Erosion control needed for Havelock sewage treatment plant after floods

8:50 pm on 10 February 2022

By Maia Hart Local Democracy reporter

Emergency works are needed at Havelock's sewage treatment plant, after last year's major flood event caused significant erosion.

18072021 News Photo: Scott Hammond/ Stuff
South of the Kaituna Causeway

Flooding in Havelock in July last year, north of the sewage ponds. Photo: LDR / Stuff / Scott Hammond

Now there's a risk sewage will leak into the Kaituna River.

The plant, built in 1984, has two oxidisation ponds and discharges treated sewage into the Kaituna River, in Havelock.

Speaking at an assets and services meeting last week, Marlborough District Council operations and maintenance engineer Stephen Rooney said the council had monitored the embankment on the side of the ponds, and at the Kaituna River edge for "quite some time".

In a report prepared for the meeting, Rooney said erosion of the Kaituna River and wastewater treatment ponds had caused the river edge to slowly creep closer to the wastewater ponds over many years.

He said the July flooding had increased erosion and made it significantly worse than it had been previously.

He said there was a high risk further floods would collapse the bank which in turn could cause the contents of the ponds to empty into the Kaituna River.

Any further flood would likely have to be significant, similar to what occurred in July last year, Rooney said.

"We certainly will monitor it. It would have to be a flood where the river system is full, and where water might flow across the causeway," he said.

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Water filtration plant opened in Seddon.
Stephen Rooney

Marlborough District Council operations and maintenance engineer Stephen Rooney. Photo: LDR / Stuff / Scott Hammond

Previously it had been said the treatment plant needed to move due to the risk of rising sea levels, and there was "potential that the ponds might be decommissioned".

However, the report said the decision had since been made that the ponds would form part of the new wastewater treatment processes.

"Erosion control was not considered while options for the future treatment of wastewater from Havelock were being reviewed," the report said.

The report said rock would be needed, and was likely to come from the Pukaka Quarry. This would be placed and used to "armour" the embankment against future erosion.

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Vox Pop
sea level rise in Havelock.
Sewerage Pond
Sewage pond

A sewage pond at the Havelock sewage treatment plant. Photo: LDR / Stuff / Scott Hammond

But Rooney said at the meeting, they also needed to consider they were competing with other parts of the region for the rock.

"The rivers team has given us some proposals to slow that down and rectify it. Sadly, it is going to take some rock, about 1000 tons," Rooney said.

"The difficulty being that we are in competition for that rock, they are using it and trucking it, as we speak for Wairau River repairs."

He said there was nowhere to stockpile the rock, which meant it would have to be put in place as it arrived, making it a "little bit more difficult".

Marlborough councillor Francis Maher asked if there was a breakdown of how much of the repairs would be covered by insurance, and how much would have to come out from the council.

But Rooney said the insurance assessors were still "deliberating". The estimated cost of the work was $162,500.

"If it's approved our main cost will be the excess, but that excess is spread across the whole of council's claim from the July event," he said.

Councillor Cynthia Brooks said reading the report made her understand just how fragile the set-up in Havelock was.

"Obviously, there's more or less a desperate need to fix it. So, good luck with the rock, hijack some if you can," Brooks said.

The assets and services committee approved the embankment repairs to go ahead as soon as practical. The matter was forwarded to full council for consideration.

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