Assessing the effectiveness of rip current swimmer escape strategies, Shelly Beach, NSW, Australia

Rip flow dynamics have important implications for swimmer escape strategies, with recent field studies indicating flow is often contained within the surf zone, re-circulating onto shallow bars. Combining physical measurements in a variety of conditions with various escape strategies allows insights into the safest response by individuals caught in a rip. A three day experiment was conducted at Shelly Beach, NSW in December, 2011. Lagrangian measurements of rip flow using GPS drifters were obtained. Participants with attached GPS were deployed in groups of 3 to 5 in rip currents to simulate various escape actions such as floating with the rip current, and swimming in a parallel direction at varying distances from shore. Day 1 and 2 measurements captured an open beach rip current and an adjacent topographic rip current in moderate energy conditions. Day 3 measurements were obtained on an open beach rip current at a more exposed section of the beach under higher energy conditions. Results were analysed by duration and assessed as being either (i) positive outcome (high chance of safe exit); or (ii) negative outcome (greater potential for hazard). Mean durations were Float (4 min), and Swim (2 min). Of the eight escape scenarios tested, half had potential negative outcomes, including 2 of 3 Float options and 2 of 5 Swim options. Negative outcomes for Floats were related to surf zone exits, and multiple circulations. Negative outcomes for Swims related to swimming against longshore directed circulation. Neither strategy was clearly more likely to result in a successful outcome across all scenarios. Further investigations are currently being conducted in a greater range of hydrodynamic and morphological conditions.