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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />METHOD OF CALCULATION <br /> <br />Maior Basins <br />The method used to estimate the anticipated amounts of storm water runoff for the major basins T A- <br />I and TA-2 is the SCS method, Technical Release 55 "Urban Hydrology for Small Watersheds" by <br />Soil Conservation Service, June 1986. <br /> <br />Off-site basin areas were determined from the USGS Map, as shown in the Appendix - <br />HydrologiclHydraulic Calculations - Major Basins. <br /> <br />Soil information was obtained from "Soil Survey of Elbert County, Western Part, Colorado" by Soil <br />Conservation Service, July 1980. <br /> <br />The on-site and off-site soil types are as indicated below: <br /> <br />S.C.S. SOILS <br /> <br />SYMBOL <br /> <br />NAME <br /> <br />HYDROLOGIC <br />GROUP <br /> <br />5 <br />6 <br />9 <br />22 <br />35 <br />41 <br /> <br />Bresser Sandy Loam <br />Bresser Sandy Loam <br />Bresser - Truckton Sandy Loam <br />Haplustolls <br />Peyton-Elbeth Sandy Loam <br />Tmckton Sandy Loam <br /> <br />B <br />B <br />B <br />B <br />B <br />B <br /> <br />Curve numbers were determined by the representative ground cover and hydrologic soils group. <br />Precipitation values of 2.8 inches and 4.2 inches were used for storms with 10-year and 100-year <br />recurrence intervals, respectively. A Type "II" storm with 24-hour duration was used for design. <br />Runoff quantities for Basins T A-I and T A-2 are tabulated in the Appendix - HydrologiclHydraulic <br />Calculations - Major Basins and are shown on the Drainage Plan in the rear pocket. The culvert <br />crossings at TA-I and TA-2 were sized to convey the lO-year storm and limit roadway overtopping <br />to a maximum depth of I foot. <br /> <br />2 <br />