Sea walls' narrative kept alive

Construction of sea walls on the Otago Peninsula began in the late 1860s as a dray road between Portobello and Dunedin moved from high on the hill to the water's edge.

On the other side of the harbour, an example of 1870s-era walling remains in the old railway causeways near Blanket Bay, on State Highway 88 to Port Chalmers.

Many early sea walls on Portobello Rd were moved in the 1920s; new walls were built using the old style of construction and included original materials.

The Peninsula Rd board, which had wide-reaching powers and even issued dog licences, was responsible for construction and employed wallers.

The board's minutes show small contracts were often awarded to local farmers or builders until World War 2, Dunedin-based independent archaeologist Dr Jill Hamel said.

"They learned from one-another. There was no trimming of rock, unlike stonemasons who were apprenticed. It was another skill entirely.

"They would use rocks which came to hand. The ad hoc development meant the walls are incredibly variable.

"No two 100m sections were the same, really. It's modern construction which has uniformity."

Prisoners - some of them Maori political prisoners of war transported to Otago in the late 1860s during the wars in Southern Taranaki - were used to build the Anderson's Bay causeway.

Dunedin City Council transportation and operations projects engineer Evan Matheson said council was committed to maintaining the walls.

"Council acknowledge it's a fantastic seawall left by city forefathers, and we are keen to maintain it because of the obvious aesthetic and historic value, and as a tourist feature.

"There has been a maintenance backlog which was inherited. We've been in catch-up mode for the last five to six years but are approaching the stage where the worst sites have been attended to and now getting to preventative rather reactive work."

By March, the council will have allocated three contract packages in the past 12 months, each worth about $200,000.

"Contractors construct up to 40sq m of wall a week with a small four- to six-man team."

But repairing existing walls is not cheap; recent repairs to 100sq m of wall between Deborah Bay and Carey's Bay cost between $20,000 and $25,000.

"It is very robust, and we'd expect, with maintenance, to get 100 years-plus out of hand-built walls. The mass placed rock is not as robust, and not that much cheaper, surprisingly."

The council was now compiling a list of areas to be upgraded, and surveying areas outside the harbour, such as walls near Allan's Beach and Papanui Inlet.

•Unearthing harbour's past

As redevelopment work is undertaken around Otago Harbour, small but significant nuggets of the area's history are often uncovered.

In 2006, the newly constructed walkway between Magnet St and Ravensbourne revealed some 19th-century walling.

A member of the public noticed some unusual rock formations on the harbour edge. The Otago Regional Council asked the contractors building the walkway to contact the Historic Places Trust about the find.

The trust employed archaeologist Dr Jill Hamel to investigate and she discovered the wall was built more than 110 years ago.

Dr Hamel said the retaining wall, or titching, was built along a causeway in 1892. It is located beside the Ravensdown wharf.

The basalt rock retaining wall was thought to have been built to help form the causeway where the railway line was located.

The line has since been moved away from the shore, because of erosion. The wall can be seen only at low tide.