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HomeMy WebLinkAboutPROSPECT SPORTS CLUB - FDP240002 - SUBMITTAL DOCUMENTS - ROUND 2 - Responses (2)FINAL DRAINAGE REPORT 19 OLD TOWN SQUARE #238 | FORT COLLINS, CO 80524 | 970-530-4044 | www.unitedcivil.com P ROSPECT S PORTS Lot 5 Prospect Park East P.U.D Fort Collins, CO Prepared for: RB+B Architects, Inc. 315 E. Mountain Ave, Suite 100 Fort Collins, CO 80524 Date: April 2 nd , 2024 Fort Collins Utilities Redlines Water, Wastewater & Stormwater Thank you for the opportunity to review the se plans. I encourage you to contact me to discuss questions & revisions prior to resubmittal. dmogen@fcgov.com or 970-305-5989 Reviewed by: Date : Dan Mogen 04/26/2024 F INAL D RAINAGE R EPORT P ROSPECT S PORTS F ORT C OLLINS ,CO i U22014_Drainage Report City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: Prospect Sports Fort Collins, Colorado Project Number: U22014 Dear Staff: United Civil Design Group, LLC. is pleased to submit this Preliminary Drainage Report for the Prospect Sports site in Fort Collins, Colorado. In general, this report serves to document the stormwater impacts associated with the proposed improvements related to the existing site. We understand that review by the City of Fort Collins is to assure general compliance with standardized criteria contained in the Fort Collins Stormwater Criteria Manual (FCSCM). This report was prepared in compliance with technical criteria set forth in the Fort Collins Stormwater Criteria Manual. If you should have any questions or comments as you review this report, please feel free to contact us at your convenience. Sincerely, United Civil Design Group Nate Stroud, PE, LSIT Project Manager COMPLIANCE STATEMENT I hereby attest that this report for the Final drainage design for Prospect Sports was prepared by me or under my direct supervision, in accordance with the provisions of the Fort Collins Stormwater Criteria Manual. I understand that the City of Fort Collins does not and will not assume liability for drainage facilities designed by others. Registered Professional Engineer State of Colorado No. 52985 update UCDG Response:Updated. F INAL D RAINAGE R EPORT P ROSPECT S PORTS F ORT C OLLINS ,CO 6 U22014_Drainage Report Basin EX1 Basin EX1 represents on-site runoff that drains to the existing property to the south and ultimately to the detention pond within Tract A of the Prospect Park East P.U.D. There is a very small portion of this basin that has existing public concrete sidewalk, but the majority of the existing site is undeveloped. Proposed Basins The following basins provide proposed drainage delineations for the site in its improved condition. Refer to Appendix A for hydrology computations and Appendix B for calculations related to Water Quality, Low Impact Development, and other hydraulic features. Basin A Sub-basins A1-A8 (see Drainage Plans attached) include the area of the site being collected by the proposed storm sewer infrastructure and are a majority of the site. These basins consist of roofs, asphalt and concrete paving, and landscaping. Runoff within these basins is conveyed to grass swales and bioretention ponds via sheet flow, curb, inlets, and storm sewer. Ultimately runoff is conveyed through the proposed storm sewer to the existing lake/pond across Sharp Point and ultimately released to the Cache La Poudre River. Basin OS1 Basin OS1 represents the portion of the proposed site draining offsite to the south undetained. This basin consists of concrete sidewalk, asphalt pavement, and landscaping. In its improved condition, this basin will continue to function as most of the existing site did with conveying flows offsite to the south property and ultimately to the detention pond within Tract A of the Prospect Park East P.U.D. There is also proposed asphalt offsite, to the south of Basin OS1 that will be conveyed to the south with flows from Basin OS1. Although there are some pervious areas being directed to the south, it should be noted that the original drainage report showed all of the developed site being conveyed south. Because of this and the minimal pervious areas being conveyed south in the proposed condition, no negative impacts are foreseen. Detention and Water Quality No detention is being provided for the site due to previously discussed site constraints and as documented in the variance request. However, water quality is provided and will be achieved through the use of bioretention ponds per the Fort Collins Stormwater Criteria Manual. Low Impact Development (LID) In December of 2015, Fort Collins City Council adopted the revised Low Impact Development (LID) policy and criteria which requires developments within City limits to meet certain enhanced stormwater treatment requirements in addition to more standard treatment techniques. The proposed development will be required to meet the newly adopted LID criteria which requires the following: -Treat no less than 75% of any newly added impervious area using one or a combination of LID techniques. -Treat no less than 50% of any newly added impervious area using one or a combination of LID techniques when at least 25% of any newly added pavement is provided with permeable pavement. The following measures are implemented with this proposed development: I.Northern Bioretention Pond Basins A5, A6, and A 8.1, combined for 5,905-sf of proposed composite impervious area, are designed to be conveyed to the northern bioretention pond. The proposed impervious area treated through the bioretention ponds includes roof areas, and landscaping. All bioretention ponds will be designed with underdrains which will be conveyed to the proposed storm sewer onsite. It should be noted that groundwater was encountered during boring for geotechnical analysis of the soil in December of 2022. With the bioretention ponds, groundwater would have a negative impact on how the system functions as it relates to water quality and LID purposes. After analyzing groundwater depths in this area, groundwater would be at a depth of approximately 8 feet below existing ground, corresponding to an elevation of 4893.50. The bottom impervious?impervious? UCDG Response:Correct, this has been updated.UCDG Response:Correct, this has been updated. Sheet 1 of 2 Designer: Company: Date: Project: Location: 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, Ia Ia =27.1 % (100% if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = Ia/100)i =0.271 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV =0.11 watershed inches (WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i) D) Contributing Watershed Area (including rain garden area)Area = 21,787 sq ft E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =206 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 =6 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 =118 sq ft D) Actual Flat Surface Area AActual =848 sq ft E) Area at Design Depth (Top Surface Area)ATop =1900 sq ft F) Rain Garden Total Volume VT=687 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 =0.5 ft Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours Vol12 =206 cu ft iii) Orifice Diameter, 3/8" Minimum DO =7/16 in Design Procedure Form: Rain Garden (RG) NKS United Civil Design Group March 11, 2024 Prospect Park North Bioretention Pond UD-BMP (Version 3.07, March 2018) Choose One Choose One 18" Rain Garden Growing Media Other (Explain): YES NO UD-BMP_v3.07 Bio Ponds north, RG 3/11/2024, 9:55 AM please remove orifice calc. FC does not include orifices on the underdrain. UCDG Response:This has been removed. Sheet 2 of 2 Designer: Company: Date: Project: Location: 5. Impermeable Geomembrane Liner and Geotextile Separator Fabric A) Is an impermeable liner provided due to proximity of structures or groundwater contamination? 6. Inlet / Outlet Control A) Inlet Control 7. Vegetation 8. Irrigation A) Will the rain garden be irrigated? Notes: Design Procedure Form: Rain Garden (RG) NKS United Civil Design Group March 11, 2024 Prospect Park North Bioretention Pond Choose One Choose One Choose One Sheet Flow- No Energy Dissipation Required Concentrated Flow- Energy Dissipation Provided Plantings Seed (Plan for frequent weed control) Sand Grown or Other High Infiltration Sod Choose One YES NO YES NO UD-BMP_v3.07 Bio Ponds north, RG 3/11/2024, 9:55 AM Complete? UCDG Response:This has been completed but excel sheet would not let us choose an option for both #5 and #8,just one or the other.We answered #5 and #8 will be a no. Sheet 1 of 2 Designer: Company: Date: Project: Location: 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, Ia Ia =52.3 % (100% if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = Ia/100)i =0.523 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV =0.17 watershed inches (WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i) D) Contributing Watershed Area (including rain garden area)Area = 87,317 sq ft E) Water Quality Capture Volume (WQCV) Design Volume VWQCV =1,238 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 =12 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 =913 sq ft D) Actual Flat Surface Area AActual =998 sq ft E) Area at Design Depth (Top Surface Area)ATop =2331 sq ft F) Rain Garden Total Volume VT=1,665 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 =1.0 ft Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours Vol12 =1,238 cu ft iii) Orifice Diameter, 3/8" Minimum DO =15/16 in Design Procedure Form: Rain Garden (RG) NKS United Civil Design Group March 19, 2024 Prospect Park Southern Bioretention Pond UD-BMP (Version 3.07, March 2018) Choose One Choose One 18" Rain Garden Growing Media Other (Explain): YES NO UD-BMP_v3.07 Bio Ponds south, RG 3/19/2024, 1:54 PM please remove orifice calc. FC does not include orifices on the underdrain. UCDG Response:This has been removed.