Abstract
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.
Highlights
The swash zone is a dynamic region that is alternately covered and uncovered by waves
One main difference of the present work from Li and Barry (2000) is that a comprehensive bottom boundary layer model (Cheng and Chiew, 1998), which considers the effects of exfiltration, is incorporated in the coupled surface-groundwater flow model, while the Chezy law was employed in Li and Barry (2000)
We further examine the effects of exfiltration on bottom boundary layer evolution and on bed shear stress using log-law model in Cheng and Chiew (1998), which is applicable for exfiltration only
Summary
The swash zone is a dynamic region that is alternately covered and uncovered by waves. The water level changes in the lagoon can induce groundwater dynamics near the beachface, which can subsequently affect seepage flow into (or out of) the beach. The work is mostly related to porous flow in coastal structures, the model could be applied to gravel barrier beaches Another coupled surface-subsurface flow model is that by Steenhauer et al (2012), which modelled air pressure as well as high seepage rates within gravel beaches, using Forchheimer law. We aim to develop a surface-groundwater flow model for a sandy barrier beach. One main difference of the present work from Li and Barry (2000) is that a comprehensive bottom boundary layer model (Cheng and Chiew, 1998), which considers the effects of exfiltration, is incorporated in the coupled surface-groundwater flow model, while the Chezy law was employed in Li and Barry (2000).
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