Wave hazards on microtidal shore platforms : testing the relationship between morphology and exposure

Open-ocean rocky coasts are dangerous environments when there is a coincidence of recreational activities occurring in areas of high wave energy. Management of drowning fatalities and near-drowning incidents on these landforms is difficult as traditional approaches to beach safety cannot be easily transferred to rocky shores. In this study, we take a morphological approach to quantifying the relative danger of shore platforms in microtidal regions. Platform elevation and nearshore water depth are key variables in determining the likelihood of wave overtopping of the platform edge. The relationship between these variables is tested along a 70-km-long section of the Otway Ranges coast in Victoria, Australia. It is found that exposure is highly variable along short (100 m scale) sections of shore platforms. This variability is driven by the complexity of the nearshore morphology which can have metre-scale relief. As exposed platforms may occur in areas of low wave energy, the morphological exposure index is combined with nearshore wave energy to produce a risk rating. Risk, like exposure, was found to be highly spatially variable. The relationship between elevation and water depth has the potential to provide managers with a tool for assessing safety on rocky shores.