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• <br />Location SEDCAD+ Identifier Acres <br />the azea between the southeast i 1-2-1-2 0.30 <br />quadrant of the development waste <br />pile and the interceptor ditch D-1 <br />the north sloping top ojthe devel- ~ 1-3-1-I 0.17 <br />opment waste pile <br />the sideslopes of the north facing /-3-/-2 0.38 <br />portions of the waste development <br />pile <br />4.2 Curve Number (CN) <br />Curve numbers reflect the runoff potential of an area (a value of 100 represents an impervious area where 100% <br />of the water would run off), and is a function of soil type (a "C" used in this analysis) and the land use. For this <br />analysis, the CN value is (reference the SEDCAD+ guide): <br />1) For undisturbed portions of the watershed, overland flow: 63 (for Arid and Semiarid Rangelands, Oak, <br />fair cover). <br />2) For the pile slopes, overland flow: 91 (no vegetation or cover). <br />4.3 Hydrograph Response Shape and Overland Flow Lengths <br />• Hydrograph response shapes reflect the rapidity with which water runs off a watershed, rated in SEDCAD+ as fast, <br />medium, or slow. A slow response shape would correspond to a forested azea or an area with a lot of obstructions, <br />while a fast response shape would correspond to an unvegetated or poorly protected area. These ratings aze for <br />overland Flow. Once overland flow is surpassed, a fast rating is assigned. <br />Lengths of overland flow (sheet and rill drainage) are direct input parameters in SEDCAD+ for sedimentology <br />analyses, and have an indirect influence on other parameters, such as LUC. The maximum permissible lengths of <br />overland flow used within this analysis, with corresponding hydrograph response shape parameters, are presented <br />in the following table. <br />4.3-1 Lengths (in feet) of Overland Flow and Hydrograph Response Shapes (Slow, Medium, or Fast) <br />Vegetative Cover Slopes less than or equal to 25% Slopes over 25% <br />Oak Brush, etc. 225 (S) 175 (M) <br />Bare, Unprotected Soil 125 (M) 75 (F) <br />4.4 Control Practice Factor <br />The SEDCAD+ Model considers the sediment loss from an area with a given cover and conservation practice, as <br />compared to that of a field in continuous fallow, by introduction of a Control Practice (CP) Factor. The CP is a <br />function of Canopy Cover and Percent Ground Cover. The CPs used in this analysis were selected from the <br />SEDCAD+ guidelines. <br />• <br />(West Elk bone Pinc Gulch Development Waste Pile SAE, 12 October 1995. Page 5 of 7) <br />