Coastal Flood Risk Assessment

In many parts of the world, design standards now require the assessment of risks. Measures of risk are often qualitative, with descriptors such as “high,”“low,”“intolerable,” or “negligible.” The practitioner is thus left with the task of reconciling the qualitative assessment of risks with the quantitative demands of design. Probabilistic techniques are being used increasingly for the design and assessment of sea defenses. In this paper the use of probabilistic techniques in risk assessment for sea defenses is considered. The respective advantages and disadvantages of different techniques are discussed. Some new approximate methods are described and compared with existing approaches. Example calculations based on 21 years of synthesized wave and water level data are presented for the case of wave overtopping. The different methods are employed to calculate the probabilities of exceeding the overtopping threshold for two structures. The results are used to discuss what might be considered practical and realistic in terms of risk assessment for sea defenses, and to identify areas where further research could be beneficial.