Abstract
Alongshore flows strongly driven by tides and waves is studied in the context of a one-dimensional numerical model. Observations from field surveys performed in a semi-enclosed lagoon (1.7 km×0.2 km) outside Xai-Xai, Mozambique, are used to validate the model results. The model is able to capture most of the observed temporal variability of the current, but sea surface height tends to be overestimated at high tide, especially during high wave events. Inside the lagoon we observed a mainly uni-directional alongshore current, with speeds up to 1 ms−1. The current varies primarily with the tide, being close to zero near low tide, generally increasing during flood and decreasing during ebb. The observations revealed a local minimum in the alongshore flow at high tide, which the model was successful in reproducing. Residence times in the lagoon were calculated to be less than one hour with wave forcing dominating the flushing. At this beach a high number of drowning casualties have occurred, but no connection was found between them and strong current events in a simulation covering the period 2011–2012.
Highlights
Reefs are common features along the coasts of the tropical oceans and often define semi-enclosed areas that can be densely populated
In this paper we investigate the current dynamics at the beach of Xai-Xai, southern Mozambique
The mean speed for these drifters were between 0.6 m sÀ1 and 0.8 m sÀ1, which is a little higher than the current speed measured by the SeaGuard at the same time
Summary
Reefs are common features along the coasts of the tropical oceans and often define semi-enclosed areas that can be densely populated. This is because such lagoons define particular ecosystems subject to fisheries, development of tourist industries, and in recent years fish-farming. Coastal erosion is of major concern, so it is important to study ocean currents, tides, waves and wind influencing erosion processes. At Xai-Xai there is a fringing reef running parallel to the coast defining a lagoon about 1.7 km long and up to 200 m wide, see Fig. 1. The water exits the lagoon mainly through the gaps in the eastern end
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