Nick on Floods

Rivers can be useful to human society in many ways. They provide a source of water, they can be pretty to look at, and in their lower reaches they are often surrounded by fertile soils and relatively flat land that's easy to build on.

That flat land is the floodplain. All rivers flood. Flooding is an entirely normal thing for a river to do. Hence, floods represent one of the most common natural hazards and are experienced in every country. So anyone who lives near the bank of a river can expect to be flooded every now and again.

Predicting just when an inundation will happen is a different issue. River flooding is usually caused by heavy rainfall and we can forecast rain. The Environment Agency issues flood warnings and people can be prepared.

But some types of 'flash floods', caused by heavy, highly localised rainfall, are very difficult to forecast. This was the situation in Boscastle, north Cornwall, in August 2004. The River Valency, normally little more than a trickle, suddenly became a surging torrent. It swept away more than 100 cars but, amazingly, no one was killed.

Fifty two years before, almost to the day, much the same thing happened just along the coast in north Devon. Torrential August rain caused flash floods to surge through several towns and villages, though Lynmouth was the worst affected. No fewer than 34 people lost their lives on that occasion.

Britain's coastline is also prone to floods from the sea. The most dangerous of these, the storm surge, drowned more than 300 people on Britain's east coast in 1953. Such devastating floods may be 'freak events', but their frequency is likely to be on the increase. Global warming will probably bring more intense rainfall as well as sea level rise. At some point in the future the results are likely to exceed the worst we have seen to date.

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