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HomeMy WebLinkAboutDrainage Reports - 10/01/1987Final Approved Report No n FINAL DRAINAGE REPORT FOR LEMAY PLAZA P.U.D. FORT COLLINS, COLORADO OCTQBER 1987 u r Prepared by: Parsons & Associates Consulting Engineers 432 Link Lane Plaza Fort Collins, Colorado 80524 Project No.: 87.18 PDQ n INTRODUCTION The purpose of this study is to determine the quantity of storm water runoff generated.by this project, the manner in which this runoff will be accommodated by the proposed development and its transportation into the proposed Lemay Avenue storm sewer system. Drainage calculations for Lemay Plaza P.U.D. follow the methods and parameters as outlined in the City of Fort Collins' Storm Drainage Design Criteria. The Rational Method was used to calculate peak flows for 10-year and 100-year storms. Times of concentration were calculated using. the "Overland Flow Equation", Page 3-5 of Criteria, and. using a channel flow time calculated from -Figure "Estimate of Average Flow Velocity for use with the Rational Formula", Larimer County Stormwater'Management Manual. The sump inlets were sized by using the Sump Nomograph, Figure 5- 2, Page 5-10 of Criteria. Complete drainage calculations are included in the Technical Appendix. SITE DESCRIPTION The site is located in Section 36, Township 8 North, Range West of the Sixth Principal Meridian, County of Larimer, State of Colorado. The Lemay Plaza P.U.D. consists of approximately 1.87+ acres. The project is bounded on the North by Conifer Street, on the East by iemay Avenue, on the South by Lake Canal and on the West by a detention pond (referenced to as "Detention Pond 105" in Evergreen Park Basin Major Storm Drainage Study, dated February 1981, by Engineering Professionals Inc). The site historically drains from East to West with the natural drainage flowing towards Dry Creek. PROPOSED LAND USE The proposed development of this site is commercial. It will not be constructed in phases. HYDROLOGIC ANALYSIS The Rational Method has been used to calculate the stormwater. runoff.for the 10-year and 100-year return period storms for the Lemay Plaza P.U.D.. The.enclosed Drainage Exhibit defines Sub - Basins A through E, and Table I summarizes the results of the _ hydrologic analysis of these sub -basins. The historic runoff flows were not considered for this development, because of its location adjacent to "Detention Pond 105". The Evergreen Park Basin Major Storm Drainage Study, dated February 1981, indicates that Detention Pond 105 has been sized to accommodate the runoff from the surrounding area, of which Lemay Plaza P.U.D. is a portion of. A 65' wide easement runs' parallel with the Southerly property line on Lemay Plaza P.U.D.. This easement will be used to transport the major storm runoff from Detention Pond 105, as well as other areas and detention ponds located within the Evergreen Park Drainage. Basin. This' runoff will be directed into a proposed storm `sewer inlet located at the Southeasterly property corner of the Lemay Plaza P.U.D.. The combined 100-year runoff = 55 c.f.s.. Nuisance flow and any runoff from the minor storms will be transported from the Westerly property line of Lemay Plaza P.U.D. to the same storm sewer system adjacent to Lemay Avenue. CONCLUSION Drainage from and onto Lemay Plaza P.U.D. has been accomplished by means of curb and gutters, concrete pans., -open channels and storm sewers. Prepared under the direct supervision of: Todd A. Shimo a, P.E. 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ASS 0 CIA TES PROJECT CALCULATIONS FOR CONSULTING ENGINEERS MADE BY DATE NECKED SY—OATE SHEET OF FL Comes, Cams& SOS24 ILA w-,, I, Wo 4 Ws Q.Z. 0.4fd (e (r -1710 T-s I - msz ol� • I i 1 (1) 10 CPS 0 1 pit. Epp T 10 I—s J- L -7 ......... .. .... .... TT-: -LAI -7;. 1��, ---------- -i I "17 4 -T - ----- -------- .... ...... . ...... _2 No Text