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Stream Channel Parameters and Changes <br /> Exhibit 55B Due to Longwall Mining-Induced Subsidence Page 16 <br /> CHANGES IN STREAM CHANNEL HYDRAULIC CHARACTERISTICS <br /> The channel characteristics for each of the basins (as shown in Table 3) were analyzed using <br /> geomorphic and sedimentation engineering relationships and formulas to determine the extent and <br /> type of change to each channel segment. These relationships were then used to estimate the <br /> amount of sediment yield change. <br /> Hydrologic review has determined that the following basin characteristics will not change <br /> significantly as a result of subsidence: <br /> 1. Mean annual runoff <br /> 2. Peak discharge <br /> 3. Dominant discharge <br /> 4. Forest cover <br /> Mean annual runoff,peak discharge, and the dominant discharge are greatest for the lower end of <br /> each stream segment studied,priming these areas of the channel for maximum geomorphic change. <br /> Therefore, this analysis focuses primarily on the lower portion of each stream segment. <br /> Computations were performed for the lowest channel reach within the influence of the mining. <br /> A principle of fluvial morphology, as confirmed by Manning's equation, is that the channel width <br /> and channel depth will respond to changes in slope as shown in the following table. <br /> Channel Width Channel Depth <br /> Slope Increase Larger Smaller <br /> Due to Subsidence <br /> Slope Decrease Smaller Larger <br /> Due to Subsidence <br /> The deformation of the ground surface due to subsidence results in a change in the existing channel <br /> slope. The magnitudes of changes were first computed based on the subsidence model output, <br /> 831-032.921 Wright Water Engineers, Inc. <br /> December 2020 <br />