Longshore and cross-shore suspended sediment transport at far infragravity frequencies in a barred environment

Field measurements of near-bed current velocities and sediment concentrations within a barred nearshore environment revealed a large flux coupling at far infragravity frequencies (<0.005 Hz). In the presence of strong longshore currents (time-averaged maximum = 0.92 m s−1), up to 30% of the longshore and 65% of the cross-shore suspended sediment transport can be attributed to far infragravity oscillations. While the former was always directed with the longshore current, the latter was variable in direction both spatially and temporally. A number of features of the measured far infragravity energy fit characteristics of a shear wave: (a) a large positive correlation between the long wave energy magnitude and the longshore current velocity; (b) the presence of a preferred frequency for the measured long wave; (c) a spatial variability in the ratio of cross-shore to longshore velocity at the preferred frequency; (d) the relatively small surface expression of the long wave compared to the large magnitude velocities recorded at the preferred frequency.