The nearly 150-year-old structure has had 23,000 tonnes of rock added around it in the past three years, including 14,500 from October last year to July.
The latest $657,000 project included 27-tonne rocks being used for the first time, and eight tetrapods placed at the head of the breakwater.
Waitaki District Council project and assets officer Grant Rhodes said the rocks were sourced from Ngapara’s Broken Hill Quarry and made a massive difference. Not being able to find substantial rock had been a ‘‘killer’’ for previous protection work.
The scale of the project gave Mr Rhodes the confidence it would work to protect the breakwater.
‘‘I’m actually pretty excited about it. I think it has turned out really, really well . . . just because of the depth of the armouring we’ve got now, it’s not just three or four metres out to the structure,’’ Mr Rhodes said.
‘‘It’s getting about 15m out at the toe — it’s a huge amount of armouring.’’
The breakwater required new maintenance as it was deteriorating, including major undermining to the seaward side, substantial cavities and stress fractures.
Undertaking extensive work would help prolong the breakwater’s life.
‘‘The hope is that the bulk rock armouring will remain in place for decades to come. Although regular maintenance of up to 2000 tonnes of rock per annum is expected.
‘‘We also plan to continue manufacturing tetrapods in the future and place them to further bolster the rock protection.’’
A helicopter survey of the breakwater was taken on Tuesday, to monitor rock above and below the water.
Monitoring would be ‘‘critical’’ to determine rock loss in the future. The survey report was expected within the next fortnight, he said.
