New Guidance to Prevent Seawall Overtopping

Dealing with overtopping is important to minimize down time and other impacts on coastal facilities.
Dealing with overtopping is important to minimize down time and other impacts on coastal facilities.
Chesil Beach in Dorset UK is a typical barrier type beach.
Chesil Beach in Dorset UK is a typical barrier type beach.
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In the UK and elsewhere in Europe, many kilometres of coastline are protected by sea walls and other coastal defences. These structures help to protect the coastline against erosion and coastal flooding.

Reduction of flood risk from wave overtopping of these structures is a key requirement for the effective management and improvement of coastal defences, particularly in the face of rising sea level due to climate change.

To provide designers with updated guidance on the design of coastal defences, HR Wallingford is leading a new project to produce a European Overtopping Manual. The new manual will incorporate newly devised techniques to predict wave overtopping at seawalls, flood embankments, breakwaters and other shoreline structures facing waves.

The UK's Environment Agency is the lead funder, with the work also supported by operational agencies in the Netherlands, Germany and Belgium. The new Overtopping Manual and associated calculation tools will be available in the summer of 2007.

For many years, engineers in UK have used the Environment Agency's Overtopping Manual to design sea defences. In the Netherlands a similar manual by the Technical Committee for Waterfront Structures (TAW) has been used.

Now HR Wallingford has formed a team with experts from the UK (University of Edinburgh), the Netherlands (Infram) and Germany (BAW and University of Braunschweig) to develop both a new commonly agreed European Overtopping Manual, and a set of advanced calculation tools, based on the results of UK, Dutch and European research.

'Since the release of the Environment Agency Overtopping Manual in 1999, significant new research has taken place in this area, said HR Wallingford's Professor William Allsop.

'DEFRA and the Environment Agency have funded a range of laboratory and field studies and we have the results of the EC CLASH and the EPSRC Violent Overtopping by Waves projects.

These studies have all generated new data and methods which will be of benefit to engineers'.

The new manual will be freely available over the web and supported by web-based programs for calculation of overtopping discharge and design details, together with appendices showing photographs and video of examples of overtopping processes, graphical presentations, case studies, and example calculations.

HR Wallingford is also working on a DEFRA funded project to map barrier beaches in the UK. Barrier beaches around the UK are important, not only in terms of defence against flooding but also in their own right as important coastal geomorphological features. The present understanding of the behaviour of barrier beaches is far from complete. This makes their successful and cost efficient management a challenging task, especially in the face of rising sea levels.

HR Wallingford, together with the University of Southampton and the Channel Coastal Observatory, has begun to map, classify and review barrier beaches around the coast of England and Wales.

This work is part of the DEFRA/ Environment Agency funded research project FD1924, 'Understanding Barrier Beaches, A Scoping Study', which will ultimately provide better knowledge and practical guidance and advice on their management.

'We want to look at all the issues that influence barrier beach management, said Dr Stuart Stripling, project manager for HR Wallingford. 'To do this, we really need support and information from those who have an interest in the future evolution of barrier beaches or spits, or in their immediate environment'.

The project team has set up a dedicated website - www. barrierbeaches. org. uk - to allow interested parties to contribute to the research. 'In particular we would welcome information and views on present problems and management issues relating to barrier beaches, said Dr Stripling. 'By taking a few minutes to visit the site and complete our on-line questionnaire, coastal engineers and others can help to guide the future management of barrier beaches and the environments that they create'.

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