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• <br />HYDROLOGIC DOCUMENTATION <br />SMALL AREA EXEMPTION <br />SUBSTATION <br />The following calculations demonstrate the amount of sedimrnt fence surface area required to adequately handle <br />the runoff from the substation area. <br />Runoff peak discharge calculations were performed utilizing the SEDCAD+ computer model consistent with the <br />methodology previously discussed . The sediment fence was designed to handle the peak discharge from a 10- <br />year, 24-hour storm evrnf_ <br />The curve numbers (CN) used were obtained from Procedures Cor Determining Peak Flows in Colorado and <br />Technical Release No. 55. Based on soil type and vegetation cover, curve numbers were determined for the <br />following condition. <br />Disturbed <br />Soil Type: C <br />Ground Cover: Dirt Road <br />Cover Type: None <br />CN: 89 <br />• <br /> <br />All other hydrology inputs are sho~m on the attached SEDCAD+ computer printouts <br />$ydrolseyBesulls <br />Peak Discharge: <br />Sediment Fence Permissivity: <br />Required Surface Area: <br />0.25 cfs <br />l5 gaUminlR= or 0.033 cfs/R= <br />0.25 cfs/0.033 cfs/ft' = SR= <br />The required length of fence should be determined assuming Slow depth of l foot. Actual fe:~x installation <br />should be a minimum of 1.5 feet to allow for freeboard and a factor of safety on the permissivity. <br />% R-o ~- <br />5vgmiT7A~ Dn-IE $/a~9G <br />