Floods testing New Zealand Civil Defence


It would be fair to say that the last four days in New Zealand have tested Civil Defence as heavy rainfall across much of the country has caused evacuations and property damage. But no place has suffered as much as the Bay of Plenty town of Edgecumbe, which was completely swamped when the neighbouring Rangitaiki River broke through its banks.

As the flood waters go down in Edgecumbe, a major clean up is just starting. No one will be able to go home for several days. The flooding in Bay of Plenty follows flooding that has happened over the previous 72 hours as New Zealand feels the lash of former Cyclone Debbie, which pounded Australia last week. Rainfall from Debbie caused rivers in New South Wales and Queensland to reach near record levels, whilst winds reaching over 200km/h battered the coastal towns.

When it reached New Zealand the remnants of Debbie first struck between Whanganui and Cape Reinga. Very humid unstable air triggered powerful thunderstorms with very high precipitation rates (up to 45mm/hr), which caused flash flooding to break out. Then prolonged heavy rain in the upper reaches of the Whanganui, Whangaehu and Manawatu Rivers caused evacuations to break out across Rangitikei and Whanganui Districts in anticipation of record flooding. At the same time the Moutoa Floodgates on the Manawatu River were opened to relieve pressure.

Overnight on Wednesday and into early Thursday morning, concerns were raised about the rising Rangitaiki River and how well the Matahina Dam could cope with the water level. The flooding is a substantial event for its type in New Zealand. Over 1600 people were made to leave their homes when the stopbank between the Rangitaiki River and Edgecumbe township gave way on Thursday morning. Whakatane and numerous small settlements around the Bay of Plenty were also cut off or threatened by the rising river levels.

It needs to be remembered that the stop banks protecting Edgecumbe were designed for an event significantly less than a 500-year return period event. In light of this, despite the outcome the banks did the job that that their design parameters were intended for. That is of no comfort to the residents in the adjacent streets who by the time you read this would have had a restless night wondering what they would be going home to.

The flooding in Edgecumbe is not the only flood headache for Civil Defence with significant flooding happening on other rivers in the district including the Whakatane. But as the first significant New Zealand community to be subject to a mandatory evacuation order in recent times, it is certainly the biggest.

 

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