Author(s): M. A. X. Van Baak
Linked Author(s):
Keywords: Storm; Erosion; UNIBEST-TC; Probabilistic Methods; Dikes; Morphology; Risk of Flooding
Abstract: At present, short-term morphological change is not taken into account during the safety evaluation of coastal sea defences along the Dutch coastline, mainly due to the uncertain prediction of the associated effects. In the Netherlands, coastal defence structures are subjected to strict safety criteria stated by the national government. The performance evaluation of these coastal structures is done with risk assessments to analyse the short-term morphological effects of a storm on the safety of coastal structures. Expression of these effects in erosion depth or local seabed change is not sufficient. It is far more sensible to discuss these effects in terms of probability of failure or required crest height of the coastal structures. The application of morphological models as well as a probabilistic interpretation is a necessity to determine the probability of failure for evaluation purposes. During a case study for the Pettemer sea dike situated in the Northwest of the Netherlands, a process based timedependent cross-shore model called UNIBEST-TC (Van Rijn et al., 2001) is used to assess the seabed evolution during a single storm at the sandy barred seabed in front of the sea dike. Furthermore, a probabilistic shell has been created to determine the additional risk due to these morphological changes. Contrary to the expectations, the probability of failure shows no significant increase due to the seabed erosion of the nearshore, whereas this seabed erosion just in front of the sea dike appears considerably. The increase in depth-limited wave heights remains marginal as well. This is mainly caused by the relocation of sand in seaward direction resulting in a longer and gentler, but deeper foreshore, with almost equal wave reducing capabilities as the original foreshore.
Year: 2003