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Stream Channel Parameters and Changes <br /> Exhibit 55B Due to Longwall Mining-Induced Subsidence Page 6 <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 thalweg2 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. <br /> 831-032.921 Wright Water Engineers, Inc. <br /> December 2020 <br />