Laserfiche WebLink
Stptemhn 1998 Seneca IIW South Expansion • Drainage and Sediment Control Plan ~ 3 <br />2.8 Curve Number, CN <br />M The run-off curve number is a factor relating the amount of rainfall to the amount of run-off for <br />a given azea. Curve numbers were assumed based on supplied vegetation and soils information. <br />Where no vegetation or soils data was available, average conditions were assumed. Where <br />multiple conditions existed within the watershed, a weighted average curve number was <br />assigned. A summary of the curve numbers used for this evaluation is presented in Table 1. <br />TABLE 1 <br />SENECA IIW (South Expansion Areal CURVE NUMBER <br />Arse <br />Condition Cover Type Hydrologic <br />Condition Hydrologic <br />Soil Grou Curve <br />Number <br />Undisturbed As en/Mountain Shrub Good (>70%I B 30 <br /> Good 1>70%1 C 41 <br /> Good 1>70%1 D 46 <br /> Sa ebrush Good 1>70%1 C 47 <br /> Good (> 70%I D 55 <br /> Mesic Draina a Fair 130%<x<70%I C 81 <br /> Herbaceous Good 1>70%) D 85 <br /> Herbaceous Good 1>70%I C 74 <br />Disturbed Pit & Pre-Stri ed Bare C 91 <br /> Haul Rcad Bare C 91 <br /> Reclaimed Good 1>70%1 B 62 <br />3.0 SEDIMENTATION CALCULATIONS <br />The sediment calculations used to model the Seneca IIW (South Expansion) mine site were <br />performed utilizing the SEDCAD+ Computer Modeling Program developed by Civil Software <br />Design. The SEDCAD+ Computer model calculates annual sediment yield using the Revised <br />Universal Soil Loss Equation (RUSLE). The input parameters used in the sedimentation <br />analyses aze presented in the following sections. <br />3.1 Rainfall Factor, R <br />LJ <br />A rainfall factor of 30 was used for the Seneca IIW (South Expansion) mine site. This factor is <br />consistent with other recent erosion analyses performed for the Seneca Mine. <br />3.2 Soil Erodibility Factor, K <br />The soil erodibility factors for the subject site were determined based on soil survey information <br />(Nyenhuis, 1997). The values are shown on Table 2 (Soil Conservation Service, 1983). <br />TABLE 2 <br />SOIL ERODIBILITY FACTOR <br />Soil Type Soil Tsxture Soil Erodibility <br />Factor lKl <br />Routt Cla Loam 0.28 <br />Wlnevada~5 litro Com lex Loam 0.37 <br />Binco Cla Loam 0.28 <br />Coutis Silt Loam 0.37 <br />Aaber Cla 0.28 <br />S litro Loam 0.20 <br />Montgomery lt%¢tson Mtn:ng G.a>.p ' ]65 S Union Bau[eu¢rd, Suite 460' lakearood, Colorado 80118 • (970f 76?5740 <br />