Interpretation of tracer experiments with fine-grained dredging material at the Belgian Continental Shelf by the use of numerical models

Radioactive tracer experiments were used by HAECON NV to give insight into the transport of the dredged material in Belgian coastal waters. The experiments showed that material dumped less than 25 km from the coast recirculated rapidly to the coast, while material dumped further from the coast disappeared from the Belgian Continental Shelf. The degree of recirculation was however not well determined, due to large uncertainties in the experiments. A vertically integrated sediment transport model is therefore used to simulate the dispersion of dredged material in the Belgian coastal waters. The model is a semi-Lagrangian model, based on the Second Moment Method. The bottom stress is calculated under the influence of prevailing currents and waves. Although many uncertainties still remain in the modelling of sediment transport, this simple sediment transport model gives satisfying results in simulating the tracer experiments. By a careful interpretation of the experimental and model results, new insight is obtained about the existence of the turbidity maximum in the Belgian coastal waters.