Swash zone sediment dynamics: A comparison of a dissipative and an intermediate beach

High frequency measurements of water depth, current velocity and suspended sediment concentration were used to investigate sediment transport processes in the swash zones of a dissipative beach and a steeper (intermediate) beach. Infragravity frequency motions dominated velocity spectra of the dissipative beach swash, while incident wave frequencies dominated the velocity spectrum of the intermediate beach swash. Velocity variance, the ratio of local wave height to water depth, mean bed shear stress and the mean friction velocity were greater on the intermediate beach. Mean suspended sediment concentrations were an order of magnitude greater on the intermediate beach. Infragravity frequencies dominated the oscillatory component of sediment transport on the dissipative beach. Incident wave frequency sediment transport dominated the intermediate beach. A maximum in the net shoreward transport occurred in approximately the mid swash zone on both beaches, suggesting accretion in the shoreward half of the swash, and erosion in the seaward part of the swash. Net sediment transport rates were lower on the ebb tide than on the flood tide, despite similar incident wave conditions.