Auckland’s dams expected to reach full capacity for first time in almost two years   

Today’s weather system is expected to push Auckland’s water supply dams to 100 per cent full for the first time since September 2023.

Head of water Sharon Danks says staff are eagerly keeping an eye on the total storage level as the rain continues.

“As of 4pm today, our total storage was sitting at 99.8 per cent, and we’re expecting it to have reached 100 per cent sometime tomorrow.

“Since the start of April, both our Wāitākere and Hūnua dam catchments have had just over 1000 millimetres (or one metre) of rain – to put that in perspective, it’s roughly 50 per cent more than what we consider normal for this four-month period.

“One benefit of the recent wet weather is that we’ve been able to make the most of our dam water sources, which means we haven’t needed to rely as heavily on our Waikato treatment plants.

“That’s important because treating water from the Waikato River costs around five times more than treating water at our Ardmore treatment plant, which serves four Hūnua dams.

“This is due to the more intensive treatment required and the extra energy needed to pump it into the city.”

Danks says seven of Auckland’s 10 main water supply dams were already full and spilling by midday Tuesday (July 29) but Wairoa dam in the Hūnua Ranges is traditionally the last to fill.

“Our Wairoa dam is large, and has comparatively smaller inflows, so it’s generally the last of our dams to fill to the brim.

“Our western dams on the other hand fill up faster because they have a higher infill to volume ratio – like having more taps to fill up a bath – so they are likely to fill up much more quickly.

“It’s pretty normal for them to fill up, drop down and replenish about five times a year.”

Latest weather forecasts indicate the wetter-than-normal weather is likely to continue through the rest of winter and possibly into early spring.