Coupled surface-subsurface flow model

When investigating the fate of flow in the Trinity River Delta (TX), evidence revealed possible contribution to the surface water budget from the subsurface. Thus the FrehdC model is being further developed to enable simulation of surface-subsurface flow exchange.

 

As a first step, a novel numerical solution to the 1D Richards equation is proposed to achieve conservative, efficient and robust simulations for variably-saturated subsurface flow. The new method applies a predictor-corrector type numerical scheme with a post-allocation procedure to enforce mass conservation. This method is still being improved to enable 3D simulation with coupled surface hydrodynamics. The figure below shows validation of the proposed method (PCA) against Hydrus-1D and Warrick's analytical solution using an infiltration problem.

For more info:

  • Li, Z., Ozgen, I. and Maina, F.Z., 2021, A mass-conservative predictor-corrector solution to the 1D Richards equation with adaptive time control, Journal of Hydrology, (592)12580

In the second step, a variably-saturated groundwater solver (with the PCA method) is coupled to the FrehdC model to simulate surface-subsurface exchange. The new model is named Frehg. The first application of the Frehg model is to investigate the discrepancies in modeled surface-subsurface exchanged caused by using simplified surface flow equations (i.e. diffusive wave vs. full shallow water equation). Ongoing development of Frehg focuses on simulating density-driven surface and subsurface flow, which will help us to understand the salt dynamics in coastal regions. 

For more info:

  • Li, Z. and Hodges, B. R., 2021, Revisiting Surface-Subsurface Exchange at Intertidal Zone with a Coupled 2D Hydrodynamic and 3D Variably-Saturated Groundwater Model, Water, submitted
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