Addressing the International Rip Current Health Hazard
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Rip currents are concentrated seaward flows of water originating in the surf zone of beaches that are responsible for hundreds of injuries and fatal drownings worldwide annually. Calculating the exact number of deaths is hindered by logistical difficulties in collecting accurate incident reports, but the estimated annual average is about 59 in the United States (US), 53 in Costa Rica, and 21 in Australia. Previous research shows rip drownings are caused by a combination of personal and group behaviors with the physical environment. The co-incidence of a rip and swimmers, the ‘hazard,’ results from gaps in knowledge and in communication: we do not know how to accurately predict rip currents, and existing scientific understanding hasn’t fully infiltrated the practiced knowledge of the general public or policy makers designing beach access. This dissertation presents five papers examining the geophysical and social causes of rip-related deaths. Paper 1 reviews present rip current knowledge. Paper 2 demonstrates a novel method for mapping bathymetry within rip channels – topographic low spots in the nearshore resulting from feedback amongst waves, substrate, and antecedent bathymetry. The location and orientation of rip channels are investigated in Paper 3, which analyzes the degree of anisotropy in bathymetric surfaces. Paper 4 builds on rip detection by evaluating beachgoer knowledge alongside rip presence to evaluate physical environment control on swimmer exposure. Finally, because current research demonstrates lifeguard presence is a highly effective mitigation against drowning, Paper 5 identifies one way communities may fund beach lifeguard programs. Thus, the dissertation provides both cutting edge methods to improve prediction and warning systems with the geocomputation demonstrated in papers 2 and 3, and it provides more affordable short-term mitigation practices in papers 4 and 5, for increasing safety by designing and building geomorphologically informed beach access and funding lifeguard programs. As a whole, the dissertation evaluates both human and physical geographies of rip currents, a naturally occurring phenomenon that becomes hazardous when entered by vulnerable individuals. Results can inform policy makers of a range of rip fatality mitigation methods: developing frequent nearshore maps to observe rip channel behavior, automating the detection of rip channels, designing beach access controls informed by morphology, and funding lifeguard programs.
Trimble, Sarah Margaret (2017). Addressing the International Rip Current Health Hazard. Doctoral dissertation, Texas A & M University. Available electronically from