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iJ ~ Q r. I" ....... ....V,J ~ . Water Resources The flow of the Gunnison River through the study corridor is derived almost exclusively from upper Gunnison basin runoff. The discharge of the river is regulated by water releases from the Curecanti Project and by di"er'sions through the Gunnison Tunnel. The watershed boundaries along the river form a relatively narrow corridor that follows the outer rim of the canyon. This results in many small drainage paths toward the river that have extremely steep gradients, short channel lengths, and relatively small watershed areas. Because the corridor is located in the semi-arid portion of the region, these gullies flow for only brief periods during the spring snowmelt and during intense summer thunderstorms. Although runoff from this source is sporadic, it does have a significant effect on flOw by creating rock dams and changing the course of the river. River flow has been gaged continuously since 1903 by the U.S. Geological Survey about 1/4 mile (0.4 km) below the Gunnison Diversion Tunnel. Discharge for that period has averaged 1,380 cubic' feet per second (39 m3/s), or 999,800 acre~feet/year (1.2 billion m3/yr). The Gunnison Tunnel was constructed with a diversion. capacity of approximately 1,000 cfs (30 m3/s). These diversion generally occur from April through October and have reduced the daily flow of the river below the tunnel. During the latter part of the irrigation season in 1936, 1949, and 1950, there was no flow in this reach of the river. The Curecanti Project has regulated streamflow so that the discharge is more evenly distributed throughout the year. The effect of regulation is to greatly reduce the spring runoff and to increase the late summer and winter discharges. 89