Draft Environmental Assesment and Finding of No Significant Impact Gunnision River Activities February 1995

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Near Whitewater, average flows are approximately 2,600 cfs and extremes have ranged from 35,700 cfs in 1920 to 106 cfs in 1934. Under natural conditions, the river was characterized by high flows in the spring and early summer due to snowmelt and lower flows in the late summer and winter. Storage of water in the Aspinall Unit and other reservoirs such as Taylor Park has reduced high spring flows and increased flows during other periods of the year. Figure 2 on the next page shows how the monthly distribution of flows has been affected by storage and other water uses. Individuals and water user groups began using Gunnison River water in the 19th century with establishment of numerous irrigation water rights. A water right is a real property right which allows the holder to use a certain portion of the river's water for beneficial use. Most of the water rights on the Gunnison River and its tributaries are direct diversion rights which allow the owner to take water out of the river or stream; however, water is not always physically present in a stream to meet the needs of the water rights. In ,§hostage cases,, "senior" (earlier in time) water right holders can place a "call" on the river - -a request to the State Engineer to force some of the water users with junior rights to cease or lower their diversions and let the water pass downstream to the senior right. Significant senior diversion rights, established between 1900 and 1910, include the Gunnison Tunnel of the Uncompahgre Project (1,300 cfs) and the Redlands Diversion Dam (750 cfs). An example of how water rights are administered might be: in a dry year, flows above the Redlands Diversion Dam might fall to 600 cfs; in response, the Redlands Water and Power Company could request a call on the river to try to maintain their diversion of 750 cfs. They would ask the State Engineer to shut off upstream junior rights on the Gunnison River or its tributaries. This can, and has in the past, affected water users along the river from Gunnison and Lake Counties to Mesa County. For example, on streams upstream from Blue Mesa Reservoir, junior water users were historically shut down when the Redlands Diversion Dam or -Ounnison Tunnel placed calls on the river. In addition to direct diversion rights, there are storage rights, which allow a water user to store water in a reservoir for later release. Water stored under the State water rights system can later be released when needed for a downstream use. Once stored, the water can be released and protected past all other water rights such as the Gunnison Tunnel and Redlands Diversion Dam, even if there is a call on the river. The largest single storage right on the Gunnison River is the 939,206 acre -foot decree for Blue Mesa Reservoir. A block of storage water in Blue Mesa- - estimated at 148,000 acre -feet- -has been set aside to mitigate impacts of the Dallas Creek and Dolores water projects on endangered fish and will be used for the interim agreement water -- supply. Calls on the river have decreased since the Aspinall Unit began operations in the 1960's. This is because the Unit stores water in high flow periods when there are no shortages and increases river flows by hydropower releases in normally low water periods as shown in Figure 2. Thus, senior water right holders such as the Redlands Diversion Dam, have had more dependable water supplies and junior water rights have been less likely to be "called out." 13