Fairlight: Defending England’s Precious Coastland
Publication: NCE 29 September 2007
Journalist: Jackie Whitelaw
Sea Slide: Engineers are draining the cliffs at a cove in Sussex to stop them sliding into the sea, along with 400 homes in the village of Fairlight. Jackie Whitelaw reports.
In my memory, Fairlight Cove on the south coast near Hastings was a magical spot where you went with fish and chips, a chilled bottle of white wine and a moonlit swim on a hot summer’s night.
Not in recent times, however. The beach is pretty much gone, buried under a significant landslip that has, over the past few years, seen four homes lost to the sea and dozens more imminently approaching the brink. Currently contractors from Dean and Dyball are marauding around the cove 24 hours a day with a selection of equipment from the boys own book of construction plant, working to stabilise the slip.
So, not ideal for a picnic, but the place retains its magic in a different way. Local residents and at least one black and white cat make up a regular, entranced audience, for the workers on the beach, auditing progress on the £3.7M scheme that is going to save their homes in the cliff top village of Fairlight.
Operations are being managed from a site compound established rather delightfully, in the car park of the nearby Smuggler’s Inn. “There is a good reason why we are here,” says Dean and Dyball contracts manager Allister Humby. And it is not just the prospect of a pint of Harvey’s bitter at the end of the working day, apparently.
The contractor had scouted out the location for its site headquarters when it was bidding for the job because it is right beside flood gates and a waterway that give access to the sea near the cove. “But it would still be a 2km trek to the site for men, plant and materials. And there was a risk of rock-falls, so we rejected it in favour of a cliff-top location overlooking the site and decided to cut a road down from the top,” Humby says.
“Trouble was, when we arrived to start work, the cliff-top location had fallen into the sea. So we came here.”
That is an indication of just how rapidly the land is slipping into the Channel 25m a year by some estimates. In this case, though, it is not just the sea that’s to blame but the silty clay that makes up the 35m high cliff that Fairlight village sits on. It is sopping wet and sliding.
The solution proposed by consultants Geotechnical Consulting Group and Halcrow to client Rother District Council is to dry the cliff out by draining it and installing wells to lower the water table so there is no water in the slip planes. A rock bund is being built to protect the re-profiled cliff from the sea’s wave energy and any loss of material at the bottom of the landslip.
And that is what Dean and Dyball has been doing since June, with a scheduled completion date of December.
It has not, however, been a great summer for working on soggy clay on a moving slip. “When it rains perched water sits in ponds and the surface is really sticky and slippery,” Humby says. “Like a skating rink.”
Work has been planned to progress on many fronts. The rock bund is being built from the beach with limestone arriving direct by ship. But the plant that was to move and place the rock had to be got down to the shore. This involved cutting a road through the moving slip. At the same time gravel land drains are being cut to channel water in the cliff down and out to sea. And drilling is underway for the first of 56, up to 30m deep, 175m-diameter well points that will be used to lower the water table in the slip to help it dry out.
Dean and Dyball works manager Phil Stokes was charged with making the first cut for the road down to the beach. “He couldn’t use too big a machine at the start,” Humby says. “We started with a 5t excavator and then moved up to a 12t as we stabilised the ground with the drains.”
Dean and Dyball is sinking ten primary 1m-wide by 2m-deep land drains in the slip face that collect into an individual run at the bottom, taking the water out to sea. These are themselves fed by a fan of secondary gravel drains. The well points at the top will be connected ultimately to a compressor that will push the water from the ground into a carrier drain that will take the flows away.
Humby is phlegmatic about the problems caused by the wet, high summer. “June and July were exceptionally bad,” he says. “We couldn’t get on to the landslip on certain days and the rain caused more slippage in the works. But the round stabilised quite well once the drains started going in.” Humby insists, however, that he is still on schedule for a December finish. A bit late in the season for a moonlit beach party…maybe next year.
BUILDING THE BUND
Placing 57,000t of limestone
Creating the rock bund means working 24 hours a day, to take advantage of the tides. And 57,000t of limestone from the Carrieres du Boulonnais quarry near Boulogne, France, is being shipped over in 1800t loads.
Once it reaches Fairlight it is offloaded into a smaller 500t ship that tracks back and forth two or three times a high tide to the beach.
The rock is then shifted to a stock pile by a couple of 35t dump trucks before being driven round to the rock bund area – avoiding protected dinosaur footprints – at low tide for placing.
“We have to achieve a place density of 1.85t/m3,” says Dean and Dyball contracts manager Allister Humby. “To prove that, we created a 10m trial panel of bund, we weighed every rock and there were 513 of them. The survey calculations demonstrated we were getting the density required. From then on, it’s been like building a jigsaw puzzle without a picture.”
The bund has been designed for a 1:50 extreme event, according to bund designer, Halcrow’s Dr Louise Trim. The 6.2m-high bund is 240m long with the backslope measuring 5.9m, the crest 4.8m and the front slope 21.9m.