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SVeam Channel Parameters <br />Exhibit SSA and Changes Due to Mining-Inducetl Subsidence Page 10 <br />from the increase in slope as identified in Table 4. <br />SUMMARY <br />Stream channel characteristics will change as a result of subsidence. This analysis of stream <br />channels was undertaken to determine the magnitude of change resulting from the change in <br />channel slope. The changes to stream channel parameters were analyzed using standard <br />procedures of the sedimentation and geomorphic engineering professions based on the effects of <br />thalweg slope changes (either increase or decrease) due to mining-induced subsidence. The <br />results are summarized in Table 5. <br />The maximum estimated change in channel width is seven feet, and the maximum change in <br />channel depth is 0.4 feet. Changes in new regime width and depths occur in a slow process that <br />may take from 3 to 5 years or more. The likely change in sediment yield is not expected to be <br />• more than 5 percent from the values given in Table 2. <br />The mining-induced subsidence impacts on existing stream channel pazameters and basin <br />sediment yield are not significant. Furthermore, any changes in channel characteristics will occur <br />gradually and reach the new regime over a period of several years. <br />REFERENCES <br />U.S. Geological Survey. 1985. James Kircher. Estimation of Natural Streamflow <br />Characteristics in Western Colorado. Water Resources Investigations Report 85-4086. <br />U.S. Geological Survey. 1988. John Elliot. Regionalization of Mean Annual Suspended <br />Sediment Loads in Streams, Central, Northwestern, and Southwestern Colorado. Water <br />Resources Investigations Report 87-4193. <br />• D:\Work\W WE\831-032\620hrz\Exhibit SSA 2004.dw <br />DRAFT <br />