Determination of risk to users by the spatial and temporal variation of rip currents on the beach of Santiago Bay, Manzanillo, Mexico: Beach hazards and safety strategy as tool for coastal zone management

Beaches are one of the most popular sites used for recreation and spare time by people, being a zone with a constant evolution due to the combined effects of coastal currents, waves and tides. Sometimes, interaction of these processes with local bathymetry causes formation of rip currents (RCs), which are related with accidents to swimmers that even cause drownings. These accidents are strengthened by the lack of information and awareness of RCs, in addition to poor and insufficient beach surveillance. Santiago Bay (SB) (Manzanillo, Mexico), has beaches with great recreational value visited by many tourists every year. Unfortunately SB is not exempt of having potentially dangerous RCs (there is not an official number of accidents reported), and their spatial and temporal variation has not been extensively studied. Due to this lack of data, several research campaigns have been made since 2013 to identify, register and characterize RCs in order to use the information for elaborating new strategies of risk assessment, beach management and assure safety regulations in recreational beaches. In the field survey different data were collected: position, width and RCs intensity, using mobile devices such as a GPS Ashtech Mobile Mapper 10, and two self-made buoys equipped with internal GPS Garmin DC 40. After processing the data, six RCs were constantly identified in the area of study, with intensities ranging from 0 to 1.5 m/s approximately, and widths from 20 to 60 m, and were found to be more recurrent and strong on later spring and summer, as because these period more energetic waves (swell) generated by storms (located as far as the South Pacific) arrive and interact with local bathymetry and tides, favoring the generation and intensification of the RCs. The collected data will be especially useful for the implementation and validation of numerical hydrodynamic models that will be used for spatial and temporal forecasting of potentially dangerous RCs at SB.