Hydrology of the Walker River Basin

Science to Sustain At-Risk Terminal Lakes

Walker Lake is one of the few perennial, natural terminal lakes in the Great Basin. Terminal lakes are surface-water drainage in topographically closed basins. Under natural conditions, evaporation from the lake surface typically is the primary component of basin outflow. Due to high evaporation rates in the Great Basin, the water-levels and salinity of terminal lakes are extremely sensitive to changes in streamflow. Most streamflow in the Walker River Basin originates as snowmelt from the Sierra Nevada. Prior to the late 1800s, most of the water flowed into Walker Lake. Since then, agricultural diversions have increased to the point that, except during flood flows, most streamflow is consumed by agriculture. Between 1882 and 1994, upstream diversions contributed to the decline of Walker Lake of about 140 feet and the total dissolved solids (TDS) concentrations increase from 2,500 mg/L to 13,300 mg/L. In 2004, the TDS was about 15,000 mg/L. Compared to the Great Salt Lake, Walker Lake is relatively fresh and supports a diverse ecosystem including the threatened Lahontan cutthroat trout (LCT). The LCT has adapted to the high TDS of terminal basins. However, diversions have contributed to the lowering of Walker Lake and increased TDS to concentrations that threaten its survival.

The ecosystems and recreational uses of Walker Lake and other terminal lakes in the Great Basin have become at-risk due to consumptive water use. The goal of section 2057 of Public Law 107-171 is to provide water to selected at-risk terminal lakes in Nevada in order to sustain their ecosystems. This study will provide scientifically sound data and tools to parties involved in the Walker River Mediation so they can evaluate alternatives for supplementing flow to Walker Lake.