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Stream Channel Parameters and Changes <br />Exhibit 55B Due to Longwall Mining-Induced Subsidence Page 12 <br /> <br /> <br /> <br />831-032.923 Wright Water Engineers, Inc. <br />December 2021 <br />IMPACTS OF SUBSIDENCE ON STREAM CHANNELS <br />The projected subsidence under each of the 8 studied stream channels in the study area was <br />calculated using Surface Deformation Prediction System (SDPS), Version 6.2G (Department of <br />Mining Engineering, University of Kentucky; Department of Mining and Minerals Engineering, <br />Virginia Polytechnic Institute and State University), as calibrated using site-specific subsidence <br />data. Exhibit 60E presents a detailed discussion of the subsidence evaluation. <br />All longwall panels were set at an elevation of zero, with the stream channel represented above <br />based on overburden thickness. In utilizing SDPS, each stream channel reach was represented as <br />a series of points (spaced 200 feet apart) with X, Y, and Z coordinates. The Z value for each point <br />is the approximate overburden depth based on 10-foot overburden contours provided by MCC. <br />Subsidence and changes to channel slope were determined along the profile. <br />Table 4 shows that the most significant changes will occur in the tributaries overlying a significant <br />portion of both the B-seam and E-seam panels. The E-seam mining thickness is projected to be <br />14 3 feet at a maximum to the west, and 11 feet at a maximum to the east. The B-seam thickness <br />is projected to be 9 feet in the most southerly panel, and 14 feet at a maximum to the north. The <br />Sunset Trail panels mined in the E-seam are expected to have similar mining thickness values, <br />with lower mining heights projected near the eastern end of the panels. <br />Basin Number 3 is the Horse Gulch basin, a tributary to Minnesota Reservoir. Because the B- <br />seam has already been mined, this basin will only be affected by proposed E-seam mining. Basin <br />3 channel’s slope will increase by a maximum 10.6% and will decrease by a maximum 2.9% due <br />to E-seam mining. Because the pre-mining average slope of this channel is 11.1%, the slope <br />changes due to subsidence do not create any reaches with negative or flat slopes. Maximum <br />subsidence along the stream profile is approximately 8.3 feet. The pre- and post-mining profiles <br />for Basin 3 are shown in Figure 21. This figure demonstrates that the overall channel slope is not <br /> <br />3 Practically speaking, the maximum mining height with the current longwall is 13.5 feet; therefore, WWE <br />used a height of 13.5 in the computer modeling.