Repairing the hole under the sea wall that caused large sinkholes to appear in the Esplanade at St Clair is set to hit ratepayers in the pocket.
But just how hard is yet to be worked out.
Contractors worked into last night, around the 10.30pm low tide to try to plug a gap under the St Clair sea wall. The gap appeared when spring tides in the past few days carried away more than 1m of sand from the beach in 24 hours.
This exposed the bottom of the sea wall in front of the South Coast Board Riders Association clubrooms. Water then sucked sand and soil fill from behind an original wall about a metre behind the existing sea wall, creating sinkholes in the walkway either side of the St Clair Surf Life Saving Club's rescue boat launch ramp.
The holes continued to grow in size yesterday, spreading north.
Dunedin City Council network maintenance engineer Peter Standring said a preliminary examination revealed no other obvious places where water was getting under the wall. Its integrity appeared to be intact.
However, engineers would make a more extensive assessment of the wall and its anchors, which reach 6m back into earth.
While a long-term solution would need to be considered, the immediate focus was on blocking the gap to stop more of the paved area caving in.
Council contractors were to begin inserting sheet piling under the ramp at low tide last night, completing the job at low tide this morning. The main area affected was in front of the Board Riders club rooms around the ramp.
A ground-penetrating radar was run over the rest of the Esplanade yesterday morning and no evidence was found of ''any great voids'' elsewhere, but the area would remain cordoned off until after further tests. The precast concrete-slab sea wall was built in front of the existing seawall in 2004.
The fill behind the old wall, built in 1913, and the existing anchors were not touched at the time, Mr Standring said.
The new sea wall has been beset with problems. Rusted balustrades had to be replaced at a cost to the council of $346,000, and stairs and ramps were damaged in heavy seas.
They are to be repaired at a cost to the council of about $125,000, after a year's negotiations with the wall's designers, and subsequent owners of that company, which will pay the other half of the costs.
Council transportation operations manager Graeme Hamilton said the repairs would sit with the council this time because the problem was not with the wall itself.
''At this point, I can't see any other source of money, other than council money. And, no, it won't be cheap.''
Costs would be determined after the extent of the problem, which could be localised, was known. But, whatever the outcome of that work, costs were likely to be significant.
Mr Hamilton urged people to ''bear with'' the council.
The Esplanade was a big investment the council wanted to protect.
There would always be issues and repairs required in that sort of environment, Mr Hamilton said.
''If you are going to poke things into the eye of the ocean, beware of what you are doing, because you get a lifetime's work.''
Parks and recreation services manager Mick Reece, who is in charge of protecting the city's reserves, echoed Mr Hamilton's comments.
''This is not some lovely little Tauranga beach. It is a pretty tough piece of coastline.''
Several years ago, there were major problems in the Moana Rua Rd area, where the sea dragged away sand from the dunes below playing fields, taking field lights with it.
No other parts of the beach had been affected this time.
''Building this kind of hard solution [a sea wall] ... there's not a permanent fix here. It's a constant battle.''
An onlooker told the Otago Daily Times she had sneaked inside the cordon yesterday morning to take a photo of a large hole when her foot created a new hole.
''It was pretty soft and I didn't even put my full weight on it when the brick just dropped. I got a hell of a fright,'' said the woman, who declined to be named.
