Rip current variability and hazard along a macro-tidal coast

The role of beach safety management is becoming increasingly important along much of the macro-tidal, high-energy Atlantic coast of England, which experiences mean spring-tidal ranges of 4.1-7.4 m and average significant wave heights of 1.2 m and 2.7 m in summer and winter, respectively. Growing pressures on beach resources due to increasing visitor numbers means an understanding of the nature of hazards Surrounding the recreational beach user is paramount. Rip currents are responsible for 80% of all recorded incidents (2005-2007) along this coast. Most investigations into rip Current dynamics have been reported from micro- and meso-tidal environments and macro-tidal rip systems have rarely been considered. This research assesses the spatio-temporal variability of macro-tidal rip Current systems and their associated hazards along the west coasts of Devon and Cornwall between May and October 2007. Analysis of seasonal morphological and hydrodynamic datasets coupled with detailed lifeguard incident data and daily rip observations have identified some key drivers of recreational rip hazards and 'mass rescue' events on low-tide bar/rip and low-tide terrace and bar/rip beaches; 1) Small long-period swell-waves, that favour development of accretioary rip systems, shoal to the inner transverse bars generating strong alongshore variations in wave breaking and enhancing rip current activity: 2) Well developed, phase-offset low- and mid-tide bar/rip morphologies lead to the generation of active rip systems during low- and mid-tidal stages; 3) Large (spring) tidal ranges expose low-tide bar/rip systems, activating rip currents and increasing tidal cut-off potential and the rate-of-change of alongshore rip location through low- and mid-tide. Low-tide times during spring tides coincide with lifeguard patrol hours and hence times of high beach usage.