LINKING COASTAL BOULDER DEPOSITS TO EXTREME SEA LEVEL EVENTS: THE NEED FOR MORE FIELD BASED DATASETS (Invited Presentation)

Coastal boulders and boulder fields potentially provide useful information for examining the hydraulic characteristics of extreme sea level events such as tsunamis or storm waves that have struck a particular coast in the past. Boulder transport models are commonly used to reconstruct the hydraulic characteristics needed for boulder transport. Since the 1990s a suite of inverse and forward models have been applied to the identification and size estimation of coastal boulders and boulder fields globally. The primary aim of such modelling is usually to attribute a depositional mechanism with one particular focus of modelling studies focussed on efforts to attribute tsunami or storm waves to the deposits. Inverse model can estimate the minimum wave height and velocity necessary to slide, rotate, or saltate the boulder. In contrast, forward models are used to estimate hydraulic parameters such as the maximum wave velocity or wave runup height as this is a product of the boulder transport distance. Boulder transport models commonly contain relatively few parameters because they have been developed by simplification of the overwash process. As such boulders transport models contain large errors and considerable uncertainty. Current efforts to homogenise the reporting of boulder datasets is applauded but there remains a clear need for field studies on boulder fields of known tsunami or storm origin. Such datasets provide validation for models and are vital for advancing efforts to better link boulder deposits with hydrodynamic processes.