located to the east. An existing motorcycle dealership and repair shop is located to the southwest. A proposed development to the north of Prospect Road will likely consist of commercial, light industrial, and affordable housing. Land to the south and southeast is currently used for agriculture and agriculture related businesses. According to the NRCS soils map survey, the native soils consist of Nunn Clay Loam (Type C ) soils. These soils have a moderately low infiltration rate when thoroughly wet. The site is not located within any of the 12 Fort Collins major drainage basins according to the City of Fort Collins Master Drainage Plan, but runoff drains into the Cooper Slough/Boxelder Basin. This basin is bound by I-25 at Prospect Road. The site is currently a vacant lot covered with native vegetation. Historically, the site drains south/southwest at an approximate slope of 0.5% until it crosses under I-25, and flows west into an existing detention pond. There are no existing drainage facilities on site. There are small irrigation laterals on site formerly used for agricultural purposes. PAGE 3
II. MAJOR DRAINAGE BASIN INFORMATION The site is currently not in any Fort Collins Major Drainage Basin, but drains into the lower portion of the Cooper Slough/Boxelder Drainage Basin. The Boxelder Creek and Cooper Slough Basin encompass approximately 265 square miles, beginning north of the Colorado/Wyoming border and extending southward into east Fort Collins, where it ends at the Cache la Poudre River. The basin is primarily characterized by farmland with isolated areas of mixed-use residential development and limited commercial development. It is anticipated the lower part of the basin will undergo urbanization in the future. Recently, a series of 4 X 12 box culverts were constructed under Prospect Road at Boxelder Creek just west of I-25, but no master planning improvements are proposed for this site. The Lake Canal is located east of the site, but the proposed drainage improvements will not influence irrigation facilities. III. FLOODPLAIN INFORMATION The site is located in the FEMA Flood Panel 08069C1003G, and is within FEMA Flood Zone AE. Boxelder Stormwater Authority obtained a Conditional Letter of Map Revision (CLOMR) and are currently constructing a large regional detention pond and unplugging existing culverts under I-25. The goal of these construction projects is to remove a large section of developable land, including the subject property owned by Paradigm Properties, from the Boxelder Creek Floodplain. Once construction is complete and approved, Federal Emergency Management Authority (FEMA) would need to approve a Letter of Map Revision (LOMR) before the site is officially removed from the floodplain. Boxelder Stormwater Authority expects FEMA to approve the LOMR. The site is not located within any City of Fort Collins floodplain. IV. PROPOSED DRAINAGE FACILITIES The proposed drainage patterns will generally match existing drainage patterns, flowing north to south. A portion of the site will be detained off-site in an existing detention pond southwest of the site. There are existing drainage easements to allow this off-site detention. The remaining runoff will be detained in a proposed detention pond in the southwest corner of the site. From the detention pond, runoff flows south through a series of culverts and grass channels under I-25 and into the off-site detention pond. The northern portion of the site reaches the proposed detention pond through overland flow and channelized flow via culverts and swales. The southern portion of the site will flow into the on-site detention pond via sheet and channelized flow. The portion of flow detained in the off-site pond will either bypass the on-site pond or overflow the on-site pond through a spillway. According to Table 3.2-1 Zoning Classification Runoff Coefficients, the C value for Commercial zoning is 0.85. From Table 4.1-2 Land Use Percent Impervious, Commercial PAGE 4
zoning has an assumed percent impervious of 80%. There are no anticipated off-site flows running onto the site. From the assumed runoff coefficient and percent impervious an approximate required detention volume can be calculated. Using the 100-year storm from the City of Fort Collins Rainfall Intensity-Duration-Frequency Table and the Modified FAA Method the approximate detention volume required is 4.21 acre-ft (200,000 ft 3 ). There is an off-site detention pond that was sized to detain 2.14 acre-feet of runoff from the 100-year event for this site. Approximately 2.07 acre-feet (90,000 ft 3 ) of on-site detention is required. The pond will have a release rate of the 2-year historic event of approximately 5.61 cfs. Low Impact Development (LID) requirements area required on all new or redeveloping property, which includes sites required to be brought into compliance with the Land Use Code. These require a higher degree of water quality treatment with one of the two following options: a. 50% of the newly added or modified impervious area must be treated by LID techniques and 25% of new paved areas must be pervious. b. 75% of all newly added or modified impervious area must be treated by LID techniques, The four-step process will be used to achieve this goal. Some common LID techniques will be used, including; constructing a wetland detention pond, and a wetland channel/bioswale to convey runoff to the pond. Also, a vegetative buffer will be incorporated to prevent continuous impervious area to run into the pond. Individual lots will use techniques such as permeable pavers, sand filters, rain gardens, or tree filters before directing runoff to the regional detention pond. V. REFERENCES City of Fort Collins Stormwater Criteria Manual, City of Fort Collins, Adopted December 2011. Urban Storm Drainage Criteria Manual, Volumes 1, 2, and 3, Urban Drainage and Flood Control District, April 2008. PAGE 5
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2 Soil Map Larimer County Area, Colorado 499850 499910 499970 500030 500090 500150 500210 500270 500330 500390 Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/22/2017 Page 1 of 3 4490300 4490360 4490420 4490480 4490540 4490600 4490660 4490300 4490360 4490420 4490480 4490540 4490600 4490660 105 0' 6'' W 40 34' 0'' N 499850 499910 499970 500030 500090 500150 500210 500270 500330 500390 40 34' 0'' N 105 0' 6'' W 104 59' 42'' W 40 33' 48'' N Soil Map may not be valid at this scale. 40 33' 48'' N 104 59' 42'' W N Map Scale: 1:2,560 if printed on A landscape (11" x 8.5") sheet. Meters 0 35 70 140 210 Feet 0 100 200 400 600 Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
3 Soil Map Larimer County Area, Colorado MAP LEGEND MAP INFORMATION Area of Interest (AOI) Soils Area of Interest (AOI) Soil Map Unit Polygons Soil Map Unit Lines Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Spoil Area Stony Spot Very Stony Spot Wet Spot Other Water Features Transportation Background Special Line Features Streams and Canals Rails Interstate Highways US Routes Major Roads Local Roads Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Larimer County Area, Colorado Survey Area Data: Version 11, Sep 23, 2016 Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Mar 20, 2015 Oct 15, 2016 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Sodic Spot Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/22/2017 Page 2 of 3
Soil Map Larimer County Area, Colorado 4 Map Unit Legend Larimer County Area, Colorado (CO644) Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 76 Nunn clay loam, wet, 1 to 3 percent slopes 15.6 100.0% Totals for Area of Interest 15.6 100.0% Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/22/2017 Page 3 of 3
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7 Table 3.2-1. Zoning Classification - Runoff Coefficients Land Use Runoff Coefficient (C) Residential Urban Estate 0.30 Low Density 0.55 Medium Density 0.65 High Density 0.85 Commercial Commercial 0.85 Industrial 0.95 Undeveloped Open Lands, Transition 0.20 Greenbelts, Agriculture 0.20
8 Table 4.2-2. Land Use - Percent Impervious Land Use Percent Impervious (%) Residential Urban Estate 30 Low Density 50 Medium Density 70 High Density 90 Commercial Commercial 80 Industrial 90 Undeveloped Open Lands, Transition 20 Greenbelts, Agriculture 2 Offsite Flow Analysis (when Land Use not defined) 45
9 Composite C Values I-25 Prospect Design Point Basin(s) Asphalt Area (acres) Concrete Area (acres) Gravel (acres) Pavers (acres) Lawns (acres) Total Area Minor (2-YR) Major (100-YR) (C = 0.95) (C = 0.95) (C = 0.50) (C = 0.50) (C = 0.10) (acres) Composite "C" Composite "C" (Cf x C) Existing E1 E1 0.00 0.00 0.00 0.00 0.00 16.910 0.15 0.19 Developed D1 P1 0.00 0.000 0.00 0.000 0.000 8.720 0.85 1.00 D2 P2 0.00 0.000 0.00 0.000 0.000 8.190 0.85 1.00 Total - 0.00 0.000 0.00 0.000 0.000 16.910 0.85 1.00 Notes: Runoff Coefficients per Table 3.2-1 - Zoning Classification Major Storm Runoff factored per Table R0-12 MAP Rational Method.xlsx 9/26/2017
10 Impeviousness I-25 Prospect Design Point Basin (s) Asphalt Area (acres) Concrete Area (acres) Gravel (acres) Pavers (acres) Lawns (acres) Total Area Percent (I = 100) (I = 100) (I = 40) (I = 50) (I = 0) (acres) Imperviousness Existing E1 E1 0.00 0.00 0.000 0.00 0.00 16.9100 2% Developed D1 P1 0.00 0.000 0.00 0.000 0.000 8.720 80% D2 P2 0.00 0.000 0.00 0.000 0.000 8.190 80% Total - 0.00 0.000 0.00 0.000 0.000 16.910 80% Notes: Percent Impervious Table 4.1-2 CAG Rational Method.xlsx 9/26/2017
Preliminary Basin Flow Calculations I-25 Prospect Basin Flows (cfs) Intensity (in/hr) Initial/Overland Time Travel Time Final T C Area Minor Major Major T C (min) 2-yr 10-yr 100-yr 2-yr 10-yr 100-yr Minor T C (min) Velocity (fps) c t t (min) Channel Type Slope (%) Minor t ov Major t ov (min) a (min) a Length (ft) Basin (s) a (acres) Composite "C" Composite "C" Length (ft) Slope (%) Design Point Existing E1 E1 16.9100 0.15 0.19 1000 0.50 70.78 67.99 0 0.60 PA 1.55 0.00 10.00 10.00 2.21 3.78 7.72 5.61 9.59 24.48 Developed D1 P1 8.7200 0.85 1.00 1000 2.00 11.73 4.69 750 1.00 PA 2.00 6.2500 17.98 10.94 1.70 2.90 7.42 12.60 21.49 64.70 D2 P2 8.1900 0.85 1.00 1000 2.00 11.73 4.69 750 1.00 PA 2.00 6.2500 17.98 10.94 1.70 2.90 7.42 11.83 20.19 60.77 Total - 16.9100 0.85 1.00 2000 2.00 16.59 6.64 1500 1.00 PA 2.00 12.5000 29.09 19.14 1.32 2.25 5.75 18.97 32.34 97.23 Notes: 1.87(1.1 CC ) 1 D / 2 t = ov S 1 / 3 HM = Heavy Meadow, TF = Tillage/field, PL = Short pasture and lawns, BG = Nearly bare ground, GW = Grassed Waterway, PA = Paved Areas Velocity alues from Figure 3-3/Table RO-2 Estimate of Average Flow Velocity for use with the Rational Method b c CAG 10/17/2017 f 11
12 Ex-Pr Difference 9/26/2017 Project: Location: Project Number:2276.00 Date: 9/26/2017 Paradigm Properties I-25 & Prospect Fort Collins, Colorado PROPOSED ft 3 acre-ft. 'C' value 0.85 183631.7 4.2156 'C' * 1.25 1 Area 16.91 acres Release Rate 5.61 DETENTION POND SIZING (100-Year) Required detention 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 9.950 168.25 50476.35 1683.0 48793.4 1.1201 10 600 7.720 130.55 78327.12 3366.0 74961.1 1.7209 15 900 6.520 110.25 99227.88 5049.0 94178.9 2.1620 20 1200 5.600 94.70 113635.2 6732.0 106903.2 2.4542 25 1500 4.980 84.21 126317.7 8415.0 117902.7 2.7067 30 1800 4.520 76.43 137579.8 10098.0 127481.8 2.9266 35 2100 4.080 68.99 144884.9 11781.0 133103.9 3.0556 40 2400 3.740 63.24 151784.2 13464.0 138320.2 3.1754 45 2700 3.460 58.51 157973.2 15147.0 142826.2 3.2788 50 3000 3.230 54.62 163857.9 16830.0 147027.9 3.3753 55 3300 3.030 51.24 169083.1 18513.0 150570.1 3.4566 60 3600 2.860 48.36 174105.4 20196.0 153909.4 3.5333 65 3900 2.720 46.00 179381.3 21879.0 157502.3 3.6158 70 4200 2.590 43.80 183947 23562.0 160385.0 3.6819 75 4500 2.480 41.94 188715.6 25245.0 163470.6 3.7528 80 4800 2.380 40.25 193179.8 26928.0 166251.8 3.8166 85 5100 2.290 38.72 197491.9 28611.0 168880.9 3.8770 90 5400 2.210 37.37 201803.9 30294.0 171509.9 3.9373 95 5700 2.130 36.02 205304.3 31977.0 173327.3 3.9790 100 6000 2.060 34.83 209007.6 33660.0 175347.6 4.0254 105 6300 2.000 33.82 213066 35343.0 177723.0 4.0800 110 6600 1.940 32.81 216515.6 37026.0 179489.6 4.1205 115 6900 1.890 31.96 220523.3 38709.0 181814.3 4.1739 120 7200 1.840 31.11 224023.7 40392.0 183631.7 4.2156 100-Year Volume 125 7500 1.790 30.27 227016.8 42075.0 184941.8 4.2457 130 7800 1.750 29.59 230821.5 43758.0 187063.5 4.2944 135 8100 1.710 28.92 234220.4 45441.0 188779.4 4.3338 140 8400 1.670 28.24 237213.5 47124.0 190089.5 4.3639 145 8700 1.630 27.56 239800.7 48807.0 190993.7 4.3846 150 9000 1.600 27.06 243504 50490.0 193014.0 4.4310 155 9300 1.570 26.55 246902.9 52173.0 194729.9 4.4704 160 9600 1.540 26.04 249997.4 53856.0 196141.4 4.5028 165 9900 1.510 25.53 252787.6 55539.0 197248.6 4.5282 170 10200 1.480 25.03 255273.4 57222.0 198051.4 4.5466 175 10500 1.450 24.52 257454.8 58905.0 198549.8 4.5581 180 10800 1.420 24.01 259331.8 60588.0 198743.8 4.5625 185 11100 1.400 23.67 262781.4 62271.0 200510.4 4.6031 190 11400 1.380 23.34 266028.1 63954.0 202074.1 4.6390 195 11700 1.360 23.00 269071.9 65637.0 203434.9 4.6702 200 12000 1.340 22.66 271912.8 67320.0 204592.8 4.6968 205 12300 1.320 22.32 274550.8 69003.0 205547.8 4.7187 210 12600 1.300 21.98 276985.8 70686.0 206299.8 4.7360 Page 1
NOTES: DATE EAST PROSPECT ROAD REVISION N NO. INTERSTATE 25 - OFF RAMP PROPOSED ROAD FRONTAGE ROAD PROPOSED ROAD FRONTAGE ROAD Know what's below. Callbefore you dig. R LEGEND: Basin Runoff Summary SURVEY & CONTROL NOTES NOT FOR CONSTRUCTION 2276.00 PROJECT: PRELIMINARY 10/17/17 DATE: OVERALL DEVELOPMENT PLANS FOR PARADIGM ODP CJD DESIGNER: DRAWING NO. SHEET NO. DRAFTER: ENGINEERING & SURVEYING 4045 St. Cloud Drive, Suite 180 Loveland, CO 80538 [P] 970-622-2095 [F] 307-742-7403 DP1 1 OVERALL DRAINAGE EXHIBITRJP TWC CHECKED BY: OF TWC APPROVED BY: NW 1 4 OF SECTION 22, T7N, R68W, 6TH P.M., CITY OF FORT COLLINS, COUNTY OF LARIMER, STATE OF COLORADO 1