Environmental controls on surf zone injuries on high-energy beaches

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 body boarding activity. In this paper we address the primary environmental controls on SZIs along the high-energy meso-macrotidal surf beach coast of SW 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 focussed on bathers. Shore-break related SZIs disproportionately 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 range when waves break on the steepest section of the beach. In contrast, rip related drownings occur disproportionally near neap low tide, coinciding with maximized channel rip flow activity, under shore-normal incident waves with Hs > 1.25 m and periods mean wave period 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 highly interannually 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/months in advance is therefore of paramount importance to predict the primary surf-zone life risks along this coast.

Coastal drowning in Costa Rica: incident analysis and comparisons between Costa Rican nationals and foreigners

“…Alignment of climatic and economic conditions may be related to the increased fatal drowning numbers in Guanacaste and Puntarenas in those years (Fig. 3c), consistent with observations by Castelle et al (2019), in which drowning was more likely to occur on warm sunny days due to increased number of beachgoers.…”

“…Meteorological conditions also affect the number of beachgoers, who in general prefer sunnier and hotter days (Castelle et al 2019). On the Costa Rican Pacific Coast, these conditions are exacerbated during the onset of the warmer phase of El Niño-Southern Oscillation (ENSO; Instituto Meteorológico Nacional 2020) causing a reduction in rainfall and frequency, and an increase in ambient temperatures along Puntarenas and Guanacaste (Wayle et al 1996;Waylen and Sadí, 1999).…”

16 years of topographic surveys of rip-channelled high-energy meso-macrotidal sandy beach

“…www.nature.com/scientificdata www.nature.com/scientificdata/ improve a range of state-of-the art shoreline change models from the time scale of hours to decades 2,21,44,45 , to validate remotely-sensed shoreline estimation from publicly available satellite images 46 , to identify the morphological controls on spine injuries and drowning on surf beaches 47,48 , and to address the uncertainties in past and future multi-decadal shoreline evolutions 49,50 . In addition, a couple of intensive field experiments have been performed at Truc Vert beach 51 .…”

Predicting drowning from sea and weather forecasts: development and validation of a model on surf beaches of southwestern France

“… 42 Here, the life-risk was found to systematically increase with the wave factor Wf , which is in line with Castelle et al , but contrast with Scott et al 43 in UK where hazard was maximised for just below average Wf . In a previous study, 44 it was qualitatively shown that the beach morphology, which has a profound impact on rip current hazard, was important to the number of drowning incidents. Given the low number of studied seasons and events, and the likely contrasting beachgoer profiles between seasons, it was not possible to robustly address the influence of the bathymetry.…”

“…Our models tend to overestimate the risk on days associated with moderate to high risks; some variables may thus be unknown, related to the beach morphology and the beach attendance. First, the summer beach morphology along the Gironde coast is very variable with rip channel exhibiting different morphologies from one summer to another, 44 and even in space with more gently sloping and less channelized beaches northwards. Given that, for instance, the relative depth of the rip channels is critical to rip current flow speed, 46 and thus physical hazard, and that beach type also influence attendance 47 consideration of a constant beach morphology is limiting.…”