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1999 Yoast Mine " 1312 Drainage and Sediment Control Plan ~ 3 <br />given area. Curve numbers were assumed based on supplied vegetation and soils information. Where no <br />vegetation or soils data was available, average conditions were assumed. Where multiple conditions existed <br />within the watershed, a weighted average curve number was assigned. A summary of the curve numbers used <br />for this evaluation is presented in Table 13-12.1, Yoast Mine Curve Number. <br />TABLE 13-12.1 <br />YOAST MINE CURVE NUMBER <br />Area <br />Condition Cover Type Hydrologic <br />Condition Hydrologic <br />Soil Grou Curve <br />Number <br />Undisturbed As en/Mountain Shrub Good 1>70%) B 30 <br /> Good (>70°h) C 41 <br /> Good (>70%) D 48 <br /> Sa ebrush Good (>70%1 C 47 <br /> Good 1>70%) D 55 <br /> Mesic Drainage Fair <br />(30%<x<70%) C 81 <br /> Herbaceous Good 1>70%1 D 85 <br /> Herbaceous Goodl> 70°~1 C 74 <br />Disturbed Pit &Pre-Stripped <br />Spoil Bare <br />Bare C <br />C 91 <br />86 <br /> Haul Road Bare C 91 <br /> Reclaimed Fair 130%-70%I B 71 <br />3.0 SEDIMENTATION CALCULATIONS <br />• The sediment calculations used to model the Yoast Mine site were performed utilizing the <br />SEDCAD4 Computer Modeling Program developed by Civil Sofrwaze Design. The SEDCAD4 <br />Computer model calculates annual sediment yield using the Revised Universal Soil Loss Equation <br />(RUBLE). The input parameters used in the sedimentation analyses are presented in the following <br />sections. <br />3.1 RAINFALL FACTOR, R <br />A rainfall factor of 30 was used for the Yoast Mine site. This factor is consistent with other recent <br />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 13-12.2, Soil Erodibility Factor (Soil Conservation <br />Service, 1983). <br /> <br />Revised 6/99 <br />Montgomery Watson Mining Group * 165 S. Union Boulevard, Suite 460 * Lakewood, Colorado 80228 *(303J 763-5140 <br />