Precipitation Zones of West-Central Nevada

Thomas J. Lopes and Rose L. Medina

ABSTRACT
Whether Nevada can sustain its fast rate of growth depends in part on accurately quantifying the amount of water that is available, including precipitation. The Precipitation-Zone Method (PZM) is a way of estimating mean annual precipitation at any point. The PZM was developed using data from west-central Nevada and northeastern California, but preliminary analysis indicates it can be applied to the entire state. Patterns in the spatial distribution of precipitation were identified by mapping station locations and plotting 1971-2000 precipitation normals versus station elevation. Precipitation zones are large areas where precipitation is linearly related to elevation. Four precipitation zones with different linear relations were delineated; these zones cover much of west-central Nevada. Regression equations with adjusted R2 values of 0.89 to 0.95 were developed for each zone. All regression equations estimate similar precipitation rates at 4,000 feet, but the slopes of the regression equations become progressively shallower to the south. A geographic information system, 30-meter digital elevation model, and the regression equations were used to estimate the distribution and volumes of precipitation in each zone and in hydrographic areas of the Walker River Basin. Comparison between the PZM and Parameter-elevation Regressions on Independent Slopes Model (PRISM) indicate PRISM estimates are linearly related to elevation at low elevations in each zone, but PRISM estimates become non-linear at high elevations and are up to 2.5 times greater than the normals. However, PRISM under-estimates more than it over-estimates precipitation compared to the PZM. The PZM estimated the same or larger volumes of precipitation compared to PRISM in three of the zones, and the larger volumes mostly were from areas that receive greater than 15 inches/year of precipitation. Additional work is needed to accurately estimate mean annual precipitation throughout Nevada.

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Environmental Hazards Associated with Historic Mining on Water Quality in Nelson, Nevada

Douglas B. Sims and Brett C. Bottenberg

ABSTRACT
The present study focuses on the potential environmental hazards of historical mining within Nelson, Nevada, located 45 miles south of Las Vegas, Nevada. Historical mining practices in this area included extraction processes that produced large quantities of naturally occurring heavy metals due to concentration techniques utilizing cyanide, mercury, acids, bases and solvents. Milling processes of the time focused on the removal of the precious metals from milling slurry through several stages. The unusable portion of the slurry and processed ore residual (i.e. the mill tailings) can contain high concentrations of mercury, barium, copper, chromium, arsenic, lead and cyanide. During the operation of these mines, there were little, if any, environmental regulations governing the transport and disposal of waste rock and/or mill tailings. The materials were commonly disposed of in large piles adjacent to the mine or milling sites with little, if any, consideration to isolation or containment. Waste and tailings were typically placed in the most practical and convenient locations, often in washes or drainage channels. Deposited material is susceptible to being transported downstream in response to run off from storm events flowing in these washes. On September 14, 1974, a large storm event hit the town of Nelson. During that storm, it was reported that a wall of water traversed through the Eldorado Canyon and later rose to 30-40 feet at the mouth of the Eldorado Canyon at Nelsons Landing (Martin et al, 1974; Valentine, 2004). The flood waters generated in the upper Eldorado canyons flowed through the former mining areas and may have transported mining related waste to Lake Mohave at Nelson’s Landing.

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California and Nevada Geographic Response Maps for Lake Tahoe, Truckee, Carson, and Walker River Basins

John Watermolen and Mark Lampinen

ABSTRACT
Geographic Information Systems play a critical role in helping first responders and incident commanders make better decisions and communicate what resources are needed to contain any type of potentially hazardous spill. The Nevada Division of Environmental Protection and the California Department of Fish and Game Office of Spill Prevention and Response, facilitated by the U.S. Environmental Protection Agency, Region 9, cooperated to provide seamless maps and exchange of data to help emergency responders with Geographic Response Plans for the Truckee River, Carson River, Walker River, and Lake Tahoe Basins.

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