Total flood defence is a myth: we must learn to live with the water

Keith Beven in the Conversation: Floods happen. Rivers have always inundated their floodplains and the sea has always tried to reclaim land that has been taken from it.

...During the storms in December 2013, the highest storm surge since 1953, there were 26 breaches of the sea defences in East Anglia. But forward warning saw timely evacuations, properties protected and the Thames Barrier raised to counter the highest water level since it was built. Because there had been the will to protect and money to do so, nobody died. How much are we prepared to spend now, especially if as climate models suggest flooding will increase in the future?

...Low-lying areas at risk were avoided as sites for permanent habitation in the past. Flood plains were left as water meadows, and crops were planted in spring time to avoid winter flooding. With nothing to be damaged, the impact was minor. In 1954, the UK’s record highest annual rainfall was recorded at Sprinkling Tarn in the Lake District. The total that year was over 6,500 mm, the equivalent of 21 Cockermouth floods falling in a single year. Yet a trawl through the Cumberland and Westmoreland Gazette for 1954 reveals discussion of the fact that it did not stop raining, but little in the way of reports of damages – because there was little on the flood plains to be damaged.

Flood defences change that approach, bringing an unwarranted air of invincibility. Defences lower the risk of damage from moderate flooding, but this year, or the next, or within 10 years, at some point a flood that exceeds their capacity will arrive. The aim should be to reduce the impact of a flood when it does happen by limiting how the amount of people and property at risk behind the defences. Instead, building defences tends to encourage development behind the embankments or walls. In this way, even if overtopping floods occur rarely, the damages from those that do occur rapidly increase, even with major investment in flood defences....

Arundel Castle with grounds flooded in February 2014, shot by hehaden, Wikimedia Commons via Flickr,  under the Creative Commons Attribution-Share Alike 2.0 Generic license