Manuel Victor Poio’s research while affiliated with Norwegian Meteorological Institute and other places

Xai-Xai Beach is a shallow semi-enclosed lagoon, about 2,000m long, 200m wide and 3m average depth, protected from ocean swell by a reef about 0.75m above the Mean Sea Level, with small gaps along its extension. Despite being protected from ocean waves, the lagoon, which is popular with tourists, is a dangerous place to swim, with an average of 8-9 drownings each year. The present paper examines the longshore and rip currents in the lagoon as the potential cause for these fatalities. Drifters were deployed for measuring the magnitude and direction of the nearshore currents. Unidirectional, northwards, longshore currents, with velocity up to 1.4ms-1 and strong rip currents, with velocity up to 3.4ms-1, 5-10m width and duration of less than 5 minutes, were observed. The observed rip currents pose a real danger even to experienced swimmers; hence it is concluded that they are the major cause of the deaths. The areas of major incidence of rip currents were identified. The result allows us to recommend a zoning of the beach into three areas as follows. The southern part, with weak currents, is classified as a “safe area”, flagged green, and is recommended for swimming. The northern part, with strong rip currents, is classified as a “hazardous area”, flagged red, and prohibited for swimming. In the intermediate zone, classified as a “moderate area” and flagged yellow, swimmers should proceed with caution. Regular patrols by lifeguards and beach assistants are highly recommended during the summer, the peak tourism season. Keywords: longshore currents, channel rip current, swimming, drowning, beach zoning, beach safety

This report summarizes the 2013 field experiment at Tofo Beach, Tofo, Inhambane, in which measurements of bottom topography, currents, sea level, and surface waves were collected. A visual assessment of the surrounding areas was also made, and some comments are made concerning the morphology at Tofo Beach. Keywords: Nearshore dynamics, beach morphology

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 kmÂ0.2 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 À1. 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 2011e2012.