Suchergebnisse

Abstract. A Bayesian network (BN) approach is used to model and predict shore-break-related injuries and rip-current drowning incidents based on detailed environmental conditions (wave, tide, weather, beach morphology) on the high-energy Gironde coast, southwest France. Six years (2011–2017) of boreal summer (15 June–15 September) surf zone injuries (SZIs) were analysed, comprising 442 (fatal and non-fatal) drownings caused by rip currents and 715 injuries caused by shore-break waves. Environmental conditions at the time of the SZIs were used to train two separate Bayesian networks (BNs), one for rip-current drownings and the other one for shore-break wave injuries. Each BN included two so-called "hidden" exposure and hazard variables, which are not observed yet interact with several of the observed (environmental) variables, which in turn limit the number of BN edges. Both BNs were tested for varying complexity using K-fold cross-validation based on multiple performance metrics. Results show a poor to fair predictive ability of the models according to the different metrics. Shore-break-related injuries appear more predictable than rip-current drowning incidents using the selected predictors within a BN, as the shore-break BN systematically performed better than the rip-current BN. Sensitivity and scenario analyses were performed to address the influence of environmental data variables and their interactions on exposure, hazard and resulting life risk. Most of our findings are in line with earlier SZI and physical hazard-based work; that is, more SZIs are observed for warm sunny days with light winds; long-period waves, with specifically more shore-break-related injuries at high tide and for steep beach profiles; and more rip-current drownings near low tide with near-shore-normal wave incidence and strongly alongshore non-uniform surf zone morphology. The BNs also provided fresh insight, showing that rip-current drowning risk is approximately equally distributed between exposure (variance reduction Vr=14.4 %) and hazard (Vr=17.4 %), while exposure of water user to shore-break waves is much more important (Vr=23.5 %) than the hazard (Vr=10.9 %). Large surf is found to decrease beachgoer exposure to shore-break hazard, while this is not observed for rip currents. Rapid change in tide elevation during days with large tidal range was also found to result in more drowning incidents. We advocate that such BNs, providing a better understanding of hazard, exposure and life risk, can be developed to improve public safety awareness campaigns, in parallel with the development of more skilful risk predictors to anticipate high-life-risk days.

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.