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Beavers can give engineers a run for their money any day

Reading Ian Johnson's letter (NCE 1 November) brought back very clear memories to me of the storms of 1968 that caused the severe flooding of the Wey Valley in the Guildford, Chertsey and Weybridge areas.
Some 180mm of rain fell in the 48-hour period leading up to those floods, which saw river levels rise by 5m in Guildford.

I recall driving during the height of the storm and also saw water cascading off agricultural areas onto roads. As a junior engineer working for Guildford Rural District Council at the time, I worked for months afterwards in the clean-up and analysis of the causes and lessons.

While it makes sense to try to avoid rapid run-off onto highways, one of the main conclusions I recall was that it was the cleaning out of ditches and removal of the balancing capacity that many of the old village ponds, and the general shortening of run-off routes to streams and rivers, that had contributed to the problem.

If one is going to intercept agricultural run-off by digging out ditches and putting land drains as Ian Johnson suggests then this must be coupled with adequate balancing storage to slow down the arrival of the flow into the main water courses.

Nature, of course, does this very effectively – if left to its own devices – by clogging up ditches and forming bogs and marshes, sometimes with a little help from some of our capable engineering cousins in the animal kingdom such as beavers.

Lytchett Matravers, Poole, Dorset, BH16 6AY

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