Surface-groundwater flow numerical model for barrier beach with exfiltration incorporated bottom boundary layer model

A surface-groundwater flow model is developed for the swash flow on a barrier beach. The non-linear shallow water equations are used to simulate the surface flow. Laplace's equation is used to describe the groundwater flow and is solved using the Boundary Integral Equation Method to provide potential heads and normal potential derivatives at and within the boundaries of the barrier. An exfiltration incorporated bottom boundary layer sub-model is used to obtain bed shear stress. The groundwater model is verified against the numerical test results in Kazemzadeh-Parsi and Daneshmand (2012) for the groundwater flow through a rectangular dam. The coupled surface-groundwater model is validated against the prototype-scale BARDEX II experimental results (Turner et al., 2016). The steady-state groundwater flow comparisons show excellent agreement in phreatic surfaces. The comparisons of groundwater flow under the action of waves show reasonably good agreement with experimental results in phreatic surfaces. The simulated time averaged pore velocities for the runs with and without waves are in satisfactory agreement with experimental results in general, and certain discrepancies are observed near the beach side. The bed shear stress variation due to exfiltration is investigated by incorporating the modified logarithmic bottom boundary layer model of Cheng and Chiew (1998) in the coupled surface-groundwater flow model. The results confirm that as exfiltration increases, bed shear stress decreases as a result of thickening of the bottom boundary layer.