Improved guidance for assessing the overtopping of
sea defences

Advances in our understanding of overtopping processes have been acquired from recent European wide research projects. Experts from these projects are now collaborating to produce a manual that presents a state of the art description of available methods for assessing overtopping and its consequences.

Understanding future changes in flood risk, from waves overtopping seawalls and other structures, is a key requirement for the effective management of coastal defences. Occurrences of loss of life and economic damage due to the hazardous nature of wave overtopping are becoming more frequent, and coastal managers and users are becoming more health and safety conscious. Seawalls make up most of these defences, and range from simple earth banks through to vertical concrete walls and on to more complex composite structures, and each of these require different methods for assessing the overtopping. In the UK, Environment Agency guidance on seawall design will be updated so that issues such as climate change, sea-level rise, and increased awareness of hazards, can be better taken into account.

Research for Defra and the Environment Agency, carried out at HR Wallingford, has provided techniques for predicting the mean overtopping discharge, and the consequent flood volumes and drainage requirements, for a range of seawall types. In the Netherlands and Germany there has been continuous research into overtopping at embankments and dikes, and the recent European research project CLASH has expanded our understanding of overtopping. Additional support for the manual has been offered by colleagues in Denmark and Italy.

One major step forward has been the production of updated guidance on the design of coastal defences. This is being produced by HR Wallingford, with inputs by European partners, in the form of the European Overtopping Manual.

The European Overtopping Manual will incorporate new techniques to predict wave overtopping at seawalls, flood embankments, breakwaters and other shoreline structures facing waves. Supported by web-based programmes for the calculation of overtopping discharge and design details, the manual’s appendices will give photographic and video visualisations of overtopping processes, graphical presentations, case studies, and example calculations.

TThe project is funded in the UK by the Environmental Agency, in Germany by the German Coastal Engineering Research Council (KFKI), in the Netherlands by Rijkswaterstaat, Netherlands Expertise Network on Flood Protection. A full list of organisations that are involved in the project is on the Partners' page.