You will have solved nothing while creating a host of new problems.Īmong these problems, the Environment Agency points out, are:ġ. If you cut it off from its floodplain by turning it into a deep trench, you might raise its capacity from, say, 2% of the water moving through the catchment to 4%. You can increase the flow of a river by dredging, but that is likely to cause faster and more dangerous floods downstream when the water hits the nearest urban bridge (something the residents of towns like Taunton and Bridgwater should be worried about). Is that not bleeding obvious? A river's capacity is tiny by comparison to the catchment from which it draws its water. Since the floodplain volume is usually many times larger than the channel volume, the concept becomes a major engineering project and a major environmental change." Dredging of river channels does not prevent flooding during extreme river flows … The concept of dredging to prevent extreme flooding is equivalent to trying to squeeze the volume of water held by a floodplain within the volume of water held in the river channel. It reflects what his advisers in the Environment Agency have been trying to say for years, before being sat on by ministers wanting instant answers to complex problems and then – as the government still plans – being sacked in droves.Ī presentation by the agency, called To Dredge or Not to Dredge?, spells out the problems in terms that even ministers can understand: "The river channel is not large enough to contain extreme floods, even after dredging.
Coming from the man who insisted in November that he would do what he could to help farmers keep the hills bare, this was an astonishing and welcome turnaround.
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