2:34pm Thursday 6th February 2014
Sir – Richard Knowles (Letters, January 23) is dismayed by the prospect of river dredging.
Rivers naturally silt up and if we wish to continue living in urban areas beside them, some level of maintenance is required. It is surely not beyond the wit or endeavour of humans to commence dredging on the lower reaches of any river.
On the Thames, one could start just above the Thames Barrier. I estimate that a team of 20 could cover 50 metres a day and clear the entire length of the Thames over a period of ten years, at a cost of about £10m.
As to the effectiveness of dredging it is simply a matter of physics (or mathematics). An increase of five per cent in the capacity of a river would allow more water to be moved out to sea at times of flood and, more importantly, before the flood waters build up. Dredging also allows the banks to be raised in places where they are low.
All this costs money but nothing like the millions required for an extra river around Oxford. The antipathy of the EA to dredging arises more from its hope of saving money at a time when its budget is being slashed. There is no scientific basis for their objections to dredging.
Tree-planting schemes and storage of water on land would only have a marginal impact on flooding. There is virtually no transpiration from trees in the winter and all of the low-lying fields around the Thames already remain deep in water for several weeks during and after the floods.
It is possible that nothing much can be done to avert the catastrophic events of say 1852 or 1947 but, for the most recent flooding, better planning (and dredging) would probably have been effective.
Dr G. Ledger
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