Flooding: Ready for more?

The top story on the Kent and Sussex local news early last month was how torrential rain had brought flash flooding to the south east, shutting a shopping centre in Bexley and drowning cars in the streets of Hastings. Since then there have been regular reports of local flooding around the country as the rain continues to fall.

But so far there has been no repeat of the summer 2007 conditions that trapped 10,000 people on the M5 overnight, swamped the Mythe water treatment works in the Midlands and made thousands homeless in Hull.

By the end of the emergency 55,000 properties had been flooded, 7,000 people rescued, 13 had died and the insurance bill had topped £3.5bn, without counting the cost of lost working days or the impact on the NHS and other emergency services.

Extraordinary weather

The weather that produced the 2007 floods was extraordinary − equivalent to a one-in-250-year flood. Drainage expert and former managing director of Micro Drainage Aidan Millerick kept a close eye on events at Thatcham in Berkshire, not least because he used to live there and some of the firm’s staff still do.

“In the 30 days prior to 20 June there had been 113mm of rain − twice the long-term average. On top of that wet ground, on the night of 20 July we had 100mm of rain, but the real problem was that 82mm of that rain fell in just six hours,” says Millerick. “Local folklore that the drains and gullies were blocked was irrelevant as they couldn’t have taken that level of rainfall, at a guess they could manage 15%. So we have to analyse what happens to the above-ground flow.”

“The real problem was that 82mm of that rain fell in just six hours. The drains and gullies couldn’t have taken that level of rainfall.”

Aidan Millerick, Micro Drainage

More than 1,000 homes were flooded in Thatcham, all by surface water pluvial flooding, which until 2007 had been largely ignored by the flooding agencies, which were concentrating on the damage that could be caused by river and sea inundation.

Millerick spent the months after the floods tracking that above-ground flow. “We worked it up pro bono, we were very interested. You never get an extreme live event against which to test your models and ours correlated exactly with the insurance claims.”

What the study revealed, he says, is that plans to route excess water through the streets as outlined in the Department for Environment Food and Rural Affairs report, Making Space for Water, need to be backed up with some research on the volumes that can be carried safely. “A half a metre moving at one metre a second would sweep adults off their feet and vehicles off the ground. This is what happened at Thatcham just outside a local primary school just as the children were coming out to meet their parents,” says Millerick.

Precautionary measures

Much of the blame for the general damage around the country was directed at developments on flood plains or at too high a density. “But at Thatcham it wasn’t local development that caused the problems,” says Millerick. “It was the farmland above the town. The ground was so saturated it held up only between 10% and 20% of the rainfall.” The rest of the water poured through the town and the local council is now looking at putting in underground storage to halt flows in the event that conditions are repeated.

Underground storage would be sustainable urban drainage systems (SUDS) of the hard variety.

“If you ask me two years on if we are any better prepared to deal with major floods I’d have to say ‘only marginally’.”

David Balmforth, MWH

And SUDS, particularly the soft versions of swales and ponds, feature prominently in the recommendations of Sir Michael Pitt’s review of the events of 2007 and the Flood and Water Management Bill draft that is expected to be enacted in the next few months (see box at end).

“Pitt’s was a good report,” says MWH technical director and ICE vice president and flooding expert David Balmforth. “I am very positive about it. It has strategically changed our thinking.

“But if you ask me two years on if we are any better prepared to deal with major floods I’d have to say ‘only marginally’.

“The really significant event that has gone on in the foreground is the establishment of the joint forecasting centre between the Environment Agency and the Met Office, which will give significant benefit allied to the fact the Met Office forecasting is a lot better anyway. And I think the emergency response would be better. The hearts and minds of those agencies are brought in and if there was a similar emergency there would be better co-ordination.

Physical measures to manage flooding are taking longer, admits Balmforth. “With critical water infrastructure for instance, the water companies have a much better handle on the flood risks and where the at risk properties are, but whether we are better at protecting them, I expect we’d struggle at the moment,” he says. However, action is moving closer.

Strategies moving forward

For example at Mythe, Severn Trent and its consultant Mouchel are moving forward on a strategy to protect the works which sits beside the rivers Severn and Avon. Some of the £32M flood damage was still being repaired last month. A temporary flood barrier is expected to be replaced by a more permanent flood wall in the coming months. Severn Trent delivery manager Colin Church says this is happening all around the Severn Trent region.

“We provided temporary flood defence to five sites and now we have a rolling programme to put permanent flood defences at each of those,” says Church.

The Floods and Water Management draft Bill that followed Pitt’s review has been generally well received, says Balmforth.

“One of the key references out of Pitt is to tidy up the legislation and that opportunity has not been taken.”

David Balmforth, MWH

“The stuff that was desperate is in − like the removal of the right to automatically connect for developers. The disappointment is that one of the key references out of Pitt is to tidy up the legislation and that opportunity has not been taken.”

This is particularly relevant for SUDS where there has been a long running dispute over who should adopt them. The Bill sorts that out in one respect − local authorities will have a duty to adopt SUDS.

The problems arise when the plan is to drain the SUDS into the sewers, which are managed by the water companies. They have no obligation (and therefore no funding) to take water from land drains and certain SUDS elements can be construed as draining land. So the uncertainty and disputes are likely to continue.

But as Balmforth says: “If we just look at the short-term measures we are missing a key element of Pitt. The key issue is our thinking and how we shift from defence to creating resilient communities. We need a rethink in how we design the urban area.”

Learning lessons

Balmforth chairs an interinstitution panel on flooding that is looking to do just that.

The ICE, Royal Institute of British Architects, Royal Institution of Chartered Surveyors, Landscape Institute, Royal Town Planning Institute and Chartered Institution of Water and Environmental Management are looking at how to design urban areas to accommodate the passage and storage of water more safely in floods, control run off and get an amenity bonus. “We want to visibly place water in the urban community, improving its visual appeal, biodiversity and help deal with the heat island effect in hotter summers,” explains Balmforth.

It seems we have learned lessons from 2007, are a little better prepared, and if you are of an optimistic mind, the flooding of 2007 could result in an improvement in all our lives.