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Stream Channel Parameters and Changes <br />Exhibit 55B Due to Longwall Mining-Induced Subsidence Page 6 <br /> <br /> <br /> <br />831-032.923 Wright Water Engineers, Inc. <br />December 2021 <br />EXISTING STREAM CHANNEL CHARACTERISTICS <br />The existing stream channel characteristics have been defined for various parameters, including <br />channel slopes, peak flow rates for a variety of frequencies of occurrence, flow velocities for each <br />of the frequencies, sediment transport regime, stage-discharge relationships, channel profiles, and <br />channel and over-bank stability. <br />The existing channel shapes were related to the dominant discharge (2-year frequency of <br />occurrence). Sediment transport has been defined for each stream using the annual sediment load; <br />however, sediment transport is a long-term value and represents the full range of flows including <br />the 10-year and 100-year frequency peak discharges. <br />For each of the existing stream channels, many hydrologic and stream channel parameters were <br />defined and evaluated, including: <br />1. Mean annual runoff <br />2. Peak discharges for the 2-year, 10-year, and 100-year frequency floods <br />3. Mean annual sediment yields <br />4. Average thalweg 2 slopes <br />5. Channel characteristics (consisting of width and depth relationships as well as other <br />geomorphic properties) <br />6. The range of the channel slopes from near mouth to upper reach <br />Other factors that influence the long-term channel characteristics include the forested area and <br />frequency of landslides. <br /> 2 Line following lowest part of a valley, i.e., invert of channel.