I predict and model saline-to-freshwater interfaces under different climatic and geologic conditions
A lot of research has focused on the intrusion of saltwater, also known as brine, in coastal regions because of drinking water concerns. However, saltwater also develops beneath inland deserts, where high rates of evaporation creates groundwater with high salinity. For example, the aquifer underlying the southeastern extent of an arid salt flat known as Salar de Atacama (SdA) in northern Chile contains an 8 km-long interface between fresh and saline fluids that exhibits a slope of approximately 5 degrees. Homogenous, isotropic models fail to capture this geometry, predicting slope angles for an interface at approximately 42 degrees. I investigate the conditions that impact brine-to-freshwater interface dynamics. Those conditions include both hydrologic factors, such as increasing rates of evaporation and decreasing rates of recharge, and geologic factors, such as faulting and low-permeability layers of rock. I use the USGS-made SEAWAT program to model how the interface responds to those different hydrologic and geologic factors, and I then compare those results to the field conditions that I observe. Metrics for evaluating interface response include slope angle, migration rate, and time to reach dynamic equilibrium. From this modeling, I expect saltwater creep to occur when recharge is less than average, which will likely happen in many deserts as a result of climate change. I also expect that geologic layers with low permeability will encourage the horizontal migration of the salt-to-freshwater interface by acting as a sort of platform that supports the denser brine’s expansion beneath the fresh groundwater. For now, I am focusing on SdA, but I look forward to extending this work to other desert regions as well. Results from my work has implications for the stratigraphic impact on brine migration, arid hydrogeology under changing climate conditions, and groundwater development in brine-rich, arid regions.
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