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Water Proofing

With floods becoming a matter of course in the UK, flooding expert David Balmforth explains what he thinks should be done.Flooding by Margo Cole.

The 2007 floods in the UK were a wake-up call to a situation many experts had been predicting for years. ICE water panel member and MWH director David Balmforth says: “We should not have been surprised by the 2007 floods.    

Although they were 1:100 events, there is a 50% chance of a flood of that severity happening somewhere in the UK in any year. By 2050 it could be 100%.”

In the aftermath of the floods, the government commissioned Sir Michael Pitt to look into what happened and what could be done differently in the future. His review concluded: “The scale of the problem is likely to get worse. We are not sure whether last summer’s [2007’s] events were a direct result of climate change, but we do know that events of this kind are expected to become more frequent. The scientific analysis we commissioned as part of this review shows that climate change has the potential to cause even more extreme scenarios than were previously considered possible. The country must adapt to increasing flood risk.”    

As chair of the group that produced the ICE report “Flooding: Engineering Resilence,” published alongside the Pitt Review, Balmforth agrees. “Flooding is not something we will be able to prevent in all cases,” he says. “It’s the price we pay for burning carbon into the atmosphere. We are going to have to move from a defence approach where large structures are built to hold back flood water to building resilience within our communities so they can better cope with future floods.”    

We have to move from a defence approach to building resilience within our communities so they can better cope with floods  

This will require a “significant shift in our thinking” away from the traditional idea of protecting property to recognising flooding is going to occur and learning to live with it, according to Balmforth. “We can’t protect everyone from flooding in the future – it’s unaffordable,” he says.    

The first step is to stop making the situation worse by building in flood risk areas. After that, the focus switches to people at risk of flooding to see if their homes and work places can be made resilient. Balmforth believes flooding should be considered at a far earlier stage than it is now in new developments and regeneration projects. “We need to give flood water more space in urban areas so it doesn’t get into buildings or threaten life,” he says.    

“We need to rethink the way we design roads and the way we lay out housing, and we need to be doing it now. Once the buildings are in place, there is no longer the opportunity.”    

Examples from the Netherlands show how this can be achieved, with ditches (or swales) carrying clean storm water alongside urban roads and capable of coping with higher flow conditions in emergencies. Removing storm water from main sewers prevents them from overflowing during flood conditions, while keeping the storm water above ground means residents are more aware of water on a day to day basis, and the water could provide an amenity in the form of ponds and canals.   

Harvesting rainwater  

As part of a £1.4M surface water management strategy, Dwr Cymru Welsh Water is trialling a simple, cost effective rainwater harvesting device that will reduce water flows into the sewerage system, thereby reducing downstream flooding and pollution incidents.    

The first device has been installed at the Cilfynydd sewage treatment works and educational centre in South Wales.   

“Reducing the quantities of surface water that enter the combined sewerage system is vital, and a rainwater harvesting strategy can be a key part of this, while at the same time reducing customers’ bills,” says sewerage manager at Dwr Cymru Welsh Water David Bayliss. “Water collected by the system will initially be used only for toilet flushing, but this may be extended for garden watering and other external uses that don’t require water of drinking quality,” he explains.

Indications so far suggest that, if such a system was fitted to a typical metered three bedroom terraced house, significant savings in water could be achieved, reducing customers’ bills as well as reducing water flows into the sewerage system.  

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