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Stream Channel Parameters <br />Exhibit 55A and Changes Due to Mining-Induced Subsidence Page 3 <br />to define basic hydrologic characteristics related to each stream. This information is summarized <br />in Table 2. While there are differences in soils and vegetation within the study areas, for the <br />purpose of this conceptual analysis, conservative estimates of water yield and sediment yield <br />have been adopted which are reasonable for both areas. <br />Average Annual Runoff <br />The mean annual runoff expressed in acre-feet (AF) per year per squaze mile is a fundamental <br />pazameter for determining annual average sediment yield. Total annual precipitation varies <br />widely throughout the 526-square-mile basin of the North Fork at Somerset. In the higher <br />elevations of the entire North Fork basin, precipitation can total up to 50 inches per yeaz. Annual <br />precipitation for the drainage basins near West Elk Mine typically falls in the 22-inch to 30-inch <br />range. Precipitation in excess of that portion lost to evapotranspiration and deep percolation, and <br />that ultimately becomes streamflow, also varies widely in the basin. <br />• Woodward-Clyde conducted a water balance analysis for Horse Creek and Lick Creek for 1978 <br />to 1980. The study, based on the Lick Creek stream gaging station, indicated an average annual <br />runoff of 8.9 inches, representing 475 AF per squaze mile <br />MCC's Exhibit 18 indicates an annual runoff approaching 1,000 AF for one square mile for a <br />variety of North Fork watersheds. However, that finding is modified by their reference to much <br />lowered water yields in South Prong and Horse Creek for the 1977 to 1978 period, which were <br />lower than the driest year yields of the regional basins. <br />The North Fork gage neaz Somerset provides the best long-term runoff data in the region, with 69 <br />years of continuous gaging records. The 69-year period of record identifies a mean annual runoff <br />of 630 AF per square mile; the runoff magnitude is significantly affected by the higher <br />precipitation values at higher elevations in the drainage basin. <br />Analyses of water yield by William Lorah of W WE for the Division No. 4 Water Court approved <br />water augmentation plan, indicated that typical annual water yields for tributaries of Dry Fork <br />DRAFT <br />