Assessing the joint probability of sea conditions: A robust approach

The design of breakwaters and other coastal structures around the UK requires the assessment of the joint probability of extreme waves and sea levels. There is a standard simplified approach applied within the UK that uses joint exceedance contours of waves and sea levels. This simplified approach can be non-conservative and lead to the under-design of coastal structures unless correction factors are applied. These limitations have been known for a number of years and alternative, more robust, methods have been applied in the past. These alternative methods are risk-based as they enable the probability of the consequence (structural or serviceability failure) to be established. The more robust methods are not, however, widely used in current practice. This paper describes the development of a statistically robust nearshore multivariate extremes data set around the coastline of England. The dataset can, in principle, be used to undertake risk-based design of structures, thereby overcoming the limitations of existing practice.