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Seeam Channel Parameters <br />Exhibit SSA and Changes Due to Mining•Induced Subsidence Page 7 <br />In utilizing the CISPM program, each stream channel reach was defined as to location by "X" <br />and "Y" coordinates. Channel slope changes along with the magnitude of the subsidence were <br />determined for relatively short stream lengths of approximately 100 feet or less. The results of <br />the computer modeling far all 11 of the potentially affected stream channels are shown in <br />Table 4. The slope change, either positive or negative, was either added to or subtracted from the <br />existing channel thalweg slope as determined from computations based upon USGS topographic <br />maps with a contour interval of 40 feet. <br />Table 4 shows that the most significant changes will occur in the tributaries overlying the <br />southern portion of the mined permit area where E Seam mining thickness is projected to be at a <br />maximum (14 feet). For these channels, the maximum changes in slope are an increase of 2.5 <br />percent and a decrease of 2.5 percent. Since the pre-mining average slope of these channels <br />ranged from 8.5 percent to 19.5 percent, the slope changes due to subsidence do not create any <br />• reaches with negative or flat slopes. Slope impacts magnitudes are greatest in the lower reaches <br />of basins 29 and 32, where the pre-mining slopes are approximately 4.8 percent and 4.0 percent, <br />respectively. The pre- and post-mining profiles for Basins 29, 32 and 36, shown in Figures 14, <br />15 and 16 respectively, demonstrate that the overall channel slope is not significantly impacted <br />by subsidence. <br />Basins 5, 6, 26 and 31 generally overly mining panels with thicknesses ranging from 9 to 12 feet. <br />The subsidence from mining in these azeas will result in changes in the slopes of the stream <br />channels ranging from a maximum increase of 1.9 percent to a maximum decrease of 1.7 percent. <br />These slope changes will be insignificant on the stream channels where existing average slopes <br />range from 5.3 percent to 18.4 percent. <br />The Dry Fork above Minnesota Reservoir (Basin 35) is the receiving water body for Basins 4 <br />through 6 and 26 through 33; Basin 34 is tributary to the Dry Fork below Minnesota Reservoir. <br />The channel thalweg for the Dry Fork spans multiple E Seam panels. Maximum subsidence <br />along the stream profile is approximately 9.3 feet. Channel slope in the lower reach is upwards <br />. of 5.6 percent and average slope for the entire reach is approximately 5.3 percent. Slope changes <br />DRAFT <br />