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Section II - Understanding the Water Supply The Gunnison River Basin The Gunnison River originates where the East and Taylor Rivers join at Almont, Colorado in Gunnison County. From that point, the Gunnison flows 25 miles to Blue Mesa Reservoir, the largest and most upstream of the three reservoirs comprising the Aspinall Unit. Blue Mesa Reservoir releases water into Morrow Point Reservoir which discharges into Crystal Reservoir. From Crystal Reservoir, the Gunnison flows approximately 2 miles to the Gunnison Tunnel (irrigation diversion for the Uncompahgre Project), located just upstream from the Black Canyon of the Gunnison National Monument (Monument). From the Gunnison Tunnel and through the Monument and the Gunnison Gorge, the river tlows for 28.9 miles to the confluence with the North Fork. It then travels 74,9 river miles to its confluence with the Colorado River at Grand Junction. A TT" Geological S"rvey streamflo'" gaging station is located near the upstream boundary of the Monument (0.4 miles downstream from Gunnison Tunnel). This gage is considered the measurement point when water deliveries under the proposed contract to the Monument are discussed. The area of the Gunnison River watershed is 3,965 square miles at this point. Historical flows have averaged 1,384 cubic feet per second (cfs) and have ranged from 19,000 cfs (1921) to no flow (1936, 1949, and 1950). Another important gaging location is at Whitewater Colorado, located 8 miles upstream from the Colorado River confluence. At this point the Gunnison River drains 7,928 square miles. Average flows are approximately 2,600 cfs and extremes have ranged from 35,700 cfs (1920) to i06 cfs (1934). Even with the Aspinall Unit, there is considerable variability in Gunnison River flows from year to year because of variable amounts of snowfall during winter months. For example, flows through the Monument averaged 396 cfs during the drought year of 1977, and 2,943 cfs during the high water year of 1984. Flows in June 1984 averaged over 8,000 cfs through the Monument. Because of the high natural variability in the water supply, agencies are examining the concept of providing a variable amount of water to the Monument from the Aspinall Unit. Water Rights Gunnison River water use began in the 19th century with establishment of numerous irrigation water rights by individuals, organizations, and government agencies. A water right is a real property right which allows the holder to use a certain portion of the river's water for beneficial purposes, Beneficial uses include irrigation, drinking water, industrial uses, recreation, and fish and wildlife. Water is not always physically present to meet the needs of water rights. Water rights are administered by the State Engineer's office in accordance with the date they were recognized in the adjudication system (their seniority). There are more than 5,000 direct diversion decrees that have been perfected and are presently in use on the Gunnison River and its tributaries upstream from Delta. Significant senior diversion rights, established between 1900 and 1910, include the Gunnison Tunnel of the Uncompahgre Project (1,300 cfs) and the Redlands Diversion (750 cfs). 4