干旱区生态环境知识资源中心

An essential component to the ground water budget for the Las Vegas Valley (LVV) in southern Nevada is discharge from the ground water system. Discharge for the LVV has been based on estimates made more than 50 years ago of 35,524,224 m(3) per year as evapotranspiration (ET) and 0 m(3) per year as subsurface outflow. Newly published values for recharge based on a more robust data set (70,308,360 m(3)) indicate a large imbalance associated with the earlier discharge estimates, providing the basis for the reevaluation conducted in this study. ET estimates in this study, as opposed to previous studies, were assigned a range in values that included an approach that assigned higher weight to the unique soil, plant, water, and climatic conditions that existed in predevelopment (1905) LVV. The earlier discharge estimates also assumed that the basin was hydrologically closed; however, based on our evaluation, a range in yearly discharge by subsurface outflow from 1,480,176 m(3) to 19,735,680 m(3) could be assigned. Likewise, a range in yearly ET from 20,475,768 m(3) to 78,819,372 m(3) could be assigned. Based on newly published recharge values, closure can only occur if higher values are assigned to both the subsurface outflow and/or ET components of ground water discharge. We cannot provide a complete water balance closure with our ground water discharge estimate of 64,140,960 m(3). However our reevaluation gives support to the higher recharge estimates and provides the rationale for future studies to be conducted based on a more rigorous scientific assessment.