Designing and delivering a flood defence scheme to protect a Cornish village that had been ravaged by flood waters 28 times in the past 50 years was always going to be a tall order. Especially when it had to be up and running within a tight three-year timeframe.
Factor in the additional headaches of Sladesbridge being located at the confluence of three rivers, with the valley floor a Special Area of Conservation - the highest European habitat designation - as well as being a Site of Special Scientific Interest, and the picture is complete.
But Halcrow’s Exeter-based team more than rose to the occasion, going on to win the 2005 Institution of Civil Engineers South West Region prize for the year’s best project. It was also shortlisted for the 2005 British Construction Industry Awards in the Prime Minister's Better Public Building Award, Small Civil Engineering Project (final five), and Best Practice (final three) categories.
It was delivered both ahead of time and under budget and created 9ha of new wetland habitat in the process.
The brief
Briefed by the Environment Agency in 2001, previous studies had failed to identify an acceptable solution on economic grounds. This was subsequently addressed and granted ‘special case’ status by the Department for Environment, Food and Rural Affairs (DEFRA). The project was also accelerated by the Environment Agency after additional funds were released for flood defence works following floods in late 2000.
Halcrow was duly commissioned to develop a flood defence solution that addressed the best compromise between environmental impact, technical performance and economics. The team also had to reduce the flood risk to an annual probability of just one in 75.
As the designer, lead consultant, site supervisor and ECC project manager, Halcrow:
- produced a project appraisal report and environmental statement
- secured all planning approvals
- executed the detailed design and supervision of the construction
- liaised continuously with residents and landowners
- held public meetings
- carried out hydrological and hydraulic modelling
- supervised geotechnical investigations and topographical surveys
- carried out benefit/cost analyses
- undertook value engineering and risk management exercises
- produced all detailed design drawings, specifications and contract documents
The benefits
The completed scheme protects a 1.2km length of the Rivers Camel and Allen. Unique flood walls, designed to resemble local Cornish hedges and embankments, were built from material won from the floodplain, which created the wetland. The project has not only reduced the flood risk, but enhanced the local environment.
Local residents’ views were incorporated wherever possible, and as one villager was quick to testify: “The scheme looks wonderful – very environmentally fitting with the area. It works – there was a flood warning two weeks ago and at last I can relax knowing I am safe.”
Such sentiments were echoed by Deborah Clark, South West Regional Flood Defence Committee chairman who said: “It encapsulates much of what is important in flood relief schemes in that it is good for both the community and the environment”.