## 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 figure below shows validation of the proposed method (PCA) against Hydrus-1D and Warrick's analytical solution using an infiltration problem.

In the second step, the subsurface solver is coupled with the FrehdC model, forming a high-performance surface-subsurface flow model named Frehg. Detailed description of the Frehg model can be found in the references listed below. The Frehg model will be used to perform coupled surface-subsurface flow over complex topography at multiple spatial scales.

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
- 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, 13, 902