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d = dry unit weight in pounds per cubic foot <br />Pc,Pm,Ps = percentages of clay, silt, and sand, respectively <br />Wc,Wm,Ws = coefficients for clay, silt, and sand, respectively <br />The above formula and coefficients were taken from "Design of Small Dams," Bureau of <br />Reclamation, 1974, pp. 778 and 779. The average percentages of clay, silt and sand for the project <br />area were estimated by a qualified geotechnical engineer during the field investigation for the soils <br />and foundation investigation for the project plant facilities. <br />The coefficients and percentages used were as follows: <br />Pc = 10 percent Pm = 50 percent Ps = 40 percent <br />We = 40 percent Wm = 72 percent Ws = 97 percent <br />d = 40x.10+72x. 50+97x.40=78.8 <br />It was also assumed that since the drainage basins are small, no sediment would be deposited until <br />it reaches the sediment control ponds. <br />. Thethree-year sediment yield is calculated as follows: <br />Sediment Volume = (AxAr)TonsNr x 2.000 IblTon x 3 yr <br />(Acre-feet) 80 Ib/cu ft x 43560 sq fUacre <br />Sediment volume calculations for sediment ponds are included in Illustrations 4, 5, 6, 6A and 7. <br />The sediment volume requirements are also shown on the pond drawings, Maps 34, 78, 79, 80 and <br />BOA. <br />Peak runoff flow rates were initially estimated using procedures set forth in SCS-TP-149 (Rev. <br />1973) "A Method of Estimating Volume and Rate of Runoff from Small Watersheds." In all cases, <br />runoff curve numbers (RCN) were selected assuming antecedent moisture condition two (AMC II) <br />prevailed. Disturbed areas were assumed to be the same as "farmstead" areas in Table 2 <br />(NRCS-TP-149). Undisturbed areas were assumed to be the equivalent of "fair range without <br />mechanical treatment", in Table 2 (NRCS-TP-149). Hydrologic soil groups were taken from the <br />NRCS soil survey data previously discussed. <br />Total runoff volumes for 10-year, 24-hour storms were determined from Figure 3 of NRCS-TP-149 <br />which is a solution of the runoff equation: <br />• <br />(Perrnit Renewal #3, 8199) V-11 <br />