OCR Text |
Show __3__ Another term used in studies of water consumption is streamflow depletion. Streamflow depletion is the annual quantity of water that enters a valley, or flows to a land area, minus the annual quantity that leaves the valley, or flows off the land area. It usually is less than consumptive use. It may be expressed as an average rate of flow or converted to depth over the area considered. Evapo-Transpiration Measurements. Measurements of evapo-transpiration have been made for various crop plants and native plants growing in tanks or lysimeters. Determinations for different crops and different types of native vegetation, growing separately or together, have been made on field plots, sections along streams, irrigated farms, irrigation projects, portions of river valleys, and entire drainage basins. In general, methods of evaluating evapo-transpiration involve determinations of inflow, outflow, and changes in quantities of moisture stored underground. In tank tests, water is supplied as needed to maintain normal plant growth, or to maintain water tables at definite depths. In lysimeter tests, percolation is measured and deducted from quantities of water supplied by irrigation or precipitation. In plot tests, water supplied by irrigation or precipitation is measured and portions consumed by plants determined from analyses of soil samples. Plot tests are practicable only when water tables are too deep to be reached by downward movements of moisture following irrigation or rainfall. For relatively large areas, determinations of evapo-transpiration are based on measurements of precipitation, streamflow, irrigation deliveries, drainage outflows, changes in elevation of water tables, and differences in amounts of water stored in the soil. The method of de- |
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Original book: [State of Arizona, complainant v. State of California, Palo Verde Irrigation District, Coachella Valley County Water District, Metropolitan Water District of Southern California, City of Los Angeles, California, City of San Diego, California, and County of San Diego, California, defendants, United States of America, State of Nevada, State of New Mexico, State of Utah, interveners] : California exhibits. |