A REEVALUATION OF THE GROUND WATER BUDGET FOR LAS VEGAS VALLEY, NEVADA, WITH EMPHASIS ON GROUND WATER DISCHARGE¹

Abstract

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 LW has been based on estimates made more than 50 years ago of 35,524,224 m3 per year as evapotranspiration (ET) and 0 m3 per year as subsurface outflow. Newly published values for recharge based on a more robust data set (70,308,360 m3) 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) LW. 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 m3 to 19,735,680 m3 could be assigned. Likewise, a range in yearly ET from 20,475,768 m3 to 78,819,372 m3 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 m3. 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.

Relationships Between Water Table and Model Simulated ET

“…Although the water table was below 7.9 m from the land surface, model outputs and water table fluctuations still showed a good relationship. Previous studies have reported similar relationships for the shallow water tables (Nichols ; Devitt et al ; Sophocleous ). This may be due to regular pumping of groundwater into the surface that acts as a linkage between water table and ET.…”

Effects of long-term water table drawdown on evapotranspiration and vegetation in an arid region phreatophyte community

“…Water table depth is often cited as a principal factor controlling ET rates in phreatophyte communities (Robinson, 1958;Emery, 1970;Sala et al, 1996;Devitt et al, 2002;Nichols, 2000); however, little is known about this response. Thus, it is hard to predict changes in ET rates for any site that could result from a change in the position of the water table.…”

Multiyear riparian evapotranspiration and groundwater use for a semiarid watershed

“…Riparian ET can be derived from surface water sources like recently fallen precipitation in the streams and vadose zone and from groundwater sources acquired by phreatophytic plants or directly evaporated from base flow in the river. Accurate estimates of ET at watershed and basin scales are necessary for sound water resource management, especially in basins where there is limited water to support human communities and natural riparian ecosystems (e.g., Devitt et al, 2002;Lines and Bilhorn, 1996;Scott et al, 2000;Steinwand et al, 2006;Westenburg et al, 2006). Over the last decade, many studies in the western US have advanced the understanding of riparian ET by making direct micrometeorological and physiological ET measurements for different riparian cover types Dahm et al, 2002;Devitt et al, 1998;Gazal et al, 2006;Schaeffer et al, 2000;Scott et al, 2000Scott et al, , 2004Scott et al, , 2006aUnland et al, 1998).…”