| OCR Text |
Show desert lands of southeastern Utah are most likely to flood, especially during summer ( Whitaker 1969). Peak flows for extremely rare, probable maximum floods have been estimated to be more than 2,000 cubic feet per second ( cfs) for a one- square- mile drainage area and about 10,000 cfs for a 15- square- mile drainage area ( Cripen and Bue 1977). I I. E. Reservoir Hydrology II. E. 1. Description. Lake Powell was created in 1963 with the completion of the Glen Canyon Dam. During the following 17 years, a 186- mile stretch of the Colorado River was transformed into the United States' second largest reservoir. At a maximum operating level of 3700 feet, Lake Powell has a mean depth of 167 feet and a maximum depth of 561 feet. It covers a surface area of 255 square miles and stores a volume of 26,753,000 acre- feet ( Paulson and Baker 1980; USBR 1981). I I. E. 2. Operation. The Bureau of Reclamation's long- range operating criteria for Lake Powell are complex and are undergoing revision. These criteria are required by the Colorado River Basin Project Act ( Public Law 90- 537), which also establishes guidelines for their adoption. The criteria were published in the Federal Register on June 9, 1970, under the title " Criteria for Coordinated Long- Range Operation of Colorado River Reservoirs." They provide guidelines and regulations for coordinated operations of the Colorado River Storage Project reservoirs in the Upper Basin and Lake Mead in the Lower Basin. Operations are administered consistent with applicable federal laws, the United States and Mexico International Boundary and Water Treaty, and interstate compacts and decrees relating to the use of Colorado River water. A formal review of the operating criteria is made by the Secretary of the Interior at least every five years, and annual reports on past and contemplated annual operations are issued by the Bureau of Reclamation. Whenever Lake Powell's storage is equal to or greater than that of Lake Mead's, releases greater than 8.23 million acre- feet annually are made from Lake Powell ( a) to the extent they can be applied to downstream consumptive uses, ( b) to maintain equal storage in Lake Powell and Lake Mead, and ( c) to avoid using the emergency spillways of Glen Canyon Dam. Except during flood conditions, all releases are through the Glen Canyon Power Plant; and when necessary, adjustments in ( a) and ( b) above are permissible to avoid a bypass of water around the Glen Canyon Power Plant ( USDI 1983). I I. E. 3. Reservoir dynamics. With the completion of the initial filling of Lake Powell in June 1980, the water storage capacity of the Colorado River system was increased by two to three years of mean annual discharge. To utilize this resource effectively, the Bureau of Reclamation has applied a two- dimensional reservoir model to evaluate selective withdrawal methods that would meet peaking power needs and maximize 13 |
