Aratu plans to install three high-strength steel debris nets to reduce woody debris in waterways. The nets will cost over $500,000 each and are the first for the Tairāwhiti region. Aratu is implementing various measures to minimise debris entering waterways after severe weather events. Photo: Supplied via LDR
A Gisborne forestry firm plans to install three steel debris nets to reduce the amount of woody debris clogging waterways after severe storms.
Aratu chief executive Neil Woods said the region paid a high price for the devastation caused by cyclones Hale and Gabrielle, and that the firm was working on ways to limit the impact of their operations.
The Swiss-designed nets will be the first of their kind for the Tai Rāwhiti region and will cost more than $500,000 each, Woods said.
"We have learnt much from the cyclones and are determined to keep lifting our game."
Since Cyclone Gabrielle, Gisborne ratepayers have spent more than $1.2 million removing woody debris from two of Gisborne's beaches, and taxpayers have contributed $53m for the debris's cleanup in the region.
Aratu Forests recently had its Forest Stewardship Council Certificate and Programme for the Endorsement of Forest Certification suspended.
Woods said one of the principles of the certifications is that you cannot have operations that breach regulations, which means absolutely no debris can enter waterways.
He said at present, they cannot meet those criteria, because a natural event could mean a tree could fall into the waterway.
As far as Woods is aware, there is only one other forestry firm in New Zealand using Geobrugg steel nets, which is Rayonier Matariki Forests near Wairoa in Hawke's Bay.
The Hawke's Bay net has been tested over several storms now, Woods said.
"It's accessible to clean it out and catches a fair amount of debris."
Hoards of slash along Midway Beach in Gisborne. Photo: Ashleigh McCaull / RNZ
Another forestry firm operating in the region, Ernslaw One, supported the use of Geobrugg debris traps over the conventional wooden or iron debris traps currently in use, a spokesperson said in a statement.
Subject to gaining resource consent, Woods said the firm plans to install the first net spanning a waterway near Wakaroa Forest by the Waimata River, which flows through Gisborne City.
The proposed net for Wakaroa forest will be 25m wide and 7m high, with high-tensile wire ropes, anchored in place by 20 or more rock anchors, each drilled 6-8m into the rock.
Following the installation of the first net, Aratu also hoped to install another two nets at private properties bordering Te Marunga and Waimanu.
"We saw those three as real top priority sites because of what's downstream of them.
He said they have identified areas that are reasonably straightforward to access.
"So that we can clean it quickly [following storms]," Woods said.
He said their decision to install the nets has nothing to do with the enforcement order currently sought by the Gisborne District Council for Aratu to remove forestry slash from steep land near Tolaga Bay.
Aratu first proposed the nets in 2019, following a 2018 storm, he said.
After community and council consultation, they submitted a resource consent in March to install two debris nets across tributaries of the Waimata and Uawa rivers.
However, after almost three years of consultation with the council and "considerable investment", Aratu withdrew their application.
"We felt that we needed to step back and reconsider how we presented the project," says Woods.
Gisborne District Council director sustainable futures Joanna Noble said the 2019 application was delayed because the supporting information was inadequate.
"The council was concerned about the potential adverse effects of the proposed slash catcher and so decided to publicly notify the 2019 application."
Artificial intelligence
Woods said the debris nets are just one part of a toolbox of measures Aratu are planning to use to minimise woody debris hazards.
A new artificial intelligence program, integrated with high-resolution drone footage, gives details to contractors on where to remove large woody debris from sites, which is used on a monthly basis.
Prior to 2018, non-commercial waste was often stored on or over the edge of a landing. This is no longer done. Now, no waste material should be left unless it is deemed very low risk, he said.
"They probably don't look clean to a novice that hasn't experienced harvesting before, it's not a paddock, but it's a lot less than what we were leaving," he said.
Additionally, the firm is using a 3D road engineering programme to identify stable locations to store excess material.
LDR is local body journalism co-funded by RNZ and NZ On Air.