Texas A&M University
The high-degree of geological heterogeneity and hydraulic-connection with Brazos River associated with the Brazos River Alluvium Aquifer, Texas USA, has led to varied hypothesis about its groundwater flow system. The most conductive middle portion of the alluvium, comprised of sand and gravel, is separated from underlying aquifers by low-permeability shale. A surficial clay layer causes localized confinement in the otherwise unconfined aquifer and also effects recharge from the surface. River morphology and intense seasonal flow regimes, further add to the challenges in modeling the flow system. This study seeks to compare several conceptual models of river-aquifer interactions in order to determine the paradigm that best fits current data, which includes conditions during the 2011 drought and flooding from Hurricane Harvey. A range of probable conceptual models are numerically modeled using small-scale fine grid 2D-transects in a variably saturated code, HYDRUS. To start, conceptual models with simple geometries and boundary conditions, incorporating few processes and parameters, are tested against observed water-table data. Each time modeled results fail to fall close to the data, conceptual model is revised by adding new possible factors/processes instead of parameter calibration. (Parameters and processes made more complex include aquifer lithology, river morphology, riverbed geology, seepage face geometry, confined vs. unconfined conditions, inter-aquifer exchange, and groundwater recharge.)This approach provides a systematic way to narrow down important factors that controls river-aquifer interaction under certain conditions and also involves less parameterization. Such a study will not only deepen our understanding about flux exchange dynamics of the system but will also set a range of guidelines for future modeling and management endeavors.
Texas A&M University
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