Public get first-ever look at south Auckland's Hūnua Range regenerating forest

Tuesday, 19 November 2019

After taking over a forestry right in Auckland's Hūnua Ranges, Watercare is aiming for 3.5m native trees to be planted around its Upper Mangatawhiri Dam.

Strips of gravel weave their way through the hilly terrain of the Hūnua Ranges.

Felled pine trees that resemble oversized Jenga pieces line the stoney roads.

In their place stand mānuka, māhoe, kānuka, makomako, kōhūhū, puahou, karamū and harakeke.

Covering more than 1900 hectares, the mix of native and exotic forest saturate the range.

With the capacity to hold 16.2 gigalitres, Upper Mangatawhiri is Auckland's second largest dam.

* Millions of trees to be planted in Hunua Ranges to ensure Auckland's water supply

* Hunua dams 95.7 per cent full and 'spilling in normal fashion'**

It's hard not to notice the grandeur, but the natives serve a much more essential purpose.

In the two years since Watercare took ownership of the commercial pine forest, they've planted 400,000 natives over 110 hectares in a bid to maintain Auckland's water supply.

About 50 members of the public toured the 1900-hectare forest at the Hūnua Ranges.

The are four dams southeast of the Hūnua Ranges that supply more than 60 per cent of Auckland's water.

And for the first time ever, members of the public were given a guided tour of one of the larger dams, Upper Mangatawhiri, and the regenerating forest.

Native trees prevent sediment run-off, the number-one enemy from a water-supply point of view, Watercare say.

The regenerated natives will hold the soil together, meaning there will be less slips and run-off.

Watercare will plant more than 3 million native tress over the next 30 years in a bid to protect water supply.

And because forestry activity will be reduced and ultimately phased out, there will be little bare land subject to erosion.

The council-controlled organisation can also regulate what's used in the catchments.

Commercial forestry often use herbicides to control weeds, which can end up in the water.

There were occasions when Watercare suspected there were herbicides in the water, so they decided to pump from elsewhere.

The dams at Hūnua Ranges provide two-thirds of Auckland's water.

With the capacity to hold 16.2 gigalitres, Upper Mangatawhiri is the second-largest Auckland dam.

Minibuses chauffeured about 50 people to the dam at the weekend, where they were given a tour of the valve tower, a Watercare spokeswoman said.

The public were able to see and hear about the work done to maintain the city's water supply.

At the moment, water storage is about 88 per cent full, with Aucklanders using 2.9 billion litres of water in the last seven days.

While it may seem like water is plentiful, the city has had its fair share of shortages, mainly attributed to a lack of rainfall.

Earlier this year, Aucklanders failed to heed the call to save water in a bid to curb declining levels in the city's storage dams.

In July, the storage lakes which supply most of Auckland's water were nearly 20 per cent below their July average, at 63.45 per cent.

And in 2017, when the so-called 'Tasman Tempest' hit, heavy rainfall sent huge amounts of sediment into the dams.

It caused processing problems for the Ardmore Water Treatment Plant, which filters the water from the Hūnua dams.

Aucklanders were asked to save 20 litres of water per person per day for six weeks while Watercare worked to fix the problems.

By 2048, Watercare estimates 3.7 million native trees will have been planted, both through hand planting and seed dispersal by drones.

It's a strategy Watercare says will directly impact the city's water supply, increase native fauna and flora in the region, and provide more recreational opportunities for the public without the restrictions imposed by commercial forestry.