UCLA

Coastal flooding is a growing socioeconomic and humanitarian hazard. Sea level rise will raise beach groundwater levels, potentially inundating low--lying areas from groundwater exposure while simultaneously propagating swash impacts onto higher beach and backshore elevations. Generally, coastal flood modeling efforts characterize only surface flows, neglecting swash zone processes such as infiltration and porous media flow. Swash zone processes are multi-phase, shallow, and transient presenting numerous modeling and observational challenges. In this dissertation, a novel numerical model, SedOlaFlow, is developed by integrating the free-surface resolving Reynolds-averaged Eulerian two-phase sediment transport model, SedWaveFoam, with the surface wave solver, olaFlow, in the OpenFOAM framework. This tightly--coupled, surface--subsurface model enables the direct investigation of interactions between swash surface and subsurface flows and is validated with laboratory flume observations. Swash-groundwater interface dynamics are analyzed to determine the mechanisms modulating the bi-directional swash--beach groundwater relationship. Elevated beach groundwater levels amplify wave runup extent through beach face saturation and turbulence dampening. Environmental conditions (e.g., beach characteristics, wave conditions) influence the beach groundwater impact on wave runup. The swash--groundwater relationship increases and alters the timing of coastal vulnerability. Sea level rise will further exacerbate coastal flooding impacts through beach groundwater--swash interactions. Inclusion of the swash--groundwater relationship in coastal hazard planning and modeling is fundamental to accurate wave runup predictions and assessment of coastal flooding risk.