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r~ u EXHIBIT SSA STREAM CHANNEL PARAMETERS AND CHANGES DUE TO MINING-IlVDUCED SUBSIDENCE INTRODUCTION TO STUDY Wright Water Engineers, Ino. (WWE) and Ernest Pemberton, P.E.t, have determined the extent to which projected subsidence will impact stream channel stability and sediment transport at Mountain Coal Company's (MCC) West Elk Mine. The following text summarizes WWE's approach and findings. This discussion applies to the South of Divide (SOD) permit revision area, herein referred to as the study area. Figure 1 shows the drainage basins of 14 streams in the vicinity of the mining azeas. Each basin has an identification number that will be used throughout this discussion of stream channel parameters and subsequent changes. As shown in Figure 1, Basins 4 through 6 and 26 through 35 aze located in the Dry Fork of Minnesota Creek (Dry Fork) drainage; Basin 36, Lick Creek, is a direct tributary to Minnesota Creek. Minnesota Creek is a tributary to the North Fork of the Gunnison River (North Fork). Table 1 identifies which streams maybe impacted by the proposed mining. Due to the fact that impacts to tributaries would be maximized in the lower segments of the streams, this study focuses on the lower reaches of the tributary watersheds. As shown in Table 1, the mine azea will underlie portions of 13 separate minor tributaries of the Dry Fork and Lick Creek in the study azea. A detailed discussion of the mine plan and projected subsidence for these areas is given in Exhibit 60B. The remaining two basin channels were determined to be outside the influence of mining activities. The stream channels for Basins 4 and 34 were modeled to verify that they were outside the influence of mining. tAdjunct Scientist with WWE, Former Head of Sedimentation and River Hydraulics Section, Hydrology DepaRment, Chief Engineer and Assistant Commissioner's Office, U.S. Bureau of Reclamation. 831-032.620 Wright Water Engineers, Inc.