First 'slash nets' planned for Gisborne forestry blocks
Thursday, 17 October 2024
A Gisborne forestry company plans to be the first in the region to install slash catching nets in a bid to prevent the sort of destruction caused by storms like Cyclone Gabrielle.
Aratu Forests wants to put the Swiss-designed high strength steel cable nets in three of its pine plantations in the coming years.
The company, which is presently facing enforcement action by Gisborne District Council for poor harvesting practices, says its decision to install the nets has nothing to do with the council’s application for the order.
The company wants to put the nets on private properties bordering its plantations in Te Marunga, Waimanu and Wakaroa forests.
The nets, which are used around the world and elsewhere in New Zealand, are installed above river beds and are designed to capture material as it flows downstream, while allowing water to continue to pass through and over the top of them.
The company proposes to install the first net in its Wakaroa forest, on a tributary of the Waimata River. The Waimata River flows through Gisborne city and large rain events see it swell with forest debris and slash, which jams against bridges and ends up on city beaches.
The net would catch debris coming out of about 590hectares of the 1700ha forest, which straddles other catchments.
The nets cost more than $500,000 each.
The net proposed for Wakaroa forest would use high-tensile wire ropes and be held in place by more than a dozen anchors, each drilled 6-8metres into rock and injected with cement. The net would be about 25metres wide and 7metres high.
It would be installed in partnership with Swiss company Geobrugg, which has installed more than 250 debris flow barriers in about 25 countries, including New Zealand.
The net would be designed to capture all material flowing downstream in a 1 in 100-year event. In events greater than that, the net was designed to fill up and then let material pass over top.
After a heavy rain event the net would be inspected for woody material and cleared as soon as possible.
Aratu intended to apply for resource consent to build all three nets in the next few weeks, and hoped to start construction of the Wakaroa net next year. It will seek a consent term of 35 years, allowing it to make decisions around where it did and didn’t plant trees in future.
Aratu said it could have all three nets built within 2-3 years.
The company said it planned to improve its forestry management practices and limit woody debris mobilisation to the point that any slash nets it builds could be taken down after 35 years.
Aratu’s chief executive Neil Woods said the nets were “an extra layer of protection that have been successfully used overseas and in New Zealand”.
“They’ve proven to be very effective at saving lives, buildings and land from the impacts of woody debris and rock falls,” he said.
“We’re committed to being a responsible custodian of the environments we operate in, so we’re pleased to be advancing our plans with today’s announcement,” Woods said.
“Debris nets are one part of a toolbox of measures we are using and plan to use to minimise woody debris accumulating in plantations and migrating down waterways after storms,” he said.
“The region paid a high price for the devastation caused by cyclones Hale and Gabrielle. Like all forestry companies in Tairāwhiti, we work in a very challenging environment with many trees planted on highly erodible soils on steep hill slopes,” he said
“We have learnt much from the cyclones and are determined to keep lifting our game to limit the impacts from our operations,” Woods said.
The nets would be the first in the Tairāwhiti region. A net similar to those proposed was installed in Hampton forest, in Hawke’s Bay, in 2021.
Aratu had previously proposed to build a slash net following storms in 2018 but withdrew a resource consent application because “the pathway to getting approval was unclear”.
Aratu managed 35,000ha of forestry plantation land across Tairāwhiti. It employed more than 200 permanent staff.