Gisborne forestry firm develops plan to battle woody debris

Aratu chief executive Neil Woods says the firm is working on ways to limit the impact of its operations, including a plan to install steel debris nets to catch woody debris.

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 says the region has paid a high price for the devastation caused by Cyclones Hale and Gabrielle, and that the firm is working on ways to limit the impact of its operations.

The Swiss-designed nets will be the first of their kind for the Tairāwhiti region and will cost more than $500,000 each, Woods says.

“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 clean-up in the region.

Aratu Forests’ Forest Stewardship Council Certificate and Programme for the Endorsement of Forest Certification was recently suspended.

Woods said one of the principles of the certifications was that you could not have operations that breach regulations, which meant no debris could enter waterways.

At present, they could not meet those criteria because a natural event could mean a tree could fall into the waterway, he said.

Woods said as far as he was aware, only one other forestry firm in New Zealand was using Geobrugg steel nets - Rayonier Matariki Forests near Wairoa in Hawke’s Bay.

The Hawke’s Bay net had been tested over several storms.

“It’s accessible to clean it out and catches a fair amount of debris.”

Another forestry firm operating in the region, Ernslaw One, supports the use of Geobrugg debris traps over the conventional wooden or iron debris traps, a spokesperson said in a statement.

Subject to gaining resource consent, Woods said the firm planned to install the first net spanning a waterway near Wakaroa Forest by the Waimatā River, which flows through Gisborne city.

The proposed net for Wakaroa Forest is 25 metres wide and 7m high.

Each net is made up of flexible rings of high-tensile steel, which enables water to flow through. They are anchored in place by 20 or more rock anchors, each drilled 6-8m into the rock.

After the installation of the first net, Aratu also hopes 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.”

Woods said they had identified areas that were reasonably straightforward to access ”so we can clean it quickly [after storms]”.

Their decision to install the nets had nothing to do with the enforcement order being sought by Gisborne District Council for Aratu to remove forestry slash from steep land near Tolaga Bay, he said.

Aratu first proposed the nets in 2019, after a 2018 storm.

After community and council consultation, it 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 its application.

“We felt that we needed to step back and reconsider how we presented the project,” Woods said.

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.”

Woods said the debris nets were just one part of a toolbox of measures Aratu was planning to use to minimise woody-debris hazards.

A new artificial intelligence programme, integrated with high-resolution drone footage, gives details to contractors on where to remove large accumulations of woody debris from sites, which is used on a monthly basis.

Before 2018, non-commercial waste was often stored on or over the edge of a landing. This was no longer done. Now, no waste material should be left unless it was deemed very low-risk, he said.

“They probably don’t look clean to a novice who hasn’t experienced harvesting before. It’s not a paddock but it’s a lot less than what we were leaving.”

Additionally, the firm is using a 3D road engineering programme to identify stable locations to store excess material.