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12-18-85 <br />Therefore, Curve No. 72 was selected to complete the hydrologic <br />• calculations from Figure S-3, Hydrologic Soil Cover Complex and <br />Associated Curve Numbers of "Procedures far Determining Peak Flows in <br />Colorado" by Soil Conservation Service, USDA ,. March, 1980. <br />Stipulation No. 16 <br />Within thirty (30) days of permit issuance, the applicant must provide <br />the Division with detailed pond outflow calculations demonstrating that <br />the 12-inch diameter principal spillway will not dewater the majority of <br />water in the sediment pond before 24-hours following a design storm. If <br />these calculations show an inadequate holding time, the principal <br />spillway/dewatering device must be redesigned, and reconstructed within <br />60 days of permit issuance. <br />Stipulation No. 16 Response <br />In the Drainage and Sediment Control Plan Appendix, Appendix 1, runoff <br />from a 10-year, 24-hour precipitation event is 2.23 acre-feet. Peerless <br />Resources, Inc. plans to leave the gate on the principal spillway open a <br />calculated distance to allow dewatering of the runoff from a 10-year, <br />24-hour event in approximately 30 hours. <br />• <br />Maximum head on principal spillway opening - 7.0 feet <br />Average flow through orifice - 2.23 Ac-Ft ~ 30 hours = 0.9 cfs <br />Where: Q = Ca 2 gh <br />Q = 0.9 cfs <br />C = 0.6 from page 4-34, Civil Engineering Handbook, <br />McGraw-Hill <br />a = orifice area <br />hmax = 7.0 <br />haverage = 3.5 <br />g = 32.2 <br />for hmax <br />for h <br />average <br />a=~ <br />• C 2 gh <br />a= <br />0.9 <br />0.6 2(32.2) (3.5) <br />-7- <br />