Application of Dutch reliability-based flood defence design in the UK

Increasing concern about recent and potential impacts of flooding in the UK are leading to the adoption of risk-based methods for planning, appraisal, design and operation of flood defences. Probabilistic methods for assessment and design of flood defences are relatively well developed in the Netherlands because of the potentially devastating impacts of flooding. However, for reasons described in this paper, reliability methods developed in the Netherlands are not universally applicable in the UK context. This paper describes a test application of a reliability method developed for ring dykes in the Netherlands to the flood defence system at the Caldicot Levels in South Wales. Although constrained by data limitations (even at this relatively data-rich site, by UK standards) the reliability method provides estimates of the probability of failure of the flood defence system, identifies weak system components and identifies which parameters contribute most to the probability of failure. The study has provided recommendations for the future development of reliability-based methods for flood management in the UK.