Observations from wave basin experiments and wave-resolving numerical simulations demonstrate the effect of wave-current interaction on shear stress around a sandy mound. Observations from the wave basin show that the mound deformation rate and morphological patterns depend on the mixture of waves and currents in the incident flow conditions. A SWASH nonhydrostatic numerical model was used to expand the parameter space of wave-current conditions observed in the flume and characterize the response of the near-bed shear stress to the mound. The model was validated with observations from wave-alone, current-alone, and wave-current flume tests and then ran for a suite of numerical flow conditions which isolate the impact of the ratio of wave-current energy on the bed shear stress. Results show how the current-to-wave ratio impacts the spatial heterogeneity of shear stress across the mound, with the region of shear stress intensification around the mound and the location of the peak shear stress becoming asymmetric with more mixed wave-current flows. These results show the nonlinear response of shear stress patterns to combined wave-current flows and how these patterns may impact eventual sediment transport and mound evolution.

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Accurate predictions of the fate of sand nourishments in the nearshore are critical to the management of eroding shorelines. The effectiveness of these nourishments depends on wave and current conditions, which vary with nourishment shape, size, and location. Here, observations of artificial sand mounds, including a new laboratory experiment, are examined to characterize the impact of a range of wave and current conditions on mound evolution and to inform coastal management techniques.@en

Observations of waves, currents, and bathymetric change in shallow water (<10-m depth) both inside and offshore of a migrating inlet with strong (2–3 m/s) tidal currents and complex nearshore bathymetry show over 2.5 m of erosion and accretion resulting from each of two hurricanes (offshore wave heights >8 m). A numerical model (Delft3D, 2DH mode) simulating waves, currents, and morphological change reproduces the observations with the inclusion of hurricane force winds and sediment transport parameters adjusted based on model-data comparisons. For simulations of short hurricanes and longer nor'easters with identical offshore total time-integrated wave energy, but different peak wave energies and storm durations, morphological change is correlated (R² = 0.60) with storm intensity (total energy of the storm divided by the duration of the storm). Similarly, the erosion observed at the Sand Engine in the Netherlands is correlated with storm intensity. The observations and simulations suggest that the temporal distribution of energy in a storm event, as well as the total energy, impacts subsequent nearshore morphological change. Increased storm intensity enhances sediment transport in bathymetrically complex, mixed wave-and-tidal-current energy environments, as well as at other wave-dominated sandy beaches.

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