Nearshore currents and safety to swimmers in Xai-Xai Beach
Keywords:
alongshore currents, rip currents, swimming, drowning, beach zoning, beach safetyAbstract
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.References
Anon (2009) Contribuição Económica do Turismo na Praia de Xai-Xai de 2003 á 2008. Not published. Available on the web page: http://fedocas.blogspot.com/2009_10_14_archive.html
Brander RW, Short AD (2000) Morphodynamics of a large-scale rip current system at Muriwai Beach,New Zealand. Mar Geol., 165:27–39.
Christensen, K.H.; Breivik, Ø.; Gammelsrød, T.; Hoguane, A.M.; Noca B. Furaca da Silva, N.B.F.; Taskjelle, T.; Manuel V. Poio, M.V. (2013) - Waves and dangerous currents at Xai-Xai Beach, Mozambique. Norwegian Meteorological Institute, Institute Technical Report Series, No 17/2013, p21, (ISSN: 1503-8025). Available on the web page: https://www.researchgate.net/publication/265865041_Waves_and_dangerous_currents_at_Xai-Xai_Beach_Mozambique Hearn, C.J.; Parker, I.N. (1988) - Hydrodynamic processes on the Ningaloo coral reef, Western Australia. Proceedings of the 6th International Coral Reef Symposium, 2:497-502.
Kraines, S.B.; Yanage, T.; Isobe, M.; Komiyama, H. (1998) - Windwave driven Circulation on the coral reef at Boray Bay, Miyako Island. Coral Reefs, 17:133-143.
Lascody, R. (1998) - East central Florida rip current program. Natl Weather Dig, 22:25–30.
Leon, M.P.; Nishi, R.; Kumasaka, F.; Takaesu, T.; Kitamura, R.; Otani, A. (2008) - Reef Rip Current Generated by Tide and Wave during Summer Season: Field Observation Conducted in Yoshiwara Coast, Ishigakijima, Okinawa, Japan. Proceedings of the 11th International Coral Reef Symposium, Ft. Lauderdale, Florida, 7-11 July 2008. Session number 15.
Lushine, J.B. (1991) - A study of rip current drownings and weather related factors. Natl. Weather Dig., 16:13–19.
Nadaoka, K.; Nihei, Y.; Kumano, R.; Yokobori, T.; Omija, T. Wakaki, K. (2001) - A field observation on hydrodynamic and thermal environments of a fringing reef at Ishigaki Island under typhoon and normal atmospheric conditions. Coral Reefs, 20:387-398.
Nharreluga, B.A.S. (2014) - Fatores que influenciam nas correntes de deriva litoral na praia de Xai-Xai. P47., MSc dissertation in Applied Oceanography, School of Marine and Coastal Sciences, Eduardo Mondlane University. Mozambique. Not published.
Schmidt, W.; Woodward, B.; Millikan, K.; Guza, R.; Raubenheimer, B.; Elgar, S. (2003) - A GPS-tracked surf zone drifter. J. Atmos. Ocean. Technol. 20(97):1069–1075. doi:10.1016/B978-0-12-415990-7.00003-X Sete, C.I.; Ruby, J.; Dove, V. (2002) - Seasonal Variation of Tides, Currents, Salinity and Temperature along the Coast of Mozambique. Technical Report, Instituto Nacional de Hidrografia e Navegação, Maputo. Available on the web page: http://hdl.handle.net/1834/188.
Silva, N.B.F. (2012) - Effect of a barrier reef on waves and currents at Xai-Xai Beach. P51., MSc dissertation in Applied Oceanography, School of Marine and Coastal Sciences, Eduardo Mondlane University. Mozambique. Not published.
Short, A.D. (1999) - Handbook of Beach and Shoreface Morphodynamics. p379., John Wiley & Sons Ltd. Baffins Lane, Chinchester.
Symonds, G.; Black, K.P.; Young, I.R. (1995) - Wave-driven flow over shallow reefs. J Geophy Res, 100(C2):2639-2648.
Short, A.D. e Hogan, C.L. (1994) - Rip Currents and Beach hazards: Their Impact on Public Safety and Implications for Coastal Management. Journal of Coastal Research, Special Issue no.12 : Coastal Hazards p.197-209.
Symonds G, Black KP, Young IR (1995) Wave-driven flow over shallow reefs. J Geophy Res, 100(C2):2639-2648.
Taskjelle, T.; Barthel, K.; Christensen, K.H.; Furaca, N.; Gammelsrød, T.; Hoguane, A.M.; Nharreluga, B. (2014) - Modelling alongshore flow in a semi-enclosed lagoon strongly forced by tides and waves. Estuarine, Coastal and Shelf Science, 149(2014):294-301. DOI: 10.1016/j.ecss.2014.09.008.
Published
Versions
- 2020-03-27 (1)
- 2020-03-27 (1)
