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Defence tactics

Geotechnics A planning row is delaying a £200M development on Carlyon Bay in Cornwall. Bernadette Redfern reports.

A1.3km line of steel sheet piling stands to attention on an empty beach in Cornwall. It was to form the foundations of a new sea defence structure, protecting £200M worth of holiday homes and leisure facilities against an extreme 1 in 200 year storm.

But hopes of building the wall were dashed last week when deputy prime minister John Prescott ordered the council to refuse planning approval (News last week).

Developer mpersand ought the site at Carlyon Bay in late 2002 with planning approval from Restormel Borough Council to build holiday houses and apartments across the beach and refurbish Carlyon Bay's disused Coliseum concert hall, plus build a wall to defend them when the English Channel turns hostile.

Approval for defences giving protection against a 1 in 30 year event was granted in 1990 and renewed in 1996. But even then there were environmental objections to the scheme in general, and the wall in particular, which became official opposition when the Environment Agency was formed a decade ago.

Ampersand called in specialist HR Wallingford and consultant MLM to design a more robust structure, providing 1 in 200 year protection. 'We have spent over two years and £500,000 working with the best designers in the country - if not the world - on the defences, ' says Ampersand construction director Tim Renwick.

The new defence consists of a 2m high wave return wall sitting on top of a 4m wide, 1.6m deep C32/40 concrete raft foundation.

Steel sheet piles and rock boulders in front of the wall would support and add mass to the structure. The level of the beach would be raised by approximately 1m, extending it seaward by 16m, and so preventing all but the most extreme waves reaching the defence (see diagram).

But piling operations have halted while the Government Office for the South West reviews the scheme. It will decide whether the wall should be subjected to a full public inquiry.

'It is an unusual step, ' says Restormel Borough Council's manager of policy and major applications Tony Lee. 'Usually these things are only called into question if they are of strategic or national importance, which this is not, ' he says.

The Government Office would not reveal why the project was coming under scrutiny but did say that projects that generate a lot of local interest can fall under the spotlight. This project has certainly done that. 'I've had 100 letters of support for this project, and only six against it, ' says Lee.

However, one of those six letters was a 200 page dossier compiled by local protest group CarlyonBayWatch. The group has been campaigning against the entire £200M development for years and recently fixed its attention on the new wall design.

Contained in the submission were three reports prepared by local experts questioning the technical integrity of the sea wall.

Perhaps the most startling contention was that the sea wall could actually sink if the sand below it failed to support its mass. 'The long term stability of the structure must be suspect as it is in effect floating in the sand.

In other words it is not keyed in to the rock below. Therefore the possibility of lateral and vertical settlement cannot be ruled out, ' says author of one report, retired flood defence engineer and local resident John Woods.

'This is just not possible, ' counters scheme designer MLM project director, John Hawkins.

'The wall is not floating, it is a gravity structure bearing on good founding strata. It is to be founded in the beach deposits well above normal high tide level and its base is sized to ensure that allowable bearing capacities in saturated sand are not exceeded.

The toe of the sea wall is below the active movement zone of the beach. In addition a rock toe will protect the sea wall from being undermined, ' he explains.

Another expert, local engineer Dr Mike Fennessy of Consultant Coastal Research, has also expressed concern that the introduction of a wave return wall will serve only to make the beach more reflective, increasing scour at the toe of the structure and dramatically lowering the beach level.

But experts from HR Wallingford, which carried out hydraulic design and threedimensional model testing, disagree. 'The purpose and design of the beach recharge is to prevent scour in front of the sea wall caused by wave reflections from it, and the widening of the beach will prevent waves from reaching the wall except in the most extreme conditions, ' says Wallingford director Ian Cruickshank.

Ampersand says it is unwilling to hang around for months, perhaps even years, waiting for a public inquiry to agree its scheme.

Following the Environment Agency's decision to lodge an objection to the new wall design last week, the developer said it will forge ahead with construction of the original design, providing mere 1 in 30 year protection.

It is an outcome that nobody much wants, but existing planning consent gives Ampersand the upper hand.

With a 1 in 200 year design ready for construction, 1 in 30 year protection could be the best that Carlyon Bay will get.

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