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Home My WebLink AboutPROSPECT PARK PUD - FINAL - 21-95A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTAPPENDIX PAGE Historic Drainage ................................................ 1 - 2 Offsite Storm Flow Analysis ................................ 3 - 18 Developed Drainage .......................................... 19 - 30 Water Quality Pond Analyses ............................ 31 - 42 SWMMModeling ................................................ 43 - 48 Erosion Control Calculations .............................. 49 - 52 January 22, 1996 Prospect Park PUD REFERENCES 1. Storm Draina a Desi n Criteria and Construction Standards, City of Fort Collins, Colorado, May, 1984. 2. __ -- Phase I thugh Phase IV, Greenhorne &O'Mara, Inc., ro September, 1991. 3. H drolo is Anai sis ana na, „ Draina a Fort Collins Colorado, Lidstone & Anderson,. Inc., February 4, 1993. 4. Drainage Criteria Maunal, Urban Drainage and Flood Control District, Wright -McLaughlin Engineers, Denver, Colorado, March, 1969. Prospect Park PUD January 22, 1996 Final Drainage Report Page 4 to a 36-inch round, 2.3 foot high catch basin with a 24-inch opening at the top for overflow. The overflow entrance will be protected from debris by a grating of No. 4 rebar (see detail in Appendix). In a 100-year storm approximately 30 cfs could be passed to pond A. With a flow depth of 0.5 feet (WSEL = 5017.5), the pond outlet will pass approximately 10 cfs. The remaining 20 cfs will pass over the two weirs in the sidewalk to the south of the pond. Basin D3 will drain via curb'and gutter to a 2400t sidewalk chase to water quality pond B. The 10- and 100-year design flows for Basin D3 are 3.58 and 7.32 cfs respectively. The water surface elevation required for water quality detention is 5019.0 (depth of pond is 2.0 feet). The overflow pipe elevation is set at 5019. No overflow weirs are necessary. Any overflow from Basin. D3 will be. passed through the outlet pipe. The water qualitydetention volume will be released over 40 hours. The outlet structure will be similar to that described .for pond A. Basin D4 will drain to the existing entrance roadway_ to the west of the site. Flow will travel by curb and gutter to a road inlet southwest of the site that outlets into the Canal Importation Channel. Per discussions with the City -of Fort Collins, no water quality control will be required for this basin. The 10- and 100-year design flows from this basin .are 0.83 and 1.36 respectively. IV. EROSION CONTROL Erosion control will be of considerable importance on this project due to the proximity of the site to existing wetlands. The :water quality. control ponds will be constructed first and the site graded so that flow. will pass through these ponds. A silt fence will be placed between the two ponds. Permanent vegetative erosion control will be used in conjunction with landscaping in.areas:surrounding the. buildings and parking areas. Erosion control calculations and cost estimate are presented in the Appendix. V. CONCLUSIONS Compliance with Standards All drainage analyses have been. performed according to the City of Fort Collins Storm Drainage Design Criteria Manual (SDDCM) and the Urban Drainage and Flood Control District's Drainage Criteria Manual. A variance is requested for on -site detention for flood control purposes since on -site detention would add to the flood peak rather than diminish it. Prospect Park PUD January 22, 1996 Final Drainaoe Report Pape 3 Specific Details The existing fifteen (15) foot curb inlet in the south flowline of Prospect Road will require relocation due to the proposed street widening, adjacent to the site. Stormwater from adjacent streets will continue to be conveyed to existing storm sewer appurtenances in Shields and Prospect. An analysis of existing off -site flow to the storm sewer and the ability of the relocated storm sewer to convey this flow indicates that all off -site flow will pass through the site via the storm sewer (see Appendix). No overtopping of Prospect Road occurs so no off -site will pass onto the site via surface flow. A 42-inch RCP will be adequate to pass the off -site flows through the site. The storm sewer will outlet at an elevation of 5015.0. The 100-year water, surface elevation for the Canal Importation Channel is 5015.4. Grouted rip rap will be required for outlet protection. The developed site was divided into four basins.,z Basin D1 will convey flow via a curb cut, swale and culvert to water quality pond A: The roof runoff from half of the building on the east side of the site will be conveyed directly .into the culvert under the Shields Street entrance. The 10-year and 100-year design flows for Basin D1 are 3.72 and 5.91 cfs respectively. Basin D2 flows drain via curb and gutter to water quality pond A. The 10- and 100-year design flows for Basin D2 are 10.81 and 21.57 cfs respectively. No curb and gutter will exist north of Pond A, so flow from subbasin Dia will sheet flow directly into the pond. Water quality pond A is designed to capture and store the first .flush from the parking lots. In discussions with the City of Fort Collins it was determined that the primary water quality concern is from the parking areas. Using -criteria presented in UDFCD-SDCM a water quality capture volume of 3900 cf was determined necessary to adequately treat the first flush from the parking areas. Approximately 80 percent of the site drains to water quality pond A, therefore the pond size is approximately 80 percent of the water quality capture volume (3120 cf). All flows to this pond in excess of the water quality capture volume will be released from the pond via an outlet structure and overflow weirs to the Canal Importation Channel. The water surface elevation required for water quality detention is 5017.0 (depth of pond is 2.3 feet). The overflow pipe elevation is set at 5017. The overflow weirs pass over the sidewalk to the south of the pond at an elevation of 5017.10. The water quality detention volume will be released over 40 hours. The outlet structure for pond A is a modified version of the standard water quality pond outlet as described in the UDFCD-SDCM (see detail in the Appendix). The outlet structure consists of a 4-inch perforated PVC pipe per UDFCD.standards. A 12-inch perforated ADS or PVC pipe will be placed around the 4-inch perforated pipe. Gravel will be poured in the annular region. The 12-inch pipe will be anchored I Prospect Park PUD January 22, 1996 Final Drainaae Report Paae 2 111. DEVELOPED DRAINAGE Developed Conditions The proposed development .of the site includes 4 commercial buildings with associated parking areas and utility services. Three (3) drive entrances will serve the site - off West Prospect Road, from South Shields Street and a shared access with Prospect 11 P.U.D.. Design Criteria and References Drainage criteria outlined.in both the City_of fort Collins Storm Drainage Desigr Criteria Manual,(SDDCM) and Storm Drainage, Criteria Manual :by the Urban Drainage and Flood Control District (UDFCD-SDCM) have been`used..for this Preliminary Drainage Study. The reports entitled, "Hydrologic Analysis and Final Hydraulic Design West Prospect Road Drainage" by Lidstone & Anderson, 'Inc. and "Final Design Report for the Canal Importation Channel Phase I Through Phase IV", by Greenhorne & O'Mara, Inc. have been referenced. Hydrologic and Hydraulic Criteria The Rational Method has been used to estimate peak stormwater runoff from the proposed development. A 10-year and 100-year design storm were used to evaluate the proposed drainage system. Conveyance structures wew sized using a 10-year design storm. Rainfall intensity data for. the Rational: Method was taken from Figure 3-1 of SDDCM. The City of Fort Collins Storm Drainage Design Criteria has been used for all hydraulic calculations. General Drainage Concept Off -site flows from Prospect Road and areas north of Prospect Road will be routed through the site to the Canal Importation Canal via a 42=inch storm sewer. On -site developed stormwater runoff will be conveyed through the Prospect Park site by overland flow and vertical curb, through two water quality ponds to the Canal Importation Channel. No detention for flood control purposes are required for this site due to the proximity of the site to the Canal Importation Channel and the lag in peak discharge from the proposed site and the Channel (see Appendix). Final Drainage Report for Prospect Park P.U.D. I. GENERAL LOCATION SITE DESCRIPTION General Location and Site Description This report summarizes the results of a storm drainage investigation for the proposed Prospect Park P.U.D. site. The project is located in the NE Quarter of Section 22, Township 7 North, Range 69 West of the 6th Principal Meridian in Fort Collins, Colorado. The project is bounded by W. Prospect Road to the north, S. Shields Street on the east, Prospect Park PUD and the Northwood Apartments on the west and the Canal Importation Channel on the south (See Vicinity Map). The 5.92 acre site is located in northwest Fort Collins in a predominately residential area and is currently vegetated with native grasses and weeds. The!surrounding land use patterns are residential. II. HISTORIC DRAINAGE Historically, the site drains from the northwest to the southeast to the Canal Importation Channel at slopes ranging from 1.03% to 3.54%. Historic flow from the project site is 3.9 cfs for the 2-year storm and 14.4 cfs for the 100-year. storm (see, Appendix). The Canal Importation Basin hydrology, tributary to the. Prospect Park site, (SWMM File No. MULANEYD.0) was conducted by the City of Fort Collins Stormwater Utility Department for 100-yr developed conditions. The. Prospect Park . P.U.D. site is included in SWMM Subarea 32 and the. Canal. Importation Channel identified as Element No. 387. Areas north of Prospect Road drain to the south onto Prospect Road and are collected in sump or grade inlets. The inlets are piped together and discharge onto the project site from the north through a.42„ diameter concrete, pipe. ; All flow in Prospect Road for a 100-year design storm is captured in the inlet system. Stormwater from the 42" pipe is currently conveyed in, an .open channel east.along Prospect and then south along Shields to the Importation Channel. Historic flow through the project site from offsite sources is' 73 cfs.. Calculations for the inlet capacities are presented in Appendix A. There are noexisting irrigation laterals on the site. Per the Greenhorne and o'Mara Importation flood profiles (sheet 5 of 5), the 100- year water surface elevation for the Canal Importation Channel is 5015.4. W. WQ STRW W. PROPM RW PROJECT LOCATION l W. DPW Itm N N.T.S. J:\ACAD\DET\VCNTYMP.DWG NORTHERN ENGDfEERING SERVICES """MULLANEY PpppgRTy v m s sam �r 0O'� ....�._ - __ VKMM NAP Northern Engineering Services, Inc. January 22, 1996 Mr. Glen Schleuter City of Fort Collins Stormwater Utility 235 Mathews Fort Collins, Colorado 80522 RE: Prospect Park P.U.D. Fort Collins, Colorado Project Number: 9520.00 Dear Glen: Northern Engineering is pleased to submit this Final Drainage Report for Prospect Park P.U.D. for your review. It represents a study of existing and proposed stormwater characteristics of the project site. This report was prepared in compliance with technical criteria set forth in the, City of Fort Collins, Storm Drainage Design Criteria and Construction Standards manual. If you should have any questions or comments as you review this revised report, please feel free to contact me at your convenience. Sincerely, NORTHERN ENGINEERING SERVICES, INC. Cairole Berns , E.I.T. rim '�,T1�T� `''• „ Roger . Curtis, P.E. �..., 420 S. Howes, Suite 202 • Fort Collins, Colorado 80521 • (970) 221-4158 • Fax (970) 221-4159 Final Drainage Report for Prospect Park P.U.D. City of Fort Collins, Colorado January 22, 1996 Prepared For: Ed Mullaney Tim Sittema Prepared By: Northern Engineering Services, Inc. 420 South Howes, Suite 202 Fort Collins, Colorado 80521 (970)221-4158 Fax (970)221-4159 Project Number: 9520.00