Hawke's Bay Regional Council investigating Ngāruroro tributary dam sites

The braided portion of the Ngaruroro River. Hawke's Bay Regional Council is investigating building a dam on a tributary on the mid-reaches of the Ngāruroro to supplement flows. Photo / Paul Taylor

A dam on a tributary of the Ngāruroro River in Hawke's Bay is being investigated as a possible solution to future summer water shortages in the region.

Hawke's Bay Regional Council's draft Regional Water Assessment has predicted an annual 32 million cubic metre shortage of water across the region by 2040.

Leaders have long warned that climate change could turn the Heretaunga Plains, known as the "fruit bowl of New Zealand", into a dust bowl during summers as water users compete for a scarce resource.

A Hawke's Bay Regional Council spokesperson said the council was investigating sites for a small to medium-size publicly-owned dam of up to 20 million cubic metres on a tributary in the mid-reaches of Ngāruroro, near the Whanawhana cableway, but they are yet to determine if any of the sites are feasible.

A 2019 Water Conservation Order on the upper Ngāruroro, still in the process of an appeal by private stakeholders, would mean dams were not possible in those reaches, but an order was not granted by the Environment Court for the lower reaches, below the cableway.

"A dam is being investigated as an option for supplementing flows of the Ngāruroro and the lowland streams of the Heretaunga Plains in summer, to balance the cumulative impacts of water being removed from aquifers by all users in the hot summer months," the regional council spokesperson said.

Dams are a hot topic in Hawke's Bay at the moment.

Proponents of the failed Ruataniwha Dam in Central Hawke's Bay are seeking to extend its consents to 2030, with a view to reigniting it in a new form. Currently the consents expire in 2024.

Hawke's Bay Regional Council says the Ngāruroro tributary dam proposal was an extension of the work done during a plan change process know as TANK, which focused on the future of the Tūtaekurī, Ahuriri, Ngaruroro and Karamū waterways.

The council was working with landowners, mana whenua and other stakeholders around the proposal, the spokesperson said.

"Any viable options would require robust community input before they became part of the suite of tools our region has to combat the impacts of climate change."

The draft Hawke's Bay Regional Water Assessment, commissioned by the council and yet to be released in its full form publicly, predicts an annual water shortfall compared to demand of 32 million cubic metres by 2040 and a 46 million cubic metre shortfall by 2060.

The regional council spokesperson said that as climate change reduces the volume of water Hawke's Bay has available, reducing demand on its own may not be enough and supply options will provide more water to support the environment and meet demand.

Hugh Ritchie, a director for Water Holdings Hawke's Bay, said he believed the Ruataniwha Dam consents they hold and plan to use for the Makaroro Storage Scheme are still the most effective way to address water security across the entire region and ensure environmental flow in Central Hawke's Bay.

He said the Makaroro Storage Scheme would be able to hold 100 million cubic metres of water and use about 20 million of that figure to provide an environmental flow of 5200 litres per second, compared to lows of 800 litres per second in 2019.

The regional council sold the consents to Water Holdings Hawke's Bay after the Supreme Court found in 2017 that the Minister of Conservation acted illegally by trying to make 22ha of Ruahine Forest Park available for exchange to Hawke's Bay Regional Investment Company Ltd (HBRIC) for the $330 million Ruataniwha dam project, after about $20m of ratepayers' money had already been invested into the project.

Hawke's Bay Regional Council announced trials for Managed Aquifer Recharge along the Waipawa River near the end of last year as a way to address the regional water shortage. Photo / Warren Buckland

Tom Kay, freshwater advocate for Forest & Bird, said dams tended to have a negative environmental impact, citing a 2017 paper, Damn the Dams by Mike Joy of Victoria University of Wellington and Kyleisha Foote of Concordia University Montreal.

"A review of 165 scientific papers revealed that 92 per cent of them reported a decrease in ecological health in response to flow regulation. This suggests that altering natural flows by dams is detrimental," the paper reads.

Kay said dams also get in the way of the free movement of native fish up and down the river and he would prefer to see solutions like wetland restoration and reforestation.

"Even when fish passage is provided to allow fish upstream, fish still have to get downstream again, and tend to end up swimming through turbines or a dam outlet and being killed by the pressure," Kay said

"If they can't swim out to sea to breed, then we lose those tuna and their lineages forever."

Trevor Le Lievre, spokesman for Wise Water Use, said engineered solutions were a last resort.

"If a water issue still remains, only then should engineering solutions be investigated," Le Lievre said.

The provisional Hawke's Bay Regional Water Assessment from Hawke's Bay Regional Council highlighted several possible ways to address water security in the region on the supply side.

Another potential solution, Managed Aquifer Recharge, involves capturing water from rivers and streams when flows are high and using it to recharge aquifers.

The regional council spokesperson said a trial site for the Managed Aquifer Recharge trials had been identified and a Cultural Impact Assessment has been completed.

"We are finalising the resource consent applications and planning to lodge in the near future."

The spokesperson said the regional council was also investigating opportunities to encourage industry to develop in areas, such as Wairoa, that have a relative abundance of water.

The spokesperson said the regional council's Kotahi Plan would be an opportunity for the community to have their say on how to address the water supply.

"The Kotahi Plan, which must be agreed by the end of 2024, is an opportunity for the community to decide how water is managed in Hawke's Bay, including allocation policy and how we apply water efficiencies, conservation and demand reduction initiatives," the spokesperson said.