Inquiry begins into Rangitaiki stopbank breach

By ROSALEEN MacBRAYNE

An independent investigation is under way into why the Rangitaiki River stopbank breached during the Eastern Bay of Plenty flooding.

Results should be made public in about two weeks.

A 100m stretch of protective embankment - built in the 1970s to 100-year flow standards - broke just above Edgecumbe on July 18 after three days of heavy rain.

River water poured over farmland, parts of the urban area and into the Fonterra factory.

The last of the dirty ponded water on the drenched Rangitaiki Plains should be off the farms in a few more days, thanks to hundreds of volunteers and up to 60 pumps working round the clock.

The breach occurred a few hours before the river logged its peak flow - 5m above normal. That was officially a 100-year event, Environment Bay of Plenty chief executive Jeff Jones confirmed yesterday.


A former civil engineer who worked on river control for 20 years, Mr Jones has commissioned a "well-qualified special geotechnical engineer" with a national reputation to do the independent review. He would not name him because the council wanted the inquiry done "without undue influence from any sources".

Mr Jones said the stopbank should not have breached, "even with the huge amount of pressure that was on it".

"It didn't fail because water overtopped it, as can sometimes happen. It just blew out."

He said he was shocked at the results.

After a 1987 earthquake, the regional council checked the stopbanks and carried out remedial work to make sure they were still safe. They were further strengthened after major floods in 1998 when some areas of bank leaked water.


Mr Jones said the council would also do its own review, including the cause of flooding from the Whakatane River.

* Mr Jones was full of admiration for two of his staff who came up with a bit of Kiwi ingenuity to help control floodwaters.

Engineers Bruce Crabbe and Tony Dunlop dropped a modified shipping container into a gap in a controlled cut above the Thornton bridge, near Whakatane.

At high tide the container doors are closed to keep river water from flowing out on to the sodden plains. At low tide, when the water level falls, the doors are opened to allow floodwater to return to the river.

The prototype was such a success that more containers were built to use on other cuts.