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Stream Channel Parameters and Changes <br /> Exhibit 55B Due to Longwall Mining-Induced Subsidence Page 9 <br /> plotting technique was adopted to analyze the small tributary basins under consideration. The <br /> results are consistent with the regional analyses for the North Fork. <br /> Sediment Yield <br /> The mean annual sediment yield for each of the streams is presented, for convenience, in terms of <br /> 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 published and unpublished data combined with site-specific information and basin characteristics.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 comparison with other mountainous regions <br /> with similar vegetative cover and similar characteristics for which sediment yield data were <br /> available. The typical suspended sediment concentrations of similar streams were taken into <br /> 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 /> 831-032.921 Wright Water Engineers, Inc. <br /> December 2020 <br />