Data on cross-shore sand transport were obtained during two tidal cycles on a dissipative macrotidal pocket beach in the outer Gironde Estuary (SW France). Sediment samples were collected, using streamer traps, at different elevations above the bed across the surf zone whilst measuring nearshore waves and cross-shore currents on the beach. During the experiment the tidal range reached 3.8 m and the current speeds on the beach were up to 0.5 m s−1. Wave activity was characterised by a variable significant height, ranging from 0.3 m at low to 0.94 m at high tide, due to the sheltering effect of a nearshore sand bank.
The study found that the median grain size of the transported sediment ranged from 0.207 mm to 0.333 mm, decreasing slightly away from the bed, with less than 0.056 mm variation throughout the water column. This vertical distribution was assumed to be related to a near uniform mixing by saturation of turbulence and to large scale vertical eddies under breaking and/or broken waves.
The fluxes calculated using the sediment captured in the streamer traps increased exponentially or linearly towards the bottom, whilst some curves had an S-shaped profile. These results confirm the general theory of a decrease in sediment transport rate away from the bed. However, the S-shaped profile may be due to coherent vortex structures which led to strongly irregular patterns. Finally, the sediment fluxes appeared to be higher during the ebb than during the flood tide, indicating a tidal influence on sediment transport.
