A return to construction and maintenance techniques similar to those used in the 19th century is ensuring the future of the historic sea walls around Otago Harbour, writes Sam Stevens.
Time, tides and decades of neglect have taken their toll on some sections of the Otago Harbours sea walls.
However, under the guidance of the Dunedin City Council, work is progressing on repairing the damage and neglect.
No-one is happier than Dunedin-based independent archaeologist Dr Jill Hamel, who has researched, photographed and inspected much of the harbour's sea wall.
She was enthusiastic about the structure's historical and cultural significance. Much of it is classed as category one by the Historic Places Trust, the majority of it being built between 1920 and 1940.
"It involved local people and communities . . . It is a vernacular structure and at 40km, it's one of biggest masonry structures in New Zealand . . . made from millions of hand-placed rocks," Dr Hamel said.
But in the middle of last century, traditional construction methods gave way to more modern thinking.
After World War 2, machinery was increasingly used to dump rock to reclaim parts of the foreshore, and the nature of many walls changed as concrete, brick and demolition materials were used to make repairs.
The traditional ideas made their return at the end of last century, but by then there had been nearly 40 years of mending and meddling with concrete, with some 1960s and 1970s sections of wall even repaired with brick and other demolition material.
"By then they were in a shocking state."
Dr Hamel said concrete structures were often ineffective in the long term, as happened in Edwards Bay where about 20 concrete blocks were piled up in the 1960s, only to be undermined by sea water.
More recently, modern methods have proven more effective, such as the rocks and earth compacted with machinery on Portsmouth Dr more than 10 years ago.
But since the late 1990s, stone workers have often been seen setting stone into new and existing walls. "They are in far, far better condition than in the 1980s," Dr Hamel said.
The Dunedin City Council spends between $750,000 and $1 million on walling projects - in construction and maintenance.
The first large-scale construction of a "dry" wall, similar to the historic structures, took place in late 1999 near Vauxhall, when Portobello Rd was widened.
Dunedin stonemason Paul Cahill, now a civil contracts manager for Delta Utility Services, worked on the 1km-long project and says aesthetic considerations were balanced with the need to protect roading assets.
"The Romans were doing it thousands of years ago, so I can't claim ownership of that way of making walls, and it was part of the specification and resource consent.
"Laying walls out that way made sense, but it still involved a steep learning curve. We certainly spent a week or two feeling our way."
Wallers on the project, which finished in late 2000, often started work early in the day to work around tides. The rock was sourced from cuttings or roading nearby Hand-built walls have an advantage over concrete and other structures as water is able to run through them and drain away.
The angle of the walls - between 45 degrees and 60 degrees pitch at Vauxhall - and their irregular "face" surface helps dissipate the force of the waves.
It is also easy to add culverts and repair corners battered by the prevailing conditions, as small areas of interlocking rock can be removed and shored up.
"There's not a lot of work for stonemasons . . . Those skills are in decline. They are very skilled at what they do . . . like the Dooleys in Oamaru, who have been doing it for several generations," Mr Cahill said.
"But the harbour walls keep people employed. Guys who work on walls couldn't dress a block - it's like the difference between a skilled carpenter and hammer hand.
"People should not be put off. What I've seen recently is good, and it's landscaping guys who are doing it and the standard is fine."
Walling is "hard on fingers and nails" and demanding in winter. Mr Cahill said those who did well had "an eye for it", the knack of being able to visualise sections of wall before building them.
"Some people just do it. They are placing three or four rocks to someone else's one. If they don't have the knack it's slower because people will try a rock, lift it off, try another.
"It takes longer and you get paid by square metre. Sure and steady wins race, and it's not the biggest, strongest man in world. Often the lithe and strong are better off."
Harbour walls are constructed using prismatic basalt rock - a hard rock which can be broken into semi-regular shapes - from Blackhead Quarry.
Based on traditional theory, but using the "honey-comb" technique, developed by Mr Cahill and Bruce Blucher in 1999, rocks are laid on their long axis into the wall and are locked into position by surrounding stone without use of concrete or other binding material.
A textile cloth is laid behind the wall to stop fines, and "face" rocks lock in to a base of 150mm (or bigger) rocks. The wall is constructed on a trench which lies back away from the water at about 45 degrees into the bank.
"The face rock cannot be released because all are held in by friction. You should be able to walk up a steep sea wall without any rock shifting under foot.
"If a section fails because of a storm, it falls sideways and jams - all the rocks are contained by pressure of the other rocks," Dr Hamel said.
But in some places - near Macandrew Bay and Company Bay, for example - increased traffic and the need to improve road safety has led to road widening.
Dr Hamel said some walls may be gone, or been buried with some top stones removed, but they are far from forgotten.
"Burying them avoids destroying a historical feature. Very little of the old rock is reusable, and is often uneven in style and origin.
"I go along before it is covered, and each wall is described, photographed and the records are lodged with Hocken, DCC and Historic Places Trust.
"There is a certain amount of anxiety if they are altered or removed but I've often had people say it's nice to see them being hand-built again."
