Abstract
Pilot Valley is an 828-km2 arid-region endorheic basin in western USA. Bounding mountain ranges rise as much as 1,900 m above the nearly flat 379-km2 playa floor. Up to 3.8 m of Pleistocene Lake Bonneville mud and thin oolitic sand layers form the surface layer of the basin floor. Groundwater conditions were evaluated using data from shallow monitoring wells and borings, springs, infiltrometer measurements, slug and dilution tests, geophysical transects, and precision elevation surveys. Alluvial fan groundwater discharges at fan/playa interface springs and underflows to the shallow basin sediments along the western side of the basin; the groundwater only underflows along the eastern side. Precision surveying established a Lake Bonneville shore-line break in slope as the cause of the spring discharges. Tectonic tilting causes groundwater to flow from east to west and to the topographic low. Monthly measured and pressure transducer data established seasonal pressure responses and upward groundwater gradients. All basin groundwater is lost to evapotranspiration at the topographic low, where a thin salt pan has developed. Groundwater evolves from fresh to hypersaline near the alluvial fan/playa interface where there is an inverted salinity gradient and a groundwater pressure ridge. The pressure ridge and inverted salinity interface are due to: (1) osmotic pressure established between the oolitic sand of high hydraulic conductivity and the overlying low-hydraulic-conductivity lake mud at the fan/playa interface, and (2) the collision between fresh groundwater flow driven by a steep hydraulic head and hypersaline groundwater flow driven by a nearly flat hydraulic head.
Highlights
Endorheic basins are catchments with internal drainage and do not terminate in a marine environment
Field and laboratory investigations included: (1) geophysical studies and lake bed coring to help defined the shallow hydrostratigraphy, the depositional relationships between alluvial fan and lake bed deposits, and the evolution of Lake Bonneville sedimentation (2) the development of a water budget, (3) precision elevation surveying to evaluate the origin of alluvial fan/playa interface springs, and to provide ground surface elevation data for analysis of water levels and the spatial orientation of hydrostratigraphic units, (4) construction of shallow monitoring wells and manual and pressure transducer water level measurements to define horizontal and vertical groundwater flow directions and timing, (5) infiltrometer measurements to determine infiltration rates of alluvial fan, stream channel, and playa sediments, and (6) laboratory determinations of groundwater density
The hydrogeology of the Pilot Valley is typical of endorheic basins in arid, block-faulted regions
Summary
Endorheic basins are catchments with internal drainage and do not terminate in a marine environment. They are found on all continents and cover approximately 20% of the total Earth’s surface (Fig. 1; Dorsaz et al 2013; Nichols, 2007). Most endorheic basins develop in arid regions with drainage networks terminating in alluvial plains, lacustrine mud and salt flats, and fresh to hypersaline lakes (Yechieli and Wood 2002). Groundwater systems in endorheic basins are regulated by water inputs (precipitation, surface water and groundwater inflows), outputs (evapotranspiration and groundwater discharge), structural and stratigraphic relationships, soil texture, groundwater salinity, aeolian processes, and climatic effects (Tyler et al 2006; Tweed et al 2011). Because the average worldwide precipitation in endorheic regions is only 54.1 mm year−1 compared to the average for exoreic regions of 321.5 mm year−1 (Meybeck et al 2001), these regions only account for 2.3% of the total worldwide annual
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
