Modeling Waves and Water Levels at the Entrance of a Bar-Built Estuary Under Variable Inlet Orientations

Abstract Bar-built estuaries are shallow dynamic coastal systems with hydrodynamics influenced by rivers, tides, waves, and intermittent inlets. A numerical model based on Delft3D + SWAN was calibrated and validated against waves and water levels around Carmel River State Beach, CA, USA. The model was applied to explore swell propagation patterns in Carmel Bay at kilometer length-scales and the role of inlet orientation and curvature in water levels and the propagation of gravity waves through an inlet and a shallow lagoon in meter length-scales. Numerical simulations indicate that offshore westerly swell refracts further into the beach than northwesterly swell, which has important implications for potential cyclical northerly littoral drift under westerly swells. Gravity waves propagate into the inlet which is less than 20 m wide during high tides only. Inlet orientation and curvature influence how far gravity waves can get into the inlet. Gravity wave energy can reach about halfway through the inlet for curved and oblique inlets and all the way into the lagoon entrance for a straight inlet. Observed and simulated water levels in the lagoon were always perched above the ocean water levels. Simulations indicate that inlet orientation and curvature influence the magnitude of water level perching in the lagoon. Maximum mean water levels in the lagoon occur under a curved inlet, followed by an oblique inlet. Results from this study can inform breaching practices in managed bar-built estuaries that require lagoon water level control for flooding prevention and habitat protection.