Flood update from Environment Bay of Plenty

Environment Bay of Plenty engineers are today studying ways to close off a stopbank breach that continues to pour water over the already flooded Rangitaiki Plains.

They are also looking at engineering options that would allow more water from the floodplain to return to the river and get safely out the sea.

Rangitaiki River

On Sunday, a stopbank breach 1.5km upstream of Edgecumbe sent floodwaters across farmland and resulted in the evacuation of a number of homes in Te Teko, Edgecumbe and Thornton. The breach of the eastern bank is now about 150m wide. Water from the breach is flowing east towards the Whakatane River and north towards the coastal road between Whakatane and Matata. Last night, water began to flow over this road and pond on the other side of it.

Yesterday, to try and get rid of water from the flooded areas, a controlled cut was made through the stopbank at East Bank upstream of Butler’s Nursery in Thornton. The cut, which can be closed if necessary, allows floodwater to flow into the river without letting river water flow out.

Environment Bay of Plenty group manager community relations Bruce Fraser says the cut has helped reduce the rate of the flow heading east towards the Whakatane River. However, water is still building up on the plains because of the amount of water still coming through the breach.

At 5am, monitoring at Te Teko logged the Rangitaiki River at 4m above normal flow levels. At its peak, at 6am on Sunday, the river was 5.38m above its normal flow, so it is falling but still very slowly.

Since midnight, the Matahina Dam has reduced the amount of controlled spill into the Rangitaiki River from 440 cumecs (cubic metres a second) down to 340 cumecs. This should help to reduce the river flow today, though any significant rain could change that situation. Plans are in place to handle up to 50mm of rain without affecting river levels through storage at Matahina and upstream at Aniwhenua Dam. Aniwhenua has been lowered in preparation for this.

The electrical substation at Edgecumbe, which was earlier at risk of being flooded, now appears secure.

This morning, Environment Bay of Plenty engineers again flew over the flooded areas to check overnight changes to the situation. A National Institute of Water and Atmospheric Research jet boat is currently (this morning) sounding the depth of the breach to find out how far the river has cut down into it.

When they have that information, Environment Bay of Plenty engineers will review possible engineering options for closing the breach. It would be best done once river levels have fallen further but they may not be able to wait that long. Key to it is being able to get heavy vehicle access through flooded, muddy paddocks.

Engineers will also look at ways they can increase the flow of water off the Rangitaiki Plains, back into the river, and out to sea.

It is not yet certain how much water is flowing through the breach, but it may be about a quarter of the Rangitaiki River’s total flow.

Whakatane River

Whakatane River levels are reducing steadily. They had dropped from a peak of 7.7m on Sunday morning to 3.92m at Valley Road by early this morning.

Flood levels within the Whakatane township are falling the Sullivan Lake area but not in Awatapu.

General

Environment Bay of Plenty is constantly monitoring the state of the Rangitaiki Plains stopbanks, both from the air and the ground. “There is still a massive amount of water around,” Mr Fraser says.

The Rangitaiki Plains covers about 27,000 ha. It is estimated more than half that area has been flooded.

The weather has improved with no rain overnight. Rain is expected in the evening of July 20th.

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