Auckland water crisis: One dam nearly full following recent heavy rain

One Auckland dam has nearly filled following recent days of heavy rain, but residents are still urged to follow water-saving efforts.

The Upper Nihotupu Dam in the Waitākere Ranges has seen a storage boost from 51 percent full on Wednesday morning to 93 percent full on Tuesday. In total, it can hold roughly two billion litres.

Watercare chief executive Raveen Jaduram says over the past week, Auckland's total water storage level has risen from 45 percent to 55 percent.

"It's good to see the dam levels moving in the right direction, but it would be premature to celebrate now. We have to remember, the historical average for this time of year is 79.8 percent - and we're still a long way from there."

Jaduram says further rainfall will bump up the total water storage level but its overall impact will depend on where the rain lands.

The rain needs to fall in the Hūnua Ranges since the dams in that area are much larger than the dams in the Waitākere Ranges, and it takes "significantly more" rainfall to fill them up after a period of dry weather.

"To put this in context, all of the water in our five western dams, when full, would only half fill Mangatangi Dam in the Hūnua Ranges."

The storage capacity of Auckland's dams.
The storage capacity of Auckland's dams. Photo credit: Watercare

Mangatangi Dam holds 35 billion litres of water, and all the Hūnua dams combined have a capacity of 77.1 billion litres, which makes up 82 percent of Auckland's water storage. Jaduram says they typically receive enough rain to recharge over the course of a year, whereas the smaller Waitākere dams may recharge five times. These smaller dams hold a total of 17.2 billion litres.

It means the Waitākere dams can be full or spilling over when the Hūnua dams are still low, he says.

Although the Upper Nihotupu Dam's storage dramatically increased over the course of a week, Mangatangi Dam only rose from 45 percent to 50 percent capacity in the same time period.

Jaduram says while total dam storage is now more than half full and more rain is expected to fall in July, outdoor water restrictions will continue and Aucklanders are still urged to save water.

"We still need a lot of rain to fill up our dams, and the outlook is for a very dry second half of 2020, particularly between August and November. We need to be in the best possible position at the start of summer, so please keep doing your bit to reduce your water usage. Aucklanders have done a fantastic job so far, and we need to keep up the good habits we've adopted during the drought."

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