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0.005 = x x = 0.0008 <br />25 4 <br />Therefore, the best "C" value for the pre-mine irrigated pasture is 0.025 + 0.0008 = 0.0258 <br />Post-Mine Conditions <br />Irrigated Pasture - 2008 Cover Data <br />The vegetation data is from the report 2008 Vegetation Sampling for Phase 2 Bond <br />Release: Irrigated Pasture and Dryland Pasture. <br />0.4% Noxious Weeds <br />0.3% Annual Forbs <br />26.4% Perennial Grasses <br />45.7% Perennial Forbs <br />15.9% Litter <br />Alfalfa is classified as a forb due to the branching structure of its vascular system. <br />However, in terms of its effect on erosion and soil cohesion, it has many similarities to <br />grass. Both plants provide a semi-continuous blanket of vegetation across the ground <br />surface, reducing the direct impact erosion of rainfall by shielding the soil. Also, the root <br />structure of alfalfa is a branching one, which increases soil cohesion. Figure 4 shows a <br />cross section of the alfalafa plant and its root system. <br />RUSLE does not take into account all of the properties of alfalfa in calculating the erosion <br />prevention it provides. In order to mitigate this, the alfalfa will be split into a Canopy <br />portion and a Ground portion for determining the "C" factor in RUSLE. Based on the <br />extensive root structure generated from the central taproot of the plant, and the consistent <br />cover that alfalfa provides, 50% of the alfalfa will be treated as Ground Cover. <br />According to BIO-Logic's report, alfalfa provides a cover of 44.6%. Applying the above <br />determined split gives 22.3% to Canopy Cover and 22.3% to Ground Cover, the totals for <br />RUSLE are as follows: <br />0.4% Noxious Weeds <br />0.3% Annual Forbs <br />26.4% + 22.3% (Alfalfa) = 48.7% Perennial Grasses <br />45.7% - 22.3% Alfalfa = 23.4% Perennial Forbs <br />15.9% Litter <br />SL-12 DRAFT 20AUG10.wpd 22