PAPER NO: 140 Probabilistic methods for 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 defences.

In this paper the use of probabilistic techniques for risk assessment of sea defences is considered. Where a long set of simultaneous records of wave conditions and water levels are available a time series of the key design quantity (eg runup or overtopping) derived from the basic variables may be generated. This time series of the derived quantity, which has been termed the 'structure function' by Coles & Tawn (1994), may be processed using standard methods to determine extreme values and hence design criteria.