WRIR 01-4195:
Ground-Water Discharge Determined from Estimates of Evapotranspiration,
Death Valley Regional Flow System, Nevada and California
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The Death Valley regional flow system (DVRFS) as delineated by Harrill and others (1988, sheet 1) covers an area of 15,800 mi2 of southern Nevada and southeastern California. This ground-water flow system is west of Las Vegas, Nevada, and includes parts of Clark, Esmeralda, Lincoln, and Nye Counties, Nevada and Inyo and San Bernardino Counties, California. Death Valley, the largest valley within the flow system, forms the southwestern boundary of the flow system.
The DVRFS is centered about the Nevada Test Site (NTS) and Yucca Mountain. The NTS is fairly extensive at approximately 1,375 mi2 and serves as the primary continental location for testing nuclear devices. Yucca Mountain, which borders the NTS on the west, is the site for a potential high-level nuclear waste disposal facility. The U.S. Department of Energy is currently evaluating the risk to the general public associated with past testing activities and the future storage of high-level radioactive waste as required by Federal and State mandates. As part of this evaluation, studies are being done to develop ground-water flow and transport models of the region. The accuracy of these models and confidence given to their results are dependent on an understanding of the region's geology and hydrology. Ground-water discharge is a major component of the hydrology controlling ground-water flow throughout the region.
Accurate estimates of ground-water discharge from the DVRFS are crucial to developing realistic simulations of ground-water flow and contaminant transport away from the NTS and Yucca Mountain. Although early reconnaissance studies completed in the 1960s and 1970s (Malmberg and Eakin, 1962; Walker and Eakin, 1963; Pistrang and Kunkel, 1964; Malmberg, 1967; Cardinalli and others, 1968; Rush, 1968; Winograd and Thordarson, 1975) provide general estimates of regional discharge from many of the major valleys in the region, the methodologies and techniques applied often differed among the various investigations. More accurate and defensible estimates of regional ground-water discharge across the DVRFS require that a more thorough and consistent approach be applied to all major discharge areas within its boundaries.
The U.S. Geological Survey, in cooperation with the U.S. Department of Energy, began long-term studies to refine and improve estimates of mean annual ground-water discharge from the Ash Meadows (Laczniak and others, 1999) and Oasis Valley discharge areas (Reiner and others, 2002). In 1998, the U.S. Geological Survey, also in cooperation with the U.S. Department of Energy, initiated a 2-year effort to extend the knowledge gained and techniques developed during these investigations to estimate ground-water discharge from other major discharge areas throughout the DVRFS. The latter effort is the focus of this report.
The purpose of the study was to reduce uncertainty in estimates of ground-water discharge from the DVRFS by refining existing estimates for most major discharge areas in the flow system (fig. 1). Discharge areas evaluated specifically for this study include Chicago Valley, the Franklin Well area, Franklin Lake, the Shoshone area, Stewart Valley, and the Tecopa/ California Valley area in California and Sarcobatus Flat in Nevada (fig. 1). Estimates for Ash Meadows and Oasis Valley in Nevada, although studied and documented independently as part of more detailed efforts (Laczniak and others, 1999; and Reiner and others, 2002, respectively), are included for completeness. For reasons given in a later section, estimates for other major discharge areas, namely Death Valley in California and Pahrump and Lida Valleys in Nevada, are not given.
The report presents estimates of mean annual ground-water discharge and evapotranspiration, and describes the general procedure used to make the estimates. This effort resulted in many digital products that are available from the USGS node of the National Spatial Data Infrastructure (NSDI). These revised estimates of ground-water discharge can be used to improve general concepts of regional flow and as input to models simulating ground-water flow and transport, and should increase confidence in model-based risk assessments of past, ongoing, or future activities at the NTS and Yucca Mountain site. To provide readers, and flow and transport modelers, with a quantification of the error associated with these estimates, an uncertainty analysis is included as an appendix.
The authors express their appreciation to the U.S. Fish and Wildlife Service, the National Park Service, the Bureau of Land Management, and the many private landowners in the area that openly provided access to their property. The authors wish to thank S.R. Reiner for providing meteorological data and imagery from the Oasis Valley area. Author appreciation also is due to the U.S. Department of Energy for continued support given to this and other investigations of ground-water discharge throughout the Death Valley region.
Much of the land in the Death Valley region is owned and administered by the U.S. Government (fig. 2). The primary stewards of these Federal lands are the National Park Service, U.S. Forest Service, Bureau of Land Management, U.S. Air Force, U.S. Department of Energy, and U.S. Fish and Wildlife Service. Much smaller parcels of privately owned land are concentrated in a few agricultural areas, mining centers, and recreational gateways including Pahrump, Amargosa Farms, Amargosa Valley, and Beatty, Nevada, and Tecopa and Shoshone, California.
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