Whakatāne cannot rely on its current stopbanks to protect it in the future, the Bay of Plenty Regional Council has been told.

At a meeting last week, councillors were updated on Project Future Proof - the regional council’s plan to raise floodwalls and stopbanks in Whakatāne town centre by 800 millimetres – by senior environmental engineer Mark Townsend.

Chairman Doug Leeder introduced the report, saying ex-cyclone Debbie, in 2017, was best remembered for causing the Edgecumbe floods, but what many people didn’t realise was that Whakatāne River had also come close to overtopping its banks during that storm.

Townsend talked about his experience watching the Whakatāne River rise during the 2017 storm and how close the town was to evacuating at 3am.

“The only reason it didn’t go over the top was because the sea was, basically, dead flat. At 3am, I was on the phone to Civil Defence and we were preparing to evacuate Whakatāne, but we knew that the tide was going down. They said, ‘You’ve got half an hour’.”

Luckily, the water receded.

Townsend said though strengthening Whakatāne’s flood defences had been “in the train” before that, the experience reinforced the importance of it and helped accelerate the work the council wanted to do.

Remedial work is also happening on the Riverside Drive stopbanks and stopbanks from the McAlister Street pump station to the boat ramp at The Heads, and there were areas of uncontrolled seepage in the Kakahoroa Drive, Quay Street and Whakatāne Boat Ramp areas.

Planned work included installation of sheet piles to control seepage, seepage trenches to collect any water that gets past the piles, raising the stopbank and a floodwall.

The stopbank along Kakahoroa Drive, between the McAlister St pump station and the Whakatāne i-Site, will be the focus for this year.

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The regional council’s plans for this year include increasing the height of the stopbank between McAlister St and the Whakatāne Yacht Club and increasing the height of the flood wall between the yacht club and the information centre.

The height of the concrete slab wall, which will sit on the town side of the Warren Cole Walkway, would range from 600mm at the yacht club end to 1.7 metres at its highest point near the information centre.

Townsend said his team had been working with Ngāti Awa to put some designs on that wall, etched into the concrete panels on the river side of the wall.

The new wall would provide enough capacity for the regional council to protect meet its level of service in protecting the Whakatāne town centre until 2040.

Townsend presented a graph to councillors showing the stopbank height required to keep pace with projected sea level rise over the next 100 years. The graph showed even with the work currently planned, a further decision would be required by 2040 to either raise the stopbanks again, carry out work in the upper catchments to slow water flow, or reduce the level of service and enter a phase of managed retreat.

He said it was very likely that raising the stopbanks upstream from the McAlister Street pump station would also need to be done in another 10 years.

Ōkurei Māori Constituency councillor Te Taru White asked what a retreat from Whakatāne might look like.

Townsend said due to the flatness of Whakatāne, managed retreat would have to be abrupt.

“I don’t want to scare people,” he said. “Managed retreat usually means to retreat from the worst-affected areas slowly and progressively move further and further back. Whakatāne is so flat behind the stopbanks that it might not be progressive, it might be a once-off. But there’s obviously a lot of rhetoric going to happen first.”

Tauranga general constituency councillor Kat MacMillan commented that it was important to get the balance right with consultation so people weren’t afraid, but were prepared to accept the new reality.

“I think it’s a really delicate situation with not scaring the horses in terms of ‘this is the reality of climate change, sea levels rising, extreme events’, but having some sense of ‘we have to do this’.”

The regional council has engaged with Whakatāne District Council staff, along with Te Rūnanga o Ngāti Awa. It plans to update Whakatāne’s new councillors soon and seek written support from Ngāti Awa.

A programme of public engagement will follow this, including open days where the public will have the chance to share feedback. Consent preparation is already under way for the Kakahoroa west stopbank raising works, and the council hopes to begin physical works in March.