Nearshore currents and safety to swimmers in Xai-Xai Beach
Palabras clave:
alongshore currents, rip currents, swimming, drowning, beach zoning, beach safetyResumen
Xai-Xai Beach is a shallow semi-enclosed lagoon, about 2,000m long and 200m wide and average 3 m depth, protected from ocean swell by a reef, 0.75m above the Mean Sea Level, with small gaps along its extension. Despite being protected from the ocean waves there have been notices of casualties, on average 8-9 cases per year, by drowning. The present paper examines the alongshore and rip currents as the potential causes for the observed drowns. Drifters were deployed as to measure the magnitude and direction of the nearshore currents. Unidirectional, northwards, alongshore currents, with velocity up to 1.4ms-1 and strong stationary rip currents, with velocity up to 3.4ms-1, 5-10m width and a period of less than 5 minutes, were observed. The observed rip currents posed a real danger even to experienced swimmer, hence it is concluded that they are the major cause of the observed death. The areas of major incidence of rip currents were identified. The result allowed for the zoning of the beach in three zones as follows: southern part, with weak currents, labeled green zone, recommended for swimming; northern part, with strong rip currents, labeled red zone, where swimming is prohibited; and the intermediate zone, labeled yellow zone, where swimming should be done with caution. Regular patrols by lifeguards and beach assistance it is highly recommended during the summer, the peak tourisms season.Citas
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