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• Stream Channel Parameters <br />Exhibit SSA and Changes Due to Mining-Induced Subsidence Page 5 <br />Figure 2provides asemi-logarithmic plot of the peak discharge rates. The semi-logarithmic <br />plotting technique was adopted to analyze the small tributary basins under consideration. It is <br />consistent with the regional analyses for the North Fork. <br />Sediment Yield <br />The mean annual sediment yield for each of the 12 streams is presented, for convenience, in <br />terms of three units ofineasurement: <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• published and unpublished data combined with site-specific information and basin <br />characteristics. <br />Sediment yield pazameters for similaz 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 />chazacteristics, photographs, maps, aerial photos, and after making comparisons with other <br />mountainous regions with similaz 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 square mile per yeaz 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 /> <br />831-032.620 Wright Water Engineers, Inc. <br />