Numerical model of swash motion and air entrapment within coarse-grained beaches

► We model key mechanisms of the water exchange between swash and subsurface. ► Focus is on filtration and pore-air pressure build-up within the unsaturated beach. ► Validation is carried out with measurements from large-scale laboratory experiments. ► Swash model is consistent with experimental results on two coarse-grained beaches. ► The insights contribute to better understanding and modelling of key swash processes.