New $3.5m Pokapu Rd bridge aims to reduce flooding in Moerewa, Ōtiria

Northern Advocate

21 Mar, 2023 04:00 PM4 mins to read

GHK Piling foreman Darryl Nisbet and Northland Regional Council rivers project manager Meg Tyler at the site of the new Pokapu Rd bridge, where concrete fill is being poured into pile holes to contain loose rock. Photo / NRC

Work has started on a $3.5 million road bridge, the aim of which is to reduce the floods that regularly devastate the Northland settlements of Moerewa and Ōtiria.

In recent years, the two low-lying settlements have been inundated several times as floodwaters leave the riverbeds of the Waiharakeke River and Ōtiria Stream, instead flowing directly across the floodplain into town.

It is hoped the new, 60-metre-long bridge will change that by allowing the waterways to stay in their natural paths.

Newly elected Northland Regional Council member Geoff Crawford, who chairs the Taumarere Flood Mitigation Working Group, said the project was unusual because it wasn’t trying to “tame” nature, unlike most flood mitigation projects.

“This one is actually restoring the Ōtiria Stream to its natural flow in accordance with new national freshwater Te Mana o te Wai principles,” he said.

The natural flow had been blocked decades ago with the construction of Ngapipito and Pokapu Roads and Ōtiria’s railroad embankment.

Crawford said the area was unusual because during a one-in-100-year flood, 70 per cent of the flow from Ōtiria Stream and 80 per cent of the Waiharakeke River’s flow travelled across the floodplain.

In most rivers that was reversed, with about 80 per cent of floodwater contained within the riverbanks and only 20 per cent on the floodplain.

That was largely because the two waterways were perched atop ancient lava flows that were too hard to carve deep channels into.

Crawford said the local community came up with the idea of returning the water to its natural path and into an area better able to cope with large volumes of water.

To achieve that, the regional council had worked with the local community, the Taumarere Flood Mitigation Working Group, local marae, Ngāti Kopaki and Ngāti Te Ara kaumatua, kuia and kaitiaki, Far North District Council and Kānoa Regional Economic Development and Investment Unit (which administers grants from the former Provincial Growth Fund).

Kaitaki Wiremu Keretene at the old Pokapu Rd bridge over Waiharakeke River, which is blamed for worsening the floods that afflict Moerewa and Ōtiria. Photo / Peter de Graaf

The first stage of the project, completed last year, saw the construction of the downstream section of a $1.4m, 80m-long spillway at Ōtiria.

Stage two, which recently started and is due to be completed by Christmas, will see the existing 18m Pokapu Rd bridge replaced with a new, 60m-long bridge, tripling the volume of floodwater that can pass under it.

“In previous floods this water would typically be diverted, in part by the existing bridge structure and railroad, downstream to land at Ōtiria and Moerewa,” Crawford said.

The new bridge is being built on multiply owned whānau land with the blessing of its shareholders.

The third and final third stage will involve excavating the remaining 800m of spillway and removing the old Pokapu Rd bridge.

The Waiharakeke River in flood, just downstream from the Pokapu Rd bridge. Photo / Peter de Graaf

In future floods, most water should travel down the new spillway and into the Waiharakeke River past the lava flow, where the river is much wider and deeper.

Engineers’ calculations show that while floods would still occur, areas currently subjected to half-metre-deep flooding should see that reduced to ankle-height instead.

57 per cent of the projects total $7m cost is funded by Kānoa, with another 28 per cent from local and Northland Regional Council river rates.

In recent months the project had secured the remaining 13 per cent, or $1m, from Far North District Council’s Better Off Fund.

The new single-lane bridge and footpath are being built by contractors Ventia.

Workers pour site concrete fill into pile holes at the site of the new Pokapu Rd bridge. Photo / supplied

As part of the council’s procurement requirements, Ventia had hired two recently graduated students from Bay of Islands College and one local youth for training, up-skilling and long-term employment.

Two kaitiaki had also been employed as cultural monitors during construction, due to the area’s rich Māori history and many sites of significance.

In a separate project, completed in 2021 and funded by Waka Kotahi New Zealand Transport Agency, a bottleneck was removed from Ōtiria Stream further downstream to reduce the flooding that used to regularly close State Highway 1 at the bottom of Moerewa’s Turntable Hill.