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Stream Channel Parameters <br />Exhibit 558 and Changes Due to Mining - Induced Subsidence Page 6 <br />Sediment Yield <br />The mean annual sediment yield for each of the 12 streams is presented, for convenience, in terms <br />of three units of measurement: <br />1. Tons per year <br />2. AF per year <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published and unpublished data combined with site - specific information and basin characteristics. <br />Sediment yield parameters 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 similar characteristics for which sediment <br />yield data were available. The typical suspended sediment concentrations of similar streams were <br />taken into consideration for comparison and for "reasonableness" checks. <br />The adopted sediment yield rate of 0.03 AF per square 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 />.J <br />831 - 032.810 Wright Water Engineers, Inc. <br />