Environmental controls on lifeguard-estimated surf-zone hazards, beach crowds, and resulting life risk at a high-energy sandy beach in southwest France

Abstract

Understanding and predicting surf zone risks is of paramount importance to prevent drowning incidents and severe spine injuries on beaches globally. This study holistically addressed life risk at La Lette Blanche beach, southwest France, during the lifeguard-patrolled summer period (July-August) 2022, where intense rip currents and shore-break waves co-exist at different times and locations along the beach. Beach crowds and the levels of rip current and shore-break wave hazards were estimated hourly by lifeguards during patrolling hours. Wave, tide and weather conditions were also continuously recorded, providing comprehensive insights into the primary environmental controls on surf zone hazards and beach attendance. Results show that the daily average rip current hazard increases with large, long-period and near shore-normal waves, while the shore-break wave hazard is increased for long-period, near shore-normal waves and large tide ranges. Beachgoer crowd numbers increase on warm, sunny and light wind days although a severe heat wave occurring in July 2022 significantly decreased daily average beach crowd and deeply affected beach use. Days characterized by strong hazards and large beach attendance were associated with the largest amount of lifeguard rescues and drowning incidents, although correlations decreased by the end of the summer. This is hypothesized to be the signature of evolving lifeguard strategies (e.g. preferred locations of the supervised bathing zone, prevention measures) as they progressively increase their understanding of the surf zone hazards variability in both time and space at their beach as a function of tidal stage and incident wave conditions. Warm, sunny and light-wind sunny days (maximizing beach crowds), with large, long-period shore-normally incident waves and large tide range (maximizing surf zone hazards) were the most risky days, with shore-break waves and rip current hazards notably peaking at different times of the day. This study shows that lifeguards can be a valuable source of data to improve understanding of the environmental controls on beach crowd, surf zone hazards and life risk at the beach, which provides critical information to the development of holistic beach risk predictors.