Mesoscale wave energy dissipation over heterogeneous sediments
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Measurements describing the evolution of wave energy spectra as waves propagate across a large shoal are described. The shoal is shore oblique, 2 km by 10 km in extent, with relief of up to three meters over bathymetry with ambient depth 10-12 m. The region is sediment starved, and bottom roughness displays spatial variability due to rock outcrops. Field measurements intended to investigate the effects of this shoal on waves, currents, and sediment transport in its lee reveal strong cross-shore gradients in energy density and energy flux, well outside of the surf zone, in conditions of minimal wind, which are attributed to bottom friction. The dissipation displays the expected frequency dependence, in that it decreases in significance as wave frequency increases, but this trend is not as strong as available theoretical predictions would suggest.