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Show XH-62 UPDATING THE HOOVER DAM DOCUMENTS tributary areas and into smaller subareas for estimating and computational purposes. A sufficient number of climatic stations are operated to obtain the necessary temperature and precipitation information required for the evapotranspiration formula. Research programs in developing techniques for automatically identifying and measuring irrigated acreage through computer manipulation of satellite digital data may ultimately aid in the assessment of cropped acreage. A weak link in estimating the beneficial consumptive use by agriculture over broad areas is in assessing the actual water supply available, its adequacy as a full supply, and its relationship to consumptive use. Municipal and Industrial: Most of the population residing within the boundaries of the Lower Colorado River system live in metropolitan Phoenix, Tucson, and Las Vegas. These cities and their surrounding environs have the mutual problem of providing an adequate current and future water supply for a growing community in a water-short area. In addition to an almost continuous flow of studies concerning these problems, adequate production and effluent records are usually available to adequately assess water use. Less than 20 percent of the total population is classified as rural having a significantly lesser per capita use of water. In general, the rural population was considered to have a net water use rate of about 30 gallons per capita per day. Consumptive use of water for thermal power generation and the mineral resource industries constitutes about 2.5 percent of the total estimated beneficial consumptive use within the tributary areas. In general, information regarding the annual use of water by the mineral resource industry is inadequate. The increasing trend for recycling and the methods of achieving compliance with quality of water standards are changing. Unit water-quantity requirements for mineral production and processing may have been modified significantly as compared to a decade ago. Reservoir Evaporation: There are adequate records available to estimate the annual evaporation from the major reservoirs in the tributary areas. Information on the fluctuation of water levels in the smaller reservoirs and stockponds is nearly nonexistent. Evaporation from these smaller impoundments has been estimated on the basis of either "full" or "average" capacity prevailing throughout the year. Monitoring water-surface areas through remote sensing techniques may remedy this condition to some extent. Beneficial Consumptive Uses and Losses Summaries of the Colorado River system annual water uses, 1971-75, by States and type of use are shown in tables C-2 through C-6. Water use within the selected reporting areas is discussed below. UPPER COLORADO RIVER Summaries of estimated annual consumptive uses and losses in the Upper Colorado River Basin for each of the reporting years, broken down by State, reporting area, and type of use are shown in tables UC-3 through UC-7. Estimated main stem reservoir evaporation is shown in table UC-1. Agricultural uses accounted for over 60 percent of the total Upper Basin consumptive uses and losses. Irrigated acreage during the 5-year period averaged about 1,470,000 acres, with apparently little variation from year to year. Irrigation consumptive use did, however, show large variations from year to year due to climatic conditions. In 1971 and 1972, precipitation, temperature, and runoff were at or slightly below normal over the Upper Basin as a whole. In 1973, the basin experienced exceptionally large amounts of precipitation along with below-average temperatures. This combination resulted in decreased irrigation needs. Conditions completely reversed in 1974, when near drought conditions prevailed over most of the basin. Irrigation requirements that year were the highest of the 5-year reporting period. A large portion of the irrigation requirement was met with carryover reservoir storage. As table UC-2 shows, major reservoir storage (excluding main stem reservoirs) decreased in 1974 by 16 |
