When Cyclone Gabrielle slammed into Wairoa, Opoiti Bridge between Wairoa and Gisborne suffered a severe washout. Raging floodwaters overtopped the Tiniroto Road bridge and ate away the riverbank at its northern end – leaving part of the road hanging in thin air. The damage was so bad that the bridge had to be closed.

Thanks to collaborative efforts between Wairoa District Council, WSP, and local contractor QRS, the riverbank and bridge are now back to full strength and fully repaired.

A week after Cyclone Gabrielle, Opoiti Bridge was the first on the East Coast to be equipped with a temporary Bailey Bridge which spanned the damaged part of the bridge. This enabled traffic to continue flowing while the new embankment was constructed - minimising disruption to motorists.

WSP Napier-based work group manager for bridges and structures Natalia Uran-Botero says the washed-out riverbank needed a complete redesign.

Following hydrological and ground investigations, WSP’s bridge team developed a new design that used locally available materials. This was achieved through close collaboration with the Wairoa District Council and QRS, a partnership that continued throughout the rebuild.

“Usually with these kinds of washouts, we fill them back up and protect the riverbank with rocks and boulders. But because of the volume of earth that was swept away and the height of the bridge, it wasn’t that simple,” says Natalia.

Designed in 1938 and built in 1941, Opoiti Bridge is 96 metres-long. The new embankment at its northern end has been especially designed to handle severe weather events. It features almost two thousand cubic metres of engineered fill. Neat terraces now sit where once there was a yawning chasm - supported by 1,900 cubic metres of boulders – known as riprap. Once grassed, the embankment will be even more resilient to flooding.

Natalia says it’s great to see the permanent repair now finished.

“We know what we’ve done is sound and resilient. It’s pleasing to have collaborated as a project team to extend the life of this important asset.”

QRS construction manager Mike Wilson says working with WSP on the project was an incredibly rewarding experience, describing it as a fantastic collaborative effort, with everyone involved bringing their expertise and commitment to delivering an outstanding result.

"Being part of such a great team made the project truly special. We entered the project for an award at the local CCNZ awards, and while we didn’t take home the top spot, the positive feedback we received on the project was a testament to the hard work and dedication of everyone involved. It was an awesome job to be a part of, and the collaboration with WSP made it a standout success.”

Wairoa District Council senior project engineer Andrew Heron also noted the success of the project and final repairs. "Despite some challenges sourcing materials, the teams from QRS, WSP, and WDC worked well together to get the job done. Completing the full repair has allowed us to reopen the road completely, with an improved level of service.”

20 December 2024

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