This occurred just hours before a peak flow 5m above normal levels. Water poured through the stopbank and on to farmland, roads and houses on the Rangitaiki Plains.
The Fonterra Dairy factory just out of Edgecumbe was also hit by the floodwater.
No one doubts that this is a huge volume of water, but questions have arisen because Rangitaiki River stopbanks are made to 100-year flow standards.
Environment Bay of Plenty has commissioned an independent investigation to find out why it was breached.
“We need to know exactly what happened so we can take steps to ensure it doesn’t happen again,” says EBoP chief executive Jeff Jones.
“This is extremely important to EBoP and the communities living in the shadow of our stopbanks.”
Mr Jones says the stopbanks are designed to hold floodwater — not to fail.
“The Rangitaiki River stopbank should not have breached like it did, even with the huge amount of pressure that was on it,” Mr Jones says.
“It didn’t fail because water overtopped it, as can sometimes happen, it just blew out.”
The Edgecumbe earthquake in 1987 and major floods in the region in 1998 have raised concerns about Rangitaiki stopbanks and their stability.
They have been investigated and reinforced during the years to prevent the kind of breaches seen last month.
The Government will provide more assistance to flood-affected parts of Bay of Plenty, including agricultural recovery, repairing schools, fixing roads and giving direct help to low income earners and people who had to be evacuated.
This brings the total Government support to an estimated $30 million.