Ten years of lessons learned from English levee performance during severe flood events

The Environment Agency have carried out a structured review of defence performance after each of the five major events from the 2007 Summer floods, up to and including the winter 2015/16 floods. This presentation draws out overarching conclusions about how English flood defences perform during floods based on real life experience, and how this has driven and is driving improvements to asset management and design, supported by research. The five reviews covered all major breaches or near-breaches, but also assessed assets that survived in spite of being loaded beyond their design. Each review typically started with site visits to collate factual information but also to understand the local asset managers’ point of view and collect anecdotal evidence, essential to establish the story of the flood event. This was used to determine the failure modes that occurred, supported by hydraulic/geotechnical modelling as required. Key conclusions were that visual condition can only tell so much about risk of breach, and that local irregularities are often the trigger for failure. This has influenced how the Environment Agency prioritises its asset management investment in relation to Condition Grade, and has initiated focused studies to identify weak points such as transitions and historical channel crossings.