Beyond inner slope instability: a method to quantify the residual dike strength by wave overtopping

Climate change increases the risk of grass dikes being breached as hot weather weakens grass covers while more frequent high water is present. This can result in initial damage to the dike cover, in which case the dike does not fully breach. Understanding of the residual dike strength is essential from a flood risk perspective to efficiently design dikes against extreme events. This study assesses the residual dike strength by wave overtopping by evaluating a newly developed framework for the failure probability of overtopping waves of grass-covered river dikes. A method following this framework is used to derive fragility curves that describe the failure probabilities at varying water levels. To extend the current Dutch safety standards, fragility curves obtained by wave overtopping can be combined with the instability occurrence.