Temporal and spatial variation in intertidal sedimentation rates

Sediment deposition and erosion rates are reported for an intertidal zone in the Burry Inlet, South Wales. Measured deposition rates over the salt marsh are compared with deposition rates calculated from observed suspended sediment concentrations. Notably, it is concluded that residual turbulence at slack water should not be discounted when calculating deposition rates. Grain-size distributions of suspended sediments over the marsh surface, during flood and ebb tides, contrast with the grain-size distribution of deposited marsh sediments, the latter being significantly coarser. These data in conjunction with mass budget calculations are used to relate total annual deposition and sediment supply by tidal action during settled meteorological periods. The analysis suggests that episodic storm-induced sediment transport is probably an important mechanism for introducing coarse sediment on to the marsh surface. Finally, it is noted that seasonal reworking of the sandy non-cohesive sediments may be related to variations in the intensity of wave-breaking throughout the year.