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HomeMy WebLinkAboutDrainage Reports - 09/01/1979CORNER CONSU[7INq COMPANY p.o. box 646 foRT colliNs, coloRAdo 80522 Pl w (303) 482-6650 � MANAgEMENT/ENGINEERING THE PIER CONDOMINIUMS DRAINAGE REPORT September, 1979 CORNE« CONSU[TINq COMPANY P.o. box 646 foRT collet, coloRAdo 80522 Pl-brve (303) 482-6650 MANAGEMENVENCIINEERING September 6, 1979 Mr Bob Smith City Drainage Engineer City of Fort Collins P.O. Box 580 Fort Collins, Colorado 80522 Dear Mr. Smith: We are pleased to submit this Drainage Report for The Pier Condominiums. Should you have any questions, please feel free to contact US. Sincerely, CORNELL CONSULTING COMPANY _ /I Bill Blackwell, EIT Chief, Design and Production BB/ fsr Enclosure THE PIER CONDOMINIUMS DRAINAGE REPORT ABSTRACT The Pier Condominiums is a proposed ten (10) acre development to be located along Boardwalk Drive north of Harmony Road, a portion of the South Half of Section 36, Township 7 North, Range 69 West, Sixth Principal Meridian, Larimer County, Colorado. The development is zoned Residential Planned and will consist of high density residential units. This report deals with storm runoff estimates, detention/storage volume and distribution, and street flows. Calculations and recom- mendations are based on the final grading plan submitted with the utility plans. I. SCOPE The purpose of this report is to present the developer with final engineering solutions to storm drainage problems at The Pier Condo- miniums. In particular, the following items are addressed: 1. An analysis of the impact of a major and a minor storm (100-year and 2-year frequency events) on the development. 2. Delineation of subbasins within the hydrologic basin and an analysis of subbasin runoff contribution to street flows. 3. Reservoir routing to demonstrate the final design's ability to handle upstream flows without damage to downstream properties. -2- I.I. METHODS In general, the storm drainage analysis was completed using the the Preliminary Draft Storm Drainage Design Criteria for the City of Fort Collins. The Rational Method with overland time of concentration was used to determine peak street flows for The Pier subbasins. The Colorado Urban Hydrograph Method was used to produce an inflow hydro - graph for routing of the upstream storm runoff through the detention ponds. Both of these methods are more fully explained in the referenced Design Criteria. Routing of the major and minor storms were accomplished using a simple computer reservoir routing model. Input was in the form of discrete points from the storm hydrographs. Points were separated by 10 minutes for the duration of the storm. Internally the program calculated change of volume, head, and release rate on a one minute time interval, but printed results on a 10-minute interval. NKIN III: HYDROLOGIC -HYDRAULIC INVESTIGATIONS Refer to Appendix B, Fold -Out Drawing, for a map of the drainage subbasins and a drainage plan showing major and minor storm discharge rates and patterns. Subbasins on the map are defined with respect to one or more of the following: property lines, topography, or grading plan. This drawing is also submitted as Sheet 5 of 6 in The Pier Condominium final utility plan set. Storm discharges for this portion were calculated using the Rational Method as explained in the "Methods" section of this report. Included in Appendix A are discharges for the 100-year and 2-year frequencies for developed conditions and the 2-year frequency for historic conditions. Also in Appendix A are calculations from the reservoir routing for the entire major drainage way from Larimer County Canal #2 to the culvert under LeMay Avenue. Calculations include idealized stage - storage curves and reservoir inflow and outflow hydrographs for each basin. -4- IV. CONCLUSIONS'AND"RECOMMENDATIONS This drainage design will satisfy all hydraulic considerations as well as provide the future community with both a safe and equitable solution to the problem of handling storm water runoff. We recommend the following: 1. Storm water runoff should be routed as shown in Appendix B, Fold -Out Drawing. 2. Detention facilities should be located and sized as shown on Appendix B. -5 - No Text �4Y�eo>_ovic �a-rd. 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