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<br />2.3.3 Watershed Sediment Production Potential <br /> <br />Figure 2.3.2 maps obvious sources of sediment in the Willow Creek watershed. However, the <br />risk or rate of sediment production from areas may vary based on many variables including <br />vegetative cover, slope, the degree of disturbance, and the distance to the Willow Creek channel. <br />Sediments may be produced by other areas of the watershed based on these same variables. In <br />the GIS, watershed characteristics were combined spatially to create a map indicating the <br />potential for areas to contribute sediments to the Willow Creek stream system. This map could <br />be used to prioritize efforts to control sediment sources in the watershed. <br /> <br />To perform a spatial mathematical manipulation, several factors were quantified. A factor was <br />assigned to quantify the risk from different types of disturbed areas that were mapped. A <br />disturbance factor of 25% was assigned to scree/talus slopes, 50% for roadways, 75% for <br />disturbed areas, and 100% for mine tailings piles. A factor was also assigned to account for the <br />distance from a particular point in the watershed to the main stream channels of Willow Creek, <br />West Willow Creek, or East Willow Creek. A distance factor ranging from 4 to 3 by 0.25 <br />increments was assigned if the point was within 10m, 25m, 50m, 100m, or 250m respectively. A <br />factor of2.5, 2, and 1 was assigned if the point was within 500m, 1000m or 2500m respectively. <br />The following mathematical manipulation was then applied spatially to estimate the likelihood of <br />generating sediment: <br /> <br />Sediment Potential = Slope * (Percent Barren + 2 * Disturbance Factor) * Distance Factor <br /> <br />Figure 2.3.3 displays an image of the potential for areas to contribute sediments based on this <br />methodology. Darker red colors indicate a high potential sediment production, and a yellow <br />color indicates an "extreme" sediment production potential that would probably be the first <br />priorities. The largest areas of extreme potential are on the tailings piles of the Amethyst and <br />Commodore Mines on West Willow Creek. Additional areas of extreme sediment production <br />potential include tailings areas on the Ridge Mine, Holy Moses Mine, Outlet Mine, and <br />Carbonate Tunnel on East Willow Creek, the toe of a disturbed talus slope on West Willow <br />Creek, and a debris/ sediment pile just downstream of the confluence. Other areas of high <br />sediment potential exist that may be effective sites for sediment source control measures. <br /> <br />The area of Figure 2.3.3 is structured similarly to Figure 2.3.2. The majority of high potential <br />sediment sources are contained in this figure. The only major area that was noted with an <br />extreme sediment potential upstream of the area displayed in the figure was on the mine tailings <br />piles associated with the Equity Mine in the far upper reaches of West Willow Creek. The pile <br />does have a high potential to wash into the stream, although stream transport energy may be <br />restricted in this area due to lower slopes and a series of ponds. <br /> <br />The method seemed to provide a reasonable representation of sediment potential. However, this <br />method could be refined based on different priorities or risks. An additional important factor <br />may be the connection of sediment sources to the stream. For instance, a toe of a scree slope or <br />tailings pile may be at the edge of the stream channel and directly available for stream transport <br />or may be currently protected by a road or flat area. Additional field investigation would be <br />required to evaluate these connections. <br /> <br />2-41 <br />