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. . .. Final Environmental Assessment Signing of an Agreement for the Administration of Water Pursuant to the Subordination of Wayne N. Aspinall Unit Water Rights within the Upper Gunnison River Basin INTRODUCTION AND PURPOSE AND NEED BacklITound The Bureau of Reclamation constructed the Wayne N. Aspinall Unit (Aspinall Unit) in the 1960's and 1970's on the Gwmison River in west central Colorado under the authority of the Colorado River Storage Project Act of April II, 1956 (Act). The purposes ofthe Act included regulating flows of the Colorado River to pennit the Upper Colorado River Basin States to more fully utilize their allocations of Colorado River water as set forth in the Upper Colorado River Basin Compact. The Aspinall Unit is located in Gunnison and Montrose Counties, Colorado, along a 40-mile reach of the Gunnison River. It consists of a series of three dams and reservoirs-Blue Mesa, Morrow Point, and Crystal. The Aspinall Unit is operated by Reclamation, while the land and water areas of the reservoirs are managed under contract by the National Park Service as the Curecanti National Recreation Area. Figure I shows the location of Aspinall Unit features within the Gunnison River Basin. The Aspinall Unit's primary storage facility is Blue Mesa Reservoir which has a water storage right for 940,75: acre-feet with an appropriation date of November 13, 1957, and a refill water right of 122,702 acre-feet. During the planning for the Aspinall Unit, there were concerns in Colorado that a storage right of this magnitude would preclude future upstream water developments and uses in the Gunnison Basin, Under Colorado Water Law, the 1957 right could "call out" junior rights (later than 1957), and in effect make these junior water rights ineffective in supplying dependable water,! To address these concerns, Reclamation's policy since the early 1960's has been to allow junior water users witlun the natural basin of the Gunnison River to develop up to 60,000 acre-feet without interference from the Aspinall Unit. The 60,000 acre-feet is a cumulative figure: 40,000 acre-feet of depletions are allowed above Blue Mesa Dam, and another 10,000 acre-feet (each) of IIn the Gunnison River Basin as elsewhere in Colorado, senior water right holders can place a "call" on the river-a request to the State Engineer to force water users with junior decrees to cease or diminish their storage or diversions and pass the called amount of water to the downstream senior water right in order to make the senior's water supply "whole,"