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State Rea. <br />(4)(e) the existing aryl the proposed culverts at the Seneca Mine. • <br />'Ihe drainage area was planimetered within each appropriate <br />Pxi ch i Tm reach bau~dary to obtain the "r>~ i Tuge Area" (see <br />E~ibit 7-7) . <br />Several procedures were used to calculate the peak di^~`h~mes <br />for the 10-year, 24-hour precipitation event. If, at the <br />entraraes of the culvert, the peak di.schaxge was determined <br />using the SIDCAD+ Program (an enhanced PC version of the <br />SIDII~Y7r II procgam) that particular discharge was used; <br />othetwise, the peak discharge was determined using the <br />"Prooechses fat ~+'A,m,;n;m peak Floors ].rl Colorado" published <br />by the So] 1 Cor7sP.rvatiol7 SetViCe. <br />Culverts will be designed, COILStIVC:ted and maintained to <br />sustain the vertical soil pressise, the passive resictarvx of <br />the fourrlation, and the weic~t of vehicles to be used. <br />Culverts will be constructed to avoid plugging or collapse and • <br />to m;T+;m;ze erosion at the inlet and outlet. All culverts <br />Will be covered With a m;,,;,mn„ depth of 1 foot of oongaacted <br />fill. <br />Culverts will be designed to prorate conveyance of the <br />10-year, 24-hour precipitation event with adequate freeboarz3 <br />to prevent over.-topping of the ditch of the e[nbanlarent. <br />Yh~en the SCS method was used to determine peak dim-ha,nes, the <br />following procedures were followed: <br />1. Determine the drainage area by planimeterirrq. <br />2. Determine the appropriate curve number based on the <br />followirxl: <br />a. Antecedent moisture conditions (AMC II) <br />b. Iard use <br />c. Vegetative Dover <br />d. Hydrologic soil coup <br />12-31 Revised 10/02/89 <br />