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Stream Channel Parameters <br />Exhibit 55 and Changes Due to Mining-Induced Subsidence <br />Page 2 <br />• EXISTING STREAM CHANNEL CHARACTERISTICS <br />The existing stream channel chazacteristics have been defined for vazious parameters, including <br />channel slopes, peak flow rates for a variety of frequencies of occurrence, flow velocities for <br />each of the frequencies, sediment transport regime, stage-discharge relationships, channel <br />profiles, and 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 <br />load; however, sediment transport is a long-term value and represents the full range of flows <br />including the 10-year and 100-year frequency peak discharges. <br />For each of the 16 existing stream channels, many hydrologic and stream channel parameters <br />were 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'' slopes <br />5. Channel characteristics for the dominant discharge (consisting of width and depth <br />relationships) <br />6. The range of the channel slopes from near mouth [o upper reach <br />O[her factors which influence the long-term channel chazacteristics are the forested area and <br />frequency of landslides. <br />BASIN HYDROLOGIC CHARACTERISTICS <br />WWE and Mr. Pemberton evaluated and studied each of the 16 stream segments and their basins <br />to define basic hydrologic characteristics related to each stream. This information is summarized <br />• '-Line following lowest pan of a valley, i.e., invert of channel. <br />