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Home My WebLink AboutFORTY THREE PRIME - PDP - PDP180014 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE RELATED DOCUMENTSeptember 26, 2018 DRAINAGE LETTER AND LID REPORT 43 PRIME Fort Collins, Colorado Prepared for: Red Raven LLC 201 Commerce Drive Unit 2 Fort Collins, Colorado 80524 Prepared by: 301 North Mason Street, Suite 100 Fort Collins, Colorado 80524 Phone: 970.221.4158 www.northernengineering.com Project Number: 1328-010 Drainage Letter and LID Report – 43 Prime Date: September 26, 2018 Project: 43 Prime Project No. 1328-010 Preliminary Development Plan (PDP) Fort Collins, Colorado Attn: City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 To whom it may concern: This letter serves to address the stormwater impacts of the proposed project known as “43 Prime”. The site is located in southeast Fort Collins and is bounded to the north by East Trilby Road, to the east by Brittany Drive, to the south by Candlewood Drive and to the west by Autumn Ridge Drive. The project site is Tract A of the Provincetowne P.U.D. Filing 2, which was approved in 2001, and was included in the drainage study by Manhard Consulting for that project. The proposed development consists of six (6) multifamily buildings, a parking area, two carports and amenity areas for residents. The project site also contains a detention area and drainage facilities that were designed and constructed as a part of the Provincetowne development. Since the project was included in the Provincetowne development, this letter is intended to show conformance with the approved drainage design, including general drainage patterns and imperviousness. This letter also documents how the project meets new Low Impact Development requirements that the City of Fort Collins has implemented since the original project was approved. Original Drainage Patterns The original Provincetowne drainage design divided Tract A into 5 basins – Basins 212, 220, 221, 225 and 406. In general, all of the basins drained from south to north, where they were intercepted by a swale along the north boundary. The exception was Basin 212, which drained west to Autumn Ridge Drive and then collected by an inlet located on Trilby. Once captured, the flows from all of the basins were conveyed to the northeast corner of Tract A and detained in Detention Pond 306. An Existing Drainage Exhibit has been provided has been provided at the back of this report for reference, along with excerpts from the original report in the appendix. Proposed Drainage Patterns The 43 Prime project has divided the site into seven drainage basins that follow essentially the same drainage patterns that were originally approved with the Provincetowne project. The proposed site is comprised of Basin A, which encompasses the parking area, and Basins B1-B3, which define building and landscape areas. Basin C encompasses areas outside of the main development, including the existing detention pond and the swale along the north property line. All of the aforementioned basins drain to the existing detention pond via swales and surface conveyance. Additionally, Basin OS1 has been defined on the west side of the project to quantify flows to Autumn Ridge Drive that will be captured by the existing inlet located on Trilby and conveyed to the existing detention pond via existing storm drains. Please see the Drainage Exhibit for more information. Page | 3 Site Imperviousness While the drainage patterns of the proposed project generally conform with the previously approved drainage design, the drainage basins themselves do not have the same extents or areas. Since a direct comparison cannot be made between the original and proposed basins, a weighted percent imperviousness has been developed. Using this approach, we find that the original drainage plan had a Composite Percent Imperviousness of 42.6% (C100=0.56) while the proposed project will have a Composite Percent Imperviousness of 39.5% (C100=0.44). This is an overall imperviousness decrease of 3.1%, which will result in decreased runoff from the project than the original report anticipated. Detention As shown in the analysis of overall Site Imperviousness, the proposed project will decrease the imperviousness of the project site when compared to the originally approved project, thereby decreasing the runoff from the project site. This decrease in imperviousness and runoff also results in a decrease in the required detention volume identified in the original Provincetowne report. Since detention and water quality were accounted for in the original drainage report and the detention required by this project is less than originally assumed, no additional detention or water quality volume is required as a part of this project, and no changes to the existing facilities are proposed. Water Quality/LID Conformance Although stormwater quantity detention is not required, stormwater quality will be addressed by permanent Best Management Practices (BMPs) and Low Impact Development (LID) requirements. The City LID requirements specify that either 75% of all newly added impermeable areas are provided LID treatment OR 50% LID treatment by which 25% of drivable surfaces are treated by permeable pavers. This project proposes to treat 75% of the new impervious areas by providing a large rain garden on the east side of the project site. This rain garden will treat 75,091 square-feet of impervious area on the site. This is 78.9% of the total impervious area within the project area, which exceeds the amount required by city code. A LID Treatment Exhibit is provided with this report. Erosion and Sediment Control During construction, the Contractor will follow the appropriate and applicable City of Fort Collins standards for erosion and sediment control. Since more than 10,000 sf will be disturbed as a part of this project, a comprehensive Stormwater Management Plan will be prepared for this project at final design. Post construction water quality and erosion control will be achieved by a fully established and stabilized site. All areas disturbed during construction will receive permanent hardscape, landscape, or building structure. Floodplains There are no regulatory floodplains associated with the project. Conclusions The proposed grading concept closely matches original drainage patterns and decreases overall site imperviousness, and additional detention is proven to be unnecessary. Stormwater quality has been provided, and meets the city requirements for Low Impact Development treatment. Therefore, it is my professional opinion that 43 Prime satisfies all applicable stormwater criteria and will effectively limit potential damage associated with its stormwater runoff. Please do not hesitate to contact me if you have questions or require additional information. Sincerely, Andy Reese Project Manager ATTACHMENT 1 HYDROLOGIC CALCULATIONS SITE IMPERVIOUSNESS COMPARISON Basin ID Basin Area (ac) Composite % Imperv. 100-year Composite Runoff Coefficient 212 0.68 33% 0.71 220 0.52 45% 0.74 221 2.18 45% 0.74 224 0.08 96% 1.00 225 1.3 39% 0.73 406 0.11 45% 0.74 Total Site 4.87 42.6% 0.56 Basin ID Basin Area (ac) Composite % Imperv. 100-year Composite Runoff Coefficient OS1 0.23 40% 0.69 A 1.62 80% 1.00 B1 0.15 68% 0.97 B2 0.03 59% 0.89 B3 0.15 39% 0.69 B4 0.45 39% 0.69 C 2.23 8% 0.39 Total Site 4.87 39.5% 0.44 EXISTING MASTER PLANNED COMPOSITE % IMPERVIOUSNESS PROPOSED COMPOSITE % IMPERVIOUSNESS CHARACTER OF SURFACE: Runoff Coefficient Percentage Impervious Project: 43 Prime Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: B. Ruch Asphalt ……....……………...……….....…...……………….………………………………….0.95 . 100% Date: Concrete …….......……………….….……….………………..….………………………………… 0.95 90% Gravel ……….…………………….….…………………………..……………………………….0.50 . 40% Roofs …….…….………………..……………….…………………………………………….0.95 . 90% Pavers…………………………...………………..…………………………………………….0.40 . 22% Lawns and Landscaping Sandy Soil ……..……………..……………….…………………………………………….0.15 . 0% Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year Cf = 1.00 100-year Cf = 1.25 Basin ID Basin Area (ac) Area of Asphalt (ac) Area of Concrete (ac) Area of Roofs (ac) Area of Gravel (ac) Area of Pavers (ac) Area of Lawns and Landscaping (ac) 2-year Composite Runoff Coefficient 10-year Composite Runoff Coefficient 100-year Composite Runoff Coefficient Composite % Imperv. OS1 0.23 0.04 0.03 0.03 0.00 0.00 0.13 0.55 0.55 0.69 40% A 1.62 0.75 0.38 0.23 0.00 0.00 0.27 0.83 0.83 1.00 80% B1 0.15 0.00 0.01 0.11 0.00 0.00 0.04 0.78 0.78 0.97 68% B2 0.03 0.00 0.00 0.02 0.00 0.00 0.01 0.71 0.71 0.89 59% B3 0.15 0.00 0.01 0.05 0.00 0.00 0.09 0.55 0.55 0.69 39% B4 0.45 0.00 0.03 0.17 0.00 0.00 0.25 0.56 0.56 0.69 39% C 2.23 0.00 0.07 0.12 0.02 0.00 2.02 0.31 0.31 0.39 8% Total Onsite 4.64 0.75 0.49 0.70 0.02 0.00 2.68 0.54 0.54 0.68 40% DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I. 10-year Cf = 1.00 Overland Flow, Time of Concentration: Project: 43 Prime Calculations By: Date: Gutter/Swale Flow, Time of Concentration: Tt = L / 60V Tc = Ti + Tt (Equation RO-2) Velocity (Gutter Flow), V = 20·S ½ Velocity (Swale Flow), V = 15·S ½ NOTE: C-value for overland flows over grassy surfaces; C = 0.25 Is Length >500' ? C*Cf (2-yr Cf=1.00) C*Cf (10-yr Cf=1.00) C*Cf (100-yr Cf=1.25) Length, L (ft) Slope, S (%) Ti 2-yr (min) Ti 10-yr (min) Ti 100-yr (min) Length, L (ft) Slope, S (%) Velocity, V (ft/s) Tt (min) Length, L (ft) Slope, S (%) Velocity, Rational Method Equation: Project: 43 Prime Calculations By: Date: From Section 3.2.1 of the CFCSDDC Rainfall Intensity: Design Point Basin(s) Area, A (acres) 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) C2 C10 C100 Intensity, i2 (in/hr) Intensity, i10 (in/hr) Intensity, i100 (in/hr) Flow, Q2 (cfs) Flow, Q10 (cfs) Flow, Q100 (cfs) Flow, WQ (cfs) OS1 OS1 0.23 5 5 5 0.55 0.55 0.69 2.85 4.87 9.95 0.4 0.6 1.6 0.18 A A 1.62 10 10 10 0.83 0.83 1.00 2.21 3.78 7.88 3.0 5.1 12.8 1.50 B1 B1 0.15 5 5 5 0.78 0.78 0.97 2.85 4.87 9.95 0.3 0.6 1.5 0.17 B2 B2 0.03 5 5 5 0.71 0.71 0.89 2.85 4.87 9.95 0.1 0.1 0.2 0.03 B3 B3 0.15 8 8 8 0.55 0.55 0.69 2.40 4.10 8.59 0.2 0.4 0.9 0.10 B4 B4 0.45 10 10 10 0.56 0.56 0.69 2.21 3.78 7.88 0.6 0.9 2.5 0.28 C C 2.23 26 26 25 0.31 0.31 0.39 1.40 2.39 5.04 1.0 1.7 4.4 0.49 DEVELOPED RUNOFF COMPUTATIONS B. Ruch September 26, 2018 Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1 Q = C f ( C )( i )( A ) Basin ID Basin Area (s.f.) Basin Area (ac) Composite % Imperv. Flow, WQ (cfs) Flow, Q2 (cfs) Flow, Q100 (cfs) OS1 0.23 4.64 0.40 0.18 0.36 1.59 A 1.62 0.00 0.80 1.50 3.00 12.79 B1 0.15 0.00 0.68 0.17 0.34 1.50 B2 0.03 0.00 0.59 0.03 0.06 0.24 B3 0.15 0.00 0.39 0.10 0.21 0.92 B4 0.45 0.00 0.39 0.28 0.55 2.46 C 2.23 0.00 0.08 0.49 0.97 4.38 Rational Summary (Proposed) ATTACHMENT 2 LID/WATER QUALITY CALCULATIONS 2YD 2YD 2YD 2YD 2YD 2YD MAIL C C T F E S F E S F E S F E S LID LID LID / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / D D D D D D D D RAINGARDEN REQUIRED VOLUME: 1,333 CU. FT. PROVIDED VOLUME: 1,496 CU. FT. TREATMENT AREA: 76,464 SF 43 PRIME SHEET NO: D:\PROJECTS\1328-010\DWG\DRNG\1328-010_LID.DWG 301 N. Howes Street, Suite 100 Fort Collins, Colorado 80521 ENGINEER ING N O R T H E RN PHONE: 970.221.4158 www.northernengineering.com DRAWING REFERENCE: LID TREATMENT EXHIBIT B. Ruch 1 in = 60 ft September 26, 2018 LID-1 DRAWN BY: SCALE: ISSUED: ( IN FEET ) 0 ATTACHMENT 3 PREVIOUS REPORT EXCERPTS This unofficial copy was downloaded on Aug-14-2018 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact Engineering Office 281 North College Fort Collins, CO 80521 USA ATTACHMENT 4 DRAINAGE EXHIBITS ST ST ST ST C C T F E S F E S CONTROL IRR CONTROL IRR CONTROL IRR CONTROL IRR CONTROL IRR CONTROL IRR F E S F E S LID LID LID / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / D D D D D D D D 2YD 2YD 2YD ST ST ST ST C C T V.P. F E S F E S F E S V.P. V.P. F E S LID LID LID / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / D D D D D D D D 221 220 406 224 221 225 224 0.08 AC 221 2.18 AC 225 1.30 AC 212 0.68 AC 220 0.52 AC 406 0.11 AC EAST TRILBY ROAD CANDLEWOOD DRIVE BRITTANY DRIVE AUTUMN RIDGE DRIVE EXISTING STORM DRAIN EXISTING STORM DRAIN EXISTING STORM DRAIN EXISTING STORM DRAIN EXISTING INLET EXISTING INLET EXISTING INLET EXISTING INLET EXISTING INLET FOR DRAINAGE REVIEW ONLY NOT FOR CONSTRUCTION CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU DIG, GRADE, OR EXCAVATE FOR THE MARKING OF UNDERGROUND MEMBER UTILITIES. CALL UTILITY NOTIFICATION CENTER OF COLORADO Know what'sbelow. Call before you dig. R NORTH DR2 EXISTING DRAINAGE EXHIBIT 18 A 1.62 AC LEGEND: EXISTING STORM SEWER EXISTING CONTOUR EXISTING CURB & GUTTER PROPERTY BOUNDARY EXISTING INLET DESIGN POINT A FLOW ARROW DRAINAGE BASIN LABEL DRAINAGE BASIN BOUNDARY PROPOSED SWALE SECTION 1 1 NOTES: 1. REFER TO THE PRELIMINARY DRAINAGE REPORT FOR 43 PRIME, DATED SEPTEMBER 26, 2018 BY NORTHERN ENGINEERING SERVICES, INC AND THE FINAL DRAINAGE AND EROSION CONTROL REPORT FOR PROVINCETOWNE PUD FILING TWO, DATED MARCH 22, 2001 BY MANHARD CONSULTING, LTD., FOR ADDITIONAL INFORMATION. BENCHMARK PROJECT DATUM: NAVD88 CITY OF FORT COLLINS BENCHMARK 24-94 NORTHEAST CORNER OF EAST TRILBY RD AND PORTNER DR., ON TOP OF THE WEST END OF A CONCRETE HEADWALL. ELEV. = 4960.69 CITY OF FORT COLLINS BENCHMARK 25-94 NORTHWEST CORNER OF EAST TRILBY RD. AND SOUTH LEMAY AVE, ON TOP OF THE SOUTHEAST EDGE OF THE CONCRETE RING TO AN ELECTRIC MANHOLE. ELEV. = 4913.16 PLEASE NOTE: THIS PLAN SET IS USING NAVD88 FOR A VERTICAL DATUM. SURROUNDING DEVELOPMENTS HAVE USED NGVD29 UNADJUSTED FOR THEIR VERTICAL DATUMS. IF NGVD29 UNADJUSTED DATUM IS REQUIRED FOR ANY PURPOSE, THE FOLLOWING EQUATION SHOULD BE USED: NGVD29 UNADJUSTED = NAVD88 - 3.19' BASIS OF BEARINGS THE BASIS OF BEARINGS IS THE NORTH LINE OF THE NORTHEAST QUARTER OF SECTION 13-6-69 AS BEARING NORTH 88° 11' 32" WEST (ASSUMED BEARING). EXISTING PLANNEDCOMPOSITE % IMPERVIOUSNESS Basin ID Basin Area (ac) Composite % Imperv. 100-year Composite Runoff Coefficient 212 0.68 33% 0.71 220 0.52 45% 0.74 221 2.18 45% 0.74 224 0.08 96% 1.00 225 1.3 39% 0.73 406 0.11 45% 0.74 Total Site 4.87 42.6% 0.56 Sheet 43 PRIME These drawings are instruments of service provided by Northern Engineering Services, Inc. and are not to be used for any type of construction unless signed and sealed by a Professional Engineer in the employ of Northern Engineering Services, Inc. NOT FOR CONSTRUCTION REVIEW SET E NGINEER ING N O R T H E RN FORT COLLINS: 301 North Howes Street, Suite 100, 80521 GREELEY: 820 8th Street, 80631 970.221.4158 northernengineering.com of 18 2YD 2YD 2YD MAIL UD UD UD C A OS1 B1 B2 B3 B4 C A OS1 B1 B2 B3 B4 OS1 0.23 AC A 1.62 AC B1 0.15 AC B2 0.03 AC B3 0.15 AC B4 0.45 AC C 2.23 AC EXISTING EXISTING STORM DRAIN STORM DRAIN EXISTING STORM DRAIN EXISTING STORM DRAIN PROPOSED AREA DRAIN PROPOSED AREA DRAIN PROPOSED AREA DRAIN EXISTING INLET EXISTING INLET EXISTING INLET EXISTING INLET EXISTING INLET PROPOSED RAIN GARDEN PROPOSED 2' CONCRETE CHASE PROPOSED RAIN GARDEN PROPOSED UNDERDRAIN PROPOSED 1'SIDEWALK CHASE PROPOSED 1' SIDEWALK CHASE PROPOSED 1' SIDEWALK CHASE PROPOSED 7.5' SIDEWALK CULVERT PROPOSED CULVERTS EAST TRILBY ROAD CANDLEWOOD DRIVE BRITTANY DRIVE AUTUMN RIDGE DRIVE LOT 2 TRACT A LOT 1 FOR DRAINAGE REVIEW ONLY NOT FOR CONSTRUCTION HYDROLOGY SUMMARY CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU DIG, GRADE, OR EXCAVATE FOR THE MARKING OF UNDERGROUND MEMBER UTILITIES. CALL UTILITY NOTIFICATION CENTER OF COLORADO Know what'sbelow. Call before you dig. R NORTH LID SUMMARY Sheet 43 PRIME These drawings are instruments of service provided by Northern Engineering Services, Inc. and are not to be used for any type of construction unless signed and sealed by a Professional Engineer in the employ of Northern Engineering Services, Inc. NOT FOR CONSTRUCTION REVIEW SET E NGINEER ING N O R T H E RN FORT COLLINS: 301 North Howes Street, Suite 100, 80521 GREELEY: 820 8th Street, 80631 970.221.4158 northernengineering.com of 18 DR1 DRAINAGE EXHIBIT 17 Basin ID Basin Area (s.f.) Basin Area (ac) Composite % Imperv. Flow, WQ (cfs) Flow, Q2 (cfs) Flow, Q100 (cfs) Treatment Area (sf) OS1 0.23 4.64 0.40 0.18 0.36 1.59 4315.00 A 1.62 0.00 0.80 1.50 3.00 12.79 59061.24 B1 0.15 0.00 0.68 0.17 0.34 1.50 5103.00 B2 0.03 0.00 0.59 0.03 0.06 0.24 784.00 B3 0.15 0.00 0.39 0.10 0.21 0.92 2921.16 B4 0.45 0.00 0.39 0.28 0.55 2.46 8565.00 C 2.23 0.00 0.08 0.49 0.97 4.38 9091.00 PROPOSED COMPOSITE % IMPERVIOUSNESS 43 PRIME ON-SITE LID TREATMENT Project Summary Total Impervious Area 89,081 sf Target Treatment Percentage 75% Minimum Area to be Treated by LID measures 66,811.05 sf Rain Garden Total Rain Garden Treatment Area 76,434 sf Total Treatment Area 76,434 sf Percent Total Project Area Treated 85.8% Basin ID Basin Area (ac) Composite % Imperv. 100-year Composite Runoff Coefficient OS1 0.23 40% 0.69 A 1.62 80% 1.00 B1 0.15 68% 0.97 B2 0.03 59% 0.89 B3 0.15 39% 0.69 B4 0.45 39% 0.69 C 2.23 8% 0.39 Total Site 4.87 39.5% 0.44 A 1.62 AC LEGEND: PROPOSED CONTOUR PROPOSED STORM SEWER PROPOSED SWALE EXISTING CONTOUR PROPOSED CURB & GUTTER PROPERTY BOUNDARY PROPOSED INLET DESIGN POINT A FLOW ARROW DRAINAGE BASIN LABEL DRAINAGE BASIN BOUNDARY PROPOSED SWALE SECTION 1 1 NOTES: 1. REFER TO THE PRELIMINARY DRAINAGE REPORT FOR 43 PRIME, DATED SEPTEMBER 26, 2018 BY NORTHERN ENGINEERING SERVICES, INC AND THE FINAL DRAINAGE AND EROSION CONTROL REPORT FOR PROVINCETOWNE PUD FILING TWO, DATED MARCH 22, 2001 BY MANHARD CONSULTING, LTD., FOR ADDITIONAL INFORMATION. PROPOSED UNDERDRAIN UD BENCHMARK PROJECT DATUM: NAVD88 CITY OF FORT COLLINS BENCHMARK 24-94 NORTHEAST CORNER OF EAST TRILBY RD AND PORTNER DR., ON TOP OF THE WEST END OF A CONCRETE HEADWALL. ELEV. = 4960.69 CITY OF FORT COLLINS BENCHMARK 25-94 NORTHWEST CORNER OF EAST TRILBY RD. AND SOUTH LEMAY AVE, ON TOP OF THE SOUTHEAST EDGE OF THE CONCRETE RING TO AN ELECTRIC MANHOLE. ELEV. = 4913.16 PLEASE NOTE: THIS PLAN SET IS USING NAVD88 FOR A VERTICAL DATUM. SURROUNDING DEVELOPMENTS HAVE USED NGVD29 UNADJUSTED FOR THEIR VERTICAL DATUMS. IF NGVD29 UNADJUSTED DATUM IS REQUIRED FOR ANY PURPOSE, THE FOLLOWING EQUATION SHOULD BE USED: NGVD29 UNADJUSTED = NAVD88 - 3.19' BASIS OF BEARINGS THE BASIS OF BEARINGS IS THE NORTH LINE OF THE NORTHEAST QUARTER OF SECTION 13-6-69 AS BEARING NORTH 88° 11' 32" WEST (ASSUMED BEARING). % & ' !! % (") #$*" & + % & ' !! % (") #$*" & + % & ' !! % (") #$*" & + 1 INCH = 60 FEET 60 60 LEGEND UNTREATED AREA RAIN GARDEN AREA RAIN GARDEN TREATMENT AREA 43 PRIME ON-SITE LID TREATMENT Project Summary Total Impervious Area 89,081 sf Target Treatment Percentage 75% Minimum Area to be Treated by LID measures 66,811.05 sf Rain Garden Total Rain Garden Treatment Area 76,434 sf Total Treatment Area 76,434 sf Percent Total Project Area Treated 85.8% V (ft/s) Tt (min) 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) OS1 OS1 No 0.25 0.25 0.31 0 N/A N/A N/A N/A 99 4.88% 4.42 0.4 0 NA N/A N/A 5 5 5 A A No 0.25 0.25 0.31 23 22.78% 2.7 2.7 2.5 563 0.50% 1.41 6.6 91 1.79% 2.01 0.8 10 10 10 B1 B1 No 0.25 0.25 0.31 0 N/A N/A N/A N/A 143 0.50% 1.41 1.7 21 2.00% 2.12 0.2 5 5 5 B2 B2 No 0.25 0.25 0.31 0 N/A N/A N/A N/A 61 0.50% 1.41 0.7 20 4.85% 3.30 0.1 5 5 5 B3 B3 No 0.25 0.25 0.31 53 6.64% 6.2 6.2 5.7 138 0.50% 1.41 1.6 76 1.96% 2.10 0.6 8 8 8 B4 B4 No 0.25 0.25 0.31 23 22.78% 2.7 2.7 2.5 563 0.50% 1.41 6.6 91 1.79% 2.01 0.8 10 10 10 C C No 0.25 0.25 0.31 140 0.91% 19.4 19.4 17.9 513 0.40% 1.26 6.8 0 NA N/A N/A 26 26 25 DEVELOPED TIME OF CONCENTRATION COMPUTATIONS Gutter Flow Swale Flow Design Point Basin Overland Flow B. Ruch September 26, 2018 Time of Concentration (Equation RO-4) ( ) 3 1 1 . 87 1 . 1 * S C Cf L Ti = − September 26, 2018