Innovative plastic flood barriers provide 'Ring of Steel'

An innovative flood barrier fabricated from recycled plastic is securing a “ring of steel” around properties in the flood-prone Stamp End area of Lincoln, as part of a £800,000 multi-agency surface water management project.

Lincolnshire County Council’s drainage team devised the novel use of Duraplas® recycled plastic profiles and posts from Centriforce Products to build a 335-metre-long low-level flood baffle.

The barrier provides an important last line of defence alongside other surface water measures to deliver 1 in 100 year + climate change flood protection around a residential Tower Block and surrounding social housing close to the River Witham.

In 2007 more than 110 properties were inundated and some 200 residents were evacuated from their homes for several days in a major incident-level flood. The County Council took on the job of resolving surface water flood protection in the area when it became a Lead Local Flood Authority in 2010.

The imaginative flood baffle has delivered a solution with very low maintenance and minimal through-life costs, necessary to ensure adoption by Lincoln City Council, expected in 2017.

Nathan Whitfield, Lincolnshire County Council’s Principal Drainage Engineer: “Conventional flood barriers like a bund or a brick wall were ruled out because of the large number of underground utilities criss-crossing the site, some of them quite close to the surface. This solution gave us the versatility to adapt the spacing of the posts, or even the route, to fit around the utilities while still getting a good 300mm depth of protective barrier underground.

“Because we needed to build a barrier to fit the site, rather than specifying a pre-manufactured product, my team opted to build the baffle out of raw materials. After digging a shallow trench, they used the recycled plastic profiles to build a parallel ‘rail and post’ construction, then filled the core and base with concrete.

“Our contractor found the posts and profiles very easy to handle and install. So they could be easily, cut, routed and shaped to deliver the design we needed.”

Led by the County Council, the project’s partners also included public authorities and private businesses and obtained £461,000 Grant in Aid partnership funding from DEFRA and £131,000 contribution from Anglian Water. The scheme also included work to optimise the capacity of the surface water sewer network in the area which was achieved by diverting peak flows to a new downstream pump station which discharges to a water course adjacent to the river.

The flood baffle will hold back any low level surface water flooding in the case of a peak flood to ensure the properties it surrounds are fully protected. Any attenuated water contained by the baffle will eventually recede into the existing local drainage systems when flows subside or in the worst case scenario could be pumped away.

The choice of recycled plastic profiles as a low-maintenance material was critical to ensuring automatic flood protection that did not need manpower or mechanical equipment to be deployed, Whitfield added: “I had used Centriforce recycled profiles before so was familiar with the benefits of the material. Unlike wood, the plastic lumber will not shrink, rot, crack or lose its colour. There is no chemical leach into surrounding soil. What better product to use when you have water up against it?

“The flood wall also needed to be durable and vandal-proof with a pleasing aesthetic to blend with the street scene. A top spar, also made from Centriforce plastic, provides a robust finishing touch.”

The project achieved cost savings through ease of construction because there was no need to move underground utilities and by ensuring a long-term low or near-zero maintenance solution.

The project’s partners were: Lincolnshire County Council, Environment Agency, Anglian Water, Witham 3rd IDB, Lincoln City Council, Bifrangi UK, National Grid and Stamp End Garage.

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