Minor drainage not to blame for summer floods

27 February 2008

Intense rainfall overpowering drains was not to blame for last summer’s floods, according to research from the University of Sheffield.

Rainfall mm per hour rates in Hull – similar to those in Sheffield – were, in fact, less than mediocre, even during the heaviest downpours last June, shifting the apparent blame for the floods away from minor drainage systems such as highway drains, sustainable drainage systems (SUDS) and sewerage systems, to the major systems they empty in to.

The research, by Sheffield University researcher, John Blanksby, appears to contradict the official Environment Agency line that most of the problems were caused because ‘drains and sewers were overwhelmed’.

Most minor systems are designed to deal with rain of a one-in-30-year intensity. On 25 June, the day of the worst flooding, intensity in Hull was at less than a one-in-five-year intensity, meaning it would have taken a serious flaw in the system for it not to cope with the levels of rain experienced.

Introducing the findings at a recent Technical Advisers Group (TAG) seminar, Banksby said it was unlikely that drains would be in such a condition, and thought the problems were caused by the sheer amounts of water in the major systems, due to the amount of rain which had fallen in the previous weeks. This caused the whole system to back up, and the rain that fell on 25 June was the final straw.

Mr Blanksby also offered some opinions on why the confusion might have occurred, including media pressure for quick answers, laziness, and hubris, meaning that people assumed they knew the answers and did not bother to carry out proper research, and the need to find someone to blame who could be expected to bear the costs.

At the same seminar, John Charlton, head of Sheffield City Streetforce, refuted the idea that poor planning decisions had added to the misery caused by the floods, pointing out that, for as long as he could remember, Sheffield had not given permission against Environment Agency advice. It was also noted the lack of drainage engineers in local government, as highlighted by Sir Michael Pitt (Surveyor, 31 January 2008), was being exacerbated by the skills shortage, the lure of private pay packages and the fact that many engineers are nearing retirement.

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