WSP07709 - Laserfiche WebLink

Home Browse Search

(I~ , , w ,-,) , .... OJ and geographic location were developed for eacn of the reporting years. Account was tak~n of precipitation and runoff salvage to de- terr(line net evaporation rates. The net evap- oratlon rates were applied against the esti- mates of average annual water-surface area to yielq the values of annual reservoir and stockpond evaporation. An\ exception to this procedure was the de- termination of evaporation from the main stem reser\toirs. Predetermined evaporation rates were applied against historical surface areas to yield values of evaporation on a monthly basis. Export,: Over 99 percent of the water ex- ported, from the Upper Basin is gaged and re- ported!on by the Geological Surveyor water user o~ganizations. The remainder was esti- mated pn the basis of past records or capacity of facilities. Thermal, Electric Uses: Records of water con- sumptively used at thermal powerplants were obtaine~ from the power utility companies. Other US,es: These include livestock usage (excludipg stockpond evaporation), municipal, urban, rural, recreation, and industrial (other , ' than thermal powerplantJ. These items repre- sent onlY, 3 percent of the total Upper Basin use. The)values presented in this report were estimateili by interpolating between 1965 and 1980 lev~ls of use as reported and estimated in the C6mprehensive Framework Study. , \ LOWER COLORADO RIVER Mainstream: The annual consumptive use of water fronl the Colorado River mainstream by the States\and exports from the system were taken from the Bureau of Reclamation annual , report entitled "Compilation of Records in Accordance with Article V of the Decree of the United States in Arizona v. California," dated March 9, 1\964. To these data were credited unmeasured subsurface return flows below Davis Dam,land surface return flows from Las Vegas 'li'ash. Estimated subsurface return flows were ~ased partly on preliminary infor- mation suprtlied by the Task Force on Ground-Wat~r Return Flows. Return flows through las Vegas Wash as a result of Lake Mead diversions into Las Vegas Valley were estimated by the same procedures used in the derivation of the 1975 return flow, as shown in the Article V compilation. For the purpose of this report. all unmeasured subsur- face return flow was credited to irrigation use and divided between California and Arizona based on their respective irrigated areas. Surface water return flow through las Vegas Wash was credited to Nevada's municipal and industrial water uses. Gross evaporation from Lake Mead is esti- mated by the Geological Survey and published in its annual Water Resource Data reports. Deductions for precipitation on the lake sur- face were made on the basis of precipitation at Boulder City, Nev. Net evaporation from Lakes Mohave and Havasu and Senator Wash Reservoir were derived from available evapora- tion and precipitation records and operating data. Since surface-water levels of the remain- ing small impoundments remain relatively constant throughout the year, an annual al- lowance of 36,000 acre-feet for evaporative losses was used throughout the report period. Annual channel losses were estimated as the outflow necessary to balance a simplified budget of inflow and outflow below Davis Dam. Apparent channel losses averaged 280,000 acre-feet annually, using 200,000 acre-feet per year as unmeasured subsurface return flow. Above Davis Dam, an annual channel loss of 100,000 acre-feet was assigned, based in part on information in the Geological Sur- vey Professional Paper 486-0. Releases from Davis Dam are used throughout this report rather than those from Hoover Dam because of an apparent error in the measurement of Hoover Dam releases. Remedial measures are underway to correct this deficiency. Tributaries: Records of measured diversions, re- turn flows, and consumpt-ive use comparable to the mainstream are not available in the tributary areas. Although diversion records are kept by a number of water-using entities, return flows are seldom measured. Most return flows are subsurface in nature and are not 12