A Numerical Study of Dam‐Break Driven Swash and Beach Groundwater Interactions

Abstract

AbstractThe dynamic interaction between swash and beach groundwater is fundamental to understanding wave runup and sediment transport processes. A numerical model that simultaneously resolves free surface and porous media flow for a variably saturated subsurface is presented. The novel numerical model, SedOlaFlow, is developed by merging the existing two‐phase, Eulerian sediment transport model, SedWaveFoam, with the surface wave solver, olaFlow. SedOlaFlow is validated with large wave flume surface and subsurface data for dam‐break driven swash over permeable gravel and sand beaches. Sediment size significantly impacts the swash‐groundwater relationship through infiltration/exfiltration and subsurface processes which modulate runup. Model results demonstrate that vertical infiltration into the upper unsaturated beach leads to a delayed groundwater table response to swash in the sand beach. Pressure fluctuations in the sand beach are not directly indicative of the swash depth or groundwater table and exfiltration may occur even when the swash depth is non‐zero. Groundwater circulation induced by a single swash event is non‐uniform and highly dynamic in the variably saturated vadose zone. Elevated ambient groundwater levels generally increase swash extent and duration. These findings establish the existence of a bi‐directional relationship between swash and groundwater flows and have significant implications on the effects of sea level rise on coastal flooding.