Observations of Nearshore Hydrodynamics and Morphodynamics During Storm and Recovery Periods on a Low-Wave Energy Beach on the Florida Gulf Coast

The relationship between nearshore hydrodynamics and beach morphology is recognizably dynamic and notoriously difficult to predict. Observations of how changing waves, currents, and tides modify surfzone morphology and beach/dune topography, during both storm conditions and succeeding quiescent periods, are important for understanding the immediate storm-induced coastal changes as well as the evolving beach conditions during the near-term recovery period and longer timespan between storms. These observations are necessary for improving and accurately initializing predictions of subsequent storm events. In order to observe the interactions of hydrodynamics and morphodynamics during storm events and recovery periods, a suite of measurements was made at Madeira Beach, Florida, located on the Gulf of Mexico, from February 2017 to July 2018, during which Hurricane Irma occurred. Offshore waves, currents and water levels were measured nearly continuously by an upward-looking acoustic Doppler current profiler in 5-meter water depth; wave runup and total water levels at the shoreline were measured every daylight hour using imagery from a stationary camera and photogrammetry techniques; a baseline large-scale bathymetry was measured in February 2017, and nearshore bathymetry was estimated daily using camera imagery and the cBathy algorithm; beach topography was measured monthly using aerial imagery and Structure-from-Motion photogrammetry processing, with intermittent walking surveys. These data are used to evaluate the changing wave runup and water levels at the shoreline during varying wave conditions, and their seasonal and storm-induced impacts on the beach profiles. Additionally, volumetric estimates of cross-shore and alongshore sediment transport on the upper beach are made and evaluated in comparison with the observed hydrodynamic forcing. The beach profile near the shoreline was found to change in concavity throughout the year, and the effects of beach slope on the wave runup parameterization are evaluated. Although this is a low-sloping, low-wave energy beach, these observations will be used to validate total water level and coastal change models, as well as improve wave runup parameterizations, that can be applicable to similar conditions at other coastal sites.