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Shingle minded

Coastal - Winter storms at Bulverhythe, Sussex, have become like Russian roulette, with every gale threatening a flood. But work is afoot to unload the gun, discovers Andrew Mylius.

Looking out of the train windows as it meanders along the Sussex coast towards Hastings, travellers are always struck by the insistent pushing of the ocean against the land's feeble defences. On one side of the carriage, the high tide laps at the shingle bank along which the railway runs. On the other, and several metres lower than the placid summer waves, is a patchwork of fields and houses.

The final leg of the journey, from Bexhill into Hastings, passes through Bulverhythe where the rural landscape gives way to solid conurbation. It is here that the coast's defences are most fragile. Two winters ago emergency repairs were needed to shore up the embankment after a winter storm tore away aged retaining sheet piles and threatened to undermine the railway. Just beyond the line 800 householders narrowly escaped flooding. Disaster came 'perilously close', reports Bulverhythe Coastal Defence Consortium (BCDC) project director Guy Hardacre.

Bulverhythe residents have not always lived so near to the brink of catastrophe. Timber groynes were constructed 2540 years ago to stem losses of shingle to long-shore drift. The taller, longer beach soaked up wave energy and offered 1:200 year storm protection.

As the groynes have aged and disintegrated, however, the upper shingle beach has steadily eroded, leaving a beautiful expanse of sand at low tide, but little useful high tide protection.

Winter waves have edged closer to the railway and its retaining walls - never really designed for the purpose of sea defence and under-maintained - have borne an increasing battering.

The close call in 2003 prompted the Environment Agency to embark on a £5M defence strengthening scheme, designed by framework consultant Halcrow and now being built by BCDC, a consortium of Westminster Dredging, contractors Dean & Dyball and Mackley Construction, and consultant Mouchel Parkman.

Nine 3.3m high rock groynes spaced at 130m intervals replace the 40 decayed timber structures, while a 750m long rock revetment will protect the centre of the beach. 'We're keeping the bank level at the same height but pushing the front out to keep the sea at bay, ' says BCDC project manager Matthew Gothard. Periodic replenishment will maintain shingle levels and ensure that the 1:200 year level of protection is retained as the sea level rises over the coming century - at a predicted 6mm per annum, says Agency deputy project manager Udo Perdok.

Some 140,000t of granite boulders are being imported by barge from Norway. Shipping subcontractor Stema transfers boulders from a 20,000t ship 4km offshore to a 1,500t vessel for the final leg to Bulverhythe beach.

Westminster Dredging is using one of its smallest vessels, a 900m 3 capacity cutter suction dredger to win the shingle for the job. Depending on the high tide, its maximum load is generally 600m 3 - 'give a bit if it's a spring tide and take if it's a neap, ' says Westminster's director of coastal engineering Ron Gardner. The shingle is pumped ashore.

Shingle is sourced on the Owers Bank, approximately 18km off Eastbourne. Excessive swell prevents Westminster discharging in around three of each week's 13 high tides, and BCDC has stockpiled shingle to enable it to keep working when the dredger is forced to lie off.

Four 45t tracked excavators fitted with grabs are being used to position the rock. Groynes and the revetment are being constructed on geotextile to prevent the boulders sinking into the beach. Perdok describes the technique as akin to dry stone walling, with the randomshaped boulders fi ted snugly to a tolerance of 250mm.

GPS gives the plant operators minute by minute updates on their accuracy, enabling any deviations from line to be rectified before work has advanced too far, and before the tide sweeps in.

Shingle is being banked up the full height of the groynes as they are completed, and the old timber groynes are being dismantled in advance of construction. Some 1,000t of competent oak planks will be reused on other coastal defence projects in the area, says Gothard.

In anticipation of the summer holidays, BCDC started work fi rst on those parts of the beach that are most popular with tourists, Glyne Gap and Combe Haven, and on the most vulnerable 150m of the beach, bang in the middle.

BCDC's contract is for 18 months, but the consortium has thrown extra resources at the project and aims to finish this autumn, a full year early. This will save the cost of closing the site this winter and restarting next spring, and the project will come out, at worst, costneutral.

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