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TIME TO GET RADICAL

David Balmforth* says we must change our ways or face the consequences of increased flood events.

It is said that the memory of flooding fades quickly. It is certainly true that in recent history flood risk has not been very high on the political agenda. Even the publication by the Office of Science and Technology's Foresight report on climate change, floods and coastal defence did little to stir the imagination of politicians or the media. However, there is nothing like a major flood to capture attention, and recent months have seen flooding in the UK on an almost unprecedented scale. Following one of the hottest and driest summers on record makes it even more remarkable. The exceptional combination of prolonged rainfall followed by very intense storms (over 100 millimetres of rainfall in 24 hours) was repeated over several weeks, creating flash floods first in the north of England, the Midlands, in the South West and finally in the Thames Valley. Few parts of England and Wales were spared. In Hull alone over 10,000 properties were flooded and over 4,000 school children could not attend school.

Flooding is one of the greatest global hazards, forming 65 percent of all natural disasters and affecting over six billion people worldwide. In the UK over two million homes are at risk of flooding with the average annual damage cost exceeding £1.4 million. More than £800 million is spent annually on flood risk management. Areas prone to flooding cannot support agriculture and cannot contribute effectively to wealth creation. Despite advances in understanding of the underlying science, and the extent of experience in flood risk management, comprehensive flood risk management is not available to most of the world's population. Even in developed countries significant parts of the population are at risk from flooding, and flood-warning systems are often rudimentary.

The cause of flooding is often complex. Flooding occurs when drainage channels have insufficient capacity to drain surface run-off. In natural systems, streams and river channels will overflow creating a flood plain which has the dual function of providing additional conveyance capacity and temporary flood storage. Flooding may be caused by local lack of channel capacity, by flow backing up from downstream overloaded channels, and by the passage of flood flow across the flood plain. It can be localised, due to the run-off from a single field, or widespread. Regions near the coast are susceptible to flooding from the sea which can be caused by particularly high tides and storm surges.

For historic and legal reasons the responsibility for managing flood risk is also complex. Many different bodies are engaged, ranging from local authorities, highway authorities, water companies, land drainage boards, the Environment Agency and individual property owners. Identifying the causes of flooding and developing a holistic solution is hampered often by the different structures and statutory duties of these bodies. This makes engagement with the public, the ultimate customer in flood defence, particularly difficult.

If all this was not bad enough, current research on climate change shows that the infrequent extreme events of recent weeks could become much more the norm in the future. By 2080 flood damage costs could rise to eight times the present value with the cost of flood defence rising by an even greater amount. Even in the unlikely event that resources became available for flood defences, such extensive construction would damage badly our ability to meet carbon reduction targets. Future flooding can only be tackled through a radically different approach.

The foundations for that approach have been laid in Defra's 'Making Space for Water' and in Planning Policy Guidance PPS25. Both these raise the need to embed flood risk management into urban design. However, current interpretation of PPS25 is unlikely to deliver the radical change that is needed without better engagement with planners. This is essential in the context of planning for three million new homes.

The Construction Industry Research and Information Association (CIRIA) has produced some valuable guidance on how to design urban areas to safely and effectively manage flood flow on the surface. It includes advice on how to design roads to also act as flood channels, to use car parks as temporary flood storage areas: even to designate parts of our urban areas to be 'sacrificial' flood areas during extreme flood events. But there is little evidence that such guidance is being taken up actively.

If we are exceptionally (and it must be exceptionally) to build on flood plains then we must allow space for flood waters to pass through. Compensating storage and sustainable drainage systems have little effect during extreme events. Conveyance capacity is the answer and we need to lay out our new urban areas to achieve this. The CIRIA Guidance should be followed. In addition, housing must be made much more flood resilient, raising living areas above street level, and using materials which are more resistive to flood damage.

For such a radical new approach to flood risk, the public will need to be convinced these measures are workable, equitable and affordable. This requires much better engagement with the public, both strategically and locally, than has been evident in the past. There needs to be a much more coordinated approach between the different stakeholders responsible for flooding in our urban areas. The Defra Integrated Urban Drainage Pilots are an important step in the right direction. An early appraisal of PPS25 and the value of strategic flood risk assessments would be a further step forward. Overall, there is a strong argument for one lead industry body with an overarching responsibility for managing urban flood risk. This could provide a welcome focal point for the public and also be the important catalyst for change.

*David Balmforth is a Technical Director with MWH, a Visiting Professor at Imperial College and Editor-in-Chief of the CIWEM Journal on Flood Risk Management.