EXTRA FLOOD FUNDING WELCOMED STEP IN RIGHT DIRECTION

Posted: Friday 16th October 2009

The Concrete Centre has welcomed the additional £16 million funding to help local councils in England tackle the problem of surface water flooding. There is concern, however, that this may be too little to make a real difference particularly as the impact of the predicted climate change could result in extreme rainfall patterns.

The new funding from the Department for Environment, Food and Rural Affairs will see £9.7 million being awarded to 77 ‘at risk’ local authorities for area for help in combating surface water flooding. Local authorities in other areas would be able to bid for a share of £5 million to help them address known local flooding problems. Over two thirds of the 57,000 homes affected by the 2007 summer floods were inundated by surface water runoff or over-loaded drainage systems rather than swollen rivers.

“The annual clean-up cost of flooding is some £1.1 billion. This cost could rise as the problem of surface water flooding is exacerbated by the impacts of climate change and increased urbanisation”, said Alan Bromage, head of civil engineering at The Concrete Centre. “Although the additional funding is welcomed, given the extent of the problem, £16 million when divided amongst so many local authorities may not be enough to protect our built environment from flooding.

Bromage believes that the most efficient use of the funding would be to direct it at the widespread adoption of concrete flood barriers and Sustainable Urban Drainage Systems (SUDS) in order to accommodate future urban development, alleviate the problem of existing overloaded drainage systems and address the potential of extreme rainfall patterns.

SUDS is a design philosophy which uses a range of techniques to manage surface water by attenuation and filtration with the aim of replicating, as closely as possible, the natural drainage prior to a site being developed. A wide range of permeable and pervious concrete SUDS solutions are available, both as in situ and precast. Pervious concrete is generally achieved by using concrete without fines, so the more granulated structure of the material allows water to pass through it, without sacrificing strength or durability. Some may have chemical admixtures included to aid porosity. There are a variety of applications for this sort of material, including concrete paving units, which allow drainage through their structure into a free-draining sub-base, to reinforced concrete slab units. These have precast void spaces which can be filled with other material e.g. gravel, or may allow grass to grow through. Grass paving, as this is known, is a widely used application particularly for hardstanding areas.

A useful and versatile SUDS technique is Concrete Block Permeable Paving (CBPP). This provides important attenuation and pollution source control and in addition CBPP does not need the additional land take requirement of ‘soft’ SUDS landscaping techniques such as wetlands and ponds.

CBPP works by allowing water to pass through the surface between each block and into an underlying permeable sub-base. Here, it is stored and released slowly either into the ground, to the next SUDS management stage or to a drainage system.

The concrete flood barrier is a modified form of the motorway safety barrier. The mass of the barrier resists the hydrostatic loading from the flood water. A key benefit is the reduced land take required compared to other options, making the system particularly well suited to restricted sites.

“Concrete flood barriers and permeable and pervious concrete drainage systems offers viable and cost effective solutions to the problem of excessive surface water run-off, a problem that if the predictions of climate change are correct could become more frequent and more widespread in the future”, explained Bromage. “The new funding announced by DEFRA is welcomed as a step in the right direction, however local authorities may need more if they are to invest in comprehensive flooding measures to meet the predicted outcomes of climate change.”




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