Urban planning engineers explore anti-flood options

It rains in Britain in the summer; persistently and, until relatively recent years, predictably. The summer weather systems would see periods of good weather interspersed with weather fronts sweeping from Cornwall up towards the north-east coast, trailing curtains of rain.

That changed, unexpectedly and catastrophically, in June and July 2007. Rather than a procession of showers, a new type of rain emerged — localised storms, dropping a lot of water in one place over a short period of time. Villages and towns were overwhelmed.

In Boscastle, a river burst its banks and swept cars down the steep valley into the heart of the village, where they formed a dam and allowed water to inundate the town and harbour. Tewkesbury’s historic abbey was surrounded by floodwater on a newly-formed island. The civil and military emergency services estimate that the rescue efforts were the biggest ever launched in peacetime.

It has become obvious that the water management infrastructure in many areas was inadequate to manage this type of rainfall. Urban planning engineers are now starting to turn to other countries for advice; countries where localised heavy rainfall is more common. Odd though it may seem, the chilly, damp UK is looking to the tropics. ‘We are looking to take lessons from wherever we can,’ said Scott Steedman, vice-president of the Royal Academy of Engineering.

Wales, with its particularly soggy reputation, is looking closely at all options. ‘We’re well aware that we were lucky in 2007,’ said Roger Falconer, professor of water management at Cardiff University. ‘If the weather systems had been a little to the west, we would have borne the full brunt.’

Currently, urban flood management in most towns is limited to the Victorian infrastructure of drains feeding into the pipes under the streets. ‘Almost every major city in the UK is facing similar problems,’ added Falconer.

Other countries employ many techniques to control floodwaters, some of which may be more applicable to the UK than others. The best method, Falconer said, is ‘to create room for the water’. This involves planning areas of parkland in the zone where flooding is likely to occur, and diverting water into these when appropriate. This technique was used in Cardiff around the new Millennium Stadium.

Asian cities tend to have large open drain channels at the roadside, with further drainage down the middle; a technique which could be applied in UK cities, said Falconer. ‘This is something we might have to look at to contain surface waters.’

South American cities such as Buenos Aires accept that floods will happen and divert surface water down designated streets away from commercial and residential areas. ‘That is something that can be considered for new developments,’ added Falconer.

Other urban planning techniques include porous pavements placed on top of drainage channels and reservoirs underneath car parks to receive floodwaters. ‘It does represent an investment, but if you look at the £3bn that the 2007 floods cost, in damages and rescue efforts, it would be worth it.’

But although many techniques could be imported, UK engineers are also looking at the problem, with one new technology about to be trialled in the Midlands.

Devised by John Greenwood of Nottingham Trent University, the SELOC (Self-Erecting Low-Cost Barrier) is, he admits, not a high-tech solution. The barrier itself, originally made of wood covered with a waterproof membrane on the side facing the flood-risk area, lies flat on the ground most of the time, hinged along its bottom edge. As the water rises, it floats, with its top edge rising with the water level. A restraint stops it when it reaches the vertical.