Edgecumbe residents whose town was devastated by flooding in April did not understand the serious risk posed by the Rangitaiki River breaching its banks, or understand formal evacuation procedures, a review has found.

The Bay of Plenty town was inundated after the Rangitaiki River breached its stopbank on April 6 following heavy rains from Cyclone Debbie.

But Civil Defence was only given the order to evacuate the town just 20 minutes before the floodwall failed - sending a wave of water and mud that destroyed 15 homes and badly damaged another 250.

Residents of Edgecumbe had a very low awareness of the risks of the Rangitaiki River breaching its banks, a review has found. Photo / George Novak
Residents of Edgecumbe had a very low awareness of the risks of the Rangitaiki River breaching its banks, a review has found. Photo / George Novak

The independent review of the Rangitaiki River Scheme, led by former finance minister Sir Michael Cullen, has found that the risks to the community were overlooked while the river scheme was being upgraded.

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Evacuation plans in case of the river flooding were also inadequate, the review found.

Speaking to Newstalk ZB's Rachel Smalley, Sir Michael said a "wide range of bodies" had failed to keep residents informed, including the regional council, district council, Civil Defence and even real estate agents who did not fully inform house buyers of the risks.

And he said the report would be "disappointing" for residents still rebuilding their lives. "People in that situation always want someone they can point the boat at and blame. In this case there's a complex series of interrelationships that don't allow that."

The review panel found the causes of the breach were complex, as water seeped into material under the wall and weakened it from below.

Blame for this happening could stretch as far back as 1973 when the wall's foundations were laid, and could also be partly due to damage from the 1987 Edgecumbe earthquake.

A concrete pad laid in 2012 next to the wall also added to the pressure on the wall which contributed to the eventual breach.

An independent review has found the failure of the Rangitaiki River's stopbank was due to a number of factors stretching back decades. Photo / File
An independent review has found the failure of the Rangitaiki River's stopbank was due to a number of factors stretching back decades. Photo / File

Some blamed the release of water at Matahina Dam for the breach downstream. But the review found no conclusive evidence that earlier reduction of lake levels at Matahina Dam would have stopped the breach, though it could have delayed the peak of the floods.

However it did find that if work at Reid's Floodway had been completed, water levels would have been almost half a metre lower and the failure may never have happened.

Bay of Plenty Regional Council chairman Doug Leeder said today the report would not answer every question for those still living with the consequences of the flood.

He said challenging conversations needed to be held, especially in the face of climate change.

"We will not shy away from the conversations that must be held with those who set the legislation around how best to manage climate change, what is an acceptable cost both financially and to the environment, and how to balance personal safety with personal choice."