Risk based inspection of flood defence dams: An application to grass revetments

In The Netherlands, inspection and maintenance are essential for maintaining stringent flood protection standards. Flood defences are assessed every 12 years to ensure they meet their risk-based safety standards,which are given as legally-binding maximum failure probabilities. Between assessments, flood defence managers are subject to risk-maintenance requirements: they must ensure that the failure probability of the defence does not increase in excess of its safety standard. However, there is no prescribed methodology to meet this requirement. In the study presented here, we developed a method which enables flood defence managers to derive inspection strategies using visual inspection data that will allow them to meet their risk-maintenance requirements.We applied the method to the assessment of grass revetments on the outer slope of the Oesterdam, one of the dams of the Dutch Delta Works. The application illustrates how – using visual inspection data, degradation information, and a failure mechanism model – inspection intervals can be derived that will ensure the risk-maintenance requirements are met.