Intermediate modelling of tidal inlet systems: spatial asymmetries in flow and mean sediment transport

Abstract

In order to identify mechanisms which determine the morphology of tidal inlet systems, experiments with a shallow water model and sediment transport model of intermediate complexity are carried out and interpreted. A highly schematised geometry is used, consisting of a rectangular outer area connected to a rectangular basin by a narrow strait. The bottom topography is either flat or constantly sloping in the landward direction and the bed is composed of fine sand. Forcing at the open boundary consists of prescribed water levels, which can represent a (shore-parallel) progressive tidal wave or a fully standing wave. The symmetry breaking effects of Coriolis force and a progressive Kelvin wave on the tidal motion, the mean flow field and the mean sediment transport field are investigated. Tidal ellipticity properties on the outer delta are also discussed. Experiments for a rectangular basin without outer area are carried out in order to compare the intermediate model results with those of a 1D idealised model. The overall agreement is satisfactory. Next the influence of earth rotation and of the progressive wave in the outer sea on mean sediment transport in the basin is investigated. It turns out that both effects, which cannot be included in the idealised model, lead to different patterns of erosion and deposition. In both sets of experiments the effects of a progressive Kelvin wave were found to be dominant over earth rotation effects in the flow and mean sediment transport fields.