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Stream Channel Parameters Exhibit 55 and Changes Due to Mining-Induced Subsidence Page 4 the yield estimate of 160 acre-feet per square mile per year based on the U.S. Geological Survey (USGS) regional regression equations (USGS 1985). The 1936 through 1947 and 1985 through 1993 periods of gaging flow on Minnesota Creek show an average annual yield for 41.3 square miles of 420 acre-feet 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 acre-feet per year should be adopted, even though site-specific data for the basins would likely indicate a mean annual runoff of less than 475 acre-feet 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 year yield estimate of 200 acre-feet 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 discharges are based on statistical evaluation of peak daily flow data collected by MCC in the permit area 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 the 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 area (USGS 1980. Figure 2provides asemi-logarithmic plot of the peak discharge rates. The semi-logarithmic plotting technique was adopted [o analyze the small tributary basins under consideration. It is consistent with the regional analyses for the North Fork. n U