Characterisation of the alongshore dynamics of an estuarine beach

Abstract

The hydrodynamics and alongshore sediment dynamics were evaluated on a meso-tidal estuarine beach, submitted to wind and vessel waves generated in an area of restricted fetch, not affected by oceanic waves. The beach morphology is characterised by two main features, a steep upper beach followed, seaward, by a low gradient terrace, both engaged in the surf zone depending on the tidal level. Sedimentologic surveys revealed the presence of coarser sand grains at the steep upper beach, finer sand grains at the low gradient terrace and a large geometrical spreading at the base of the beach face. The characterisation, based on a six-year wind data series, of the average annual wave climate in front of the beach, indicates a low energy environment where the estimated longshore transport is 14.5x103 m3.year-1, equally distributed in both directions. This study also concluded on the cross-shore distribution of the longshore sediment transport in the active part of the beach and on the contribution of each wind wave component to the longshore transport. Despite the important impact that the catamarans can have on cross-shore beach dynamics, their effect on the longshore transport is irrelevant