Rocky coast hazards and public safety: Moving beyond the beach in coastal risk management

摘要

The coast is an environment enjoyed by people around the world, yet it is also hazardous, accounting for innumerable fatalities each year. The management of day-to-day hazards is an ongoing challenge for managers because the risk of a person drowning is the result of a combination of the number of people on the shore, their vulnerability, and the wave processes occurring at any one time. As it is nearly impossible to reduce the magnitude of waves or the number of people visiting the shore, managers often rely on strategies to reduce visitor vulnerability such as the provision of lifeguards. Education is also seen as key to reducing people's vulnerability by increasing awareness of the hazards. For beaches, mor-phodynamic models are used to provide a hazard rating for such landforms and this has been very successful in reducing drownings on sandy coasts. However, on adjacent rocky coasts there has been an increase in fatalities, particularly amongst rock fishers. Fatalities occur particularly on the edge of rocky ledges, termed shore platforms, found at the foot of cliffs when people are washed into the sea by waves. Rocky coasts are currently not incorporated in the existing shoreline risk assessments and their exclusion is a major gap in coastal management especially because, unlike beach users, people recreating on the rocky coast are often unprepared for entering the water and swimming. This paper explores the underlying principles of the beach safety models and develops a hazard framework for rock coasts which is tested on microtidal shore platforms of Australia and New Zealand. The height and slope of shore platforms as well as their depth immediately offshore are identified as the key elements in determining how much wave energy can impact the platform and therefore be hazardous to people. The rocky coast hazard framework provides a simple and effective tool for the assessment of wave hazard exposure through combining platform elevation with the depth immediately offshore of the platform edge. This new framework provides managers with a rapid assessment tool for quantifying rocky coast hazards.