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• C7vII.RB -Exhibit G Water Information Page 2 north, east and west across grassey meadows on the alluvial and oolluvial deposits that cover the central portion of Dowe Flats and continue south toward St. Vrain Creek, approximate]y one-half mile south of the project area. St. Vrain Creek is one of three major stmams in Boulder County ar-d is a tributary of the South Platte River. The St. Vrain Creek basin oocarpies ahrtost the entire riorfhem half of Boulder County with headwaters located along the Continental Divide approximately 23 miles west of Dowe Flats. Streamflow in the St. Vrain Creek basin varies seasonally, usually reaching maximum flow in June because of srawnrelt nuaff. Dowe Flats is drained by an unnamed, intermittent stream system that experiences seasonal flow during the spring nuroff period and essentially rro flow during the remainder of the year. The drainages (Figure G-3) flow to the south toward St. Vrain Creek. Four irrigation ditches are present: Supply Ditch, the Highland Ditch, the Rough and Ready Ditch and the Palmerton Ditch. The rtort}rem and norttrwestem edges of the project area are bordered by the St. Vrain Supply Canal. The St. Vrain Supply Canal is a much Huger water supply canal than the ditches located to the south and flows only in the summer. The Dowe Flats watershed is divided longitudinally into east and west subbacins by • a north-south tnmding ridge (Figure G-3). 'This ridge also represents the western extent of the planned mining operations. The eastern subbasin is further divided into four subbasins based on the upstream and downstream locations of the proposed mining area. Stream channels are predominantly grass covered with oocavonal sandy or rock-bottomed segments. The stream chanrrelc are straig}tt to meandering, shallow and have a low gradient. The drainage pattern is braided in some arras. There are no incised cttanrte]s in the planned mining area. F~7evations along the drainages range from about 5,450 feet above mean sea level (ft msl) along the rrortlrern margin of the project area to about 5,300 ft msl at the southern margin. Upstream of the project area, the stream channel is much narrower and has a steeper gradient as it gains in altitude toward its headwaters. Steeper gradients also are acerriat~ with the various headwater drainages on the steepce slopes of Rabbit and Indian Mountains, east and west of the relatively flat-lying central portion of Dowe Flats. The headwater of the major ephemeral stream in the eastern subbasin is located at an elevation of about 5800 ft msl on Indian Mowtain, approximately one mile north of the project area. This stream flows by the Syntex site. The Dowe Flats watershed drains an area of approximately 4,346 acres (Table G-3) and is divided into five subbasins designated A, B„ BZ, C, and D (Figure G-3). u