Officials are blaming red tape for the devastating deluge that overwhelmed the Bay of Plenty township of Edgecumbe.

Trustpower's CEO says the torrent of water that breached a stop bank in the Rangitaiki River yesterday could not have been avoided under the company's current flood management plan.

Vince Hawksworth told Newstalk ZB this morning the company would cooperate "100 per cent" with any inquiries into the catastrophic flooding of Edgecumbe yesterday, but said the company had followed their plan to the letter.

"I'm confident we did what we were supposed to do."

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Most Eastern Bay rivers have returned to below warning levels and the Rangitaiki was receding this morning, but floodwaters continue to come through the breach on College Road in Edgecumbe.

The regional council has put rock armouring and toe loading in several at-risk areas.

These have now stabilised and there have been no stop bank failures under prolonged elevated flood levels from an over design flood.

Hawksworth said the plan, which was tied to Trustpower's resource consent, involved dropping the levels of Lake Matahina around Monday lunchtime, before the rain hit.

The flood management plan for the Matahina Dam is designed to take 100 cubic meters per second off the flood peak.

"We drop the lake - we dropped it to the lowest level allowed by the resource consent," he said.

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When the rains did hit, dumping 20 times Lake Matahina's capacity over three days, Trustpower began a controlled release of water into the Rangitaiki River.

Sites logged between 200-320mm of water falling on the Rangitaiki in 48 hours, the regional council said.

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The power company worked with the regional council to determine when and how much water should be released, Hawksworth said.

The question of whether more water should have been released earlier was a valid one, but Trustpower did not have the authority to make that call at the time, Hawksworth said.

"We have to operate within the flood management plan we've agreed to.

"We got to the level we were supposed to well ahead of the [rain] arriving and we did that by making sure we passed water early over the dam.

"The water is passed by going around spill gates, and then you get to a capacity on the spill gates.

"The reason you end up passing water is clearly you wouldn't want to get to the point where the dam filled and then spilled over the top of the dam, because you could get a catastrophic failure of the dam."

Trustpower would cooperate fully with any inquiry into the flooding of Edgecumbe, which has left thousands of people without homes.

"Clearly ... there's got to be a conversation about are the stop banks up to meeting this level of flood," Hawksworth said.

Stop banks in the Eastern Bay are designed for a one-in-100 year event, said Bay of Plenty regional council spokesman Peter Blackwood.

At their peak, river flows were more than 30 percent larger than this.

Blackwood said there had been regular reports into the stop bank's structural integrity and all upgrades had been completed before the flood.

"This level of flooding is well above the design standard of the river scheme, both in terms of flood height and duration of flood. The duration is a critical factor in seepage threats."

The stop bank was many decades old but had been recently upgraded. It would be recoverable, Blackwood said.

Bay of Plenty Regional Council activated its Whakatane flood room at midday on Wednesday and its team of flood managers worked round the clock since then to minimise flood damage.

River and stop bank inspections by Bay of Plenty regional council staff continue today. The Rangitaiki River flow has reduced to 420 cubic meters per second, down from more than 700 cubic meters per second yesterday.