Simulation of Solute Transport under Changing Gradient of Water Table

Abstract

Solute transport in aquifers is usually controlled by dynamic changes in groundwater tables. The influence mechanism of surface hydrological processes, especially precipitation, on solute transport under different water table conditions has not been studied much. Prior to the direct application of the existing solute transport mechanisms and models to the solute transport process, the following questions need to be addressed: (1) Do surface hydrological conditions (e.g., precipitation) cause changes in the gradient of the water table within a specific region? (2) If the gradient of the water table does change, how does the change influence solute transport and distribution in the aquifer? The objective of this study is to investigate how precipitation impacts the gradient of water table and to analyze how the solute transport is influenced by the change in the gradient of water table. To achieve this, we employed an analytical solute transport model for the time-varying gradient of a water table through continuous multipoint monitoring of the groundwater table data. Further, the model was applied to indoor experiments to simulate solute transport with and without precipitation. Finally, the mechanism of solute transport in the aquifer under the changing gradient of the water table was analyzed using mathematical and physical models, and the modeling results were compared with those from a numerical model to analyze the modeling reliability. The results showed that precipitation changed the previously stable gradient of the water table, which further altered the gradient of the water table and the transport path of the tracer. The tracer transport direction was primarily controlled by the flow direction in the sandy aquifer trough without precipitation. However, the route of the tracer transport was consistent with the direction of the change in the water table gradient due to precipitation. The small discrepancy between the results from the analytical and numerical models indicates that the model employed in this study is reliable.