Relating Hydrodynamic Forcing and Topographic Response for Tide-Dominated Sandy Beaches

Abstract

To relate hydrodynamic forcing and topographic response for a tide-dominated sandy beach, extensive field measurements were carried out in the intertidal zone. Hydrodynamics and beach topography were monitored during a total of 12 weeks at two different study sites: one with a featureless intertidal zone and one with intertidal bars. The results of both study sites indicate that the intertidal beach grows when wave steepness is small, whereas it erodes when wave steepness is large. Spring-neap variations in tidal current direction heavily distort this trend: strong spring tidal currents transport sediment away from the beach, resulting in enhanced erosion. Tide-induced beach volume changes are on the same order of magnitude as wave-induced changes. Besides waves and tides, the effect of variations in the amount of sediment supply is substantial, with enhanced accretion when the sediment supply is large. The effect of variations in sediment supply on the intertidal beach topography is subordinate to the effect of waves and tide, though. From this study, it is concluded that larger waves are primarily erosive, but they can also enhance the natural sediment supply. Furthermore, it is found that tidal currents can be equally important as waves in shaping the beach topography, especially during spring tide on macrotidal beaches.