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HomeMy WebLinkAboutSOLERA SUBDIVISION (1701 W. TRILBY RD.) - PDP/FDP - FDP170021 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORTDRAINAGE INVESTIGATION & SEDIMENT EROSION CONTROL REPORT for SOLERA SUBDIVISION Located in the Northwest Quarter of Section 15, Township 6 North, Range 69 West of the 6th P. M. CITY OF FORT COLLINS, LARIMER COUNTY , COLORADO (1701 West Trilby Road) Prepared for: SOLERA PROPERTIES P. O. BOX 6273 COLORADO SPRINGS, COLORADO 80934 June 2017 Project No. 1102 - GRD - 17 Prepared by: DENNIS R. MESSNER , P.E. 2015 Buena Vista Place Loveland, Colorado 80538 Telephone: (970) 461-3501 Dennis R. Messner, P. E. Consulting Civil Engineer June 19, 2017 Project No. 1102-GRD-17 Stormwater Utility Service Center 700 Wood Street Fort Collins, Colorado 80522-0580 Re: Drainage Investigation and Erosion Control Report for Solera Subdivision, Fort Collins, Colorado Gentlemen: I am pleased to submit, for your review and acceptance, this “Drainage Investigation and Erosion Control Report for Solera Subdivision, Fort Collins, Colorado.” This investigation was based upon the proposed site development plan; on-site observation; and available topographic information. The investigation and design within this report have been performed according to the criteria established in the City of Fort Collins Storm Drainage Criteria. I sincerely appreciate your time and consideration in the review of this project. If you should have any questions, please feel free to contact this office. Respectfully Submitted, Dennis R. Messner, P.E. cc: Solera Properties I hereby state that the attached “Drainage Investigation and Erosion Control Report for Solera Subdivision, Fort Collins, Colorado” was prepared by me or under my direct supervision in accordance with the provisions of the City of Fort Collins’ Drainage Criteria for the owners thereof. Dennis R. Messner Registered Professional Engineer State of Colorado No. 26109 2015 Buena Vista Place * Telephone: (970) 461-3501 * Loveland, Colorado 80538 TABLE OF CONTENTS Description Page LETTER OF TRANSMITTAL i TABLE OF CONTENTS ii & iii I GENERAL LOCATION AND DESCRIPTION A. Location 1 B. Description of Property 1 I DRAINAGE BASINS . Major Basin Description 1 . Sub-basin Description 2 III DRAINAGE DESIGN CRITERIA A. Development Regulations 2 B. Development Criteria Reference and Constraints 2 C. Hydrologic Criteria 2 D. Hydraulic Criteria 3 I DRAINAGE FACILITY DESIGN . General Concept 3 . Specific Details - Detention Facility 3 V EROSION CONTROL . General Concept 4 VI CONCLUSIONS A. Compliance with Standards 4 B. Drainage Concept 5 VII REFERENCES 5 TABLE OF CONTENTS (CONTINUED): EXHIBITS Vicinity Map Existing Conditions Exhibit Proposed Conditions Exhibit APPENDIX I Drainage Calculations APPENDIX II Charts, Graphs, Figures and Details I. General Location and Description: A. Location 1. The proposed Solera Subdivision is located in the Northwest Quarter of Section 15, Township 6 North, Range 69 West of the 6th P.M. in the City of Fort Collins, Larimer County, Colorado. 2. The site is more specifically located south of Trilby Road between Shields Street and Taft Hill Road. (Refer to the included Vicinity Map.) 3. The Trilby Road and large lot rural estates lots borders the site to the north. Rural residential estate lots border the Solera Subdivision site to the west, south and east. B. Description of property 1. The Solera Subdivision site consists of approximately 2.53 acres and is developed with an existing residence, several outbuildings and corral. 2. The existing ground cover consists mainly of sparse to moderate non-irrigated grasses and native vegetation. 3. The “Soil Survey of Larimer County Area, Colorado” prepared by the U.S. Department of Agriculture, Soil Conservation Service, indicates that the surface soils consist primarily of “Renohill clay loam.” The soil typical of this series is described as a shallow, well-drained soil that formed in material from clay shale. The “Soil Survey” identifies the runoff potential as rapid, and the hazard of erosion as severe. The soil type is classified in the ‘D’ hydrologic group. 4. The site is generally considered moderate to steep, with slopes between 3% and 8%. 5. The Solera Subdivision will involve the construction of a new single family residence. The proposed outdoor storage area is to be approximately 2.54 acres. II. Drainage Basins and Sub-basins: A. Major Basin Description 1. The subject area is located 1701 West Trilby Road. 2. The site is located within Basin 609 of the Fossil Creek Drainage Basin as identified by the City of Fort Collins’ Master Drainage Plan. The site is not 1 located within a designated flood way or flood plain. B. Sub-basin Description 1. The historic drainage pattern of the property flows from south to north. Runoff is directed to an un-named drainage course located along the south side of west Trilby Road at the northern side of the site. 2. The entire site drains to the un-named drainage course that flows to Fossil Creek. 3. The southern border of the site is located along a ridge that splits surface run off in the north and south directions. Therefore, there is no offsite run off to be considered. III. Drainage Design Criteria: A. Development Regulations 1. Design criteria from the current City of Fort Collins Storm Drainage Criteria and Construction Standards, the Urban Storm Drainage Manuals, Volumes I, II, and III and the Larimer County Urban Area Street Standards were utilized. B. Development Criteria Reference and Constraints 1. The historic drainage pattern will be affected by the proposed construction in that flow will be concentrated and channelized to some extent. The proposed construction of this site will produce an insignificant increase in runoff over the historic amount. 2. The drainage impact of this site will not adversely affect streets or utilities. C. Hydrological Criteria 1. The Rainfall-Intensity-Duration-Frequency Table for the City of Fort Collins, Table RA-7 as amended for Section 4.0 of the Urban drainage and Flood Control District Criteria, was used in conjunction with the Rational Method for determining peak flows at various concentration points. a. Spreadsheets from the Urban Storm Drainage Criteria Manual were used to first determine the weighed imperviousness for a contributing sub- basin, and then to calculate the peak runoff rates. (See the Drainage Calculation Section of this report.) 2 b. Tables RO-10 and RO-11 as amended for the City of Fort Collins for the Urban Storm Drainage Criteria Manual were used for recommended run-off coefficients values for various land cover. c. The hydrological group ‘D’ was used in the Urban Storm Drainage Criteria Spreadsheets for the on-site soils. 2. The 2-Year, 10-year and 100-year storms were analyzed in accordance with the City of Fort Collins Storm Drainage Criteria and Construction Standards. D. Hydraulic Criteria 1. Culvert pipes on-site are analyzed using smooth interior wall Corrugated Metal Pipe (CMP) pipe. a. A Mannings ‘n’ value of 0.025 is to be used for all storm pipe according to Sec.4.4.2 of the City of Fort Collins Storm Drainage Design Criteria. 3. Recommended Channel Design Roughness Coefficients are per Table MD-1 of the Urban Storm Drainage Criteria Manual Volume I. IV. Drainage Facility Design: A. General Concept 1. During a rainfall event, storm water will be conveyed to the existing drainage course located along the southern side of West Trilby Road. B. Specific Details 1. The site is considered to be Sub-Basin ‘A’, as identified on the Drainage Exhibits and contains 2.53 acres. The weighted percent imperviousness for the Existing Condition is estimated to be 11.05% and the weighted run off coefficient 0.30. The peak run off rate of run off for the Existing Condition is estimated to be: the 2-year storm is1.58 c.f.s.; the 10-year storm is 2.70 c.f.s.; and the 100-year peak runoff rate is 6.89 c.f.s. The weighted percent imperviousness for the Existing Condition is estimated to be 14.18% and the weighted run off coefficient 0.33. 3 The peak run off rate of run off for the Proposed Condition is estimated to be: the 2-year storm is 1.74 c.f.s.; the 10-year storm is 2.97 c.f.s.; and the 100-year peak runoff rate is 7.58 c.f.s. V. Erosion Control: A. General Concept 1. Temporary erosion control measures will be implemented during the construction of this project. These measures will include: a. Silt fence along the downhill side of the open construction area. b. Wattle Inlet Protection installed at the existing culvert along the existing drainage course. 2. Long term erosion control measures will be implemented after the construction of this project. These measures will include: a. Landscape planting and seeding. b. Surface treatments for drives and open storage area. 3. Maintenance of all erosion control devices will remain the responsibility of the developer until the completion of the project. 4. Wind erosion measures considered for the site during construction are roughening and water application. VI. Conclusions: A. Compliance with Standards 1. All drainage design conforms to the criteria and requirements of the City of Fort Collins Storm Drainage Criteria and Construction Standards. 2. Proposed drainage improvements generally conform to the concepts and recommendations of the City of Fort Collins Master Drainage Plan. 3. Proposed erosion control measures conform to the recommendations of City of Fort Collins standards and generally accepted erosion control procedures. 4. Proposed water quality measures will be provided to remove sediment from the flow discharged from the two detention facilities. 4 B. Drainage Concept 1. The final drainage design for the Solera Subdivision is effective for the control of storm water runoff with little or no effect on the City of Fort Collins Fossil Creek Master Drainage Plan recommendations. 2. The computed imperviousness for the site at the Existing Condition is 11.05% (“C”=0.30) and 14.18% (“C”=0.33) at the Proposed Condition. 3. The computed run off for the Existing Condition is: the 2-year storm is1.58 c.f.s.; the 10-year storm is 2.70 c.f.s.; and the 100-year peak runoff rate is 6.89 c.f.s. The computed run off for the Proposed Condition is: the 2-year storm is 1.74 c.f.s.; the 10-year storm is 2.97 c.f.s.; and the 100-year peak runoff rate is 7.58 c.f.s. VII. References: A. City of Fort Collins Storm Drainage Criteria and Construction Standards B. City of Fort Collins Master Drainage Plan C. City of Fort Collins Development Standards D. Soil Survey of Larimer County Area, Colorado E. Urban Drainage and Flood Control District Drainage Criteria Manuals, Volumes 1, 2 and 3. (City of Fort Collins Addendum) F. Larimer County Urban Area Street Standards 5 EXHIBITS APPENDIX I DRAINAGE CALCULATIONS EXISTING CONDITIONS Project Title: Catchment ID: Illustration Instructions: For each catchment subarea, enter values for A and C. Subarea Area Runoff Product ID acres Coeff. A C* CA input input input output Pasture 1.96 2.00 3.92 Street 0.06 100.00 5.68 Roof 0.08 90.00 7.10 Gravel 0.10 45.00 4.48 landscape 0.16 0.00 0.00 Corral 0.17 40.00 6.74 Drives 0.00 90.00 0.00 Sum: 2.53 Sum: 27.93 Area-Weighted Runoff Coefficient (sum CA/sum A) = 11.05 *See sheet "Design Info" for inperviousness-based runoff coefficient values. Area-Weighting for Runoff Coefficient Calculation SOLERA SUBDIVISION ONSITE BASIN 'A' - EXISTING CONDITION PROP 'A' Q2, Weighted C 6/22/2017, 2:46 PM Project Title: Catchment ID: Illustration Instructions: For each catchment subarea, enter values for A and C. Subarea Area Runoff Product ID acres Coeff. A C* CA input input input output Pasture 1.96 0.25 0.49 Pvmt 0.06 0.95 0.05 roof 0.08 0.95 0.07 gravel 0.10 0.50 0.05 landscape 0.16 0.25 0.04 corral 0.17 0.30 0.05 Sum: 2.53 Sum: 0.76 Area-Weighted Runoff Coefficient (sum CA/sum A) = 0.30 *See sheet "Design Info" for inperviousness-based runoff coefficient values. Area-Weighting for Runoff Coefficient Calculation SOLERA SUBDIVISION ONSITE BASIN 'A' - EXISTING CONDITION EXIST 'A' Q100, Weighted C 6/22/2017, 2:17 PM Project Title: Catchment ID: I. Catchment Hydrologic Data Catchment ID = "A" Area = 2.53 Acres Percent Imperviousness = % NRCS Soil Type = D A, B, C, or D II. Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3 Design Storm Return Period, Tr = 2 years (input return period for design storm) C1 = 28.50 (input the value of C1) C2= 10.00 (input the value of C2) C3= 0.786 (input the value of C3) P1= 0.82 inches (input one-hr precipitation--see Sheet "Design Info") III. Analysis of Flow Time (Time of Concentration) for a Catchment Runoff Coefficient, C = Overide Runoff Coefficient, C = 0.30 (enter an overide C value if desired, or leave blank to accept calculated C.) 5-yr. Runoff Coefficient, C-5 = Overide 5-yr. Runoff Coefficient, C = 0.30 (enter an overide C-5 value if desired, or leave blank to accept calculated C-5.) Illustration NRCS Land Heavy Tillage/ Short Nearly Grassed Type Meadow Field Pasture/ Bare Swales/ Lawns Ground Waterways Conveyance 2.5 5 7 10 15 Calculations: Reach Slope Length 5-yr NRCS Flow Flow ID S L Runoff Convey- Velocity Time Coeff ance V Tf ft/ft ft C-5 fps minutes input input output input output output Overland 0.0800 80 0.30 N/A 0.20 6.50 1 0.0840 405 10.00 2.90 2.33 2 0.0520 115 7.00 1.60 1.20 3 0.0360 55 7.00 1.33 0.69 4 0.0140 140 15.00 1.77 1.31 5 795 Computed Tc = 12.04 Regional Tc = 14.42 User-Entered Tc = 11.67 IV. Peak Runoff Prediction Rainfall Intensity at Computed Tc, I = 2.06 inch/hr Peak Flowrate, Qp = 1.56 cfs Rainfall Intensity at Regional Tc, I = 1.90 inch/hr Peak Flowrate, Qp = 1.44 cfs Rainfall Intensity at User-Defined Tc, I = 2.08 inch/hr Peak Flowrate, Qp = 1.58 cfs Calculated values for Tc & Qp are based on overide values entered for C & C-5. Shallow Paved Swales (Sheet Flow) 20 Sum CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD SOLERA SUBDIVISION ONSITE AREA "A" EXISTING CONDITION Paved Areas & EXIST 'A' Q2, Tc and PeakQ 6/22/2017, 2:13 PM Project Title: Catchment ID: I. Catchment Hydrologic Data Catchment ID = "A" Area = 2.53 Acres Percent Imperviousness = % NRCS Soil Type = D A, B, C, or D II. Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3 Design Storm Return Period, Tr = 10 years (input return period for design storm) C1 = 28.50 (input the value of C1) C2= 10.00 (input the value of C2) C3= 0.786 (input the value of C3) P1= 1.40 inches (input one-hr precipitation--see Sheet "Design Info") III. Analysis of Flow Time (Time of Concentration) for a Catchment Runoff Coefficient, C = Overide Runoff Coefficient, C = 0.30 (enter an overide C value if desired, or leave blank to accept calculated C.) 5-yr. Runoff Coefficient, C-5 = Overide 5-yr. Runoff Coefficient, C = 0.30 (enter an overide C-5 value if desired, or leave blank to accept calculated C-5.) Illustration NRCS Land Heavy Tillage/ Short Nearly Grassed Type Meadow Field Pasture/ Bare Swales/ Lawns Ground Waterways Conveyance 2.5 5 7 10 15 Calculations: Reach Slope Length 5-yr NRCS Flow Flow ID S L Runoff Convey- Velocity Time Coeff ance V Tf ft/ft ft C-5 fps minutes input input output input output output Overland 0.0800 80 0.30 N/A 0.20 6.50 1 0.0840 405 10.00 2.90 2.33 2 0.0520 115 7.00 1.60 1.20 3 0.0360 55 7.00 1.33 0.69 4 0.0140 140 15.00 1.77 1.31 5 795 Computed Tc = 12.04 Regional Tc = 14.42 User-Entered Tc = 11.67 IV. Peak Runoff Prediction Rainfall Intensity at Computed Tc, I = 3.51 inch/hr Peak Flowrate, Qp = 2.66 cfs Rainfall Intensity at Regional Tc, I = 3.24 inch/hr Peak Flowrate, Qp = 2.46 cfs Rainfall Intensity at User-Defined Tc, I = 3.56 inch/hr Peak Flowrate, Qp = 2.70 cfs Calculated values for Tc & Qp are based on overide values entered for C & C-5. Shallow Paved Swales (Sheet Flow) 20 Sum CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD SOLERA SUBDIVISION ONSITE AREA "A" EXISTING CONDITION Paved Areas & EXIST 'A' Q10, Tc and PeakQ 6/22/2017, 2:14 PM Project Title: Catchment ID: I. Catchment Hydrologic Data Catchment ID = "A" Area = 2.53 Acres Percent Imperviousness = % NRCS Soil Type = D A, B, C, or D II. Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3 Design Storm Return Period, Tr = 100 years (input return period for design storm) C1 = 28.50 (input the value of C1) C2= 10.00 (input the value of C2) C3= 0.786 (input the value of C3) P1= 2.86 inches (input one-hr precipitation--see Sheet "Design Info") III. Analysis of Flow Time (Time of Concentration) for a Catchment Runoff Coefficient, C = Overide Runoff Coefficient, C = 0.38 (enter an overide C value if desired, or leave blank to accept calculated C.) 5-yr. Runoff Coefficient, C-5 = Overide 5-yr. Runoff Coefficient, C = 0.30 (enter an overide C-5 value if desired, or leave blank to accept calculated C-5.) Illustration NRCS Land Heavy Tillage/ Short Nearly Grassed Type Meadow Field Pasture/ Bare Swales/ Lawns Ground Waterways Conveyance 2.5 5 7 10 15 Calculations: Reach Slope Length 5-yr NRCS Flow Flow ID S L Runoff Convey- Velocity Time Coeff ance V Tf ft/ft ft C-5 fps minutes input input output input output output Overland 0.0800 80 0.30 N/A 0.20 6.50 1 0.0840 405 10.00 2.90 2.33 2 0.0520 115 7.00 1.60 1.20 3 0.0360 55 7.00 1.33 0.69 4 0.0140 140 15.00 1.77 1.31 5 795 Computed Tc = 12.04 Regional Tc = 14.42 User-Entered Tc = 11.67 IV. Peak Runoff Prediction Rainfall Intensity at Computed Tc, I = 7.17 inch/hr Peak Flowrate, Qp = 6.80 cfs Rainfall Intensity at Regional Tc, I = 6.61 inch/hr Peak Flowrate, Qp = 6.27 cfs Rainfall Intensity at User-Defined Tc, I = 7.26 inch/hr Peak Flowrate, Qp = 6.89 cfs Calculated values for Tc & Qp are based on overide values entered for C & C-5. (Sheet Flow) 20 Shallow Paved Swales Sum CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD SOLERA SUBDIVISION ONSITE AREA "A" EXISTING CONDITION Paved Areas & EXIST 'A' Q100, Tc and PeakQ 6/22/2017, 2:16 PM PROPOSED CONDITIONS Project Title: Catchment ID: Illustration Instructions: For each catchment subarea, enter values for A and C. Subarea Area Runoff Product ID acres Coeff. A C* CA input input input output Pasture 1.66 2.00 3.32 Street 0.06 100.00 5.68 Roof 0.10 90.00 9.40 Gravel 0.33 45.00 14.96 landscape 0.35 0.00 0.00 Corral 0.00 40.00 0.00 Drives 0.03 90.00 2.49 Sum: 2.53 Sum: 35.85 Area-Weighted Runoff Coefficient (sum CA/sum A) = 14.18 *See sheet "Design Info" for inperviousness-based runoff coefficient values. Area-Weighting for Runoff Coefficient Calculation SOLERA SUBDIVISION ONSITE BASIN 'A' - PROPOSED CONDITION PROP 'A' Q2, Weighted C 6/22/2017, 2:53 PM Project Title: Catchment ID: Illustration Instructions: For each catchment subarea, enter values for A and C. Subarea Area Runoff Product ID acres Coeff. A C* CA input input input output Pasture 1.66 0.25 0.42 Pvmt 0.07 0.95 0.07 roof 0.10 0.95 0.10 gravel 0.33 0.50 0.17 landscape 0.35 0.25 0.09 corral 0.00 0.30 0.00 Sum: 2.52 Sum: 0.84 Area-Weighted Runoff Coefficient (sum CA/sum A) = 0.33 *See sheet "Design Info" for inperviousness-based runoff coefficient values. Area-Weighting for Runoff Coefficient Calculation SOLERA SUBDIVISION ONSITE BASIN 'A' - PROPOSED CONDITION PROP 'A' Q2, Weighted C 6/22/2017, 2:18 PM Project Title: Catchment ID: I. Catchment Hydrologic Data Catchment ID = "A" Area = 2.53 Acres Percent Imperviousness = % NRCS Soil Type = D A, B, C, or D II. Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3 Design Storm Return Period, Tr = 2 years (input return period for design storm) C1 = 28.50 (input the value of C1) C2= 10.00 (input the value of C2) C3= 0.786 (input the value of C3) P1= 0.82 inches (input one-hr precipitation--see Sheet "Design Info") III. Analysis of Flow Time (Time of Concentration) for a Catchment Runoff Coefficient, C = Overide Runoff Coefficient, C = 0.33 (enter an overide C value if desired, or leave blank to accept calculated C.) 5-yr. Runoff Coefficient, C-5 = Overide 5-yr. Runoff Coefficient, C = 0.33 (enter an overide C-5 value if desired, or leave blank to accept calculated C-5.) Illustration NRCS Land Heavy Tillage/ Short Nearly Grassed Type Meadow Field Pasture/ Bare Swales/ Lawns Ground Waterways Conveyance 2.5 5 7 10 15 Calculations: Reach Slope Length 5-yr NRCS Flow Flow ID S L Runoff Convey- Velocity Time Coeff ance V Tf ft/ft ft C-5 fps minutes input input output input output output Overland 0.0800 80 0.33 N/A 0.21 6.26 1 0.0840 405 10.00 2.90 2.33 2 0.0520 115 7.00 1.60 1.20 3 0.0360 55 7.00 1.33 0.69 4 0.0140 140 15.00 1.77 1.31 5 795 Computed Tc = 11.80 Regional Tc = 14.42 User-Entered Tc = 11.67 IV. Peak Runoff Prediction Rainfall Intensity at Computed Tc, I = 2.07 inch/hr Peak Flowrate, Qp = 1.73 cfs Rainfall Intensity at Regional Tc, I = 1.90 inch/hr Peak Flowrate, Qp = 1.58 cfs Rainfall Intensity at User-Defined Tc, I = 2.08 inch/hr Peak Flowrate, Qp = 1.74 cfs Calculated values for Tc & Qp are based on overide values entered for C & C-5. (Sheet Flow) 20 Shallow Paved Swales Sum CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD SOLERA SUBDIVISION ONSITE AREA "A" PROPOSED CONDITION Paved Areas & PROP 'A' Q2, Tc and PeakQ 6/22/2017, 2:10 PM Project Title: Catchment ID: I. Catchment Hydrologic Data Catchment ID = "A" Area = 2.53 Acres Percent Imperviousness = % NRCS Soil Type = D A, B, C, or D II. Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3 Design Storm Return Period, Tr = 10 years (input return period for design storm) C1 = 28.50 (input the value of C1) C2= 10.00 (input the value of C2) C3= 0.786 (input the value of C3) P1= 1.40 inches (input one-hr precipitation--see Sheet "Design Info") III. Analysis of Flow Time (Time of Concentration) for a Catchment Runoff Coefficient, C = Overide Runoff Coefficient, C = 0.33 (enter an overide C value if desired, or leave blank to accept calculated C.) 5-yr. Runoff Coefficient, C-5 = Overide 5-yr. Runoff Coefficient, C = 0.33 (enter an overide C-5 value if desired, or leave blank to accept calculated C-5.) Illustration NRCS Land Heavy Tillage/ Short Nearly Grassed Type Meadow Field Pasture/ Bare Swales/ Lawns Ground Waterways Conveyance 2.5 5 7 10 15 Calculations: Reach Slope Length 5-yr NRCS Flow Flow ID S L Runoff Convey- Velocity Time Coeff ance V Tf ft/ft ft C-5 fps minutes input input output input output output Overland 0.0800 80 0.33 N/A 0.21 6.26 1 0.0840 405 10.00 2.90 2.33 2 0.0520 115 7.00 1.60 1.20 3 0.0360 55 7.00 1.33 0.69 4 0.0140 140 15.00 1.77 1.31 5 795 Computed Tc = 11.80 Regional Tc = 14.42 User-Entered Tc = 11.67 IV. Peak Runoff Prediction Rainfall Intensity at Computed Tc, I = 3.54 inch/hr Peak Flowrate, Qp = 2.96 cfs Rainfall Intensity at Regional Tc, I = 3.24 inch/hr Peak Flowrate, Qp = 2.70 cfs Rainfall Intensity at User-Defined Tc, I = 3.56 inch/hr Peak Flowrate, Qp = 2.97 cfs Calculated values for Tc & Qp are based on overide values entered for C & C-5. CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD SOLERA SUBDIVISION ONSITE AREA "A" PROPOSED CONDITION Paved Areas & (Sheet Flow) 20 Shallow Paved Swales Sum PROP 'A' Q10, Tc and PeakQ 6/22/2017, 2:11 PM Project Title: Catchment ID: I. Catchment Hydrologic Data Catchment ID = "A" Area = 2.53 Acres Percent Imperviousness = % NRCS Soil Type = D A, B, C, or D II. Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3 Design Storm Return Period, Tr = 100 years (input return period for design storm) C1 = 28.50 (input the value of C1) C2= 10.00 (input the value of C2) C3= 0.786 (input the value of C3) P1= 2.86 inches (input one-hr precipitation--see Sheet "Design Info") III. Analysis of Flow Time (Time of Concentration) for a Catchment Runoff Coefficient, C = Overide Runoff Coefficient, C = 0.41 (enter an overide C value if desired, or leave blank to accept calculated C.) 5-yr. Runoff Coefficient, C-5 = Overide 5-yr. Runoff Coefficient, C = 0.33 (enter an overide C-5 value if desired, or leave blank to accept calculated C-5.) Illustration NRCS Land Heavy Tillage/ Short Nearly Grassed Type Meadow Field Pasture/ Bare Swales/ Lawns Ground Waterways Conveyance 2.5 5 7 10 15 Calculations: Reach Slope Length 5-yr NRCS Flow Flow ID S L Runoff Convey- Velocity Time Coeff ance V Tf ft/ft ft C-5 fps minutes input input output input output output Overland 0.0800 80 0.33 N/A 0.21 6.26 1 0.0840 405 10.00 2.90 2.33 2 0.0520 115 7.00 1.60 1.20 3 0.0360 55 7.00 1.33 0.69 4 0.0140 140 15.00 1.77 1.31 5 795 Computed Tc = 11.80 Regional Tc = 14.42 User-Entered Tc = 11.67 IV. Peak Runoff Prediction Rainfall Intensity at Computed Tc, I = 7.23 inch/hr Peak Flowrate, Qp = 7.55 cfs Rainfall Intensity at Regional Tc, I = 6.61 inch/hr Peak Flowrate, Qp = 6.90 cfs Rainfall Intensity at User-Defined Tc, I = 7.26 inch/hr Peak Flowrate, Qp = 7.58 cfs Calculated values for Tc & Qp are based on overide values entered for C & C-5. Shallow Paved Swales (Sheet Flow) 20 Sum CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD SOLERA SUBDIVISION ONSITE AREA "A" PROPOSED CONDITION Paved Areas & PROP 'A' Q100, Tc and PeakQ 6/22/2017, 2:12 PM APPENDIX II CHARTS, GRAPHS, FIGURES & DETAILS (11) Section 4.0 is amended to read as follows: 4.0 Intensitv-Duration-Frequencv Curves for Rational Method: The one-hour rainfall Intensity-Duration-Frequency tables for use the Rational Method of runoff analysis are provided in Table RA-7 and in Table RA-8. Table RA-7 - City of Fort Collins Rainfall Intensity-Duration-Frequency Table for Use with the Rational Method (5 minutes to 30 minutes) 2-Year 10-Year 100-Year Duration (min) Intensity (in/hr) Intensity (in/hr) Intensity (in/hr) 5 2.85 4.87 9.95 6 2.67 4.56 9.31 7 2.52 4.31 8.8 8 2.4 4.1 8.38 9 2.3 3.93 8.03 10 2.21 3.78 7.72 11 2.13 3.63 7.42 12 2.05 3.5 7.16 13 1.98 3.39 6.92 14 1.92 3.29 6.71 15 1.87 3.19 6.52 16 1.81 3.08 6.3 17 1.75 2.99 6.1 18 1.7 2.9 5.92 19 1.65 2.82 5.75 20 1.61 2.74 5.6 21 1.56 2.67 5.46 22 1.53 2.61 5.32 23 1.49 2.55 5.2 24 1.46 2.49 5.09 25 1.43 2.44 4.98 26 1.4 2.39 4.87 27 1.37 2.34 4.78 28 1.34 2.29 4.69 29 1.32 2.25 4.6 30 1.3 2.21 4.52 33 Table RA-8 - City of Fort Collins Rainfall Intensity-Duration-Frequency Table for Use with the Rational Method (31 minutes to 60 minutes) 2-Year 10-Year 100-Year Duration Intensity Intensity Intensity (min) (in/hr) (in/hr) (in/hr) 31 1.27 2.16 4.42 32 1.24 2.12 4.33 33 1.22 2.08 4.24 34 1.19 2.04 4.16 35 1.17 2.0 4.08 36 1.15 1.96 4.01 37 1.16 1.93 3.93 38 1.11 1.89 3.87 39 1.09 1.86 3.8 40 1.07 1.83 3.74 41 1.05 1.8 3.68 42 1.04 1.77 3.62 43 1.02 1.74 3.56 44 1.01 1.72 3.51 45 0.99 1.69 3.46 46 0.98 1.67 3.41 47 0.96 1.64 3.36 48 0.95 1.62 3.31 49 0.94 1.6 3.27 50 0.92 1.58 3.23 51 0.91 1.56 3.18 52 0.9 1.54 3.14 53 0.89 1.52 3.1 54 0.88 1.5 3.07 55 0.87 1.48 3.03 56 0.86 1.47 2.99 57 0.85 1.45 2.96 58 0.84 1.43 2.92 59 0.83 1.42 2.89 60 0.82 1.4 2.86 34 Table RO-10 Rational Method Minor Storm Runoff Coefficients for Zoning Classifications Description of Area or Zoning Coefficient | R-F 0.3 U-E 0.3 L-M-In 0.55 R-L, N-C-L 0.6 M-M-N, N-C-M 0.65 N-C-B 0.7 Business: C-C-N, C-C-R, C-N, N-C, C-S 0.95 R-D-R, C-C, C-L 0.95 D,C 0.95 H-C 0.95 C-S 0.95 Industrial: E 0.85 I 0.95 Undeveloped: R-C,T 0.2 P-O-L 0.25 For guidance regarding zoning districts and classifications of such districts please refer to Article Four of the City Land Use Code, as amended. 40 Table RO-11 Rational Method RunofT Coefficients for Composite Analysis Character of Surface Runoff Coefficient Streets, Parking Lots, Drives: Asphalt 0.95 Concrete 0.95 Gravel 0.5 Roofs 0.95 Recycled Asphalt 0.8 Lavms, Sandy Soil: Flat<2% 0.1 Average 2 to 7% 0.15 Steep >7% 0.2 Lawns, Heavy Soil: Flat <2% 0.2 Average 2 to 7% 0.25 Steep >7% 0.35 (4) A new Section 2.9 is added, to read as follows: 2.9 Composite Runoff Coefficient Drainage sub-basins are frequently composed of land that has multiple surfaces or zoning classifications. In such cases a composite runoff coefficient must be calculated for any given drainage sub-basin. The composite nmoff coefficient is obtained using the following formula: Tic.'A,) C = — (RO-8) Where: C = Composite Runoff Coefficient Cj = Runoff Coefficient for Specific Area (Aj) Ai = Area of Surface with Runoff Coefficient of Cj, acres or feet^ n = Number of different surfaces to be considered At= Total Area over which C is applicable, acres or feet^ (5) A new Section 2.70 is added, to read as follows: 41 2.10 Runoff Coefticient Adjustment for Infrequent Storms The ruiioff coefficients provided in tables RO-10 and RO-11 are appropriate for use with the 2-year storm event. For storms with higher intensities, an adjustment of the runoff coefficient is required due to the lessening amount of infiltration, depression retention, evapo-transpiration and other losses that have a proportionally smaller effect on storm runoff. This adjustment is appUed to the composite runoff coefficient. These fi-equency adjustment factors are found in Table RO-12. Table RO-12 Rational Method Runoff Coefficients for Composite Analysis Storm Return Period Frequency Factor (years) Cf 2 to 10 I.OO 11 to 25 1.10 26 to 50 1.20 51 to 100 1.25 1 Note: The product of C times Cf cannot exceed the value of 1, in the cases where it does a value of 1 must be used (6) Section 3. J is deleted in its entirety. (7) Section 3.2 is deleted in its entirety. (8) Section 3.3 is deleted in its entu-ety. (9) A new Section 4.3 is added, to read as follows: 4.3 Computer Modeling Practices (a) For circumstances requiring computer modehng, the design storm hydrographs must be determined using the Stormwater Management Model (SWMM). Basin and conveyance element parameters must be computed based on the physical characteristics of the site. (b) Refer to the SWMM Users' Manual for appropriate modeling methodology, practices and development The Users' Manual can be found on the Environmental Protection Agency (EPA) website Qittp://v\'W'w^epa.pov/edimrnirl/modeJs/swiTim/index.htm). (c) It is the responsibility of the design engineer to verify that all of the models used in the design meet all current City criteria and regulations. 4.3.1 Surface Storage. Resistance Factors, and Infiltration Table RO-13 provides values for surface storage for pervious and impervious surfaces and the infiltration rates to be used with SWMM. Table RO-13 also lists the appropriate infiltration decay rate, zero detention depth and resistance factors, or Manning's "n" values, for pervious and impervious surfaces to be used for SWMM modeling in the city of Fort Collins.