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Master of Science (M.S.)
Year Degree Awarded
Month Degree Awarded
Density dependent flow occurs in areas where high-salinity groundwater interacts with low-salinity groundwater to create a brine-to-freshwater interface that defies common assumptions about groundwater movement. Yet the geologic and hydrologic factors that impact interface dynamics and migration remain poorly defined. With less than 20 mm•yr-1 of precipitation and with an extremely dense (i.e. 1.2 g•cm-3) naturally occurring brine, Chile’s Salar de Atacama (SdA) provides an excellent analog for exploring interface dynamics in other arid regions. Site-specific 2-D models of the interface in the southeastern region of SdA, with interpretations of the hydrostratigraphic framework, provide an analysis for density-driven response rates to climatic change. A separate parametric, equally probable series of distributions of hydraulic conductivity provides a means for expanding analysis to other similar arid salar (i.e. “salt flat”) environments. Comparing the modeled interface’s geometry and response to perturbations in the rates of lateral recharge in each hydrostratigraphic realization yields insight into the dynamics of interface migration to coupled climatic and geologic conditions. Changes in hydrologic conditions, informed by paleoclimatic interpretations and previously modeled climate predictions, are introduced to each hydrostratigraphic realization following the interface reaching an initial dynamic equilibrium, and the interface’s response is assessed subsequent to it reaching a new dynamic equilibrium. Metrics for model evaluation include migration rate, change in the interface’s areal extent, change in interface slope, and the response rate following the introduction to a perturbation in the aquifer’s hydrology. Model analyses suggest that evaporation rates strongly control the interface’s geometry and sensitivity despite climatic and geologic conditions; continuity of high-permeability pathways controls interface slope; increasing continuity also decreases interface stability in terms of time required to reach a new steady state. While these results have implications for interface dynamics in both salars specifically and arid climates in general, they also indicate the importance of considering hydrostatigraphic continuity for saline water intrusion in coastal regions. They also provide a compelling method for assessing interface dynamics in other climatic and geologic conditions.
McKnight, Sarah, "The Climatic and Hydrostratigraphic Controls on Brine-to-Freshwater Interface Dynamics in Hyperarid Climates: A 2-D Parametric Groundwater Modeling Study" (2019). Masters Theses. 785.