Whanawhana dam: Feasibility study begins for project in Heretaunga Plains

The site for the proposed 27 million cubic metre water storage reservoir on private land on the Otamauri Stream in Whanawhana.

Machinery is in place as a feasibility study begins to decide the future of a dam for the Heretaunga Plains at Whanawhana.

The site for the proposed 27 million cubic metre water storage reservoir on private land is on a tributary of the Ngāruroro River, the Otamauri Stream.

Initially led by Hawke’s Bay Regional Council in partnership with Heretaunga Sustainable Water, HBRC has now handed the project over to its partner.

Heretaunga Sustainable Water is a group made up of those with a commercial interest in the future of the dam, including irrigators and commercial water users, mana whenua and municipal water suppliers.

HSW spokesman Xan Harding, a Hawke’s Bay grower, said the site was now undergoing in-depth geotechnical and ecological work.

The investigations would determine whether the project was economically, technically, culturally and environmentally feasible, he said.

“It would enable comparison with any other viable water security options for the Plains and would need to be developed with a strong commitment to continued water efficiency,” Harding said.

The site would harvest peak water flows from within the catchment and the Ngāruroro River in winter and store the water for release into Heretaunga’s rivers and streams during periods of peak summer demand.

Harding said the Heretaunga Plains delivered about 80% of Hawke’s Bay’s GDP and was made up of fertile growing soils supporting world-class farming, horticulture, viticulture, commercial industry, as well as the major urban centres of Napier and Hastings.

The study is fully funded and mandated by HBRC and the Crown, through existing Kānoa (Regional Economic Development & Investment Unit) funding.

Harding said an in-catchment, local facility for the Heretaunga Plains would protect the natural environment, build resilience into Hawke’s Bay’s economy, and enable sustainable growth.

“We will continue through the feasibility assessment with a view to having this completed around the third quarter of this year, at which point we will make decisions around resource consenting.

“It’s vital that commercially disciplined private sector water interests inform the decisions around economic feasibility, as they understand the regional demand profile for water and will ultimately pay for it,” he said.

At a meeting in May 2025, Harding said an ideal model for control of the dam would be to place it in the joint hands of the Napier City Council, Hastings District Council, mana whenua and Heretaunga water users, and its viability would depend on who was willing to pay what for the water.

The Whanawhana dam could hold more than twice the amount of water as the last large dam development in New Zealand, the controversial Waimea Dam.

But it would still be significantly smaller than a proposed dam on Central Hawke’s Bay’s Makaroro River, the site of the failed Ruataniwha Dam bid, which would have a capacity of 93 million cubic metres, if given the green light.

A regional water assessment in 2022, commissioned by HBRC, found Hawke’s Bay was on track to have a shortage of water in the vicinity of 25 million cubic metres by 2040.

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