A new approach to calculate extreme storm surges: analysing the interaction of storm surge components

The North Sea coast is, as well as many coastal regions, a preferred residential and industrial area. At the same time the North Sea coast is seriously threatened by storm surges. Climate change and resulting consequences will have severe effects on the safety in coastal areas. The Project XtremRisK - Extreme Storm Surges at Open Coasts and Estuarine Areas, Risk Assessment and Mitigation under Climate Change Aspects, will assist in facing this challenge. The "Source-Pathway-Receptor"-Concept will be used as a basis for risk analysis and development of new management strategies. Within the XtremRisK project, a method to assess extreme events will be developed which takes the hydrodynamics of storm surges into account. With this method, the components of a storm surge, tide, wind surge and external surge, and their interaction will beanalysed. The study focuses on analysing (i) the highest event of each component and (ii) the interaction between tide and surge as well as the interaction between surge and external surge. This detailed analysis is needed because the components do not interact linearly. With this knowledge, an extreme event based on the observed extremes of the components can be calculated. Non-linear addition leads to a lower water level than in case of linear superposition. With this approach, an extreme event can be calculated in accordance with natural law.Subsequently, extreme events will be assessed using conditions which reflect the climate change scenarios.