Risk evaluation of low cost protection structure on a macro-tidal coast

Low cost beach protection structures are often the only viable option for small coastal communities faced with coastal erosion problems, and inherent in their design is the risk of failure. Assessing this risk is an important feature in the design process. The Capricorn Coast in Central Queensland, Australia, has two main beach areas protected by rubble mound type seawalls. These structures have recently been upgraded to overcome serious erosion problems that were occurring. The design methodology used did not allow for any full assessment of risk and the complex interactions of wave height, direction, period and tide height. This paper develops a bivariate generalised Pareto distribution to model the extreme events of significant wave height and high water level as this combination impacts on the beach protection structure. The joint probability developed enables a more comprehensive description of risks associated with the structure.