Safety Analysis of the ComCoast concept, Comcoast WP 3

Abstract

ComCoast COMbined functions in COASTal defence zones is a European project which develops and presents innovative solutions for flood protection in coastal areas. The ComCoast concept is designed to develop alternative defence systems and new sustainable flood management strategies to cope with increasing hydraulic loads. The objective of this research is to give a safety assessment for different configurations within the ComCoast concept. The model that has been developed is capable of calculating the failure probabilities of different ComCoast concepts. Since the calculations are based on a two-dimensional representation of a Coast-configuration the results of the calculations give an order of magnitude of the failure probability of the ComCoast concepts. It must be noted that the calculations are based on the assumption that the primary dike and the secondary dike are infinitely strong. Consequently, failure due to instability, erosion and piping is neglected. For the two case studies given both the failure probabilities and applicability of the ComCoast-concept differ significantly. A comparison is made between the two case studies for the situation where both cases just meet the required standard. This means a crest level of 8.4m NAP for the Hondsbossche Zeewering case and a crest level of 6.8m NAP for the Perkpolder case (Variant 2). The comparison shows that very little water enters the transitional area in the Perkpolder case. On average there will be an inundation depth of 0.01m every 300 years, whereas in the situation of the Hondsbossche Zeewering this inundation depth will occur on average every 4 years. Since one of the aims of the ComCoast concept is to create a wetland (transitional area) behind the primary dike, a ComCoast option seems less suitable for the Perkpolder case. The main reason why the return periods of inundation depths are long in the Perkpolder case is that the wave climate at Perkpolder is moderate. Overtopping mainly occurs with a high water level, which goes hand in hand with high return periods.Civil Engineering and Geoscience