2011-03-17_REVISION - C1981008 (2)

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Cover Factor "C" For rangeland and pastureland, the "C" factor is directly related to the percent of the ground covered by vegetation and the type of vegetation that is present. Subsurface effects such as root mass can also be considered. The type of vegetation is important because herbaceous plants with a live cover of 25% will protect the soil much better than a site that contains an equal cover but where the cover is primarily comprised of trees or shrubs. Table 3 (from EPA 1977) shows the variation in "C" factors for varying range conditions. From the 1987 study of the dryland pasture and irrigated pasture areas, the cover breakdown is given below: Pre-Mine Conditions Irrigate Pasture - 1987 Cover Data The irrigated pasture study area had 5 percent bare ground, 23 percent litter, 0.3 percent annual forbs, 43 percent perennial grasses, and 29 percent perennial forbs for 72 percent perennial live vegetation. Note: The irrigated pasture cover data was taken from the Coal Mining Permit C-81-008: 2005-2006 Mid Term Review, which is based on the 1987 baseline survey. 0.3% Annual Forbs 43% Perennial Grasses 29% Perennial Forbs 23% Litter Ground Cover (cover that contacts the surface) = Annual forbs + Perennial Grasses + Litter Ground Cover = 66.3% Canopy Cover = Perennial Forbs Canopy Cover = 29% Using Table 3 and a canopy of 25% (short brush 0.5 meter in height) and the "G" canopy type, the graph of Figure 2 was developed. From this graph, a ground cover that contacts the surface of 66.3% yields a "C" factor of 0.03. Since the actual canopy is 29%, another chart was developed from the data in Table 2 showing the change in "C" factor versus % ground cover for a canopy of 50%. This is Figure 3, and using a ground cover that contacts the surface of 66.3%, gives a "C" factor of 0.025. Since the actual canopy is 29%, a simple interpolation is required to give the correct "C" factor: 0 "C" for canopy 2? 550 = 25 0 "C" for canopy 25-29 4 SL-12 CURRENT 11MAR11.wpd 22