V. Vuik

Fully probabilistic assessment of safety against flooding along the Dutch coast

This paper describes a fully probabilistic safety assessment of the Dutch North Sea coast, in which stochastic properties of both hydraulic loads and strength of the flood defences have been taken into account. The study has led to an overview of failure probabilities along the coast with high spatial resolution. Both dikes and dunes have been considered. Failure probabilities at individual locations have been combined to flooding probabilities per dike ring area. The vast majority of the Dutch coastal defences is quite secure in terms of flooding. This study demonstrates that generally, the Dutch dunes provide a higher degree of safety than the sea dikes. When incorporating the consequences of flooding to the analysis, the calculated flooding probabilities can be used to determine flood risks. The probabilistic method, presented in this paper, enables accurate balancing between avoided flood risks and investments to reinforce the flood defences.

Probabilistic assessment of safety against dune retreat along the Northern-Holland coast

Coastal zone management is a multidisciplinary issue that can be assessed from multiple viewpoint s such as safety, recreation, ecology and nature. A possible means for properly maintaining the various functions of the coast is sand nourishments along either the shoreface and/or the beach. To assess the influence of sand nourishments, the time-dependency of appropriate indicators of the various coastal functions can be analyzed. nHKV has conducted a study that focuses on the probability of failure for dune erosion, as an indicator for safety. For this purpose, the yearly JarKus measurements from the online OpenEarth-database are used. HKV has computed the probability of failure for dune erosion for the entire Dutch coast, from 1965 until 2010, using the dune erosion model DUROS+ and the probabilistic method FORM (‘First Order Reliability Method’), as implemented in the package PC-Ring. This approach is closely re lated to the approach of the project Flood Risks in the Netherlands (FLORIS/VNK). nThe current paper presents results of these computations, in relation to previous nourishment activities, for the region of Northern-Holland. These gained results can be used to further analyze the effectiveness of nourishments and can hence benefit future nourishment strategies by providing a decision supporting framework.