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• <br />Exhibit SSA and <br />Sediment Yield <br />Stream Channel Parameters <br />7es Due to Mining-Induced Subsidence <br />s <br />The mean annual sediment yield for each of the 11 streams is presented, for convenience, in <br />terms of three units of measurement: <br />1. Tons per year <br />2. AF per year <br />3. Cubic yards per year <br />n <br />L~ <br /> <br />The mean annual sediment yields for each basin were estimated by utilizing a wide range of <br />published and unpublished data combined with site-specific information and basin <br />chazacteristics. <br />Sediment yield pazameters for similar basins were evaluated using the USGS Water Resources <br />Investigation Report 87-4193 by John Elliott entitled Regionalization of Mean Annual Suspended <br />Sediment Loads in Streams, Central, Northwestern, and Southwestern Colorado (1988). In <br />addition, the rate of sediment production was evaluated using field observations of the basin <br />characteristics, photographs, maps, aerial photos, and after making comparisons with other <br />mountainous regions with similar vegetative cover and similaz characteristics for which sediment <br />yield data were available. The typical suspended sediment concentrations of similaz streams <br />were taken into consideration for comparison and for "reasonableness" checks. <br />The adopted sediment yield rate of 0.03 AF per squaze mile per year for the subject basins, when <br />coupled with annual water yield, results in an average annualized sediment concentration of <br />approximately 70 mg/L. This is consistent with regional analyses for the North Fork. <br />STREAM CHANNEL HYDRAULIC CHARACTERISTICS <br />The stream channel regime and chazacteristics were defined using still photographs, videotapes, <br />USGS topographic maps, detailed topographic maps prepared for the mine area, soil surveys, <br />geological evaluations prepared by John Rold (consultant to WWE), aerial photographs, and <br />related evaluations. Channel profiles portraying the pre-mining slope and the range of slopes for <br />DRAFT <br />