Chloride mass balance as a method for determining long-term groundwater recharge rates and geomorphic-surface stability in arid and semi-arid regions, Whisky Flat and Beatty, Nevada
AuthorFouty, Suzanne C.
Groundwater recharge -- Arid regions.
Groundwater recharge -- Nevada.
Geomorphology -- Nevada.
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PublisherThe University of Arizona.
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AbstractThe chloride mass-balance method can be used to evaluate long-term groundwater recharge rates, geomorphic-surface ages, modern and past root and percolation depths, and surface stability in arid and semi-arid regions. The variation of chloride concentration with depth in the soil forms the basis of the method. This variation is graphically portrayed as chloride versus depth and cumulative chloride versus depth plots. Both plots have an upper zone where chloride is concentrated by evapotranspiration and a lower zone which represents water and solute flux below the roots. Previous studies using the mass-balance method have assumed constant precipitation and chloride inputs through time, and invoked piston flow as the mechanism of water and solute transport. These assumptions are not valid in semiarid and arid regions, In unsaturated, heterogeneous sediments, or over thousands of years. Uncertainties In precipitation and chloride inputs limits the precision of long-term recharge-rate and surface-age calculations because the calculations are highly sensitive to the precipitation and chloride inputs, and bulk density values selected. The chloride method should be restricted to unconsolidated sediments to minimize the occurrence of fracture flow and runoff that complicate surface-age and recharge calculations for consolidated sediments. Surface-age calculations, using this method, are only valid for stable, nonaggrad.tng surfaces. Recharge calculations are valid only in zones where chloride concentrations at depth reflect secondary chloride.