Ōmāhu stopbank upgrade begins after Cyclone Gabrielle

Hawke's Bay Regional Council has begun upgrading the Ōmāhu stopbank, covering three kilometres of flood defences near the Ngaruroro River.

The work will raise and widen the Chesterhope Upper stopbank on the true-left bank of the river, from the Ohiwia or Okawa Stream downstream towards the State Highway 2 Ngaruroro River bridge. The scheme is expected to be completed by Christmas.

The upgrade is part of a wider flood resilience programme around Ōmāhu, which suffered major flooding during Cyclone Gabrielle. The cyclone damaged and breached sections of the existing stopbank, which were later repaired on a like-for-like basis before this larger rebuild began.

Engineers are designing the upgraded structure to withstand a flood event with a 1% chance of occurring in any year, based on revised modelling developed after the cyclone. In flood management terms, this is known as a 1% Annual Exceedance Probability event.

The revised modelling uses new data gathered after Cyclone Gabrielle. Flood probabilities are based on historical river-flow records, and an event of that scale can change engineers' assumptions by showing that larger floods may occur more often than previously estimated.

Programme scope

The Ōmāhu project is part of Hawke's Bay Regional Council's AUD $256.5 million flood resilience programme. It includes stopbank upgrades, telemetry systems, pump stations, new flood infrastructure and reviews of existing flood schemes across the region.

Most of the funding is being managed by National Infrastructure Funding and Financing under the government's Cyclone Recovery Programme. That source is expected to cover about 75% of the total cost, with the balance provided by the regional authority.

At Ōmāhu, the upgrade is one of several interventions already completed or under way. They include the new Ōhiti Road stopbank, an extension to the Ōmāhu stopbank through the 2C project, erosion protection along the Ohiwia Stream and the installation of a water-level telemetry site.

Separate stopbank upgrades are also under way at Waipawa and along the Brookfields Lower stopbank near Meeanee and Awatoto. Together, the projects reflect the scale of post-cyclone spending on flood protection in Hawke's Bay, as public agencies face pressure to strengthen river management and reduce risk to communities and farmland.

Galbraith Earthmovers will carry out the Ōmāhu upgrade. The work focuses on improving the floodbank's height and width, while related projects in the catchment address monitoring and erosion control.

A council representative said the latest construction phase was intended to strengthen the links between those pieces of infrastructure.

"Cyclone Gabrielle had a devastating impact on Ōmāhu. This upgrade builds on other work completed in the area and adds another layer of resilience for the community. The upgraded stopbank will work alongside the new Ōhiti Road stopbank, the extension to the Ōmāhu stopbank, erosion protection in the stream, and the new telemetry site. These projects complement one another, from the hills to the river mouth, so the whole system is stronger than any individual asset," said Thompson Hokianga, Councillor for Māui ki te Tonga, Hawke's Bay Regional Council.

The project also has significance for Te Piringa Hapū and the wider Ōmāhu community, where flooding affected homes, marae and land during the cyclone.

"Ōmāhu knows how important flood protection is. Our whānau, marae, homes and whenua have experienced first-hand the devastating force of floodwaters. This upgrade is an important step in our recovery and will help our people feel safer and more confident living on our own whenua," said Patricia Nuku, Kaiwhakahaere Matua (General Manager), Te Piringa Hapū.