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HomeMy WebLinkAboutPOUDRE VALLEY PLAZA MIXED-USE - MJA210003 - DOCUMENT MARKUPS - ROUND 2 - DRAINAGE REPORTFINAL DRAINAGE REPORT Poudre Valley Plaza Mixed Use Poudre Valley Plaza P.U.D. Lot 7 Fort Collins, CO Prepared for: Schuman Companies Inc. Mark Morrison 7385 Greendale Road, Unit 104 Windsor, CO 80528 701.590.0434 Prepared by: i2 Consultants, Inc. 16911 Potts Place Mead, CO 80542 Phone: 970.217.9148 Project Number: 1024-3 August 4, 2021 i2 Consultants, Inc. 16911 Potts Place, Mead, CO 970.217.9148 troy@i2-consultants.com August 4, 2021 Mr. Matt Simpson, PE, CFM Development Review Engineer City of Fort Collins Utilities 222 Laporte Avenue Fort Collins, CO 80524 RE: Final Drainage Report for Poudre Valley Plaza Mixed Use Lot 7, Poudre Valley Plaza P.U.D., Fort Collins, CO Dear Mr. Simpson: We are pleased to present this Final Drainage Report for Poudre Valley Plaza Mixed Use, Lot 7, Poudre Valley Plaza P.U.D. for your review and approval. This report has been prepared in accordance with the Fort Collins Stormwater Criteria Manual, September 2018. We look forward to your favorable review of this project and report. Please do not hesitate to contact our office if you have any questions. Sincerely, i2 Consultants, Inc. Troy W. Campbell, PE Senior Project Engineer ENGINEER’S CERTIFICATION I hereby certify that this report for the final drainage design of Poudre Valley Plaza Mixed Use, Lot 7, Poudre Valley Plaza P.U.D. was prepared by me (or under my direct supervision) in accordance with the provisions of the Fort Collins Storm Drainage Criteria Manual for the owners thereof. __________________________________________ Registered Professional Engineer State of Colorado No. 41159 (Seal) Final Drainage Report Poudre Valley Plaza Mixed Use, Fort Collins, CO August 4, 2021 Page 2 i2 Consultants, Inc. Final Drainage Report Poudre Valley Plaza Mixed Use Lot 7, Poudre Valley Plaza P.U.D. Located within the Northwest Quarter of Section 35, Township 7 North, Range 69 West of the 6th P.M. City of Fort Collins, County of Larimer, State of Colorado TABLE OF CONTENTS Page I. GENERAL LOCATION AND DESCRIPTION 3 A. Site Location B. Description of Property II. DRAINAGE BASINS AND SUB-BASINS 4 A. Major Basin B. Sub-basin and Site Drainage III. DRAINAGE DESIGN CRITERIA 4 A. Regulations B. Development Criteria Reference and Constraints C. Hydrological Criteria D. Hydraulic Criteria IV. DRAINAGE FACILITY DESIGN 5 A. General Concept B. Specific Details V. SEDIMENT, EROSION CONTROL AND STORMWATER QUALITY 7 A. Temporary Sediment and Erosion Control B. Permanent Water Quality BMPs VI. CONCLUSIONS 9 A. Compliance with Standards B. Drainage Concept VII. REFERENCES 10 VIII. APPENDICIES 11 Final Drainage Report Poudre Valley Plaza Mixed Use, Fort Collins, CO August 4, 2021 Page 3 i2 Consultants, Inc. I. GENERAL LOCATION AND DESCRIPTION A. Site Location: The proposed development is located in the northwest quarter of Section 35, Township 7 North, Range 69 West, of the 6th Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado. Furthermore, the project is north of Arbor Street Avenue and east of Shields Street. The legal description of the property is Lot 7, Poudre Valley Plaza P.U.D. The subject site is currently vacant. B. Description of Property: The subject development lot consists of roughly 0.25 acres. The area considered with this drainage report is roughly 0.43 acres. The proposed building will be within Lot 7 and the parking, landscaping, walks and accesses will be located on Tract A Poudre Valley Plaza P.U.D. The development of Lot 7 will consist of construction of a single building, walks and landscaping. A portion of the existing parking to the north of the building will be removed and replaced with this project. The site currently is vacant but has been overlot graded with the Poudre Valley Plaza P.U.D. improvements. The site is bound by Arbor Avenue to the south, existing commercial development to the north, east and west. The subject site generally slopes from south to north at varying slopes from 0% to 1%. A portion of the site drains to the east to the existing retention pond constructed as part of Poudre Valley Plaza P.U.D. The existing runoff from the subject property drains to the north in existing conveyances (curb, gutter, sheet flow) to the existing detention pond in the northeast corner of Poudre Valley Plaza P.U.D. According to the Natural Resources Conversation Service (NRCS) Web Soil Survey, the native soils in this area are Altvan-Santanta loams, 0 to 3 percent slopes (Map Unit Symbol #3), which is a Type B soil and Altvan-Satanta loams, 3 to 9 percent slopes (Map Unit Symbol #4), which is a Type B soil. Please refer to the NRCS soils information in the Appendix. Existing drainage facilities near or adjacent to the site include existing curb & gutter installed with Poudre Valley Plaza P.U.D. as well as an existing retention pond east of the site and existing detention pond north of the site. Furthermore, there is an existing storm drain system in Arbor Avenue. Final Drainage Report Poudre Valley Plaza Mixed Use, Fort Collins, CO August 4, 2021 Page 4 i2 Consultants, Inc. II. DRAINAGE BASINS AND SUB-BASINS A. Major Basin: This site is located within the Mail Creek Basin as shown on the City of Fort Collins Master Drainage Plan. This basin historically generally flows from northwest to southeast. There no agricultural irrigation facilities within 100 feet of the property boundary for the proposed site. The site is shown on FEMA panel 08069C0986G, effective 05/02/2012. The subject site is located with Zone X of the FEMA panel. B. Sub-basin and Site Drainage: The proposed site generally directs runoff north to existing improvements. A portion of the site will drain east to the existing retention pond, due to existing grades and site constraints. The subject site is shown within Basins 1, 2 and 4 of the approved Final Drainage and Erosion Control Study for Poudre Valley Plaza, Fort Collins, Colorado, dated January 23, 1996, prepared by RBD, Inc. Engineering Consultants. There is a small portion of this site in the southeast corner that flows offsite to Arbor Avenue and was not accounted for in the above referenced report. There is no offsite runoff that reaches the subject property. The drainage patterns proposed with the subject improvements are generally consistent with the drainage patterns proposed with the above referenced report. III. DRAINAGE DESIGN CRITERIA A. Regulations: This report has been prepared in general accordance with the Fort Collins Stormwater Criteria Manual, September 2018 and the Urban Storm Drainage Criteria Manual (USDCM). B. Development Criteria Reference and Constraints: The subject site has been included in the following previous reports: Final Drainage Report Poudre Valley Plaza Mixed Use, Fort Collins, CO August 4, 2021 Page 5 i2 Consultants, Inc. · Final Drainage and Erosion Control Study for Poudre Valley Plaza, Fort Collins, Colorado, dated January 23, 1996, prepared by RBD, Inc. Engineering Consultants. This report has been prepared in general accordance with the appropriate City and USDCM criteria and previous reports. C. Hydrological Criteria: Fort Collins Stormwater Criteria Manual, September 2018, as well as the USDCM. There are no deviations from the criteria in this report. The design storms for this project are the 2-year and the 100-year recurrence intervals. Runoff is calculated using the Rational Method since all basins are smaller than 5 acres. The Rational Method calculations are computed by the following: Q = ciA where: Q = Runoff in cubic feet per second c = Calculated runoff coefficient for design event i = Storm intensity in inches/hour A = Basin area in acres Hydrological calculations have been prepared in accordance with the Fort Collins Stormwater Criteria Manual, September 2018 as well as the USDCM. D. Hydraulic Criteria: Rational calculations were prepared using methodology outlined in the Fort Collins Stormwater Criteria Manual, September 2018. Hydraulic capacities were calculated using Hydraflow Express Extension for Autodesk Civil 3D, Version 2021. IV. DRAINAGE FACILITY DESIGN A. General Concept: The drainage patterns associated with the proposed improvements are generally consistent with the existing drainage patterns, flow and the drainage patterns proposed with the Final Drainage and Erosion Control Study for Poudre Valley Plaza, Fort Collins, Colorado. The proposed site generally directs runoff north to the existing detention pond in the northeast corner of Poudre Valley Plaza P.U.D. A portion of the site will drain east to the existing retention pond, due to existing grades and site constraints, as depicted within the Final Drainage and Erosion Control Study for Poudre Valley Plaza, Fort Collins, Colorado. Final Drainage Report Poudre Valley Plaza Mixed Use, Fort Collins, CO August 4, 2021 Page 6 i2 Consultants, Inc. The runoff for the site was determined using the Rational Method, as detailed above. The proposed improvements have been divided into six (6) drainage basins. The basins have been created to direct runoff to existing and proposed facilities. B. Specific Details: Basin A Basin A (0.13 acres) is in the northwestern portion of the site and contains the northwestern portion of the proposed building, concrete sidewalks and landscaping. The basin generally drains from south to north. The runoff from the building will be captured in a proposed planter with rain garden for water quality purposes. The landscape area on the west side of the building will drain to the existing access. Basin B Basin B (0.11 acres) is in the northeastern portion of the site and contains the northeastern portion of the proposed building, concrete sidewalks and landscaping. The runoff from the building will be captured in a proposed planter with rain garden for water quality purposes. Basin C Basin C (0.03 acres) is along the northeastern portion of the site and contains proposed concrete sidewalks and landscaping. The basin drains to an existing slotted drain installed with the Poudre Valley Plaza P.U.D. and to the existing retention pond located east of Lot 7. Basin D Basin D (0.12 acres) is along the southwestern portion of the site and contains the southwestern portion of the proposed building and landscaping. The basin generally drains from north to south. The runoff from the building will be captured in a proposed rain garden for water quality. The basin will be released from the rain garden to the west to the existing access. Basin E Basin E (0.03 acres) is along the southeastern portion of the site and contains the southeastern portion of the proposed building and landscaping. The basin generally drains from north to south. The runoff from the building will be captured in a proposed rain garden for water quality. The basin will be released from the rain garden to the west to Basin D. Basin F Basin F (0.01) acres is in the southeastern portion of the site and will contain landscaping. This basin is in a low area of the subject site and will drain to the existing retention pond east of Lot 7. Final Drainage Report Poudre Valley Plaza Mixed Use, Fort Collins, CO August 4, 2021 Page 7 i2 Consultants, Inc. The subject site was considered in Basins 1 and 2 of the Final Drainage and Erosion Control Study for Poudre Valley Plaza, Fort Collins, Colorado. The imperviousness for the basins are provide below: Basin 1: 68.3% (0.81 “C” Value) Basin 2: 79.6% (0.87 “C” Value) The composite imperviousness calculated for this development is 56.6%, with a “C” value of 0.62. These values are below the assumed values in the overall development drainage report. No additional detention is required as a result of the proposed development of Lot 7. The drainage design for the subject development will reduce the amount of runoff into the retention pond. A portion of the subject site was designed to drain to the retention pond in the overall report. With the proposed layout and constraints of the proposed development, a small portion of runoff will drain north to the existing pond in the northeast corner of the site and not into the retention pond. The additional flow will be from roughly 700 s.f. of sidewalk to the north of the proposed building. The drainage design for the subject site will generally conform to the overall drainage design for Poudre Valley Plaza P.U.D. The flow patterns proposed with the subject development generally follow the patterns of the overall drainage report, with exceptions noted above. The proposed drainage from this site is not anticipated to have a negative impact on the existing facilities as the existing detention pond will provide for attenuation of the developed runoff. V. SEDIMENT, EROSION CONTROL AND STORMWATER QUALITY A. Temporary Sediment and Erosion Control: Several sediment and erosion control measures will be incorporated into the initial phase of construction. The initial sediment and erosion control measures to be installed shall include sediment control logs, as well as a vehicle tracking control mat at the construction entrance, inlet protection in Arbor Avenue and rock socks within the existing flowline of the access. An initial control measure will be the installation of construction fence around the development perimeter. Furthermore, additional measures for sediment and erosion control shall consist of providing an area designated for a concrete washout area. A stabilized staging area is proposed in the parking area to the north of the subject site. The initial measures for sediment and erosion control shall be maintained and updated as necessary during the interim and final stages of the project. Final Drainage Report Poudre Valley Plaza Mixed Use, Fort Collins, CO August 4, 2021 Page 8 i2 Consultants, Inc. Additionally, any area that has been disturbed by construction activities and left exposed for more than fourteen (14) days, shall receive drilled seeding and straw mulch at 2 tons/acre, until permanent landscaping or ground cover has been provided. Four Step Process to Minimize Adverse Impacts of Urbanization Employing runoff reduction practices: Water Quality will be utilized with this development. There will be landscaping around each side of the site and no new parking areas are proposed with this development. Implementing best management practices (BMPs): Water Quality will be provided in the form of rain gardens to capture runoff from the proposed building. An underdrain will be installed in the rain gardens along the southern portion of the site. Stabilizing Streams: The runoff from the subject site drains to paved surfaces and existing detention facilities. The runoff release from the overall development will be controlled by these existing facilities. Implementing site specific and other source control BMPs: A stabilized staging area will be provided to the north of the subject site on existing asphalt. Appropriate erosion and pollution control shall be installed around the staging area. B. Permanent Water Quality BMPs Rain gardens will be installed near each corner of the proposed building to provide permanent water quality. Water quality planters/rain gardens will be installed at two (2) areas along the northern portion of the proposed building. These rain gardens will treat runoff prior to being released to existing conveyances to the north of the site. The design volume is larger than the required volume for each planter. Rain gardens will also be installed along the southern portion of the building. These two (2) rain gardens will capture and treat runoff from the building, prior to being released to the existing access. The design volume for each rain garden along the southern side of the building is larger than the required volume. These measures were selected for permanent water quality due to the site constraints regarding the proposed layout and tight tolerance for elevations. Please refer to the Appendix for water quality/rain garden calculations. The existing detention pond in the northeast corner of the overall development does not contain a water quality component. The retention pond will provide water quality for runoff that reaches the pond. Final Drainage Report Poudre Valley Plaza Mixed Use, Fort Collins, CO August 4, 2021 Page 9 i2 Consultants, Inc. VI. CONCLUSIONS A. Compliance with Standards: The drainage design is in general compliance with the Fort Collins Stormwater Criteria Manual, September 2018 as well as the Urban Storm Drainage Criteria Manual (USDCM). Furthermore, the design is in general conformance with the approved Final Drainage and Erosion Control Study for Poudre Valley Plaza, Fort Collins, Colorado, dated January 23, 1996, prepared by RBD, Inc. Engineering Consultants. B. Drainage Concept: The runoff from this site will be conveyed by existing and proposed storm drainage improvements, including proposed curb, gutter, swales and rain gardens. The drainage design for this project should not negatively impact improvements downstream or the existing storm system. Permanent water quality for the site will be provided through rain gardens to slow runoff and provide a filter for runoff prior to leaving the subject site. Final Drainage Report Poudre Valley Plaza Mixed Use, Fort Collins, CO August 4, 2021 Page 10 i2 Consultants, Inc. VII.REFERENCES 1. Fort Collins Stormwater Criteria Manual, dated September 2018. 2. Urban Drainage and Flood Control District, Drainage Criteria Manual Volumes 1, Revised August 2018, Volume 2, Revised September 2017 and the Volume 3, dated November 2010 and Updated October 2019. 3. Final Drainage and Erosion Control Study for Poudre Valley Plaza, Fort Collins, Colorado, dated January 23, 1996, prepared by RBD, Inc. Engineering Consultants. C-4PROJECT:PVP Mixed UseCALCULATED BY:i2 Consultants, Inc.DATE:8/4/2021Cf = 1.25FINAL REMARKStcBASIN DP AREA CC*CfLength SlopetiLength Slope VtttcTotal LtcID Ac Ft % min Ft % fps min min ft min min(0) (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)1A 1 0.13 0.71 0.89 85 2.0 2.9 30 1.00 1.5 0.3 3.3 115 10.65.0Use Tc = 5.0 mins2B 2 0.11 0.77 0.96 85 2.0 1.9 70 1.0 1.5 0.8 2.7 155 10.95.0Use Tc = 5.0 mins3C 3 0.03 0.56 0.70 5 0.5 2.1 20 1.0 2.8 0.1 2.2 25 10.15.0Use Tc = 5.0 mins4D 4 0.12 0.46 0.57 20 2.0 3.5 115 0.5 0.7 2.7 6.2 135 10.86.2Use Tc = 6.2 mins5E 5 0.03 0.54 0.68 20 2.0 2.8 30 0.5 0.7 0.7 3.5 50 10.35.0Use Tc = 5.0 mins6F 6 0.01 0.15 0.19 15 2.0 5.2 20 1.0 1.5 0.2 5.5 35 10.25.5Use Tc = 5.5 minsEquations:UrbanizedTovtt =Ltc =(L/180)+1060VV=CvSw0.5(1)(2) or Fig. 3-3 (3)S ^1/3Rural/Non-urban(URBANIZED)RURAL OR NON URBANIZEDTIME OF CONCENTRATION - 100-YEAR1.87(1.1-CCf)*D^1/2DATASUB-BASIN INITIAL/OVERLANDTIME (Tov)TRAVEL TIME(tt)tc CHECK Sheet 1 of 2 Designer: Company: Date: Project: Location: 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, Ia Ia =90.0 % (100% if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = Ia/100)i = 0.900 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.32 watershed inches (WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i) D) Contributing Watershed Area (including rain garden area) Area = 3,151 sq ft E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =84 cu ft Vol = (WQCV / 12) * Area F) For Watersheds Outside of the Denver Region, Depth of d6 = in Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, VWQCV OTHER =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 =8 in B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 0.00 ft / ft (Use "0" if rain garden has vertical walls) C) Mimimum Flat Surface Area AMin =57 sq ft D) Actual Flat Surface Area AActual =215 sq ft E) Area at Design Depth (Top Surface Area)ATop =215 sq ft F) Rain Garden Total Volume VT=143 cu ft (VT= ((ATop + AActual) / 2) * Depth) 3. Growing Media 4. Underdrain System A) Are underdrains provided?1 B) Underdrain system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage y =0.3 ft Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours Vol12 =84 cu ft iii) Orifice Diameter, 3/8" Minimum DO =5/16 in LESS THAN MINIMUM. USE DIAMETER OF 3/8" Design Procedure Form: Rain Garden (RG) twc i2 Consultants, Inc. August 4, 2021 PVP Mixed Use - NW WQ Planter 1039 Horsetooth, Fort Collins, CO UD-BMP (Version 3.07, March 2018) Choose One Choose One 18" Rain Garden Growing Media Other (Explain): YES NO PVP_BMPNW_WQ.xlsm, RG 8/4/2021, 4:42 AM Sheet 1 of 2 Designer: Company: Date: Project: Location: 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, Ia Ia =90.0 % (100% if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = Ia/100)i = 0.900 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.32 watershed inches (WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i) D) Contributing Watershed Area (including rain garden area) Area = 3,497 sq ft E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =94 cu ft Vol = (WQCV / 12) * Area F) For Watersheds Outside of the Denver Region, Depth of d6 = in Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, VWQCV OTHER =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 =8 in B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 0.00 ft / ft (Use "0" if rain garden has vertical walls) C) Mimimum Flat Surface Area AMin =63 sq ft D) Actual Flat Surface Area AActual =185 sq ft E) Area at Design Depth (Top Surface Area)ATop =185 sq ft F) Rain Garden Total Volume VT=123 cu ft (VT= ((ATop + AActual) / 2) * Depth) 3. Growing Media 4. Underdrain System A) Are underdrains provided?1 B) Underdrain system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage y =0.3 ft Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours Vol12 =94 cu ft iii) Orifice Diameter, 3/8" Minimum DO =5/16 in LESS THAN MINIMUM. USE DIAMETER OF 3/8" Design Procedure Form: Rain Garden (RG) twc i2 Consultants, Inc. August 4, 2021 PVP Mixed Use - NE WQ Planter 1039 Horsetooth, Fort Collins, CO UD-BMP (Version 3.07, March 2018) Choose One Choose One 18" Rain Garden Growing Media Other (Explain): YES NO PVP_BMPNE_WQ.xlsm, RG 8/4/2021, 4:43 AM Sheet 1 of 2 Designer: Company: Date: Project: Location: 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, Ia Ia =90.0 % (100% if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = Ia/100)i = 0.900 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.32 watershed inches (WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i) D) Contributing Watershed Area (including rain garden area) Area = 1,986 sq ft E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =53 cu ft Vol = (WQCV / 12) * Area F) For Watersheds Outside of the Denver Region, Depth of d6 = in Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, VWQCV OTHER =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 =4 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 =36 sq ft D) Actual Flat Surface Area AActual =240 sq ft E) Area at Design Depth (Top Surface Area)ATop =420 sq ft F) Rain Garden Total Volume VT=110 cu ft (VT= ((ATop + AActual) / 2) * Depth) 3. Growing Media 4. Underdrain System A) Are underdrains provided?1 B) Underdrain system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage y =0.3 ft Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours Vol12 =53 cu ft iii) Orifice Diameter, 3/8" Minimum DO =1/4 in LESS THAN MINIMUM. USE DIAMETER OF 3/8" Design Procedure Form: Rain Garden (RG) twc i2 Consultants, Inc. August 4, 2021 PVP Mixed Use - SW WQ Planter 1039 Horsetooth, Fort Collins, CO UD-BMP (Version 3.07, March 2018) Choose One Choose One 18" Rain Garden Growing Media Other (Explain): YES NO PVP_BMPSW_WQ.xlsm, RG 8/4/2021, 4:43 AM Sheet 1 of 2 Designer: Company: Date: Project: Location: 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, Ia Ia =90.0 % (100% if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = Ia/100)i = 0.900 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.32 watershed inches (WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i) D) Contributing Watershed Area (including rain garden area) Area = 588 sq ft E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =16 cu ft Vol = (WQCV / 12) * Area F) For Watersheds Outside of the Denver Region, Depth of d6 = in Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, VWQCV OTHER =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 =4 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 =11 sq ft D) Actual Flat Surface Area AActual =110 sq ft E) Area at Design Depth (Top Surface Area)ATop =170 sq ft F) Rain Garden Total Volume VT=47 cu ft (VT= ((ATop + AActual) / 2) * Depth) 3. Growing Media 4. Underdrain System A) Are underdrains provided?1 B) Underdrain system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage y =0.3 ft Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours Vol12 =16 cu ft iii) Orifice Diameter, 3/8" Minimum DO =1/8 in LESS THAN MINIMUM. USE DIAMETER OF 3/8" Design Procedure Form: Rain Garden (RG) twc i2 Consultants, Inc. August 4, 2021 PVP Mixed Use - SE WQ Planter 1039 Horsetooth, Fort Collins, CO UD-BMP (Version 3.07, March 2018) Choose One Choose One 18" Rain Garden Growing Media Other (Explain): YES NO PVP_BMPSE_WQ.xlsm, RG 8/4/2021, 4:44 AM