2002-11-26_PERMIT FILE - C1981022 (6)

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4 _'1 f. • HYDROLOGIC DOCUMENTATION SMALL AREA EXENR'TIO,N STORAGE AREA SAE The following calculations demonstrate the handle the srunoff tfromc they KSMart bales surface area required to adequately Flats storage site located in the main facilities area. Runoff volume and peak discharge calculations were performed utilizing the SEDCAD4 computer model consistent with the methodology previously discussed in this Exhibit. The sediment control structure was designed to handle the peak discharge from a 10-year, 24-hour storm event. 1 Hydrology Inputs All hydrology inputs are shown on the SEDCAD 4 computer printouts. The CN numbers u Pe k oFlows in Colorado dandr Te hni a 1 Releaseo No.ur55 for Determining (USDA-SCS, 1980)and consistent with previously approved hydro ogy reports. Based on soil type and vegetation cover, curve numbers were determined using Table 2-2a and 2-2d, USDA-SCS TR-55, for the following conditions: Disturbed • Soil Type: C Ground Cover: Access Road, Gravel Surface Cover Type: NA CN: 90 Area: 0.3 ac 2 Hydrology Results Peak Discharge In 0.34 cfs 10-year, 24-hour event Peak Discharge Out - Silt Fence p,33 cfs 10-year, 24-hour event Peak Discharge Out - Straw Bales 0.34 cfs 10-year, 24-hour event 3. Sediment Fence Requirements Sediment Fence Permissivity: 10 gal/min/fta or 0.022 cfs/ftZ Required Surface Area: 0.33 cfs / 0.022 cfs/ft2 = 15 ftZ The silt fence should assumes regu ar inspections and maintenanc~nufactures recommendations. Design 4. Straw Bale Requirements Straw bale Permissivity: 14 gal/min/ft2 or 0.031 cfs/ft2 Required Surface Area: 0.34 cfs / 0.031 cfs/ftZ = 11 ftZ • Note: Source is Applied Hydrology and Sedimentology for Disturbed Areas liy Barf field and Warner and Haan,: 1.987. CDMG is not in support of this factor. MR -~ ~pprav~d Nov • 2tof 2062