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8.0 HYDROLOGY AND HYDRAULICS <br />Permanent drainage ditches have been designed to carry a 100-year, 24- <br />hour storm event of 2.9 inches, and a 10-year, 24-hour storm event of 1.8 <br />inches. The runoff curve numbers used for design calculations are: CN = 88 <br />for refuse surface, and CN = 71 for undisturbed mountain brush. Peak <br />_. _ discharges were computed using the Sail Conservation Service (SCS) method <br />described in Technical Release 55. <br />Need to compute or use previous computed runoff for perimeter <br />channels, along refuse benches, and the quantity required to be <br />carried in the southern diversion ditch. <br />17 <br />