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1 <br /> 4.0 SURFACE HYDROLOGY <br /> Both pits are situated on or adjacent to unnamed intermittent stream <br /> channels which are tributaries to Lay Creek. These channels generally <br /> drain to the south. The tributary drainage channel between the School <br /> Section Pit and Lay Creek is approximately three miles long, resulting in <br /> an average gradient of about 100 feet per mile. The stream distance from <br /> ' Lay Creek to the Johnson Pit is about two miles at an average gradient of <br /> about 175 feet per mile. Lay Creek, which is an intermittent to perennial <br /> stream, flows into the Yampa River approximately three miles further <br /> downstream. <br /> r <br /> 4.1 School Section Pit <br /> The drainage basins associated with the School Section Pit are shown <br /> on Fig.6. 1 . The total drainage basin area tributary to the pit is <br /> approximately 2,400 acres. Stream channel gradients range from 2 to 25 <br /> percent with an average gradient of 7 percent. The elevations of the <br /> drainage basin tributary to the pit range from approximately 6350 feet at <br /> the pit to an elevation of approximately 7,100 feet. The design storm <br /> event and design runoff characteristics are presented in Section 6.0. <br /> -5- <br />