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A'est Elk Mine • Streams Stream hydrology and sediment transport have been conceptually quantified for the permit area by WWE and Mr. Ernest Pemberton, P.E. Mr. Pemberton was formerly the Chief Engineer for the U.S. Bureau of Reclamation, Sedimentation and River Hydraulic Section. He is a respected expert in the field. Exhibit 55 was prepared to address drainage basin characteristics and evaluate the potential effects due to mining in the Apache Rocks and Box Canyon permit areas. Since mining activities are still active in these areas, Exhibit 55 has been retained in the permit. However, the following text focuses on the drainages in the South of Divide permit area, which is also found in Exhibit SSA, but includes key fmdings of Exhibit 55 for the Apache Rocks and Box Canyon permit areas. Background on Stream Channels and Hydrology The Box Canyon and Apache Rocks permit revision areas include a portion of Sylvester Gulch, Box Canyon, the unnamed drainage west of Box Canyon, and a tributory to Raven Gulch. Approximately 1,080 acres of the Apache Rocks permit revision azea is located within the Dry Fork of Minnesota Creek basin. That portion also includes parts of the Horse Gulch, Pond Gulch, and Slide Gulch drainages, as well as two unnamed drainages east of Horse Gulch. The Apache Rocks permit revision area totals 2,502 acres and 1,424 acres (57 percent) are in the North Fork drainage. • All of the 1,440 acres within the Box Canyon permit revision and 690 acres in the West Flatiron azea are within the North Fork basin. Nearly all of the South of Divide permit area is located within the Minnesota Creek drainage basin. The exception is the small portion that extends east through Section 35, which is part of the Deep Creek drainage basin. However, the majority of the South of Divide permit area is located within the Dry Fork of Minnesota Creek (Dry Fork). In fact, of the 8.18 square miles that make up the permit revision area, approximately 5.18 square miles (or 63 percent) is located within the Dry Fork basin. 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 are several distinct stream channels within the permit area. 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 pazameters, 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. 2.05-157 Revised Jvne 2005 PRI G