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HomeMy WebLinkAboutDrainage Reports - 03/26/2013 (2)December 11, 2012 Mr. Glen Schleuter Stormwater Department City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80521 RE: Drainage Letter for Higgins Property Project #B 12030 Dear Glen, BLUE SKY Engineering City of Ft. CollinsAPproved Plans Approved By Date We have prepared this drainage letter for Higgins Property for your review and approval. The existing property is an undeveloped 14,970 square -foot lot on the southeast side of the intersection of Cook Street and Mulberry Street. The site is located in the Canal Importation Drainage Basin. This project proposes to develop a single family residence on the property. The following is a summary of the impacts to the drainage systems on and off the site. In addition, supporting calculations and a drainage exhibit have been attached. Runoff The existing site (Basin EX) drains to the southeast and has 0.03 cfs and 0.63 cfs of runoff leaving the site in the 2-year and 100-year storms, respectively. In the developed condition, approximately 0.26 acres drains to Cook Street and Mulberry Street. The area draining to the streets is defined as Basin A and will have 0.40 cfs and 1.85 cfs of runoff leaving the site in the 2- year and 100-year storms, respectively. The area draining to the southeast following the historic drainage pattern is defined as Basin B and contains no new imperviousness from the historic site. Basin B will have 0.01 cfs and 0.31 cfs of runoff leaving the site in the 2-year and 100-year storms, respectively. Detention Storage The entire site is estimated to be approximately 25% impervious when built out. Residential development typically runs approximately 40% imperviousness based on UDFCD Figure RO-3. Due to the differnece between typical and developed percent imperviousness, the size of the site, and the difficulty in providing detention we are not proposing any detention storage with this project. Water Quality The small site and proximity to adjacent storm sewer make it very difficult to provide typical water quality. The residential site will have an area of non paved surfaces at the front and rear of the lot. These areas will intercept the stormwater runoff that comes from the roof, driveway, and patio areas and provide some water quality via "disconnected impervious areas' and the grass swales to convey the runoff. This is the extent of water quality that we are proposing. 1501 Academy Ct. Suite 204 1 Fort Collins, CO 80524 1 970-217-7420 1 w .bluesky­engineeccom 7h*, \BLUE SKY Engineering Erosion Control Erosion and Sediment Control devices will be implemented on the site as needed. It is anticipated that onsite runoff will be contained by straw wattles surrounding the site. Summary Due to the size of this small site, the proposed development of the site will have minimal impact to the stormwater. The runoff from the site is less than what would typically be expected for a residential site, therefore no on site detention or downstream improvements are included with this project. If you have any questions, please contact me at 970-217-7420 or seliason@bluesky- engineer.com. Sincerely, Blue Sky Engineering Sam Eliason, P.E. 1501 Academy Ct. Suite 204 1 Fort Collins. CO 80524 1 970-217-7420 1 w .bluesky-engineer.com II CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD 11 Project Title: Higgins Property Catchment ID: Basin EX, Existing 2-year Discharge I. Catchment Hydrologic Data Catchment ID = EX Area = 0.34 Acres Percent Imperviousness = 2,00 % NRCS Sail Type = C A. S, C. or D 11. Rainfall Information I (incNhr) = C1 ' P1 f(C2 +Td)AC3 Design Storm Return Period, Tr = 2 years C1 = 28,50 C2= 10.00 C3= 0.786 P1= 0.82 inches (input return period for design storm) (input the value of Cl) (input the value of C2) (input the value of C3) (input one-hr precipitation —see Sheet "Design Info") III. Analysis of Flow Time (Time of Concentration) for a Catchment Runoff Coefficient, C = 0.06 Overide Runoff Coefficient, C = (enter an overide C value if desired, or leave blank to accept calculated C.) 5-yr. Runoff Coefficient, C-5 = 0.16 Overide 5-yc Runoff Coefficient. C = (enter an overide C-5 value if desired, or leave blank to accept calculated C-5.) Illustration sverland Reach 1 9sw i Bad—iK Flow Dhvtior CamLean1 NRCS'.ano Heavy Tillage/ Short Needy Gressetl Paveo Aroas 8 Type Meaoow Fleltl Pasture! Sere Swales/ Shallow Pawl Saes Lawns Grouts Waterways (Sheet F10w1 Cunve ante 2.5 5 711 10 15 20 N. Calculations: Reach Slope Length 6-W NRCS Flow Flow ID S L Runoff Conve Velocity Time Coeff ante V Tf ftlfl it C-5 fps minutes input Input output input output output Overland 0.0100 176 0.16 0.13 22.44 1 2 3 4 F= 5 Sum 176 Computed Tc = 22.44 Regional Tc = iu.St1 Peak Runoff Prediction using Computed Tc diction using Regional Tc Rainfall Intensity at Tc, I = 1.52 inch/hr Rainfall Intensity at Tc, I = 2.14 inch/hr Peak Flowrate, Qp = 0.03 cfs Peak Flowrate, Op = 0.04 cis Higgins - UD Rational Basin Eiesting 2yr Emsting.)ds, To and PeakQ 1211112012. 4:14 PM II CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD 11 Project Title: Higgins Property Catchment ID: Basin EX Existing 100-year Discharge I. Catchment Hydrologic Data Catchment ID = EX Area = 0.34 Acres Percent Imperviousness = 2.00 % NRCS Sal Type = C A, B, C, or D 11. Rainfall Information I (inch/hr) = C1 ' P1 1(C2 f Td)AC3 Design Storm Return Period, Tr = 100 years C1 = 28.50 C2= 10.00 C3= 0,793 P1= 2.91 inches (input return period for design storm) (input the value of C1) (Input the value of C2) (input the value of C3) (input one-hr precipitation —see Sheet "Design Info") Ill. Analysis of Flow Time (Time of Concentration) for a Catchment Runoff Coefficient, C = 0.51 Ovende Runoff Coefficient, C = (enter an overide C value if desired, or leave blank to accept calculated C.) 5-yr. Runoff Coefficient, C-5 = 0.16 Ovedde 5-yr. Runoff Coefficient, C = (enter an overide C-5 value if desired, or leave blank to accept calculated C-5.) Illustration '' overind L. EGEM Reachl daw O Hey,lnWat Raaeh 2 Flw Dtrerdw. Cairlrwnt 13nund�ey NRGS Lantl Heavy Tillage/ Shorl Nearly Grassetl Paved Areas & Type Meatlnw Fieltl F'aslure/ Bare Swalesl Shallow Paved $wales Lawns Ground Walorways (Sneol Flow] 11 Ca,i y nca ��� �� II 10 ILTA Calculations: Reach Slope Len th 5-w NRCS Flow Flow ID S L Runoff Cone velocity Time Coaff ante V Tf f01t It C3 fps minutes input Input output Input output output Overland 0.0100 176 0.16 0.13 22.44 1 2 3 4 5 Sum 176 Computed Tc = 22.44 Regional Tc = 1 U.96 Peak Runoff Prediction using Computed Tc diction using Regional Tc Rainfall Intensity at Tc, I = 5.25 inch/hr Rainfall Intensity at Tc, I = 7.42 inchlhr Peak Flowrate, Qp = 0.92 cfs Peak Flowrate, Qp = 1.30 cfs Higgins - UD Rational Basin Existing 100yr Etasbng.xls, Tc and PeskQ 12/1112012, 4:14 PM I CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD 11 Project Title: Higgins Property Catchment ID: Basin A. 2-year Discharge I. Catchment Hydrologic Data Catchment ID = A Area = 0.26 Acres Percent Imperviousness = 30.10 % NRCS Sal Type = C A. B, C, or D II. Rainfall Information I(inoh/hr)=C1•PI I(C2+Tall C3 Design Storm Return Period, Tr = 2 years C1 = 28.50 C2= 10.00 C3= 0.7B6 P1= 0.82 inches (Input return period for design storm) (Input the value of C1) (Input the value of C2) (Input the value of C3) (Input one-hr precipitation —see Sheet "Design Info") III. Analysis of Flow Time (Time of Concentration) for a Catchment Runoff Coefficient. C = 0.51 Overide Runoff Coefficient, C = (enter an overlde C value if desired, or leave blank to accept calculated C.) 5-yr. Runoff Coefficient, C-5 = 0.54 Overide 5-yr. Runoff Coefficient, C = (enter an override C-5 value if desired, or leave blank to accept calculated C-5.) Illustration /' ere�ud LEGEND Beeokl !ew O Beplrming Heacl2 Flow Dtraflm E Catduivnt NRCS Land Heavy Tillage% Short Nearly Grassed Paved Areas 8 TyFe Maacow Field Pasturo/ Bare Swalesf Shallow Paved Swales Lawns Ground Waterways (Shee; Flow) Conveyance 25 5 7E10E 15 20 IV. Calculations: Reach Sloe Len 5-yr NRCS Flow Flow 10 S L Runoff Con velocity Time Coeff ante V Tf ftih ft C-5 fps minutes input Input output input output output Overland 0.0200 8 0.54 0.06 2.28 1 0.0200 126 15.00 2.12 0.99 2 3 4 5 Sum 134 Computed Tc = 3.25 Regional Tc = 10.74 Peak Runoff Prediction using Computed Tc diction using Regional Tc Rainfall Intensity at To, I = 3.06 inch/hr Rainfall Intensity at Tc, I = 2.16 inch/hr Peak Flowrate, Qp = 0.40 cfs Peak Flowrate, Qp = 0.28 cfs Higgins - 1-10 Rational Basin A 2yr STORM A.xls, Tc and PeakQ 12/1112012, 4:13 PM II CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD 11 Project Title: Higgins Property Catchment ID: Basin A, 100-year Runoff 1. Catchment Hydrologic Data Catchment ID = A Area = 0.26 Acres Percent Imperviousness = 75.00 % NRCS Sail Type = C A. B, C, or D II. Rainfall Information I (inch/hr) = C1 ' P1 /(C2 + Td)-C3 Design Storm Return Period. Tr = 100 years C I = 28.50 C2= 10.00 C3= 0.786 Pi= 2.91 inches (input return period for design storm) (input the value of Cl) (input the value of C2) (Input the value of C3) (input one-hr precipitation --see Sheet "Design Info") NI. Analysis of Flow Time (Time of Concentration) for a Catchment Runoff Coefficient, C = 0.66 Ovedlde Runoff Coefficient, C = (enter an overide C value if desired, or leave blank to accept calculated C.) 5-yr. Runoff Coefficient, C-5 = 0.54 Ovedde 5-yr. Runoff Coefficient, C = (enter an overide C-5 value if desired, or leave blank to accept calculated C-5.) Illustration Resell Isom Will Plw Dlrerdor comment Boer.dery NRCS Land Heavy Tillage- Short Nearly Grassed Paved Areas 8 Type Meadow Field Pasture/ Bare Swells/ J Shallow Paved Swales Lawns Ground Vdale Sheet Flow) Conveyance�10 15 1 20 Y Calculations: Reach slope Len 5-yr NRCS Flow Flow D S L Runoff Convoy, Velocity Time Coats once V Tf 8/R it C-5 fps minutes input input output input output output Overland 0.0200 8 0.54 0.06 2.28 1 0.0200 126 1 15.00 2.12 0.99 2 3 4 5 Sum 134 Computed Tc = 3.27 Regional Tc = 10.74 IV. Peak Runoff Prediction using Computed To diction using Regional To Rainfall Intensity at Tc, I = 10.87 inch/hr Rainfall Intensity at Tc, I = 7.65 inch/hr Peak Flowrate, Op = 1.85 cis Peak Flowrete, Op = 1,30 cis Higgins - LID Rational Basin A 100yr STORM A.tds. Tc and PeakO 12111/2012. 4:13 PM 11 CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD 11 Project Title: Higgins Property Catchment ID: Basin B 2-year Discharge for Offsits Design I. Catchment Hydrologic Data Catchment ID = B Area = 0.09 Acres Percent Imperviousness = 2.00 NRCS Soil Type = C A. B, C, or D II. Rainfall Information I (Inch/hr) = C1 * PI I(C2 +Td)"C3 Design Storm Return Period, Tr = 2 years C1 = 28.50 C2= 10.00 C3= 0.786 Pl= 0.62 inches (input return period for design storm) (input the value of Cl) (input the value of C2) (input the value of C3) (Input one-hr precipitation —see Sheet "Design Info") 111. Analysis of Flow Time (Time of Concentration) for a Catchment Runoff Coefficient, C = 0.06 Overide Runoff Coefficient, C = (enter an ovende C value if desired, or leave blank to accept calculated C.) 5-yr. Runoff Coefficient, C-5 = 0.14 Overide 5-yr. Runoff Coefficient, C = (enter an overide C-5 value if desired, or leave blank to accept calculated C-5.) Illustration ererland Reach Bow ) Begoft li Dlrailer Comimoof NRCS Lantl Heavy Tillage' Short Nearly Grassetl Paved Areas 8 Type Meadow Flela Pasture/ Bara Swales! Shallow Paved Swales Lawns Ground Waterways Shee�Flnw Conveyance 2.5 ! _�� 10 15 II 20 IM Calculations. Reach Slope Length 5-yr NRCS Flow Flow 10 S L Runoff Convey- Velocity Time Coeff once V 7 ft/R It C-5 fps minutes Input input out ut Input output output Overland 0.0690 54 0.14 D.13 6.68 1 2 3 4 5 Sum 54 Computed Tc = 6.68 Regional I c = 1u.J0 Peak Runoff Prediction using Computed Te diction using Regional Tc Rainfall Intensity at Tc, I = 2.56 inch/hr Rainfall Intensity at Tc, I = 2,19 inch/hr Peak Fiowrate, Qp = 0.01 cfs Peak Flowrate, Op = 0.01 cfs Higgins - UD Rational Basin B 2yr STORM B.Ids, Tc and PeakQ 1211112012, 4:13 PM II CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD 11 Project Title: Higgins Property Catchment ID: Basin B 100-year Discharge for Swale B and Offsite Design 1. Catchment Hydrologic Data Catchment ID = B Area = 0.09 Acres Percent Impendousness = 2.00 % NRCS Soil Type = C A. B, C, or D II. Rainfall Information I (Inchlhr) - C1 - P1 I(C2 +Td)AC3 Design Storm Rehm Period, Tr = 100 years C1 = 28.50 C2= 10.00 C3= 0-793 Pt= 2.91 inches (input return period for design storm) (input the value of CI) (input the value of C2) (Input the value of C3) (input one-hr precipitation —see Sheet "Design Info") III. Analysis of Flow Time (Time of Concentration) for a Catchment Runoff Coefficient, C = 0.41 Overide Runoff Coefficient, C = (enter an ovedde C value if desired, or leave blank to accept calculated C.) 5-yr. Runoff Coefficient, C-5 = 0.14 Ovende 5-yr. Runoff Coefficient. C = (enter an overide C-5 value if desired, or leave blank to accept calculated C-5.) Illustration J V LEGEND Rearh2 � O Beemuirc Fl.w Direrdm Catclu..at NRCS Land Heavy Tillages Short Nearly Grasscu Paved Areas & Type Meadow Field Pastoral Bsre Swalesl Shallow Paved $wales Lawns Grountl Waterways (Sheet Flow) Conve nce 2.5 5 7 10 t5 20 Calculations: Reach Slope Len th 5-yr NRCS Flow Flow ID S L Runoff Conve Velocity Time Coen ante V Tf Nff It C-5 f minutes Input Input output input output output Overland 0,0690 54 0.14 0.13 6.68 1 Computed Tc = 6.68 2 3 4 5 Sum 54 Regional I tl = 1 U.3U N. Peak Runoff Prediction using Computed Tc diction using Regional Tc Rainfall Intensity at Tc, I = 8.90 inchlhr Rainfall Intensity at Tc, I = 7.62 inchlhr Peak Flowrate. 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