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Stream Channel Paremeters . Exhibit 55A and Changes Due to Mining-Induced Subsidence Page 9 Channel Width Channel Depth Slope Increase Lazger Smaller Due to Subsidence Slope Decrease Smaller Lazger Due to Subsidence The deformation of the ground surface due to subsidence results in a change in the existing channel slope. The magnitudes of these slope changes were first computed based on the subsidence model output, then the changes were applied to the existing channel slope to determine the ensuing channel slope. For purposes of determining changes in channel hydraulic chazacteristics, the channel slope near the confluence or mouth of each drainage was used so that the contribution of the entire basin was included. Utilizing channel regime relationships developed by the geomorphic engineering profession, it was determined that over a 3- to 5-year period or more, the channel hydraulic characteristics would change as shown in Table 5. The changes in depth and width are the maximum computed values considering both a slope increase and slope decrease. However, it should be recognized that the maximum changes in channel width and depth would not occur over the same channel reach. CHANGES IN SEDIMENT YIELD The mean annual sediment yield for each of the 11 basins will not change except for minor channel cutting and channel filling extending over a 3- to 5-yeaz period resulting from the geomorphological tendency for the existing channels to either be cut or filled. Overall, there will be a tendency for these changes in sediment production to balance out within the basins. Referring to Table 2, it is noted that the mean annual sediment yield for the subject basins ranges from approximately 6 to 220 cubic yards per yeaz. These sediment yields are not expected to • change by more than about 5 percent due to any change in hydraulic characteristics resulting DRAFT