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Home My WebLink AboutVILLAGE ON REDWOOD (FORT COLLINS HOUSINTG AUTHORITY) - PDP - PDP150012 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT1218 W. ASH, STE. C, WINDSOR, COLORADO 80550 TEL. 970.674.3300 – FAX 970.674.3303 July 15, 2015 Mr. Shane Boyle Fort Collins Utilities – Stormwater 700 Wood Street Fort Collins, CO 80522 Re: FCHA Villages on Redwood Preliminary Storm Drainage Report Dear Shane, Please accept the following letter report on behalf of the Fort Collins Housing Authority for the low income housing development demonstrating the site’s ability to comply with the City’s stormwater requirements. 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. 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 improvements. The existing site is approximately 2.7% impervious, including the west half of Redwood St. The existing 100-yr peak runoff rate to the existing detention pond and Redwood St is 18.33 cfs and 20.71 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. The existing runoff rates, stated above, are referenced for the stormwater release rates for the proposed improvements. All calculations and exhibits are attached. PROPOSED DEVELOPMENT 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 FCHA Villages on Redwood – Preliminary Storm Drainage Report July 15, 2015 Page 2 of 3 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 D4), and the remaining basin draining towards Redwood St (Basins D1, D2, and D3). In general, the basin limits are maintained for the areas draining to the existing detention pond and towards Redwood, though there is a small portion of developed area draining to the existing detention pond (Basin D4). This causes an increase of 0.05 cfs to the existing pond and is considered negligible. Runoff from Basins D1 and D2 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 D3) 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 St are estimated to be 18.38 cfs and 27.59 cfs, respectively. Detaining the developed runoff to the existing 100-yr runoff rate for the basin draining towards Redwood, in addition to accounting for the undetained portions that drain directly to Redwood, requires a detention volume of 0.125 acre-ft. The undetained portion has a runoff rate of 4.89 cfs, combined with detention pond release rate of 15.82 cfs, has a peak 100-yr runoff rate of 20.71 cfs, equal to the existing 100-yr runoff rate. All preliminary calculations and exhibits are attached for reference. LOW IMPACT DEVELOPMENT TECHNIQUES In reference to the code requirements for implementation of Low Impact Development (LID) techniques, we have looked at many options to satisfy these requirements. This project is pursuing alternative compliance in regards to substituting the permeable paver requirement by treating 100% of the site by other LID techniques. The main LID being proposed to be implemented onsite is a bioretention rain garden located near the southeast corner of the site. Approximately 80% of the developed site is proposed to be treated by the rain garden and the remaining developed area will be treated by a combination of grass buffers and grass swales. The rain garden is designed to directly spill into the detention area for events beyond the capacity of the rain garden. The rain garden is designed to have a maximum depth of 12 inches. 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. Preliminary calculations are attached for reference. 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. 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, FCHA Villages on Redwood – Preliminary Storm Drainage Report July 15, 2015 Page 3 of 3 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) 347-8917. Sincerely, Jason T. Claeys, P.E., LEED AP Interwest Consulting Group Attachments Hydrologic Soil Group—Larimer County Area, Colorado (FCHA - Villages at Redwood) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/29/2015 Page 1 of 4 4494910 4494940 4494970 4495000 4495030 4495060 4495090 4494910 4494940 4494970 4495000 4495030 4495060 4495090 494050 494080 494110 494140 494170 494200 494230 494260 494290 494320 494350 494050 494080 494110 494140 494170 494200 494230 494260 494290 494320 494350 40° 36' 24'' N 105° 4' 13'' W 40° 36' 24'' N 105° 4' 0'' W 40° 36' 17'' N 105° 4' 13'' 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: 1:1,440 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 3.4 47.1% 73 Nunn clay loam, 0 to 1 percent slopes C 3.8 52.9% Totals for Area of Interest 7.2 100.0% Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition Hydrologic Soil Group—Larimer County Area, Colorado FCHA - Villages at Redwood Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/29/2015 Page 3 of 4 Component Percent Cutoff: None Specified Tie-break Rule: Higher Hydrologic Soil Group—Larimer County Area, Colorado FCHA - Villages at Redwood Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/29/2015 Page 4 of 4 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% 20.71 6.049 47.3% 27.59 H1 compared to D1+D2+D3 To Existing Pond 3.785 0.0% 18.33 3.953 1.5% 18.38 H2+OF1 compared to D4 Totals 10.002 2.7% 39.04 10.002 29.2% 45.97 Basins Notes Historical Developed T.Alva Interwest Consulting Group 1237-112-00 7/15/2015 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: C5 C10 C100 C5 C10 C100 0.90 0.92 0.96 0.90 0.92 0.96 0.73 0.75 0.81 0.75 0.77 0.83 0.73 0.75 0.81 0.75 0.77 0.83 0.30 0.36 0.50 0.35 0.42 0.58 0.08 0.15 0.35 0.15 0.25 0.50 C5 C10 C100 H1 C 270,830 6.217 11,888 0 0 0 258,941 4.4% 0.18 0.27 0.52 H2 C 162,764 3.737 0 0 0 0 162,764 0.0% 0.15 0.25 0.50 OF1 C 2,110 0.048 0 0 0 0 2,110 0.0% 0.15 0.25 0.50 Total C 435,704 10.002 11,888 0 0 0 421,705 2.7% 0.17 0.27 0.51 COMPOSITE Hydrologic Soil Hydrologic Soil Gravel Classification B Roof Paved Walk Lawns, clayey soil Land Use Classification C Runoff Coefficient Runoff Coefficient % Impervious 100% 90% 90% 40% 0% T.Alva Interwest Consulting Group 1237-112-00 7/15/2015 % Impervious values from Table RO-3 in the Urban Storm Drainage Criteria Manual for Hydrologic Soil Classifications 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) 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 0.18 6.217 419 0.0043 45.81 495 0.0059 Paved Areas 20 1.54 5.37 51.19 15.08 15.08 H2 H2 0.15 3.737 32 0.2582 3.36 0 0.0001 Tilage/Field 5 0.05 0.00 5.00 10.18 5.00 All Overland Flow OF1 OF1 0.15 0.048 15 0.0802 3.42 38 0.0251 Tilage/Field 5 0.79 0.81 5.00 10.30 5.00 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) SUB-BASIN DATA INITIAL/OVERLAND TIME (ti ) T.Alva Interwest Consulting Group 1237-112-00 7/15/2015 DESIGN POINT Sub-basin C5 AREA (acres) LENGTH (ft) SLOPE (ft/ft) ti (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) 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 1-5yr = 1.14 in P 1-10yr = 1.40 in P 1-100yr = 2.86 in BASINS: 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 6.217 15.08 0.18 1.11 2.58 2.85 0.27 1.71 3.16 5.40 0.52 3.20 6.46 20.71 H2 H2 3.737 5.00 0.15 0.56 3.86 2.16 0.25 0.93 4.74 4.43 0.50 1.87 9.68 18.09 OF1 OF1 0.048 5.00 0.15 0.01 3.86 0.03 0.25 0.01 4.74 0.06 0.50 0.02 9.68 0.23 5-yr Peak Runoff 100-yr Peak Runoff T.Alva Interwest Consulting Group 1237-112-00 7/15/2015 City of Fort Collins - Storm Water Criteria Manual (1997) Design Point Sub-basin Area (acres) tc (min) 10-yr Peak Runoff Q n = C n I n A n 0.786651) 1 ( 10 ) 28 . 5 t c P I + = 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: 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 129,793 2.980 25,906 23,986 8,542 0 71,360 42.5% 0.29 0.36 0.43 0.59 D2 C 85,386 1.960 24,566 14,573 5,238 0 41,009 49.7% 0.34 0.40 0.46 0.60 D3 C 48,328 1.109 17,121 4,612 6,328 0 20,267 55.8% 0.38 0.43 0.49 0.62 D4 C 172,194 3.953 0 2,427 532 0 169,235 1.5% 0.05 0.16 0.26 0.51 Total C 435,702 10.002 67,593 45,598 20,640 0 301,871 29.2% 0.22 0.30 0.38 0.57 To Rain Garden (D1+D2) C 215,180 4.940 50,472 38,560 13,779 0 112,369 45.3% 0.31 0.37 0.44 0.59 To Redwood (D1+D2+D3) C 263,508 6.049 67,593 43,172 20,107 0 132,635 47.3% 0.32 0.38 0.45 0.60 T.Alva Interwest Consulting Group 1237-112-00 7/15/2015 % 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% Weighted % COMPOSITE Impervious Alawn (sq feet) Apavers (sq feet) Lawns, clayey soil Awalk (sq feet) Aroof (sq feet) 0% Pavers 40% 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 0.36 2.980 19 0.0385 3.81 332 0.0099 Paved Areas 20 1.99 2.77 6.59 11.95 6.59 D2 D2 0.40 1.960 79 0.0292 8.03 274 0.0110 Paved Areas 20 2.10 2.18 10.20 11.96 10.20 D3 D3 0.43 1.109 67 0.0425 6.19 485 0.0046 Paved Areas 20 1.36 5.94 12.13 13.06 12.13 D4 D4 0.16 3.953 37 0.0530 6.02 0 0.0001 Paved Areas 20 0.20 0.00 6.02 10.21 6.02 All Overland Flow T.Alva Interwest Consulting Group 1237-112-00 July 15, 2015 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) 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: I = rainfall intensity (in/hr) Q n = n -yr peak discharge (cfs) P 1 = one-hour point rainfall depth (in) C n = n -yr runoff coefficient t c = time of concentration (min) I n = n -yr rainfall intensity (in/hr) P 1-5yr = 1.14 in A n = Basin drainage area (ac) P 1-10yr = 1.40 in P 1-100yr = 2.86 in BASINS: 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 2.980 6.59 0.36 1.07 3.57 3.83 0.43 1.27 4.38 5.56 0.59 1.75 8.95 15.65 D2 D2 1.960 10.20 0.40 0.78 3.05 2.37 0.46 0.89 3.75 3.35 0.60 1.18 7.66 9.04 D3 D3 1.109 12.13 0.43 0.48 2.84 1.36 0.49 0.54 3.49 1.88 0.62 0.69 7.13 4.89 D4 D4 3.953 6.02 0.16 0.63 3.66 2.32 0.26 1.02 4.50 4.61 0.51 2.00 9.19 18.38 100-yr Peak Runoff T.Alva Interwest Consulting Group 1237-112-00 7/15/2015 10-yr Peak Runoff Design Point Sub-basin Area (acres) tc (min) 5-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. P1-100yr = 2.86 P1-10yr = 1.40 in. BASINS: UD-Sewer - DP/Manhole D1 Contributing Basins D1+D2 Contributing Area (acres) 4.94 C5 C10 C100 Runoff Coefficients 0.37 0.44 0.59 Overland Flow Time Length (ft) 19 Slope (ft/ft) 0.04 ti (min) 3.74 Travel Time Length (ft) Slope (%) Type of Travel Surface Cv Velocity (ft/s) tt (min) 332 0.99% Paved Areas 20 1.99 2.77 112 0.50% Paved Areas 20 1.41 1.33 102 0.50% Paved Areas 20 1.41 1.20 57 0.50% Paved Areas 20 1.41 0.67 16 0.50% Paved Areas 20 1.41 0.19 Total Time 6.15 Final Time of Concentration - tc (min) tc (min) 9.89 Intensities (in/hr) 5-yr 10-yr 100-yr 3.09 3.80 7.75 Discharge (cfs) 5-yr 10-yr 100-yr 5.71 8.21 22.70 T.Alva Interwest Consulting Group 1237-112-00 July 15, 2015 City of Fort Collins - Storm Water Criteria Manual (1997) ( ) 0 .786 1 10 28 . 5 t c P Project: Basin ID: Design Information (Input): Design Information (Input): Catchment Drainage Imperviousness Ia = 45.30 percent Catchment Drainage Imperviousness I a = 45.30 percent Catchment Drainage Area A = 4.940 acres Catchment Drainage Area A = 4.940 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 = 5 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 = 3.20 cfs/acre Allowable Unit Release Rate q = 3.20 cfs/acre One-hour Precipitation P1 = 1.14 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 = 0.37 Runoff Coefficient C = 0.59 Inflow Peak Runoff Qp-in = 5.65 cfs Inflow Peak Runoff Qp-in = 22.61 cfs Allowable Peak Outflow Rate Qp-out = 15.82 cfs Allowable Peak Outflow Rate Qp-out = 15.82 cfs Mod. FAA Minor Storage Volume = 0 cubic feet Mod. FAA Major Storage Volume = 5,448 cubic feet Mod. FAA Minor Storage Volume = 0.000 acre-ft Mod. FAA Major Storage Volume = 0.125 acre-ft 5 <- 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) 0 0.00 0.000 0.00 0.00 0.000 0.000 0 0.00 0.000 0.00 0.00 0.000 0.000 5 3.86 0.049 1.00 15.82 0.109 -0.060 5 9.68 0.194 1.00 15.82 0.109 0.085 10 3.08 0.077 0.99 15.73 0.217 -0.139 10 7.72 0.310 0.99 15.73 0.217 0.093 15 2.58 0.098 0.83 13.13 0.271 -0.174 15 6.48 0.390 0.83 13.13 0.271 0.119 20 2.24 0.113 0.75 11.82 0.326 -0.213 20 5.61 0.451 0.75 11.82 0.326 0.125 25 1.98 0.125 0.70 11.04 0.380 -0.255 25 4.97 0.499 0.70 11.04 0.380 0.119 30 1.78 0.135 0.66 10.52 0.435 -0.300 30 4.48 0.539 0.66 10.52 0.435 0.105 35 1.63 0.143 0.64 10.15 0.489 -0.346 35 4.08 0.573 0.64 10.15 0.489 0.084 40 1.50 0.151 0.62 9.87 0.544 -0.393 40 3.76 0.603 0.62 9.87 0.544 0.060 45 1.39 0.157 0.61 9.65 0.598 -0.441 45 3.48 0.630 0.61 9.65 0.598 0.031 50 1.30 0.163 0.60 9.47 0.653 -0.489 50 3.25 0.653 0.60 9.47 0.653 0.001 55 1.22 0.169 0.59 9.33 0.707 -0.538 55 3.06 0.675 0.59 9.33 0.707 -0.032 60 1.15 0.174 0.58 9.21 0.761 -0.588 60 2.88 0.694 0.58 9.21 0.761 -0.067 65 1.09 0.178 0.58 9.11 0.816 -0.638 65 2.73 0.712 0.58 9.11 0.816 -0.104 70 1.03 0.182 0.57 9.03 0.870 -0.688 70 2.60 0.729 0.57 9.03 0.870 -0.141 75 0.99 0.186 0.57 8.95 0.925 -0.739 75 2.47 0.745 0.57 8.95 0.925 -0.180 80 0.94 0.190 0.56 8.89 0.979 -0.789 80 2.37 0.760 0.56 8.89 0.979 -0.220 85 0.90 0.193 0.56 8.83 1.034 -0.840 85 2.27 0.774 0.56 8.83 1.034 -0.260 90 0.87 0.197 0.55 8.78 1.088 -0.892 90 2.18 0.787 0.55 8.78 1.088 -0.302 95 0.84 0.200 0.55 8.73 1.143 -0.943 95 2.10 0.799 0.55 8.73 1.143 -0.344 100 0.81 0.203 0.55 8.69 1.197 -0.995 100 2.02 0.811 0.55 8.69 1.197 -0.386 105 0.78 0.206 0.55 8.65 1.252 -1.046 105 1.95 0.822 0.55 8.65 1.252 -0.430 110 0.75 0.208 0.54 8.62 1.306 -1.098 110 1.89 0.833 0.54 8.62 1.306 -0.473 115 0.73 0.211 0.54 8.59 1.361 -1.150 115 1.83 0.843 0.54 8.59 1.361 -0.517 Sheet 1 of 2 Designer: Company: Date: Project: Location: 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, Ia Ia = 45.3 % (100% if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.453 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.15 watershed inches (WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i) D) Contributing Watershed Area (including rain garden area) Area = 215,180 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 = 2,779.2 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 = 1853 sq ft D) Actual Flat Surface Area AActual = 1950 sq ft E) Area at Design Depth (Top Surface Area) ATop = 2500 sq ft F) Rain Garden Total Volume VT= 2,225 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 = 3.5 ft Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours Vol12 = 2,779 cu ft iii) Orifice Diameter, 3/8" Minimum DO = 1.08 in Design Procedure Form: Rain Garden (RG) J. Claeys Interwest Consulting Group July 15, 2015 FCHA - 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 7/15/2015, 10:54 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 NO SPRINKLER HEADS ON FLAT SURFACE A) Will the rain garden be irrigated? Notes: Design Procedure Form: Rain Garden (RG) J. Claeys Interwest Consulting Group July 15, 2015 FCHA - 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 7/15/2015, 10:54 AM 120 0.71 0.213 0.54 8.56 1.415 -1.202 120 1.77 0.853 0.54 8.56 1.415 -0.562 125 0.69 0.216 0.54 8.54 1.470 -1.254 125 1.72 0.863 0.54 8.54 1.470 -0.607 130 0.67 0.218 0.54 8.51 1.524 -1.306 130 1.67 0.872 0.54 8.51 1.524 -0.652 135 0.65 0.220 0.54 8.49 1.579 -1.358 135 1.63 0.881 0.54 8.49 1.579 -0.698 140 0.63 0.222 0.54 8.47 1.633 -1.411 140 1.58 0.890 0.54 8.47 1.633 -0.744 145 0.61 0.224 0.53 8.45 1.688 -1.463 145 1.54 0.898 0.53 8.45 1.688 -0.790 150 0.60 0.226 0.53 8.43 1.742 -1.516 150 1.50 0.906 0.53 8.43 1.742 -0.836 155 0.59 0.228 0.53 8.41 1.797 -1.568 155 1.47 0.914 0.53 8.41 1.797 -0.883 160 0.57 0.230 0.53 8.40 1.851 -1.621 160 1.43 0.921 0.53 8.40 1.851 -0.930 165 0.56 0.232 0.53 8.38 1.905 -1.673 165 1.40 0.929 0.53 8.38 1.905 -0.977 170 0.55 0.234 0.53 8.37 1.960 -1.726 170 1.37 0.936 0.53 8.37 1.960 -1.024 175 0.53 0.236 0.53 8.36 2.014 -1.779 175 1.34 0.943 0.53 8.36 2.014 -1.072 180 0.52 0.237 0.53 8.34 2.069 -1.832 180 1.31 0.950 0.53 8.34 2.069 -1.119 185 0.51 0.239 0.53 8.33 2.123 -1.884 185 1.29 0.956 0.53 8.33 2.123 -1.167 190 0.50 0.241 0.53 8.32 2.178 -1.937 190 1.26 0.963 0.53 8.32 2.178 -1.215 195 0.49 0.242 0.53 8.31 2.232 -1.990 195 1.24 0.969 0.53 8.31 2.232 -1.263 200 0.48 0.244 0.52 8.30 2.287 -2.043 200 1.21 0.975 0.52 8.30 2.287 -1.312 205 0.48 0.245 0.52 8.29 2.341 -2.096 205 1.19 0.981 0.52 8.29 2.341 -1.360 210 0.47 0.247 0.52 8.28 2.396 -2.149 210 1.17 0.987 0.52 8.28 2.396 -1.409 215 0.46 0.248 0.52 8.27 2.450 -2.202 215 1.15 0.993 0.52 8.27 2.450 -1.457 220 0.45 0.250 0.52 8.27 2.505 -2.255 220 1.13 0.999 0.52 8.27 2.505 -1.506 225 0.44 0.251 0.52 8.26 2.559 -2.308 225 1.11 1.004 0.52 8.26 2.559 -1.555 230 0.44 0.252 0.52 8.25 2.614 -2.361 230 1.09 1.010 0.52 8.25 2.614 -1.604 235 0.43 0.254 0.52 8.24 2.668 -2.414 235 1.08 1.015 0.52 8.24 2.668 -1.653 240 0.42 0.255 0.52 8.24 2.723 -2.468 240 1.06 1.020 0.52 8.24 2.723 -1.702 245 0.42 0.256 0.52 8.23 2.777 -2.521 245 1.04 1.025 0.52 8.23 2.777 -1.752 250 0.41 0.258 0.52 8.22 2.832 -2.574 250 1.03 1.031 0.52 8.22 2.832 -1.801 255 0.40 0.259 0.52 8.22 2.886 -2.627 255 1.01 1.035 0.52 8.22 2.886 -1.851 260 0.40 0.260 0.52 8.21 2.941 -2.680 260 1.00 1.040 0.52 8.21 2.941 -1.900 265 0.39 0.261 0.52 8.21 2.995 -2.734 265 0.98 1.045 0.52 8.21 2.995 -1.950 270 0.39 0.262 0.52 8.20 3.049 -2.787 270 0.97 1.050 0.52 8.20 3.049 -2.000 275 0.38 0.264 0.52 8.19 3.104 -2.840 275 0.96 1.055 0.52 8.19 3.104 -2.049 280 0.38 0.265 0.52 8.19 3.158 -2.894 280 0.94 1.059 0.52 8.19 3.158 -2.099 285 0.37 0.266 0.52 8.18 3.213 -2.947 285 0.93 1.064 0.52 8.18 3.213 -2.149 290 0.37 0.267 0.52 8.18 3.267 -3.000 290 0.92 1.068 0.52 8.18 3.267 -2.199 295 0.36 0.268 0.52 8.18 3.322 -3.054 295 0.91 1.073 0.52 8.18 3.322 -2.249 300 0.36 0.269 0.52 8.17 3.376 -3.107 300 0.89 1.077 0.52 8.17 3.376 -2.300 Mod. FAA Minor Storage Volume (cubic ft.) = 0 Mod. FAA Major Storage Volume (cubic ft.) = 5,448 Mod. FAA Minor Storage Volume (acre-ft.) = 0.0000 Mod. FAA Major Storage Volume (acre-ft.) = 0.1251 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 2.35, Released January 2015 Determination of MINOR Detention Volume Using Modified FAA Method DETENTION VOLUME BY THE MODIFIED FAA METHOD FCHA - Villages at Redwood 1237-112-00 UD-Detention_v2.35.xls, Modified FAA 7/15/2015, 10:52 AM I + 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 5 0 . 395 1 . 1 S C L ti − = = ( ) 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 = Walk 90% ( ) 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 = Weighted % Impervious 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 (FCHA - Villages at Redwood) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/29/2015 Page 2 of 4