The dam on the Kaiwhata River which gave out on Thursday night. PHOTO/SUPPLIED

GIANINA SCHWANECKE
gianina.schwanecke@age.co.nz

The suspense is over after the dam formed by a landslide along the Kaiwhata River, east of Gladstone, broke on Thursday night, sending an estimated 600,000m3 of water charging downstream towards the coast.

It was a huge relief for Homewood farmer Andy Tatham, who lives downstream of where the landslip happened two weeks ago, blocking the river.

He said residents in the area had been on tenterhooks for the past few days, not sure of what would happen.

“We are so lucky that it was a clean flood,” he said.

An on-farm bridge remained intact and all stock had been moved previously, meaning there had been no loss of life.

But the massive volume of water had caused “extensive damage” to fencing over about four kilometres of his farmland.

Carterton District Council infrastructure, services and regulatory manager Dave Gittings said heavy rainfall on Thursday had helped raise the lake level, forcing water over top of the dam wall.

That flow gradually carved the dam away.

“It wasn’t a big instantaneous release,” he said.

“From what I can understand, that increase from the rain breached [the top of dam] and started chomping away at the dam wall.”

It is believed the water in the dam had risen by about 1.2 metres on Thursday night before topping over the dam at around 8.20pm.

By 9pm the lake was rapidly disappearing and by 10.10pm that night the water had almost returned to its normal level.

Gittings said it was a semi-controlled event and one of the better outcomes as the water had flown down the usual river channel without injury to residents or damage to houses downstream.

The river was still high because of the rain but no more than would be expected at this time of year, he said.

Kaiwhata Rd was reopened on Friday after debris was removed, though Fulton Hogan crews were on-site for some minor metalling repairs.

The Kaiwhata Bridge, which Masterton District Council feared would be damaged in a catastrophic failure of the dam, is still in place and safe to use.