Evaluation of the hydrologic system and selected water-management alternatives in the Owens Valley, California
Evaluation of the hydrologic system and selected water-management alternatives in the Owens Valley, California
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加利福尼亚州欧文斯谷的水文系统和选定的水管理替代方案的评估
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发表时间：
1998
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影响因子：
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通讯作者：
W. Danskin
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作者：
W. Danskin
欧文斯谷（Owens Valley）是加州中东部内华达州山脉东侧沿着的一条狭长山谷，是洛杉矶市的主要水源。该市将山谷中的大部分地表水转移到欧文斯河-洛杉矶渡槽系统，该系统将水向南输送200多英里至分配和使用区域。此外，地下水从威尔斯井中抽出或流出，以补充地表水分流到河流渡槽系统。自1970年第二条输水管道投入使用以来，补充水出口所需的威尔斯水井抽水量有所增加，当地居民担心增加抽水量可能会对环境和本地植被产生不利影响（本地碱性灌木丛和草地植物群落）在山谷中。谷底的原生植被依赖于来自降水和多层地下水系统的无限制部分的土壤水分。本报告描述了对水文系统和选定的水管理备选方案的评价，是旨在确定地下水抽水对当地植被的影响并评价减轻抽水造成的任何不利影响的备选战略的系列报告之一。欧文斯山谷的水文系统可以被概念化为三个部分：（1）受降水和蒸散影响的非饱和带;（2）由欧文斯河、洛杉矶渡槽、支流、运河、沟渠和池塘组成的地表水系统;（3）山谷填充物中的饱和地下水系统。水文系统的分析得到了“含水层系统”地下水流模型的帮助，“含水层系统”被定义为地下水系统中最活跃的部分，几乎包括欧文斯山谷的所有地区，除了欧文斯湖周围的地区。该模型进行了校准和验证的水年1963年至1988年，并用于评估水文系统的一般概念和过去的水管理措施的影响。该模型还被用来评价为减少抽取地下水对当地植被的不利影响而选定的水管理备选办法可能产生的影响。模型模拟的结果证实，水文系统的重大变化是由1970年开始从山谷中额外输出的水引起的。地下水的平均抽水量增加了五倍，泉水的流量几乎减少到零，欧文斯河以前从含水层系统获得水的河段开始失去水，本地植物的总蒸发量减少了约35%。自1988年以来，水资源管理实践都是使用该模型进行定义和评估的。模拟结果表明，自1985年以来，欧文斯山谷内的增强和缓解项目增加地下水抽水进一步强调含水层系统，并导致地下水位下降，减少蒸散。大部分地下水位下降发生在西部冲积扇之下和生产威尔斯井附近。由于水文缓冲区，如蒸散、泉水和永久性地表水特征，谷底以下的地下水位高度随着时间的推移保持相对恒定。
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. 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. Additionally, ground water is pumped or flows from wells to supplement the surface-water diversions to the river-aqueduct 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. Native vegetation on the valley floor depends on soil moisture derived from precipitation and from the unconfined part of a multilayered ground-water system. 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. 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. Analysis 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. 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 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. Results of the model simulations confirm that a major change in the hydrologic system was caused by the additional export of water from the valley beginning in 1970. Average ground-water pumpage increased by a factor of five, discharge from springs decreased almost to zero, reaches of the Owens River that previously had gained water from the aquifer system began losing water, and total evapotranspiration by native plants decreased by about 35 percent. Water-management practices as of 1988 were defined and evaluted using the model. Simulation results indicate that increased ground-water pumpage since 1985 for enhancement and mitigation projects within the Owens Valley has further stressed the aquifer system and resulted in declines of the water table and reduced evapotranspiration. Most of the water-table declines are beneath the western alluvial fans and in the immediate vicinity of production wells. The water-table altitude beneath the valley floor has remained relatively constant over time because of hydrologic buffers, such as evapotranspiration, springs, and permanent surface-water features.