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Defence is the shingle issue

Brighton's shingle beach is a key element in a new coastal defence strategy. Margo Cole reports from the sea front.

Anyone who has visited Brighton will know that the seafront fits the image of the British seaside resort perfectly - a lengthy promenade lined with hotels and guest houses, two piers (one, admittedly, a forlorn ruin), and a full complement of amusement arcades, funfairs, fish and chip shops and pubs.

However, on the beach itself, where other resorts might have sand, Brighton has shingle.

While it may be less comfortable for sunbathing or paddling, the shingle does play an important role in coastal protection, as Brighton and Hove City Council's coastal protection engineer Martin Eade explains: 'Shingle is a marvellous defence because it's full of holes. All the energy from the waves is dissipated in the interstices. It's like a sponge.'

The shingle, unique to this stretch of coast, is an important weapon in the fight to prevent flood damage and coastal erosion. However, left to the mercy of prevailing currents, it drifts along the shore from west to east, leaving sections of the coast exposed.

Since 1992 the Port of Shoreham has dredged 20,000m 3ofshingle from the west side of its harbour entrance every year and transported it by lorry to the east side. During the course of a year, it moves eastwards along the coast, ending up at Kemp Town beach alongside Brighton Marina. Eade notes: 'If they missed a year (of dredging) there would be hardly any beach left at the west end.'

Groynes trap the shingle and prevent it from being stripped away entirely, but they do not stop the drift offshore.

Halcrow has just completed a defence strategy plan for a section of coast including part of the east bank of the River Adur at Shoreham and the whole of Brighton and Hove including Brighton Marina. It fits into the shoreline management plan for Beachy Head to Selsey.

The consultant began by collecting and assessing all existing data, and sent 150 letters to interested parties such as local authorities, residents' associations, swimming clubs and conservation bodies. Although the information was comprehensive, Halcrow felt there was not enough detail about the behaviour of the currents, and set up a current meter for 30 days.

A survey of the existing structures - mainly groynes up to 120 years old on the beach sections, and walls and embankments along the river - helped Halcrow's specialists gain information about the standard of the defences and their residual life.

Having amassed all the physical evidence, the company started modelling what was happening out at sea. 'We put offshore wave data into the mathematical model and related it to what was happening inshore, ' explains Halcrow coastal engineer Rachel Fowler.

'For this study we also undertook some current and sediment modelling to look at how sediments move along the coastline.'

The consultant also used a beach plan shape model to study what was happening inshore, inputting information from surveys of the beach and wave data and grading analysis of the shingle. 'Shingle is moved by waves not currents, ' explains Fowler.

'We can model the drift of shingle along the beach and also put all the structures into the model and look at what will happen under a number of scenarios in the future.'

Coastal defence work is partfunded by the Ministry of Agriculture Fisheries & Food (MAFF), which wants to find out what would happen as sea levels rise over 50 years under four different scenarios. These are: to do nothing and let defences deteriorate; to maintain but not enhance existing defences, leading to gradual reduction in effectiveness over time; to upgrade defences assuring levels of defence remain constant as sea levels rise; and to improve the defences.

Halcrow modelled all these scenarios to 2050, taking into account a predicted sea level rise of 6mm a year resulting from climate change and an associated increase in storms.

'With climate change there will be extreme waves and extreme water levels, and we looked at a combination of both, ' says Fowler. 'We know water levels are going to rise, but increased storminess is harder to predict. There is precious little data about what effect this will have over the next 50 years, but we can look at what's happening to water levels and relate that to wave heights.'

The result of the study is a set of preferred options that have been put to the residents for approval before funding is applied for by the relevant local authorities.

Along the River Adur some of the defences are inadequate at the moment. The preferred option is to raise embankments and river walls by up to 1.1m at a cost of £6M.

If beach material is allowed to continue drifting eastwards along the open coastal section between Shoreham and Kemp Town, and the groynes are not maintained or improved, the defences at Shoreham Port could eventually fail, resulting in flood damage estimated at £70.5M. The study recommends improving the defences to protect against a 1 in 200 year storm by extending and raising the groynes and recharging the beaches by taking excess shingle from Kemp Town. The total cost would be approximately £10.5M The privately owned Marina is protected by a sea wall, which needs to be built up by just 300mm to meet 1 in 200 year standards.

If the plans get the go-ahead work could start later this year, ensuring Brighton's shingle beaches continue to provide valuable coastal protection for many years to come.

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