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• Stream Channel Paremetere Exhibit 55A and Changes Due to Mining•Induced Subsidence Page 4 of 630 AF per squaze mile; the runoff magnitude is significantly affected by the higher precipitation values at higher elevations in the drainage basin. Analyses of water yield by William Lorah of W WE for the Division No. 4 Water Court approved water augmentation plan, indicated that typical annual water yields for tributaries of Dry Fork were approximately 200 AF per square mile per year. This value compares favorably with the yield estimate of 160 AF per square mile per yeaz based on the U.S. Geological Survey (USGS) regional regression equations (USGS 1985). The 1936 through 1947 and 1985 through 2002 periods of gaging flow on Minnesota Creek show an average annual yield for 41.3 squaze miles of 385 AF per square mile. For the purpose of annual average sediment yields for the subject basins, WWE and Mr. Pemberton have concluded that an appropriate (i.e., conservative) mean annual runoff for the • subject basins of 475 AF per yeaz should be adopted, even though site-specific data for the basins would likely indicate a mean annual runoff of less than 475 AF per year per square mile. The adopted value represents a high mean annual runoff for use in conservative sediment and channel stability studies. For water rights purposes, the average yeaz yield estimate of 200 AF per year is suitable, as approved by the Colorado Water Court in 1986. Peak Runoff Rates Peak rates of storm runoff from rainfall and snowmelt events were defined for three return frequencies: 2-, 10., and 100-yeaz events. These dischazges aze based on statisfical evaluation of peak daily flow data collected by MCC in the permit azea since 1978, study of the long-term published records for the North Fork at Somerset, and statistical evaluation of published streamflow data for basins in the vicinity of West Elk Mine. Special evaluations were made of the Lick Creek, Sylvester Gulch, and Horse Creek basins using the USGS peak rate of runoff computational procedure applicable to small . basins in the Colorado mountainous azea (USGS 1985). 831-032.620 Wright Water Engineers, Inc.