Assessment of wave overtopping risk for pedestrian visiting the crest area of coastal structure

Abstract

Wave overtopping can be a great threat to the pedestrians visiting the coastal structure’s crest area, but a good tool for risk assessment is lacking. In this study, a quantitative risk assessment framework was developed, which is based on considering the overtopping impact force acting on a pedestrian’s body. The centerpiece of the framework is a model for the likelihood of overtopping accident, which is defined as being mobilized by overtopping flow at least once during a visit. The largest single wave of a given sea state at the structure’s toe is first evaluated, and the maximum overtopping force of this largest wave is then calculated using a force predictor (assuming non-breaking waves before the structure), in which the human body is approximated as a cylinder. A probabilistic instability model, which was calibrated based on real-human experiments in flood flows, was developed in this study. This model converts an instability number, i.e., the ratio of maximum impact force to ground friction, into the probability of instability, so the likelihood of overtopping accident can be quantified. By applying our model to an adult standing on a 1-on-3 sloped revetment, it was found that the model gives thresholds of tolerable overtopping conditions (in terms of discharge rate and maximum overtopping volume) very close to those suggested in EurOtop (2018). A risk assessment framework, which quantifies risk as the sum of likelihood and severity, was proposed. The merit of this framework is that it can account for different pedestrian’s body size, location of the pedestrian, structure’s slope and etc. As a demonstration, the risk assessment framework was applied to Singapore’s coastal structures. Limitations of this framework are given at the end of the paper.