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-3- • WATER SUPPLY Runoff Analysis The U.S. Geological Survey (U.S.G.S.) has maintained a number of surface runoff gauges on drainages in North Park. Table 1 summarizes pertinent data concerning the gauges. The gauges tend to be on relatively small tributaries of the Canadian and Michigan Rivers located relatively high in the drainage basins. Also included are a number of mainstem gauges which have very large tributary areas. The data from these gauges was analyzed to help estimate the runoff yield for the draws which cross the mine plan area. The gauges have tributary areas ranging from 10.1 to 480 square miles and periods of record ranging from one to 27 years. While the closest gauging stations are located on the mainstem of the Canadian River above and below the mine area, they were not used in • the regional analysis because they were only established in 1978. In addition, the U.S.G.S. established a stream gauge on Williams Draw approximately one mile downstream from the mine area. One runoff season's worth of data has been collected, but the official information is not yet available. Mean annual runoff for the gauges as published in supply papers, expressed in acre-feet per acre was correlated with normal annual precipitation. North Park is enclosed on three sides, on the west and south by the Continental Divide and on the east by the Medicine Bow Mountains. Normal annual precipitation in North Park ranges from 25 to 60 inches in the mountains surrounding the park, down to less than 12 inches west of Walden. For the purposes of this study, a conservative (high) value for average annual rainfall was used and is approximately 15.8 inches. Normal annual precipitation was taken from a map for the State of Colorado • prepared by the Water Supply Forecast Center in Salt Lake City, Utah using adjusted climatological data for the period ~(~ Leonard Rice Consulting Water Engineers. Inc.