Water storage dams in the Hunua Ranges weathering the storm well

Janie Smith from Watercare

The water storage dams in the Hunua Ranges are operating as normal, despite more than 240mm of rain falling within the past 24 hours.

Water supply manager Priyan Perera says the water levels in the dams rose significantly overnight, with Cosseys and Hayes Creek dams now full and spilling.

“Cosseys Dam rose 17% as a result of this rainfall and is now spilling,” says Perera.

“When our dams reach capacity, they are designed to spill into an engineered spillway. When this occurs, the volume of water being released is simply reflecting natural flows.

“I’m aware that some local residents are concerned we are actively releasing water from the Hunua dams, resulting in downstream flooding. This is most certainly not the case. Unlike hydroelectric dams, our dams do not have release gates – as a water supplier, our aim is to store as much water as possible. The four large dams were not full prior to this event, meaning they have been able to capture and contain a lot of the water - minimising the scale of potential flooding downstream.”

The storm has not comprised the structural integrity of the dams.

The high volume of rain has affected the clarity of the water (turbidity) in the dams. This change in water quality means that Watercare must carefully managing the incoming flows and treatment processes at Ardmore Water Treatment Plant.