The model also was used to evaluate the likely effects of selected water-management alternatives designed to lessen the adverse effects of ground-water pumping on native vegetation. The model was calibrated and verified for water years 1963-88 and used to evaluate general concepts of the hydrologic system and the effects of past water-management practices. The hydrologic system of the Owens Valley can be conceptualized as having three parts: (1) an unsaturated zone affected by precipitation and evapotranspiration (2) a surface-water system composed of the Owens River, the Los Angeles Aqueduct, tributary streams, canals, ditches, and ponds and (3) a saturated ground-water system contained in the valley fill.Īnalysis of the hydrologic system was aided by development of a ground-water flow model of the aquifer system, which is defined as the most active part of the ground-water system and which includes nearly all of the Owens Valley except for the area surrounding the Owens Lake. This report, which describes the evaluation of the hydrologic system and selected water-management alternatives, is one in a series designed to identify the effects that ground-water pumping has on native vegetation and evaluate alternative strategies to mitigate any adverse effects caused by pumping. Native vegetation on the valley floor depends on soil moisture derived from precipitation and from the unconfined part of a multilayered ground-water system. Pumpage from wells needed to supplement water export has increased since 1970, when a second aqueduct was put into service, and local residents have expressed concerns that the increased pumping may have a detrimental effect on the environment and the native vegetation (indigenous alkaline scrub and meadow plant communities) in the valley. Additionally, ground water is pumped or flows from wells to supplement the surface-water diversions to the river-aqueduct system. The city diverts most of the surface water in the valley into the Owens River-Los Angeles Aqueduct system, which transports the water more than 200 miles south to areas of distribution and use. The Owens Valley, a long, narrow valley along the east side of the Sierra Nevada in east-central California, is the main source of water for the city of Los Angeles.
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