Flooding of Coastal Flood Prone Areas: Examples, Initiation and Probabilistic Model Approach: Fid-Bau Portal

Flooding of Coastal Flood Prone Areas: Examples, Initiation and Probabilistic Model Approach

Kortenhaus, A. / Oumeraci, H.

In Germany and many other coasts in the world flood prone areas are protected by sea dikes. Generally, the design of such structures is still based on purely deterministic or quasi-deterministic approaches and is either based on the design water level superimposed by the maximum wave-run-up or on admissible wave overtopping rates under extreme storm surge conditions. Geotechnical failure modes of sea dikes are often disregarded and not properly accounted for in the design process. Analysis of failure modes of sea dikes in Germany has shown why failures of sea and river dikes have occurred in the past and how breaching of dikes develops. The key steps to predict dike breaching are therefore to (i) properly describe the hydrodynamic loading of dikes; (ii) to identify the initiation mechanisms such as erosion and impacts on the dike body; and (iii) to provide a suitable model to predict breaching. The paper will deal with a probabilistic model providing the overall failure probability of a coastal defence system in Germany and Denmark. For this purpose the breaching process of sea dikes is regarded as an essential failure mechanism. The paper will give a brief overview of developments which have been made in improving existing analytical models for dike breaching in sand dikes under constant overflow conditions. This approach is then extended towards wave overtopping conditions for clay covered sea dikes. The probabilistic model uses a detailed fault tree approach taking into account 25 failure mechanisms of sea dikes, including the time dependencies between some of them. Uncertainties of the parameters and their influence on the overall result will be discussed. Results of the model and application to a real case study are also presented.