Dannevirke's water restrictions to continue

Tararua District Council is still investigating further issues with the dam. Photo / Leanne Warr

Dannevirke will remain on an outdoor use ban until at least the end of March, according to Tararua District Council infrastructure group manager Chris Chapman.

The level 4 water restriction has been in place since early January, despite rain in February.

Chapman said the situation would be looked at again in April.

"If the Tamaki River flows drops into low flows for an extended period of time, which may still happen between now and May, we can't take all of the water Dannevirke needs or uses on a typical basis."

There was still work to be done around the dam to investigate and assess remaining leaks.

Chapman said the current leaks were causing a loss of around 15 litres per second although that loss was being recaptured.

The dam was currently up to 6.7m full.

The initial leak was discovered in July last year and it took until December for the source of that leak to be located and then the lining to be repaired.

The dam was being refilled but due to consents from Horizons Regional Council, the district council was restricted in what it could take and the consents changed according to flow levels from the Tamaki River.

Many people believed that when the dam was first built around 10 years ago, that there would never be water restrictions in the town again.

"It's always been there as ... water storage, untreated water to be used when the river drops into low flows, [that] we can take out of the dam to supplement what we're getting from the river to sustain Dannevirke's needs essentially," Chapman said.

However, prior to the construction of the dam, the consents were higher than they are now, Mayor Tracey Collis said.

While the leaks didn't help, there were also other factors which affected water supply, she said.

"We had an infrastructure failure but also, we've never had a good look at our demand. We've got an increased number of extraordinary users, we haven't looked at demand and now we've got a supply issue. It's all part of it."

Dannevirke, and the Tararua as a whole, had experienced significant growth in the past two years, and this was something that had never been taken into account when the dam was first built.

The district's population was now up to more than 19,000 whereas in 2016, it was 17,900 and Dannevirke's population was now 6200, up 500 from June 2021.

Chapman said that at the time the decision was that storage was needed.

"I suppose for the last few long-term plans, up until the last one, the assumptions around growth and population was stagnant and minor decline."

He said that possibly wasn't considered in terms of the consent.

Chris Chapman: Dannevirke's water supply issues is from a combination of factors. Photo / Leanne Warr

It was a combination of things from a reduction in consented allowance, an increase in water consumption and demand and climate change which contributed to the 2019-20 drought and subsequent infrastructure failure.

The drought was one of the theories put forward as the cause of last year's leak, Chapman said.

Another theory was mechanical failure.

"In terms of the remaining leaks until we identify where those are we can't identify or assess what's caused them and how we prevent them."

The council would be looking at different options for how they assessed and identified the remaining leakage.

"Then also looking at the design and the construction - just how it was put together in terms of if we were to build that now, what would it look like in terms of the liner, the pipes, the pumps, the valves, the meters and what opportunities are there to potentially improve its condition, its performance, its resilience - all that kind of thing," Chapman said.

He said if there hadn't been the leak, Dannevirke might not have had to go into a total hosing ban based on this summer.

However, we likely would have had to have some restriction level as the impounded supply was only intended to supplement the water supply for about 30 days.

Chapman said there were currently projects looking into demand management as well as alternative supplies of water, such as aquifers.

He said a big focus for the immediate future was getting reliable data.

"So we can understand how much water is being used and where is it going."