Process-Based Evidence of Coastal Accretion Adjacent to a Natural Inlet and Ebb-Tidal Delta on the North Florida Atlantic Coast

Abstract:

Physical mechanisms of tidal inlet accretion are difficult to document because of the episodic nature of sediment delivery to the coast from fluvial sources and the complex patterns of current magnitudes and directions arising from the interaction of nearshore waves with ebb-tidal delta bathymetry. Using monthly RTK-GPS field measurements of beach topography adjacent to a natural inlet, we document a shoreline change time series that illustrates a bi-directional, alongshore spreading pattern of accretion following an exceptionally high rainfall-discharge event in May 2009. Numerical modeling of wave set-up and nearshore currents in the vicinity of the inlet and ebb tidal delta produces depth-averaged flow velocity patterns consistent with our field observations of coastal accretion. Our results are in agreement with an accretion mechanism, proposed by other researchers, that involves sediment delivery to the margins of the ebb tidal delta during high velocity ebb flows that accompany large rainfall-discharge events, followed by onshore migration of swash bars during subsequent days to months, at a rate dependent upon the timing of nearshore wave energy delivery to the site.