Date of Award:

5-1989

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Committee Chair(s)

Christopher J. Duffy

Committee

Christopher J. Duffy

Committee

Roland Jeppson

Committee

Joseph Koebbe

Abstract

The Great Basin is a region of the Basin and Range Physiographic Province, which is completely isolated hydrologically from the sea. All precipitation that falls within the Great Basin is lost from the land surface or from the surface of closed inland lakes through evapotranspiration. Playas are often found at the base of these undrained basins. This study focuses on subsurface groundwater flow patterns in closed basins. Because all discharge from the basins occurs via evapotranspiration on and near the playa, the water table of the aquifer beneath the playa is often just below the ground surface. Fluctuations of the water table due to climatic events cause the water table to rise and dissolve the salts on the playa surface. This mass transfer can produce density gradients that in turn cause flow.

This study is an extension of the work performed by Duffy and Al-Hassan (Duffy and Al-Hassan 1988) in which numerical experiments were used to show that the free convection, caused by the variation in density of the bulk fluid properties, appears to play an important role in determining the patterns of groundwater flow beneath the playa. Their work considered only homogeneous, isotropic porous media in symmetric basins. The effects of anisotropy, periodic stratification, and asymmetric basins on the groundwater flow and transport patterns was studied here. Dimensionless parameters, the Rayleigh number and the salt nose length, L0*, were defined for each of the systems incorporated and were shown to be linearly related. The implication of this relationship is that the Rayleigh number can be used to predict basin-scale circulation patterns in the hypothetical closed basins studied. It was also determined that an equivalent anisotropic system could be defined for a horizontally stratified aquifer in order to predict basin-scale circulation patterns. An equivalent isotropic system was defined for each anisotropic system in a similar manner.

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