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Stream Channel Parameters and Changes <br />Exhibit 55B Due to Longwall Mining-Induced Subsidence Page 10 <br /> <br /> <br /> <br />831-032.923 Wright Water Engineers, Inc. <br />December 2021 <br />STREAM CHANNEL HYDRAULIC CHARACTERISTICS <br />The stream channel regime and characteristics were defined using still photographs, videotapes, <br />USGS topographic maps, detailed topographic maps prepared for the mine area, soil surveys, <br />geological evaluations prepared by the late John Rold (former State Geologist and consultant to <br />WWE), aerial photographs, and related evaluations. Channel profiles portraying the pre-mining <br />slope and the range of slopes for each stream segment are presented in Figures 3 through 20. In <br />previous versions of Exhibit 55B, USGS quads (40-foot contour interval) were used to develop <br />the pre-mining channel profile. Pre-mining channel profiles in the December 2020 update have <br />been developed based on topography provided by MCC with 20-foot contour intervals. <br />A summary of the stream channel hydraulic characteristics (width, depth, and velocity) for each <br />of the 8 drainage basins is provided in Table 3. The channel dimensions are intended to generally <br />represent each stream and provide a baseline, against which to compare potential changes due to <br />longwall mining. The slope in the lower reach of the channel potentially impacted by mining is <br />shown in addition to the average channel slope since only the lower reach will receive the full <br />basin runoff. <br />The dominant discharge is the flow for the stream that tends to shape the stream channel and help <br />establish the width and depth of the defined channel. The dominant discharge can vary based upon <br />a number of watershed conditions, but correlates best with 1- to 2-year peak flow rates. For this <br />analysis, the dominant discharge was assumed to be the 2-year return interval peak flow. <br />Erosion and sediment yield of a stream basin are normally a product of rainfall, ground cover, land <br />use, topography, upland erosion, runoff, soil types, geology, sediment, and channel hydraulic <br />characteristics. All of these factors were considered in this analysis. <br />The channel characteristics shown in Table 3 for the dominant discharge are for the stream near <br />the mouth or at a point just downstream of each segment of stream channel potentially impacted <br />by longwall mining. The width and depth values at the dominant discharge in Table 3 are <br />approximate values based upon computed physical basin regime characteristics and identification