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Stream Channel Parameters and Changes <br />Exhibit 55B Due to Longwall Mining-Induced Subsidence Page 9 <br /> <br /> <br /> <br />831-032.923 Wright Water Engineers, Inc. <br />December 2021 <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published and unpublished data combined with site-specific information and basin characteristics.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.