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-16- Mr. Richcrd Atkinson ~ May la, 19a1 Pcge Tv+o h by use of the formula given in Hoan and Earfield: D = DA DV DC DP where: D =delivery factor DA =area factor DV = vegetative factor DC =.chanr.elization fcctor DP = pit factor For D we had used factors from 0.27 to 0.30 taken from figure 5.23 on pege 223, HoanAand ecrfield; D had been computed ct betv+een 0.12 to 0.13, but used in the equation et 0.60 cue to stated limitation that the rrc~uct.cf DpD should be at least equal to the lower of D cr D for namcl veg='=lion. Values of 1.0 hed been used for factors DC erd DP in the formui_ , • In revie•r+ cf the literature, disNSSiors v+ilQ cl`~s •++aricina v+ith sedimentology in Colorado crid with hhr. Domigue.we cc r.cluc_ ;,._~ in light of the limited know- ledce in 4'Jestern v,ntersheds that it is eppror.ricte cra cnsen•a:ive to use values less than .1 for only the area factor and to use 1 for the ether 3 factors in the I'aan and Earfield formula, With this a_sumption the recampulad sediment delivery ratios compered with the previous sediment delivery ratios for the mining area detention ponds are: Sediment Delivery Patio Detention Pond Previous Cclculation Revised Calwletion Tcylor Gulch Tributcry 0.17 0.26 Streeter Gulch 0.16 0.25 Gulch A 0.18 0.29 The effect of the revised sediment delivery ratios on the calculated sediment yield end pond designs is discussed at the conclusion of the response to USI_E CP Facta s. 3. USLE CP 1=ectcrs: The Adequacy Review questioned the selection of C factor for strow mu c ing from USDA Technical Note 50. The selected value from tF~is publi~tion v+as C = 0.02 for a tons of straw mulching per acre. The soil loss v:cs then computed using this value of C at 3.17 tons per acre per year. Next the total sediment yield for 3 years v+as computed for each of the sedimentation ponds • by converting tons of sediment to acre feet of sediment and multiplying by the drainage area of each pond and by 3 years.