Whanganui River drop-out repair work on Somme Pde close to completion

Council transport manager Damian Wood says the risk of erosion remains on the rest of the Whanganui River embankment. Photo / Downer Whanganui

Work to repair and strengthen the Whanganui River drop-out site at Somme Pde is set to cost $6.6 million, with the district council forking out $2.64m.

Whanganui District Council transport manager Damian Wood said that included road reinstatement, kerb and channel, and a walking and cycling pathway to replace the footpath.

The slip site was now fully enclosed by sheet piling, he said.

“This will prevent any further debris from entering the river and signals a significant step in the completion of the project.

“Project completion is scheduled for mid-March, which isn’t far away now.”

That is six weeks later than expected, due to the complexity of the project.

A table of potential final costs was provided to the committee in June last year - ranging from $5m to $7m, “significantly higher” than the $2.5 million originally planned for.

NZ Transport Agency Waka Kotahi will provide $3.96m, with the council portion debt funded.

The risk of erosion remained on the rest of the Whanganui River embankment, Wood said.

“I would encourage elected members to actively encourage Horizons [Regional Council] to take a more proactive stance in river bank protection works and management.

“We are the ambulance at the bottom of the cliff in these situations. We are doing works to keep Somme Pde open.

“It would be nice if we had some support for preventative works.”

Councillor Kate Joblin asked what work had been done to stop ongoing issues with Somme Pde‘s asphalt after “all this work has gone on underneath”.

Wood said staff were conscious the road was a heavy vehicle route and the council needed to get its pavement design right.

Wood’s report said an assessment of river flow at very high levels and the potential for scour upstream of the new sheet pile structure had “compelled the installation of a wing wall”.

It is being installed at the upstream end of the sheet pile wall and will redirect high-water levels.

The report said managing traffic diversions around the site had been challenging, as had noise and vibration generated from the site.

More than 100,000 vehicles a week used the detour.

“We have hired specialised vibration and noise monitoring equipment to be able to quantify the volume and extent of the noise and ground vibration.

“Readings have been taken outside and inside some of the properties close by and residents’ properties that have expressed concerns.”

Levels measured outside the site fell under guidelines but still generated disruption for those close by, the report said.

“Mitigation of noise and vibration at the site includes a high-frequency driving head for the sheet pile work, which utilises a higher frequency and lower amplitude driving force, sound absorbent screens around the noisy machinery units and regular updates for those close by of work being undertaken and progress.”

Mike Tweed is an assistant news director and multimedia journalist at the Whanganui Chronicle. Since starting in March 2020, he has dabbled in everything from sport to music. At present his focus is local government, primarily the Whanganui District Council.