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West Elk Mine . basin of Minnesota Creek. The next largest percentage is Lick Creek, which contains approximately 19 percent of the South of Divide permit area. When evaluating the location of the proposed E Seam longwall panels, the emphasis on Dry Fork becomes even more pronounced. There aze several distinct stream channels within the pernvt azea. Each of these streams has been identified with an index number which provides the basis for identifying stream channel characteristics before and after mining, as presented in Exhibit SSA. WWE defined the existing stream channel chazacteristics for various parameters, including channel slopes, peak flow rates for a variety of frequencies of occurrence, flow velocities for each of the frequencies, sediment transport regime, stage-dischazge relationships, channel profiles and channel and overbank stability. The existing channel shapes were related to the "dominant discharge," which has atwo-yeaz frequency of occurrence. Sediment transport has been defined for each stream using the annual sediment load and sediment loads associated with lazge floods. Many of these streams (with the exception of Raven Creek, Deep Creek and Dry Fork as previously described) within the South of Divide permit area are ephemeral, based on U.S. Geological Survey topographic maps and extrapolation of gaged streamflow data. Flows occur only in response to snowmelt and significant rainfalls. As discussed in Exhibits 55 and SSA, WWE and Mr. Pemberton used a variety of statisfically-based methods to detemune a representative average annual yield value that would apply to these drainages. Exhibits 55 and SSA concludes that for the . purpose of computing pre and post-mining average annual sediment yields, an appropriate mean annual runoff for the subject basins of 475 acre-feet per squaze mile per year should be adopted, even though site~peci&c data for the basins indicate a mean annual runoff of considerably less than this amount. From the standpoint of water rights, analyses of water yield by WWE for the Division No. 4 Colorado Water Court for the 1986 West Elk Mine water augmentation plan indicated that the typical annual water yield for tributaries to the Dry Fork of Minnesota Creek were approximately 200 acre-feet per square mile per year. This is consistent with the average annual yield of the Dry Fork basin, which is also about 200 acre-feet per squaze mile per year based on the available data. Iu short, the appropriate average annual streamflow for the channels ranges from 200 and 475 acre-feet per square mile per year, with 200 acre-feet per square mile per yeaz being used for water rights purposes and 475 acre-feet per squaze mile being used for sediment yield purposes. In addition to computing average annual yields, W WE and Mr. Pemberton calculated floodflows for multiple return frequency events. These aze presented in Exhibits 55 and SSA. This is important because it is necessary to evaluate how the stream channels will respond to lazge flood flows after subsidence has occurred, especially with respect to sediment transport. The projected subsidence for the stream channels was determined using output from the CISPM, Version 2.0, calibrated using site-specific subsidence data. The stream channels were analyzed to determine the magnitude of change resulting from the change in channel slope. The changes to stream channel chazacteristics were analyzed using standard procedures of the sedimentation and 2.05-1 B8 Revised June 2005 PRIG, January 2006, March 2006; Rev. May 2006 PR/0