Raising the bar

IntroFlood prevention is a costly business. Which is why a new low-cost, self-erecting barrier is winning plaudits. By Heather Kirkman.

Three years ago John Greenwood, a reader in geotechnical engineering at Nottingham Trent University (NTU), had an idea. The idea, which he originally demonstrated in a home baking tray, was a self-erecting flood barrier created by placing a geomembrane in a back-filled trench and attaching it to protective rigid covers and floats.

Three years later and SELOC – the Self Erecting Low Cost flood barrier – is now ready for production having successfully retained 900mm of water along a 15m stretch as part of the barrier’s final trials at the Environment Agency (EA) Lea Marston site.

“We were delighted with the trial,” comments Greenwood. “We invited representatives from a number of relevant companies and associations and the feedback was incredibly positive. It certainly confirmed that there is great interest in, and demand for, an affordable self-erecting flood prevention system.”

Design concept
SELOC is the result of collaboration and ongoing development between three parties; Greenwood (as part of Nottingham Trent University), engineering consultant AECOM and Midlands-based materials specialist PAGeotechnical who saw the potential in Greenwood’s simple, yet highly-effective design concept.

“Existing flood prevention systems, such as tilt dams and permanent walls, are either costly to install and maintain, require manpower to activate or are visually intrusive,” comments Peter Atchison, director at PAGeotechnical, and who has been involved in the project from its start.

“In the case of SELOC we have something based on a straightforward design, which means comparatively low material and construction costs.”

What SELOC does require, however, is thorough analysis of the land that the barrier is to be installed within, a process that will be undertaken by partner AECOM. Data such as predicted groundwater conditions and soil analysis will be collated and then considered in line with overall efficiency of construction, safety in operation and convenience when not in use.

This will be undertaken prior to commencement of the installation, which is straightforward requiring only “low tech” excavation equipment and manual labour under engineering supervision.

When not in use the barrier rests at or near ground level, protected by the rigid covers. These covers are hinged from a reference kerb that can be made from timber, concrete, plastic or other composite materials. The hinge may be the geomembrane itself or a positive mechanical hinge, depending on application.

Where the barrier is constructed in an urban area or as a walkway or roadway kerbs of timber, concrete or other suitable material may be placed at the edges of the backfilled trench to support more rigid covers that can withstand traffic loading.

Overall stability of the flood barrier itself is maintained by the mass of soil backfill replaced in the trench, slabs of concrete or other material on top of the backfill and by flexible ties attached to the geomembrane. This can form an extension of the geomembrane and resist the hydraulic forces on the erect barrier. The geomembrane also acts as a cut-off to prevent flood water passing beneath the barrier.

Clever idea
“The SELOC barrier is a wonderful example of British, and specifically Midlands’ innovation at its best,” comments Janet Bailey, chair of Advantage West Midlands’ Environmental Technologies Cluster, who attended the trial. “What started as one person’s clever idea has, through the collaboration and dedication of experts from across industry and academia, become a tangible, fully-functioning technological solution.”

And it is a solution that cannot come quickly enough. The EA reports that five million people in England and Wales now live in properties at risk from flooding, and climate change continues to result in extreme weather conditions, such as those that caused the widespread devastation and distress in Cockermouth last November.

“Obviously the first priority is helping those in the UK that are at risk, both now and in the future” comments Greenwood. “And as such we’ve already seen interest from developers and the Environment Agency.

“I also believe given the costs involved in dealing with the aftermath of flooding, which in Cockermouth’s case is predicted to be in excess of £100M, insurance companies and local councils will also take a closer look at this technology.”

In addition to becoming the first affordable alternative to existing flood barrier prevention methods SELOC, which costs between £200 and £250 per metre to install, is also suitable for other applications such as temporary storage of water, protection around storage tanks where spillage could cause a hazard and control of drainage waters and balancing ponds.

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