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Geology of the National Parks - Death Valley

 

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Furnace Creek: Focus on Water

Saratoga Springs
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Islands of life

These pages are excerpted from a 1998 report on Wetland and riparian resources of Death Valley National Park and their susceptibility to water diversion activities, by Douglas L. Threloff, NPS).

Wetland and riparian areas are two of the rarest and most biologically diverse habitat types in the Mojave Desert. This generalization is based on the fact that 1) the presence of surface water infrequently occurs in an environment where rainfall levels on the valley floors rarely exceed five inches per year, and 2) many plant and animal species have physiological or life history traits which force them to reside in or directly adjacent to permanent sources of water.

The biological importance of stable and permanent water sources is particularly apparent in the vicinity of Death Valley National Park along the border of California and Nevada . Infrequent lush oases which exist in the Park as a result of spring discharge water are in obvious contrast to the dry, often barren landscapes immediately adjacent to wetland habitats. Even the casual observer can not help but notice that plant cover and animal activity is dramatically greater in these rare desert 'islands‘.

Unlike many locations across the Mojave Desert, many of the water dependent Death Valley habitats possess a diversity of plant and animal species that are not found anywhere else in the world. The existence of these species is due largely to a unique geologic history and the process of evolution that has progressed in habitats that have been isolated from one another since the Pleistocene epoch.

Desert dilemma

The same water sources that create habitat for plants and animals also tend to attract and promote human developments. Many of the larger cities and towns in the desert are experiencing significant growth. Since the region does not possess abundant surface water, much of the growth depends on the exploitation of ground water. As the water demands that are associated with industry and growing populations increase, impacts to ground water tables and spring discharges typically occur. Such activity has the potential to impact biological features that also rely on the same finite water supply.

Regional Hydrology of the Death Valley Ground Water Flow System

Principal springs along the eastern side of Death Valley National Park are fed by a regional carbonate rock ground water flow system. The size of this flow system is relatively large and includes 15,800 square miles in southern Nevada and California (PAL 1997). This same aquifer also supplies the majority of water for springs in the Ash Meadows National Wildlife Refuge area east of the Park boundary (Map 2). At least a portion of the water from the carbonate rock and associated valley fill aquifer(s) also is the source of ground water that feeds the Death Valley playa. This portion of the paper only highlights some of the pertinent attributes that are associated with the regional hydrology. Numerous references provide detailed narratives on the extent and characteristics of the flow system (Winograd and Thordarson 1975, Harrill et. al. 1988, Bedinger et. al. 1989, D'Agnese 1994).

The regional aquifer derives its recharge from precipitation that falls in the higher elevation, more northerly areas of the flow system. Ground water movement through the aquifer is generally from north to south through fractured limestone and volcanic rocks or thick alluvial deposits in the valleys. In south central Nevada, the aquifer is believed to bifurcate. At least one of the resulting flow paths ultimately terminates at the Death Valley playa. The full extent and depth of the aquifer system is unknown, and the complexity of the geology precludes a detailed understanding of the mechanics of water movement at the present time.

Water that passes through the aquifer and ultimately comes to the surface is expressed as point sources (springs or seeps) or as broad, diffuse discharge areas (playa or alkali-encrusted salt flats). Local wetland areas are subject to high rates of water loss through evaporation or plant transpiration (Dudley and Larson 1976). Maintenance of local wetlands during the summer months therefore require large volumes of water when summer temperatures exceed 105¦ Fahrenheit and annual pan evaporation rates are on the order of 100 inches per year.

Recharge to the aquifer at the present time is very limited. This fact is due to the relatively recent (less than15,000 years) development of a desert climate (Grayson 1993). As precipitation rates have declined, so have surface water percolation rates. Hence, the majority of water which issues at spring sources is the result of precipitation that fell thousands of years ago.

Travel times from up-gradient recharge areas (mountains) to down-gradient discharge areas (springs and playas) are generally believed to be on the order of thousands, if not tens of thousands of years (Mr. Doug Bedinger, pers. comm.). Conversely, the time response of individual ground water basins to pumping activities is much more rapid. These two factors combine in such a way as to suggest that while ground water storage capacities can be depleted in a relatively short period, long periods of time are necessary for replacement water to move in from unaffected up-gradient areas.

Human Reliance on Ground Water

Because human developments in the desert are reliant on substantial volumes of water, large-scale ground water pumping activities have been initiated in numerous areas in order to meet commercial, municipal, and agricultural needs (Map 3). Such activities cumulatively have the potential to deplete aquifer capacities and reduce spring discharge rates. Reduced spring flows in turn have the potential to impact biological features that also rely on a finite supply of water.

Several cities within the boundary of the regional ground water flow system are currently experiencing some of the fastest growth rates of any place in the United States. Notable examples within a 100-mile radius of Death Valley National Park include Las Vegas and Pahrump, Nevada. In the case of Las Vegas, the local Chamber of Commerce estimates that 6,000 people are moving to the city every month. Between 1985 and 1995, the population of the Las Vegas Valley increased from 550,700 to 1,138,800.

A similar situation is also occurring in the Pahrump Valley 60 miles east of the Park. This valley is currently experiencing an enormous phase of growth where the human population has risen from 8,000 to 24,000 between 1989 and 1997. Coincident with this growth is the installation of a large number of ground water wells. Forecasts suggest that annual growth rates of 13-18% for this town are likely to continue into the next century.

Many, if not all, of the commercial ventures in the planning or development phases east of the Park boundary will be completely dependent on ground water supplies. These facilities include the Longstreet hotel/casino/RV park/golf course between Death Valley National Park and Ash Meadows National Wildlife Refuge, and the development of two hay producing dairy farms in the Amargosa Valley. Serious consideration is also being given to establishing Timbisha Shoshone Indian tribe reservation trust lands at three or more sites which border the eastern side of the Park. If wells from any of these developments tap into the carbonate rock or valley fill aquifers, there may be potential impacts to springs flows or water tables inside the Park (PAL 1997).

At least one large-scale and several small-scale industrial developments are also being planned or have been developed in the local area and use ground water. The most notable example is the possible development of the nation's high level nuclear waste repository near Yucca Mountain. Water for this facility would be necessary to support infrastructure development and long-term management of stored nuclear waste. At least a few mining operations in Nevada have operations up-gradient of the Park. Examples include the Bond Gold (Barrick Bullfrog) Mine near the town of Beatty and the Rayrock Mine in the Crater Flats area near the Nevada Test Site.

While many of the above-mentioned facilities may or may not have a significant ability to individually impact the volume of water in the aquifer, they collectively have a potential to remove huge volumes of water from this limited source. In the Amargosa Valley alone, the Nevada State Engineer estimated that 2,660,393,604 gallons were pumped from the local aquifer in 1992. Much of this water does not percolate back into the ground, and is permanently lost to the atmosphere through evaporation.

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