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Stream Channel Parameters and Changes <br />Exhibit 55B Due to Longwall Mining-Induced Subsidence Page 16 <br /> <br /> <br /> <br />831-032.923 Wright Water Engineers, Inc. <br />December 2021 <br />CHANGES IN STREAM CHANNEL HYDRAULIC CHARACTERISTICS <br /> <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 <br />Due to Subsidence <br />Larger Smaller <br />Slope Decrease <br />Due to Subsidence <br />Smaller Larger <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,