The Westland District Council has agreed to investigate a new 200m wall to protect Franz Josef’s sewerage ponds in the wake of a radical shift in the nearby Waiho River.
The glacial-fed Waiho (Waiau) River is notable for its avulsing nature, meaning the bed can change radically and without warning.
This is what happened as floodwater receded following a heavy rain event in the area between January 18-20.
Within a few days, it became clear that about 95 per cent of the main river is now flowing across what was its true right bank and into the neighbouring Tatare Stream.
With the river now hard up against the existing Havill Wall protection bank alongside Franz Josef’s sewerage ponds, the Westland District Council has agreed in principle to further protect that site.
Westland Mayor Helen Lash said on February 13 that contractors had been invited to put forward proposals for a protection wall extension about 200m long.
This would include training the main river channel away from the proposed bank extension area to enable construction.
Lash said the idea was to “divert the river away” from where it is now, swinging right just below the sewerage pond site.
It was also a bid to eliminate the possibility of backflow from the river past the pond area, back towards the abandoned Scenic Hotel site.
Liaison with the West Coast Regional Council was ongoing around those aspects.
Lash said an emergency district council meeting on February 2 was to give councillors a heads-up on the emerging risk and the need for a planned response.
The council was now proceeding on that basis.
“There were several options. They know we have to sign off and spend some money,” she said.
“We made a recommendation that we would proceed with the ability to protect the ponds. That will be formalised at the next meeting.”
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Meanwhile, the council was keeping a close eye on the weather forecasts and projected rainfalls for the area given the known risk to people and infrastructure.
The February-April period is notorious on the West Coast for sudden high-intensity rain events with a high impact on the area’s infrastructure, as seen in April 2016 and March 2019.
Lash said this was always a prime consideration for the council.
“We’ve been quite comfortable to date but we’re not going to mess around.
“It’s just that concern knowing what the impacts can be. The poo ponds don’t help the matter.”
However, any bank extension now was only temporary ahead of the need to move the ponds to a better site, Lash said.
West Coast Regional Council chief executive Darryl Lew said council engineering staff and Waiho River Technical Advisory Group members spent two full days last week walking all protection structures on both sides of the river.
Their work also included capturing images via drones and the new Lidar survey of the riverbed.
Lidar uses light in a process to create three-dimensional images of a landscape, including the heights of the riverbed.
Lew said that new work was now being processed and formalised.
He expected a report from that new work including possible options around work to be done on the existing Waiho Flat stopbanks to be put before councillors on March 5.
Meanwhile, the Scenic Group whose insurers early in 2023 settled a $30 million claim against both councils in a confidential settlement, as a result of the April 2016 event, said at this stage they had no comment to make except to say they were working closely with the councils as the situation on the north bank unfolded.
Disclaimer: Te Runanga o Makaawhio chairman Paul Madgwick, who is an appointed iwi representative on the Westland District Council, a member of the West Coast Emergency Management Joint Committee and a member of the Franz Josef Joint Rating District, is also the editor of the Greymouth Star. He took no part in commissioning, writing, or editing this story.
- LDR is local body journalism co-funded by RNZ and NZ On Air