Abstract
Abstract. The two primary causes of surf zone injuries (SZIs) worldwide, including fatal drowning and severe spinal injuries, are rip currents (rips) and shore-break waves. SZIs also result from surfing and bodyboarding activity. In this paper we address the primary environmental controls on SZIs along the high-energy meso–macro-tidal surf beach coast of southwestern France. A total of 2523 SZIs recorded by lifeguards over 186 sample days during the summers of 2007, 2009 and 2015 were combined with measured and/or hindcast weather, wave, tide, and beach morphology data. All SZIs occurred disproportionately on warm sunny days with low wind, likely because of increased beachgoer numbers and hazard exposure. Relationships were strongest for shore-break- and rip-related SZIs and weakest for surfing-related SZIs, the latter being also unaffected by tidal stage or range. Therefore, the analysis focused on bathers. More shore-break-related SZIs occur during shore-normal incident waves with average to below-average wave height (significant wave height, Hs = 0.75–1.5 m) and around higher water levels and large tide ranges when waves break on the steepest section of the beach. In contrast, more rip-related drownings occur near neap low tide, coinciding with maximised channel rip flow activity, under shore-normal incident waves with Hs >1.25 m and mean wave periods longer than 5 s. Additional drowning incidents occurred at spring high tide, presumably due to small-scale swash rips. The composite wave and tide parameters proposed by Scott et al. (2014) are key controlling factors determining SZI occurrence, although the risk ranges are not necessarily transferable to all sites. Summer beach and surf zone morphology is interannually highly variable, which is critical to SZI patterns. The upper beach slope can vary from 0.06 to 0.18 between summers, resulting in low and high shore-break-related SZIs, respectively. Summers with coast-wide highly (weakly) developed rip channels also result in widespread (scarce) rip-related drowning incidents. With life risk defined in terms of the number of people exposed to life threatening hazards at a beach, the ability of morphodynamic models to simulate primary beach morphology characteristics a few weeks or months in advance is therefore of paramount importance for predicting the primary surf zone life risks along this coast.
Highlights
Sandy surf beaches are an attractive environment for a variety of recreational activities globally, including sunbathing, swimming and wading, bodyboarding, and surfing
The coast was exposed to a broad range of wave conditions, with Hs and Tp ranging between approximately 0.4 and 4 m and 5 and 16 s, respectively, with waves coming from the southwest to the north but predominantly from the west-northwest (Fig. 2a– c), resulting in highly variable amount of daily surf zone injuries (SZIs) (Fig. 2j)
Based on SZIs reported by lifeguards during the summers of 2007, 2009, and 2015, as well as tide and wave hindcasts and weather and beach morphology data, SZIs along this section of coast occurring disproportionately on warm sunny days with low wind are likely related to beachgoer exposure
Summary
Rips often originate close to the shoreline and can extend well beyond the breakers (Brander and Scott, 2016) They are capable of transporting bathers of all swimming abilities offshore into deeper water, increasing the risk of drowning through panic and exhaustion (Brander et al, 2011; Drozdzewski et al, 2012, 2015). They are responsible for an estimated 57 and 21 fatal drownings on surf beaches in the United States and Australia, respectively, alone (NOAA, 2017; Brighton et al, 2013). These channel rips exhibit considerable natural variability in terms of flow characteristics and behaviour (McCarroll et al, 2018), preventing the public promotion of any single simple and universal escape strategy for those who find themselves caught in one (Bradstreet et al, 2014; McCarroll et al, 2014, 2015; Castelle et al, 2016b)
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