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Show XII-56 UPDATING THE HOOVER DAM DOCUMENTS the Colorado River Basin is defined as ". . .all of the drainage area of the Colorado River system and all other territory within the United States of America to which waters of the Colorado River system shall be beneficially applied." The compact divided the Colorado River Basin into two sub-basins-the "Upper Basin" and the "Lower Basin," with Lee Ferry as the division point on the river. Lee Ferry, located in Arizona, is a point in the mainstream 1 mile below the mouth of the Paria River. For the purpose of this report, the Great Divide Basin, a closed basin in Wyoming, and the White River in Nevada have not been considered as part of the Colorado River system. Diversions from the system to areas outside its drainage area are considered herein as exports and have not been classified as to types of use. Beneficial consumptive use is normally construed to mean the consumption of water brought about by human endeavors and in this report includes use of water for municipal, industrial, agricultural, power generation, export, recreation, fish and wildlife, and other purposes, along with the associated losses incidental to these uses. The storage of water and water in transit may also act as losses on the system although normally such water is recoverable in time. Qualitatively, what constitutes beneficial consumptive use is fairly well understood; however, an inability to exactly quantify these uses has led to various differences of opinion. The practical necessity of administering the various water rights, apportionments, etc., of the Colorado River has led to definitions of consumptive use or depletions generally in terms of "how it shall be measured." The Upper Colorado River Compact provides that the Upper Colorado River Commission is to determine the apportionment made to each State by ". . . the inflow-outflow method in terms of manmade depletions of the virgin flow at Lee Ferry. ..." There is further provision that the measurement method can be changed by unanimous action of the Commission. In contrast, article 1(A) of the decree of the Supreme Court of the United States in Arizona v. California defines, for the purpose of the decree, "Consumptive use means diversions from the stream less such return flows thereto as are available for consumptive use in the United States or in satisfaction of the Mexican Treaty obligation." Nearly all the water exported from the Upper Colorado River system is measured; however, the remaining beneficial consumptive use, for the most part, must be estimated using theoretical methods and techniques. In the Lower Colorado River system tributaries to the mainstream, similar methods must be employed to determine the amount of water consumptively used. Reservoir evaporation loss is a consumptive use associated with the beneficial use of water for other purposes. For the purpose of this report, main stem reservoir evaporation is carried as a separate item for the Upper and Lower Basins. Channel losses within the system are normally construed to be the consumptive use by riparian vegetation along the stream channel (or conveyance route) and the evaporation from the stream's water surface and wetted materials. Seepage from the stream normally appears again downstream or reaches a ground water aquifer where it may be usable again. A decided lack of data and acceptable methodology along with the intermittent flow characteristics of many Southwest streams combine to make a reasonable determination of channel loss difficult. Channel losses have not been estimated for this report within the Upper Basin nor on the tributaries of the Lower Colorado River mainstream. Channel losses on the mainstream below Lee Ferry have been estimated primarily by the inflow-outflow method.. Methodology and Data Collection This initial report is based almost entirely on data obtained from ongoing programs and current reports. No new land use surveys were initiated. Available quantitative measurements of water were used wherever their use aided or complemented the determination of consumptive use. 10 |
