PERMFILE48385 - Laserfiche WebLink

Home Browse Search

Stream Channel Parameters • Exhibit 55A and Changes Due to Mining-Induced Subsidence Page 3 frequency of landslides. BASIN HYDROLOGIC CHARACTERISTICS WWE and Mr, Pemberton evaluated and studied each of the 12 stream segments and their basins to define basic hydrologic characteristics related to each stream. This information is summarized in Table 2. While there aze differences in soils and vegetation within the study areas, for the purpose of this conceptual analysis, conservative estimates of water yield and sediment yield have been adopted which aze reasonable for both areas. Average Annual Runoff The mean annual runoff expressed in acre-feet (AF) per yeaz pet squaze mile is a fundamental parameter for determining annual average sediment yield. Total annual precipitation varies widely throughout the 526-squaze-mile basin of the North Fork at Somerset. In the higher elevations of the entire North Fork basin, precipitation can total up to 50 inches per year. Annual precipitation for the drainage basins neaz West Ells Mine typically falls in the 22-inch to 30-inch range. Precipitation in excess of that portion lost to evapotranspiration and deep percolation, and that ultimately becomes streamflow, also varies widely in the basin. I~ U Woodward-Clyde conducted a water balance analysis for Horse Creek and Lick Creek for 1978 to 1980. The study, based on the Lick Creek stream gaging station, indicated an average annual runoff of 8.9 inches, representing 475 AF per squaze mile. MCC's Exhibit 18 indicates an annual runoff approaching 1,000 AF for one square mile for a variety of North Fork watersheds. However, that fording is modified by their reference to much lowered water yields in South Prong and Horse Creek for the 1977 to 1978 period, which were lower than the driest year yields of the regional basins. The North Fork gage neaz Somerset provides the best long-term runoff data in the region, with 69 yeazs of continuous gaging records. The 69-yeaz period of record identifies a mean annual runoff 831-032.620 Wright Water Engineers, Inc.