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Stream Channel Parameters <br />Exhibit 55 and Changes Due to Mining-Induced Subsidence Page 5 <br />• Sediment Yield <br />The mean annual sediment yield for each of the 16 streams is presented, for convenience, in <br />terms of three units of <br />I . Tons per year <br />2. Acre-feet per yeaz <br />3. Cubic yards per year <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published and unpublished data combined with site-specific information and basin 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 />characteristics. <br />Sediment yield parameters for similar basins were evaluated using the USGS's 6Vater Resources <br />/nvestigation Report 8i-~F193 by John Elliott entitled Regratalimtion oj~1~/ean .9nnua! Snspended <br />• Sediment Loads in Streams, Central, Northt7-estern, 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 similar characteristics for which sediment <br />yield data were available. The typical suspended sediment concentrations of similar streams <br />were taken into consideration for comparison and for "reasonableness' checks. <br />The adopted sediment yield rate of 0.03 acre-feet per square mile per year for the subject basins, <br />when coupled with annual water yield, results in an average annualized sediment concentration <br />of approximately 70 mg/L. "this is consistent with regional analyses for the Nortlt Fork. <br />STREAM CHANNEL HYDRAULIC CHARACTERISTICS <br />The stream channel regime and characteristics 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 />• <br />