The calamity which has befallen Cockermouth and Workington offers a grim lesson for flood defence planners: there is only so much you can do.
This week's floods in Cumbria are different in nature from recent severe inundations which hit Britain, such as the flooding of Hull and Doncaster in June 2007 and the flooding of Tewkesbury and the Severn Valley in Gloucestershire the following month. Each of those emergencies offered valuable learning experiences for flood relief experts. The first highlighted a quite new problem: surface water. The floods that devastated the Yorkshire towns had nothing to do with the usual cause of urban flooding, an overflowing river – they were caused by the sheer volume of rainwater in the streets, which overwhelmed drainage systems.
There was no warning of the danger, because no one had ever seen so much water in the gutters and nobody knew how it would behave. The Environment Agency knew all about river and coastal flooding, but surface water was a complete unknown. Now, engineers are busily studying the problem. The lessons learned from the Severn Valley was different, but equally valuable: it concerned the vulnerability of infrastructure. Previous floods had tended mainly to affect houses, but in the Tewkesbury area water pumping and electricity substations were knocked out, and thousands of people beyond the immediate flood area were threatened with major loss of services. Once again, this is a message that has been taken to heart, and now infrastructure protection is central to flood defence.
In fact, all the lessons learned from the 2007 floods were brought together in a report last year by Sir Michael Pitt, who made 92 recommendations, such as the setting up of a specialised new flood warning centre to be run jointly by the Met Office and the Environment Agency. The Government accepted every suggestion.
But what lesson can be learned from the misery inflicted upon Cockermouth and Workington? What defences could have stood against the raging River Derwent, swollen with the heaviest rainfall Britain has ever experienced in 24 hours? What defences could have prevented the quite extraordinary sweeping away of Workington's Northside Bridge, which would not have been swept away themselves?
The 2009 Derwent flood should really be compared to the Lynmouth deluge of August 1952, when a storm of similar intensity (9in of rain in 24 hours) broke over Exmoor, sending a tidal wave of water down the narrow gorge of the River Lyn and devastating the village at its bottom, killing 34 people. Call it an act of God, call it what you like; nothing could have stopped that, as nothing could have stopped the power of the Derwent this week. In the past decade, Britain has started to take very seriously the issue of flood defence, heeding the warnings of climate scientists that global warming will mean more intense winter rainstorms with floods following in their train. But there will always be some cases, as the Environment Secretary, Hilary Benn, recognised yesterday, when nature's force is just too strong.
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