Minimising the impacts of reclamation dredging at Cape Town

As part of the expansion of the Port of Cape Town, 6 million m 3 of sand is to be dredged from an offshore borrow site. The objectives of this study are to assess and mitigate the impact of the dredge hole and reclamation on the nearshore wave climate and shoreline stability, as well as the impact of dredging-induced sediment plumes. The study approach is to apply a system of coupled numerical models, comprising wave-refraction, shoreline, hydrodynamic and plume dispersion models. Five different dredge hole geometries are tested in an attempt to minimise the impact of the dredge hole on the shoreline stability. Up to 11 m of beach erosion is predicted, with a large shallow hole found to have less impact than a smaller deeper hole. Orientating the dredge hole with the long axis parallel to the wave crests is also found to reduce the shoreline impact. The sediment plumes are predicted to have a low ecological impact, although a short-term low to medium visual impact is predicted.