South Wall cracks under ravages of sea after 250 years

DUBLIN Port's Great South Wall, the biggest single construction project in 18th century Ireland, is cracking due to wear and tear.

Fissures have developed in the granite paving, and the wall is in need of continual repair. Voids have also been discovered at the base of Poolbeg lighthouse and must be filled within months to safeguard its foundations.

Given the crucial importance of the South Wall as a breakwater, Dublin Port and Docks Board expects to spend around £150,000 this year shoring up the historic structure with tonnes of rock armouring to prevent it being breached by a storm.

Mr Brian Torpey, the port's chief engineer, said some 27,000 tonnes of granite boulders had been laid on the seaward side of the wall over the past 10 years and this "expensive operation" was continuing on the river side, as funds became available.

If the wall was breached, the channel would be blocked and shipping would be prevented from getting into the port," he said. "Every year, we used to do a section of the wall, but we have switched attention to the armouring, because of the speed at which it is deteriorating."

Mr Torpey said the river side of the South Wall was being pushed out by wave action on the seaward side. "Water percolates into the wall during storms and high tide and each successive wave hitting it creates a hydraulic effect which causes movement in a wall," he explained.

Jointing in the cut granite wall has long since been eroded and the random rubble beneath it destabilised. Once stout timbers tie-bars, reduced to rounded logs, have had to be replaced by a reinforced concrete band running length ways to provide sufficient "transfer strength".

The fact that the wall was built vertically, with stone brought by road or barge from the granite quarries in Dalkey, also made it less storm proof than the sloping walls of Dun Laoghaire Harbour, which dissipate the action of the waves. But then the South Wall is much older.

"It was an amazing construction for its time, all built by hand with the aid of tripods," said Mr Torpey. "Originally three miles long, extending out into the Bay from Ringsend Gut, it was the longest sea wall in the world at one stage". Now, as a result of land reclamation, it is a mile long.

Built between 1740 and 1780, with Poolbeg lighthouse added in 1786, it provided Dublin Port with its first breakwater. Its second, the North Bull Wall, was built after 1816 and had the effect of scouring a channel 17 feet deep through sandbar beyond, ultimately creating the Bull Island.

"Engineers get very little kudos," Mr Torpey said, "and that is one amazing amenity that we get no thanks for. All we get is abuse when we want to reclaim some land to develop the port". This year Dublin Port anticipates catering for an anticipated volume of trade of 13 million tonnes.

Mr Jarlath Duggan, a bricklayer from Castleknock who enjoys walking on the South Wall, complained that the ad-hoc repairs being carried out were not adequate to secure its future. "It was a great engineering feat when it was built and it has lasted over 200 years. What it will take is a similar engineering feat today to ensure that it lasts for another 200 years. It needs a good team of stonemasons to go down there and do a proper job."

Mr Duggan said he had raised the matter with two sympathetic city councillors. "As far as I'm concerned, it's a national monument," he added.