Marlborough stopbanks at ‘catastrophic’ risk of failure

Two stopbanks protecting a small Marlborough settlement are at “catastrophic” risk of failure.

Repairs and upgrades of the stopbanks - along Peninsula Rd in Spring Creek - are expected to cost $8.7 million.

The stopbanks are critical for protecting the township of about 600 people. The town is also near State Highway 1 and KiwiRail’s main north line.

One of the stopbanks started showing signs of cracking after the 2016 Kaikōura earthquake. Cracks started to appear in the lower section of the other one in the July 2021 floods.

Andy White, the rivers manager at the Marlborough District Council, said the stopbank also had “significant overtopping” in the flood - the first of back-to-back winter floods - which was the first stage of stopbank failure.

A report prepared by White for the council’s long-term plan budget meeting in February said until the work was undertaken, the stopbanks remained at an elevated risk of failing.

“At the peak of the flood, rivers engineers reported feeling a swelling movement in the bank, suggesting an internal loss of stability,” the report said.

“Without a timely response, the situation will only worsen, both in repair/upgrade costs, and risk of catastrophic failure.”

Most of the funding would not be needed until after the next financial year, which meant the work had minimal impact on the 2024-25 draft rates rise, which was 12.65%.

The council had consulted with engineering company Beca, and Land River Sea in June last year to complete the required site investigation and survey work, ahead of concept design, White’s report said.

“Initial estimates suggest approximately 30-35,000 tonnes of rock will be required for armouring purposes alone, equating to over half the budget requested.

“Reconstruction and upgrade of the stopbanks is expected to cost the remainder of the budget after accounting for design costs and enabling works.”

Wairau-Awatere ward councillor Gerald Hope said the money needed to be spent given the risk to human life.

He reminded council of flooding in 1983, when the Wairau River, north of Spring Creek, broke its banks, and wrecked havoc in Tuamarina.

“Luckily no lives were lost but it was that close,” Hope said.

“So these things have got to be put right. The sooner the better.”

Fellow Wairau-Awatere ward councillor Scott Adams said it was an important piece of work locally, but also for transport that used State Highway 1 and KiwiRail.

“I don't like spending money but this is a key part of council responsibility. We do have to spend some big dollars,” Adams said.

Marlborough mayor Nadine Taylor said the upgrades were needed to protect the community, which from her memory had to evacuate during the July 2021 flooding.

The stopbank repairs were mooted as part of the council’s long-term plan 2024/2034 and would go out for public consultation from April 4 to May 6.

The council had submitted to the Government’s “Before the Deluge” for co-investment, but it had been unsuccessful at two previous funding rounds.

LDR is local body journalism co-funded by RNZ and NZ On Air.