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Walker River basin and Walker Lake hydrologic studies help water managers
Released: 9/16/2009 6:57:26 AM

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U.S. Department of the Interior, U.S. Geological Survey
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New hydrologic studies in the Walker River basin and Walker Lake will guide policy makers in the management of scarce water resources. Agricultural practices between 1882 and 2008 resulted in a significant drop in Walker Lake’s water level, and caused the Lake to become more saline. The increase in salinity threatens the survival of the Lahontan cutthroat trout, a native species listed as threatened under the Endangered Species Act. A scientific study to assess the complex sources of water inflow, evaporation, and groundwater interactions indifferent parts of the drainage basin is now complete.

The U.S Geological Survey began a study in 2004 to better understand the hydrology and refine the water budget of the Walker River basin and Walker Lake.  The study focused on the lower Walker River basin from the Wabuska streamflow-gaging station in northern Mason Valley to Hawthorne, Nevada.  Two new reports by the USGS provide the results of this study.

The first describes the hydrology of the Walker River basin and a conceptual hydrologic model of the relations among streams, groundwater, and Walker Lake.  Surface-water/groundwater interactions and groundwater flow directions in Smith and Mason Valleys, the most agricultural part of the Walker River basin, are also described.  The hydrology of the lower Walker River basin is considerably different than the basin upstream from the Wabuska gage.  The upper basin consists of valleys separated by consolidated-rock mountains.  The alluvial aquifer in each valley thins or pinches out at the downstream end, forcing most groundwater to discharge along the river near where the river is gaged.  The lower Walker River basin is one surface-water/groundwater system of losing and gaining reaches from Wabuska to Walker Lake, which makes determining stream losses and the direction and amount of subsurface flow difficult.

In the second report, water budgets were calculated to provide managers a range in supplemental inflows needed to maintain dissolved-solids concentrations at 8,000, 10,000, and 12,000 milligrams per liter (mg/L). From about 700,000 to 2,000,000 acre-ft are needed to dilute the lake to these concentrations from the current (2008) concentration of 17,000 mg/L. From 26,000 to 53,000 acre-ft/yr of supplemental inflow is needed to maintain concentrations of 8,000 to 12,000 mg/L.

Surface and subsurface inflow to Walker Lake total 130,000 acre-ft/yr. Virtually all outflow is evaporation from the lake and totals 162,000 acre-ft/yr. The difference between inflow and outflow is -32,000 acre-ft/yr. Storage change estimated directly is -29,000 acre-ft/yr for an imbalance of 3,000 acre-ft/yr (2 percent), which is insignificant statistically so the water budget balances.

Water budgets for the Walker River basin are based on average annual flows for a 30-year period (1971–2000).  Total surface-water inflow to the upper Walker River basin upstream from Wabuska was 387,000 acre-feet per year (acre-ft/yr).  About 223,000 acre-ft/yr (58%) is from the West Fork of the Walker River; 145,000 acre-ft/yr (37%) is from the East Fork of the Walker River; 17,000 acre-ft/yr (4%) is from the Sweetwater Range; and 2,000 acre-ft/yr (less than 1%) is from the Bodie Mountains, Pine Grove Hills, and western Wassuk Range.  Outflow from the upper Walker River basin is 138,000 acre-ft/yr at Wabuska.  About 249,000 acre-ft/yr (64%) of inflow is diverted for irrigation, transpired by riparian vegetation, evaporates from lakes and reservoirs, and recharges alluvial aquifers.

Walker Lake is the lowest point in the basin and the terminus of the Walker River.  Between 1882 and 2008, agricultural diversions resulted in a lake-level decline of more than 150 feet and storage loss of 7,400,000 acre-ft. Evaporative concentration increased dissolved solids from 2,500 to 17,000 milligrams per liter.

The reports are available on-line:

Hydrologic Setting and Conceptual Hydrologic Model of the Walker River Basin, West-Central Nevada
USGS Scientific Investigations Report 2009–5155

Water Budgets of the Walker River Basin and Walker Lake, California and Nevada
USGS Scientific Investigations Report 2009–5157

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