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HomeMy WebLinkAboutREDTAIL PONDS - PDP - PDP130030 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTBOULDER I FORT COLLINS I WINTER PARK JVA, Incorporated 25 Old Town Square Suite 200 Fort Collins, CO 80524 Ph: 970.225.9099 Fax: 970.225.6923 Toll Free: 877.444.1951 Web site: www.jvajva.com E-mail: info@jvajva.com September 6, 2013 Mr. Wes Lamarque City of Fort Collins – Stormwater Utilities 700 Wood Street Fort Collins, CO 80524 RE: Drainage Letter and Drainage Variance Request Fort Collins Housing Authority (FCHA) – Permanent Supporting Housing JVA Job No. 1980c Dear Mr. Lamarque: This letter is prepared to summarize the drainage concept, solutions and changes in impervious area associated with the site improvements for the FCHA Permanent Supportive Housing in the Redtail Sub-Division in the City of Fort Collins. JVA has met with Basil Hamdan and Glen Schlueter with the City to review the drainage concepts discussed below. JVA is presenting this drainage letter to you for approval of the storm drainage concepts and approach to detention requirements. This letter also contains a request for variance from the City’s storm drainage detention requirements. A Final Drainage Report for this project will be prepared for submittal based on the City’s feedback on this drainage letter and variance request. Once the drainage report is finalized, a copy will be submitted for review. Existing Drainage Patterns The existing 2.93 acre site is currently undeveloped. Approximately two-thirds of the site has been used to stockpile earthwork and riprap where it has been accessed from Conejos Road and Fossil Boulevard. Sub-Basins H1 and H2, shown on the attached Drainage Figure 1, sheet flow to the north and northwest. Basin H1 represents drainage that sheet flows to the existing Conejos Road. Basin H2 sheet flows to the wetlands directly west of the site. Basins H3 and H4 sheet flow along steep slopes ( > 7%) to the east and towards South College Avenue. Rational method calculations with peak flows for the individual sub-basins are attached to this letter. In summary, the site has a calculated imperviousness of 2% and a peak 100-year storm event runoff of 7.2 Cubic Feet per Second (CFS). FCHA – Permanant Supportive Housing September 6, 2013 2 of 3 BOULDER I FORT COLLINS I WINTER PARK Proposed Drainage Patterns FCHA proposes to construct a building with associated parking, driveway and roadway improvements, walks, retaining walls and other features throughout the site. The overall imperviousness of the site will increase from 2% to 37.2%. FCHA proposes to access the site from the same existing location in Conejos Road and Fossil Boulevard. Per historic drainage patterns, the majority of the site has been graded to drain towards the east and South College Avenue. The attached Figure 2 shows the proposed drainage Sub-Basins and grading plan. Respectively the peak 100-year storm event runoff from the entire site will increase from 7.2 CFS to 12.7 CFS. (See attached rational method calculations) Proposed Water Quality and Detention Facilities Under the original Drainage and Erosion Control Report for Redtail Sub-division by North Star Design, Inc. (dated November 29 th , 2005), the proposed site falls within Sub-Basins 17, 18, 19, 20, 21, 22, 23 and 24 of the Redtail Drainage Plan, Sheet 15. Excerpts of the report and drainage mapping are attached for reference. Under this previously proposed design, Tract I near the southwest corner of the site was designated for the area’s Water Quality Capture Volume needs. No stormwater detention was proposed at that time. Since the previous approval of the original 2005 Redtail report, the City has observed the need for stormwater detention from properties along the South College Avenue corridor in the vicinity of the site. The City has therefore required FCHA provide detention for the eastern majority of the site. The previously approved design for the site consisted of single family residential development with nearly 79% imperviousness over 2.86 acres, and a peak 100-year storm runoff rate of 28.5 CFS. The currently proposed FCHA development has substantially lower imperviousness at 37.2% and peak 100-year storm runoff rate of 12.7 CFS. The catchment area in question (Sub-Basins A1-A4) is 2.66 acres. The latest detention volume calculation spreadsheet provided by UDFCD (version 2.33 Modified FAA Method) estimates the need for nearly 12,000 cubic feet of detention storage when released at the historic 5-year runoff rate of 1.98 CFS, or roughly 0.76 CFS per Acre. Tract I can accommodate as much as 7,200 cubic feet of storage by use of vertical walls and 5-foot depth. Additional detention storage, approximately 4,500 cubic feet, can be provided in the median of the parking area and underground, underneath the permeable pavers. Total maximum storage with the currently proposed site layout is approximately 11,700 cubic feet. Water Quality Capture Volume (WQCV) requirement was calculated to be 2,309 cubic feet using UDFCD Best Management Practice calculation spreadsheet (version 3.02). FCHA – Permanant Supportive Housing September 6, 2013 3 of 3 BOULDER I FORT COLLINS I WINTER PARK Request for Variance to Reduce Detention Requirements As demonstrated in the previous section, it will be difficult to provide large storm event detention storage in addition to the current site layout on a steeply sloped property that was not graded with or designed to accommodate large detention requirements. In spite of a reduced area and peak runoff from previous design to current design, Tract I is not an adequate area for large storm event detention needs. On behalf of Fort Collins Housing Authority JVA Inc. is requesting variance from the City of Fort Collins WQCV and stormwater detention requirements listed below: • 100-yr storage volume release rate to be increased from the 2-year historic release rate to the 5-year or 10-year release rate. This represents a change in peak runoff from 1.4 CFS to 2.0 or 2.4 CFS. • WQCV can be considered within the 100-year storage volume rather than in addition to it. This represents a 2,309 cubic feet reduction in required volume. Erosion and Sediment Control During construction there will be temporary erosion and sediment control practices used to limit soil erosion. These temporary erosion control devices include curb rock socks, inlet protecting, stabilized construction entrance and silt fence. The detention and water quality facility in Tract I will serve as a location to further mitigate sediment and erosion conveyed from the upstream storm sewer system until landscaping is fully established. Additionally, the spillway from the detention facility will be sized and armored with riprap to prevent any erosion from the discharge from the spillway and water quality outlet. We appreciate your time and consideration in reviewing this letter and variance request. Please feel free to contact us at JVA Inc. to discuss any questions you may have, (303) 444-1951. Sincerely, JVA, INCORPORATED By: ________________________________ Jason Clayes, P.E. Project Manger ________________________________ Robin L. Kriss, P.E. Project Engineer CC: Kristin Fritz JVA Incorporated Job Name: FCHA-PSH I% C2 C100 25 Old Town Square Job Number: 1980c Streets Paved 100% 0.95 1.00 Fort Collins, CO 80524 Date: 9/5/13 Concrete Drives/Walks 100% 0.95 1.00 Ph: 970.225.9099 By: RLK Roof 100% 0.95 1.00 Fax: 970.225.6923 Gravel 50% 0.50 0.63 Playground 20% 0.20 0.25 FCHA-PSH Lawn - Flat (<2%) 2% 0.20 0.25 Historic Runoff Coefficient & Time of Concentration Calculations Lawn - Medium (2-7%) 2% 0.25 0.31 Location: Fort Collins Lawn - Steep > 7% 2% 0.35 0.44 Minor Design Storm: 2 Major Design Storm: 100 Soil Type: C/D Basin Design Data I (%) = 95% 95% 95% 50% 50% 2% 2% 2% I (%) tc Comp tc Final Basin Name Design Point Apaved streets (sf) Adrives/co nc (sf) Aroof (sf) Agravel (sf) Aplygnd (sf) Alawn- FLAT (sf) Alawn- MED (sf) Alawn- STEEP (sf) ATotal (sf) ATotal (ac) Imp (%) C2 C5 C10 C100 Upper most Length (ft) Slope (%) ti (min) Length (ft) Slope (%) Type of Land Surface Cv JVA Incorporated Job Name: FCHA-PSH I% C2 C100 25 Old Town Square Job Number: 1980c Streets, Parking, Drives 100% 0.95 1.00 Fort Collins, CO 80524 Date: 9/5/13 Concrete/Asphalt Drives 90% 0.95 1.00 Ph: 970.225.9099 By: RLK Roof 90% 0.95 1.00 Fax: 970.225.6923 Permeable Pavers 40% 0.50 0.63 FCHA-PSH Lawn - Flat (<2%) 0% 0.20 0.25 Composite Runoff Coefficient Calculations Lawn - Medium (2-7%) 2% 0.25 0.31 Location: Fort Collins Lawn - Steep > 7% 2% 0.35 0.44 Minor Design Storm: 2 Major Design Storm: 100 Soil Type: C/D I (%) = 100% 90% 90% 40% 0% 2% 2% I (%) Basin Name Design Point Apaved streets (sf) Adrives/c onc (sf) Aroof (sf) Apavers (sf) Alawn- FLAT (sf) Alawn- MED (sf) Alawn- STEEP (sf) ATotal (sf) ATotal (ac) Imp (%) C2 C100 OS-1 1 1,248 802 2,050 0.05 61.7% 0.72 0.78 OS-2 2 907 9,170 10,077 0.23 10.8% 0.40 0.49 A1 3 19,881 3,100 4,517 7,878 35,376 0.81 69.2% 0.73 0.79 A2 4 4,400 11,065 2,389 6,842 9,398 8,648 42,742 0.98 35.6% 0.53 0.59 A3 5 1,680 2,090 3,970 6,662 14,402 0.33 12.0% 0.37 0.44 A4 6 1,331 1,538 20,267 23,136 0.53 7.1% 0.38 0.46 BAINS A1-A4 19,881 7,411 14,165 6,906 16,810 14,906 35,577 115,656 2.66 37.2% 0.54 0.61 Runoff Coeff's Basin Design Data BAINS A1-A4 19,881 7,411 14,165 6,906 16,810 14,906 35,577 115,656 2.66 37.2% 0.54 0.61 BAINS OS-1 & OS-2 2,155 9,972 12,127 0.28 19.4% 0.46 0.54 TOTAL SITE 22,036 7,411 14,165 6,906 16,810 14,906 45,549 127,783 2.93 35.5% 0.53 0.60 1980c - Rational Calculations Developed C Page 2 of 5 JVA Incorporated Job Name: FCHA-PSH 25 Old Town Square Job Number: 1980c Fort Collins, CO 80524 Date: 9/5/13 Ph: 970.225.9099 By: RLK Fax: 970.225.6923 FCHA-PSH Time of Concentration Calculations Location: Fort Collins Minor Design Storm: 2 Major Design Storm: 100 Soil Type: C/D Sub-Basin Data tc Comp tc Final Basin Name Design Point ATotal (ac) C5 Upper most Length (ft) Slope (%) ti (min) Length (ft) Slope (%) Type of Land Surface Cv Velocity (fps) tt (min) Time of Conc ti + tt = tc Total Length (ft) tc =(L/180)+ 10 (min) Min tc OS-1 1 0.05 0.72 35 2.0% 3.3 Paved areas & shallow paved swales 20 0.0 0.0 3.3 35 10.2 5.0 OS-2 2 0.23 0.40 86 8.0% 5.9 Nearly bare ground 10 0.0 0.0 5.9 86 10.5 5.9 A1 3 0.81 0.73 60 2.0% 4.2 120 0.5% Paved areas & shallow paved swales 20 1.4 1.4 5.6 180 11.0 5.6 A2 4 0.98 0.53 40 2.0% 5.3 110 1.0% JVA Incorporated Job Name: FCHA-PSH 25 Old Town Square Job Number: 1980c Fort Collins, CO 80524 Date: 9/5/13 Ph: 970.225.9099 By: RLK Fax: 970.225.6923 FCHA-PSH Developed Storm Runoff Calculations Design Storm : 100 Year Point Hour Rainfall (P1) : 2.86 I = (28.5 P1) / ((10 + TC)^0.786651) Basin Name Design Point Area (ac) Runoff Coeff tc (min) C*A (ac) I (in/hr) Q (cfs) Total tc (min) ΣC*A (ac) I (in/hr) Q (cfs) Inlet Type Q intercepted Q carryover Pipe Size (in) or equivalent Pipe Material Slope (%) Pipe Flow (cfs) Max Pipe Capacity (cfs) Length (ft) Velocity (fps) tt (min) Total Time (min) Notes OS-1 1 0.05 0.78 5.00 0.04 9.70 0.36 OS-2 2 0.23 0.49 5.90 0.11 9.27 1.05 5.90 0.15 9.27 1.39 1.4 A1 3 0.81 0.79 5.60 0.64 9.41 6.00 5.60 0.64 9.41 6.00 Area Drain 15 in PVC 0.5% 6.0 6.4 280 10.0 0.47 6.07 A2 4 0.98 0.59 6.20 0.58 9.13 5.32 6.20 1.22 9.13 11.14 Fileld Inlets 15 in PVC 1.6% 11.1 11.4 160 10.0 0.27 6.47 A3 5 0.33 0.44 7.10 0.15 8.75 1.28 7.10 1.37 8.75 11.96 Area Drains 15 in PVC 2.0% 12.0 12.8 5 10.0 0.01 7.11 A4 6 0.53 0.46 11.90 0.25 7.20 1.77 11.90 0.39 7.20 2.82 Basins A1-A4 11.90 1.61 7.20 11.61 11.6 11.90 1.76 7.20 12.69 12.7 Pipe/Swale Travel Time Entire Site Direct Runoff Total Runoff Inlets Pipe 1980c - Rational Calculations Q100 Page 4 of 5 JVA Incorporated Job Name: FCHA-PSH 25 Old Town Square Job Number: 1980c Fort Collins, CO 80524 Date: 9/5/13 Ph: 970.225.9099 By: RLK Fax: 970.225.6923 FCHA-PSH Developed Storm Runoff Calculations Design Storm : 2 Year Point Hour Rainfall (P1) : 0.82 I = (28.5 P1) / ((10 + TC)^0.786651) Basin Name Design Point Area (ac) Runoff Coeff tc (min) C*A (ac) I (in/hr) Q (cfs) Total tc (min) ΣC*A (ac) I (in/hr) Q (cfs) Inlet Type Q intercepted Q carryover Pipe Size (in) or equivalent Pipe Material Slope (%) Pipe Flow (cfs) Max Pipe Capacity (cfs) Length (ft) Velocity (fps) tt (min) Total Time (min) Notes OS-1 1 0.05 0.72 5.00 0.03 2.78 0.09 OS-2 2 0.23 0.40 5.90 0.09 2.66 0.25 5.90 0.13 2.65 0.34 0.3 A1 3 0.81 0.73 5.60 0.59 2.70 1.59 5.60 0.59 2.70 1.59 1.6 A2 4 0.98 0.53 6.20 0.52 2.62 1.36 6.20 1.11 2.62 2.90 2.9 A3 5 0.33 0.37 7.10 0.12 2.51 0.31 7.10 1.23 2.51 3.09 3.1 A4 6 0.53 0.38 11.90 0.20 2.07 0.41 11.90 0.20 2.07 0.41 0.4 Basins A1-A4 11.90 1.43 2.07 2.96 3.0 5.60 1.56 2.70 4.20 4.2 Pipe/Swale Travel Time Entire Site Direct Runoff Total Runoff Inlets Pipe 1980c - Rational Calculations Q Minor Page 5 of 5 Project: Basin ID: Design Information (Input): Design Information (Input): Catchment Drainage Imperviousness Ia = 37.20 percent Catchment Drainage Imperviousness I a = 37.20 percent Catchment Drainage Area A = 2.660 acres Catchment Drainage Area A = 2.660 acres Predevelopment NRCS Soil Group Type = C A, B, C, or D Predevelopment NRCS Soil Group Type = C A, B, C, or D Return Period for Detention Control T = 2 years (2, 5, 10, 25, 50, or 100) Return Period for Detention Control T = 100 years (2, 5, 10, 25, 50, or 100) Time of Concentration of Watershed Tc = 12 minutes Time of Concentration of Watershed Tc = 12 minutes Allowable Unit Release Rate q = 0.76 cfs/acre Allowable Unit Release Rate q = 0.76 cfs/acre One-hour Precipitation P1 = 0.82 inches One-hour Precipitation P 1 = 2.86 inches Design Rainfall IDF Formula i = C1* P1 /(C2+Tc )^C3 Design Rainfall IDF Formula i = C1 * P1/(C2 +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 = 0.78665 Coefficient Three C 3 = 0.78665 Determination of Average Outflow from the Basin (Calculated): Determination of Average Outflow from the Basin (Calculated): Runoff Coefficient C = 0.26 Runoff Coefficient C = 0.58 Inflow Peak Runoff Qp-in = 1.43 cfs Inflow Peak Runoff Qp-in = 11.09 cfs Allowable Peak Outflow Rate Qp-out = 2.02 cfs Allowable Peak Outflow Rate Qp-out = 2.02 cfs Mod. FAA Minor Storage Volume = 0 cubic feet Mod. FAA Major Storage Volume = 11,960 cubic feet Mod. FAA Minor Storage Volume = 0.000 acre-ft Mod. FAA Major Storage Volume = 0.275 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 2.78 0.013 1.00 2.02 0.014 -0.001 5 9.68 0.103 1.00 2.02 0.014 0.089 10 2.21 0.021 1.00 2.02 0.028 -0.007 10 7.72 0.164 1.00 2.02 0.028 0.136 15 1.86 0.027 0.90 1.81 0.037 -0.011 15 6.48 0.207 0.90 1.81 0.037 0.169 20 1.61 0.031 0.80 1.61 0.044 -0.014 20 5.61 0.239 0.80 1.61 0.044 0.194 25 1.43 0.034 0.74 1.49 0.051 -0.017 25 4.97 0.264 0.74 1.49 0.051 0.213 30 1.28 0.037 0.70 1.41 0.058 -0.022 30 4.48 0.285 0.70 1.41 0.058 0.227 35 1.17 0.039 0.67 1.35 0.065 -0.026 35 4.08 0.303 0.67 1.35 0.065 0.238 40 1.08 0.041 0.65 1.31 0.072 -0.031 40 3.76 0.319 0.65 1.31 0.072 0.247 45 1.00 0.043 0.63 1.28 0.079 -0.036 45 3.48 0.333 0.63 1.28 0.079 0.254 50 0.93 0.044 0.62 1.25 0.086 -0.042 50 3.25 0.346 0.62 1.25 0.086 0.260 55 0.88 0.046 0.61 1.23 0.093 -0.047 55 3.06 0.357 0.61 1.23 0.093 0.264 60 0.83 0.047 0.60 1.21 0.100 -0.053 60 2.88 0.368 0.60 1.21 0.100 0.267 65 0.78 0.048 0.59 1.20 0.107 -0.059 65 2.73 0.377 0.59 1.20 0.107 0.270 70 0.74 0.050 0.59 1.18 0.114 -0.064 70 2.60 0.386 0.59 1.18 0.114 0.272 75 0.71 0.051 0.58 1.17 0.121 -0.070 75 2.47 0.394 0.58 1.17 0.121 0.273 80 0.68 0.052 0.57 1.16 0.128 -0.076 80 2.37 0.402 0.57 1.16 0.128 0.274 85 0.65 0.053 0.57 1.15 0.135 -0.082 85 2.27 0.409 0.57 1.15 0.135 0.275 90 0.62 0.054 0.57 1.14 0.142 -0.088 90 2.18 0.416 0.57 1.14 0.142 0.275 95 0.60 0.054 0.56 1.14 0.149 -0.094 95 2.10 0.423 0.56 1.14 0.149 0.274 100 0.58 0.055 0.56 1.13 0.156 -0.101 100 2.02 0.429 0.56 1.13 0.156 0.273 105 0.56 0.056 0.56 1.13 0.163 -0.107 105 1.95 0.435 0.56 1.13 0.163 0.272 110 0.54 0.057 0.55 1.12 0.170 -0.113 110 1.89 0.441 0.55 1.12 0.170 0.271 115 0.52 0.057 0.55 1.12 0.177 -0.119 115 1.83 0.446 0.55 1.12 0.177 0.270 120 0.51 0.058 0.55 1.11 0.184 -0.126 120 1.77 0.452 0.55 1.11 0.184 0.268 125 0.49 0.059 0.55 1.11 0.191 -0.132 125 1.72 0.457 0.55 1.11 0.191 0.266 Project: Basin ID: UDFCD DETENTION BASIN VOLUME ESTIMATING WORKBOOK Version 2.33, Released August 2013 DETENTION VOLUME BY THE MODIFIED FAA METHOD FCHA - PSH Basins A1-A4 0 0.1 0.2 0.3 0.4 0.5 0.6 0 50 100 150 200 250 300 350 Volume (acre-feet) Duration (Minutes) Inflow and Outflow Volumes vs. Rainfall Duration Minor Storm Inflow Volume Minor Storm Outflow Volume Minor Storm Storage Volume Major Storm Inflow Volume Major Storm Outflow Volume Major Storm Storage Volume Copy of UD-Detention_v2.33, Modified FAA 9/5/2013, 11:23 PM Sheet 1 of 4 Designer: Company: Date: Project: Location: 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, Ia Ia = 37.2 % B) Tributary Area's Imperviousness Ratio (i = Ia / 100 ) i = 0.372 C) Contributing Watershed Area Area = 2.660 ac D) For Watersheds Outside of the Denver Region, Depth of Average d6 = 0.50 in Runoff Producing Storm E) Design Concept (Select EURV when also designing for flood control) F) Design Volume (1.2 WQCV) Based on 40-hour Drain Time VDESIGN = 0.046 ac-ft (VDESIGN = (1.0 * (0.91 * i 3 - 1.19 * i 2 + 0.78 * i) / 12 * Area * 1.2) G) For Watersheds Outside of the Denver Region, VDESIGN OTHER = 0.053 ac-ft Water Quality Capture Volume (WQCV) Design Volume (VWQCV OTHER = (d 6*(VDESIGN /0.43)) H) User Input of Water Quality Capture Volume (WQCV) Design Volume VDESIGN USER = ac-ft (Only if a different WQCV Design Volume is desired) I) Predominant Watershed NRCS Soil Group J) Excess Urban Runoff Volume (EURV) Design Volume For HSG A: EURVA = (0.1878i - 0.0104)*Area EURV = ac-f t For HSG B: EURVB = (0.1178i - 0.0042)*Area For HSG C/D: EURVC/D = (0.1043i - 0.0031)*Area Design Procedure Form: Extended Detention Basin (EDB) FCHA - PSH JVA Inc. September 5, 2013 Redtail Subdivision, Fort Collins RLK Choose One Excess Urban Runoff Volume (EURV) Choose One A B C / D Water Quality Capture Volume (WQCV) 2. Basin Shape: Length to Width Ratio L : W = : 1 (A basin length to width ratio of at least 2:1 will improve TSS reduction.) 3. Basin Side Slopes A) Basin Maximum Side Slopes Z = ft / ft (Horizontal distance per unit vertical, 4:1 or flatter preferred) 4. Inlet A) Describe means of providing energy dissipation at concentrated inflow locations: Copy of Copy of UD-BMP_v3.02, EDB 9/5/2013, 11:24 PM 12,955 sq. ft. 0.297 acres 7,686 sq. ft. 3,855 sq. ft. 63,458 sq. ft. 1.457 acres LOT 12 5,340 sq.ft. 5033 FOSSIL BLVD LOT 10 1,233 sq.ft. 5021 FOSSIL BLVD TRACT I 1,739 sq. ft. TRACT F 63,458 sq.ft. 1.457 acres V:\1980c Fort Collins Housing Authority\Drawings\Exhibits\1980c FIGURE 1 - Drainage Exhibit.dwg, 9/6/2013 12:12:44 PM, RLK, 1:1 LOT 12 5,340 sq.ft. 5033 FOSSIL BLVD LOT 10 1,233 sq.ft. 5021 FOSSIL BLVD TRACT I 1,739 sq. ft. TRACT F 63,458 sq.ft. 1.457 acres 9' 9' 15 15 UE 12,955 sq. ft. 0.297 acres 7,686 sq. ft. 3,855 sq. ft. 63,458 sq. ft. 1.457 acres V:\1980c Fort Collins Housing Authority\Drawings\Exhibits\1980c FIGURE 2 - Drainage Exhibit.dwg, 9/6/2013 12:13:46 PM, RLK, 1:1 130 0.48 0.059 0.55 1.10 0.198 -0.138 130 1.67 0.462 0.55 1.10 0.198 0.264 135 0.47 0.060 0.54 1.10 0.205 -0.145 135 1.63 0.466 0.54 1.10 0.205 0.262 140 0.45 0.061 0.54 1.10 0.211 -0.151 140 1.58 0.471 0.54 1.10 0.211 0.259 145 0.44 0.061 0.54 1.09 0.218 -0.157 145 1.54 0.475 0.54 1.09 0.218 0.257 150 0.43 0.062 0.54 1.09 0.225 -0.164 150 1.50 0.480 0.54 1.09 0.225 0.254 155 0.42 0.062 0.54 1.09 0.232 -0.170 155 1.47 0.484 0.54 1.09 0.232 0.251 160 0.41 0.063 0.54 1.09 0.239 -0.177 160 1.43 0.488 0.54 1.09 0.239 0.248 165 0.40 0.063 0.54 1.08 0.246 -0.183 165 1.40 0.492 0.54 1.08 0.246 0.245 170 0.39 0.064 0.54 1.08 0.253 -0.190 170 1.37 0.495 0.54 1.08 0.253 0.242 175 0.38 0.064 0.53 1.08 0.260 -0.196 175 1.34 0.499 0.53 1.08 0.260 0.239 180 0.38 0.065 0.53 1.08 0.267 -0.203 180 1.31 0.503 0.53 1.08 0.267 0.235 185 0.37 0.065 0.53 1.08 0.274 -0.209 185 1.29 0.506 0.53 1.08 0.274 0.232 190 0.36 0.065 0.53 1.07 0.281 -0.216 190 1.26 0.510 0.53 1.07 0.281 0.228 195 0.35 0.066 0.53 1.07 0.288 -0.222 195 1.24 0.513 0.53 1.07 0.288 0.225 200 0.35 0.066 0.53 1.07 0.295 -0.229 200 1.21 0.516 0.53 1.07 0.295 0.221 205 0.34 0.067 0.53 1.07 0.302 -0.235 205 1.19 0.519 0.53 1.07 0.302 0.217 210 0.34 0.067 0.53 1.07 0.309 -0.242 210 1.17 0.523 0.53 1.07 0.309 0.214 215 0.33 0.068 0.53 1.07 0.316 -0.248 215 1.15 0.526 0.53 1.07 0.316 0.210 220 0.32 0.068 0.53 1.07 0.323 -0.255 220 1.13 0.529 0.53 1.07 0.323 0.206 225 0.32 0.068 0.53 1.06 0.330 -0.262 225 1.11 0.532 0.53 1.06 0.330 0.202 230 0.31 0.069 0.53 1.06 0.337 -0.268 230 1.09 0.534 0.53 1.06 0.337 0.198 235 0.31 0.069 0.53 1.06 0.344 -0.275 235 1.08 0.537 0.53 1.06 0.344 0.194 240 0.30 0.069 0.52 1.06 0.351 -0.281 240 1.06 0.540 0.52 1.06 0.351 0.189 245 0.30 0.070 0.52 1.06 0.358 -0.288 245 1.04 0.543 0.52 1.06 0.358 0.185 250 0.29 0.070 0.52 1.06 0.365 -0.295 250 1.03 0.545 0.52 1.06 0.365 0.181 255 0.29 0.070 0.52 1.06 0.372 -0.301 255 1.01 0.548 0.52 1.06 0.372 0.177 260 0.29 0.071 0.52 1.06 0.379 -0.308 260 1.00 0.551 0.52 1.06 0.379 0.172 265 0.28 0.071 0.52 1.06 0.386 -0.314 265 0.98 0.553 0.52 1.06 0.386 0.168 270 0.28 0.071 0.52 1.06 0.392 -0.321 270 0.97 0.556 0.52 1.06 0.392 0.163 275 0.27 0.072 0.52 1.05 0.399 -0.328 275 0.96 0.558 0.52 1.05 0.399 0.159 280 0.27 0.072 0.52 1.05 0.406 -0.334 280 0.94 0.561 0.52 1.05 0.406 0.154 285 0.27 0.072 0.52 1.05 0.413 -0.341 285 0.93 0.563 0.52 1.05 0.413 0.150 290 0.26 0.073 0.52 1.05 0.420 -0.348 290 0.92 0.565 0.52 1.05 0.420 0.145 295 0.26 0.073 0.52 1.05 0.427 -0.354 295 0.91 0.568 0.52 1.05 0.427 0.140 300 0.26 0.073 0.52 1.05 0.434 -0.361 300 0.89 0.570 0.52 1.05 0.434 0.136 Mod. FAA Minor Storage Volume (cubic ft.) = 0 Mod. FAA Major Storage Volume (cubic ft.) = 11,960 Mod. FAA Minor Storage Volume (acre-ft.) = 0.0000 Mod. FAA Major Storage Volume (acre-ft.) = 0.2746 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 2.33, Released August 2013 Determination of MINOR Detention Volume Using Modified FAA Method DETENTION VOLUME BY THE MODIFIED FAA METHOD FCHA - PSH Basins A1-A4 Copy of UD-Detention_v2.33, Modified FAA 9/5/2013, 11:23 PM Paved areas & shallow paved swales 20 2.0 0.9 6.2 150 10.8 6.2 A3 5 0.33 0.37 65 5.0% 6.3 100 1.0% Paved areas & shallow paved swales 20 2.0 0.8 7.1 165 10.9 7.1 A4 6 0.53 0.38 100 2.0% 10.5 430 25.0% Nearly bare ground 10 5.0 1.4 11.9 530 12.9 11.9 Initial Overland Time (ti ) Travel Time (tt ) tt =Length/(Velocity x 60) tc Urbanized Check ON 1980c - Rational Calculations Developed Tc Page 3 of 5 Velocity (fps) tt (min) Time of Conc ti + tt = tc Total Length (ft) tc=(L/180)+ 10 (min.) Min tc H1 1 8,068 8,068 0.19 2.0% 0.25 0.25 0.25 0.31 50 4.0% 6.9 50 4.0% Nearly bare ground 10 2.0 0.4 7.4 100 10.6 7.4 H2 2 6,553 6,553 0.15 2.0% 0.25 0.25 0.25 0.31 45 4.0% 6.6 45 4.0% Nearly bare ground 10 2.0 0.4 7.0 90 10.5 7.0 H3 3 8,560 3,846 26,418 38,824 0.89 2.0% 0.31 0.31 0.31 0.38 110 2.0% 12.1 490 10.0% Nearly bare ground 10 3.2 2.6 14.7 600 13.3 13.3 H4 4 13,411 40,517 20,410 74,338 1.71 2.0% 0.27 0.27 0.27 0.34 130 1.5% 15.2 400 10.0% Nearly bare ground 10 3.2 2.1 17.3 530 12.9 12.9 H1+H2 1 14,621 14,621 0.34 2.0% 0.25 0.25 0.25 0.31 50 4.0% 6.9 50 4.0% Nearly bare ground 10 2.0 0.4 7.4 100 10.6 7.4 H3+H4 4 21,971 44,363 46,828 113,162 2.60 2.0% 0.28 0.28 0.28 0.35 110 2.0% 12.5 540 10.0% Nearly bare ground 10 3.2 2.8 15.3 650 13.6 13.6 TOTAL SITE 0 0 0 0 0 21,971 58,984 46,828 127,783 2.93 2.0% 0.28 0.28 0.28 0.35 Initial Overland Time (ti) ti=0.395(1.1-C5)L1/2S-1/3 Travel Time (tt) tt=Length/(Velocity x 60) tc Urbanized Check ON Runoff Coeff's I = (28.5 P1) / ((10 + TC) 0.786651) Basin Name Design Point Time of Conc (tc) C2 C5 C10 C100 2 5 10 100 ATotal (sf) ATotal (ac) Q2 Q5 Q10 Q100 H1 1 7.4 0.25 0.25 0.25 0.31 2.47 3.43 4.22 8.62 8,068 0.19 0.11 0.16 0.20 0.50 H2 2 7.0 0.25 0.25 0.25 0.31 2.52 3.50 4.30 8.78 6,553 0.15 0.09 0.13 0.16 0.41 H3 3 13.3 0.31 0.31 0.31 0.38 1.97 2.73 3.35 6.85 38,824 0.89 0.54 0.75 0.92 2.34 H4 4 12.9 0.27 0.27 0.27 0.34 1.99 2.77 3.40 6.94 74,338 1.71 0.91 1.27 1.56 3.98 H1+H2 1 7.4 0.25 0.25 0.25 0.31 2.48 3.43 4.22 8.62 14,621 0.34 0.21 0.29 0.35 0.90 H3+H4 4 13.6 0.28 0.28 0.28 0.35 1.95 2.70 3.32 6.78 113,162 2.60 1.43 1.98 2.43 6.20 TOTAL SITE 38,824 2.93 1.66 2.31 2.83 7.23 Runoff Coeff's Rainfall Intensities (in/hr) Area Flow Rates (cfs) 1980c - Rational Calculations Historic Page 1 of 5