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Versatile flood barrier that doubles as a walkway is launched

A new low cost self-erecting flood barrier, that can double up as a waterside walkway when not in use, has been devised by a geotechnical academic from Nottingham Trent University.

Known as the "Greenwood flood barrier", the wooden cover lies horizontally on a concrete slab and floats upwards when inundated with water to form the wall of the flood defence.

The wooden cover is attached to an impermeable membrane, which covers a ground trench. This is backfilled with soil to keep the ground stable during flooding, and cuts off any ground water that may travel through the soil.

The cover is hinged to a ground slab, and when inundation starts a polyester float underneath rises, causing the hinge to pivot and form the wall of the flood defence barrier. Polyester ties, connected to the membrane, run down into the ground to retain the structure as the water pressure increases on the flood defence wall.

It is hoped the barrier could fill a gap in the market for a low cost, self-erecting barrier suitable for widespread use throughout the UK, where an estimated five million people live in homes at risk from flooding.

"Barriers that are currently available on the market are costly to install and maintain, too complex in their design and not self-erecting," said reader in Geotechnical Engineering at Nottingham Trent University John Greenwood. He has developed the system with consultant Faber Maunsell and PAGeotechnical.

When not in use the wood cover lies horizontally on the ground slab of the barrier "like a door lying on its side", and could be used by walkers along the waterside, added Greenwood.

A successful trial was carried out last September next to a lake at Lea Marston in Warwickshire, when the barrier rose to retain water at a height of 600mm for a 15m stretch adjacent to the lake.

"We think it's good to retain about 1m or so but most floods would not be more than about 300mm to 600mm deep."

Greenwood claimed there has already been lots of interest from developers and the Environment Agency because the current demountable flood barriers on the market still require manpower to erect.

"It fills the gap between the demountable barrier and permanent wall which are both very expensive," said Greenwood, adding that the barrier was close to gaining an international patent.

At a cost of £200 to £250 per metre to install, Greenwood said the barrier could also be attractive to developing countries vulnerable to frequent flooding.

Greenwood believes it might potentially be used for the temporary storage of water and protection against spills from tanks. If fitted with ground anchors, it could also retain water at much higher levels and then be used as a wave barrier to protect against tsunamis.

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