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By Amy Edwards 15 August 2022 6 min read

Community tree planting at Charles Street Park on the Mary River, Queensland in 2015. Photograph by Tim Odgers, Seqwater.

A trusty and reliable ‘toolbox’ is key to rehabilitating eroded sites in the vast catchments of the Great Barrier Reef and saving coral living kilometres offshore.

But CSIRO Landscape evaluation researcher Dr Scott Wilkinson’s toolbox can’t be found at your local hardware store, or in the back of a tradie's ute.

Instead of screwdrivers and spanners, the Reef Trust Gully and Stream Bank Toolbox is a best-practice guide for conducting erosion control activities in Reef catchments.

Developed by the Australian Government’s Reef Trust, CSIRO and its partners (ANU and Griffith University), the toolbox provides landscape repair practitioners, engineers, natural resource management agencies and various land care businesses with erosion management processes that are cost-effective combinations of civil engineering and revegetation approaches.

Wilkinson is the lead contributor for the third edition of the Reef Trust Gully and Stream Bank Toolbox. He is also a passionate advocate of the potential for erosion control to improve Reef water quality.

“Water quality is still the second biggest threat to the Reef behind climate change,” Wilkinson says.

“Land erosion can lead to fine sediment leaving catchments and entering the Reef, which can significantly impact on the water quality.

“Our achievements to date have been steady in regard to sediment targets for the Great Barrier Reef but there is a lot of work to do yet.”

Australia is reported to be almost halfway towards the 60 per cent target to reduce dissolved inorganic nitrogen loads by 2025 and more than halfway to the 25 per cent target to reduce fine sediment by 2025. However, progress does get interrupted from time to time by weather events such as droughts and floods. Some sites are also more complex than others.

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A key focus of protection and recovery efforts on the Great Barrier Reef are based in the catchments adjoining its coastline. Access the transcript.

Why do we need to rehabilitate catchments?

A key focus of protection and recovery efforts on the Great Barrier Reef is in the catchments adjoining its coastline.

The Reef catchments cover an area of more than 423,000 km2, and cattle grazing is the dominant land use by area. Monitoring and modelling suggest that rangelands, primarily in the Burdekin and Fitzroy catchments, contribute about three quarters of the total fine sediment load that flow into the Great Barrier Reef lagoon.

Here, the fine sediments smother corals and seagrass beds, particularly closer to the coast and at the mouth of the large rivers. In big flood events, sediment plumes can even reach the outer reefs. Nutrients which are attached to the sediment particles are delivered to coastal waters during floods and fuel algal growth which further reduces light penetration to seagrasses and other marine habitats.

In response, CSIRO has collaborated with research organisations, land holders and regional Natural Resource Management bodies, with the help of funding from the Australian and Queensland governments, to study where the sediments come from, and how to manage grazing landscapes to reduce soil erosion and sediment loss.

More recently, the focus has been directed at ways to effectively remediate gullies and stream banks, as this is where most of the sediment is coming from.

“Working with the CSIRO led consortium is a rewarding experience as it brings the technical skills, knowledge and experience from the range of technical partners together, providing high quality technical advice to us and our delivery partners,” Royce Bennett, Assistant Director of the Reef Water Quality section at the Department of Climate Change, Energy, the Environment and Water, says.

Revegetation and pile fields on the Mary River in January 2022, prior to recent flood events. Photograph by Caitlin Mill, Mary River Catchment Coordinating Committee.

What is different about the third edition of the toolbox?

Published in March 2022, the third edition of the toolbox supports the latest in best practice erosion management. This involves targeting cost-effective combinations of civil engineering and revegetation approaches and incorporating new research outcomes arising since the publication of the previous toolbox guides. It features an updated understanding of the effectiveness of certain approaches in the variable Queensland climate. The new case studies reflect what is working well and lessons from recent on-ground experience.

Jennifer Mackenzie from Terrain Natural Resource Management says the document has come a long way over recent years and was now the ‘go-to guide’ or methodology for estimating sediment savings-for landscape repair projects.

“This 3rd edition of the toolbox has adapted to keep pace with developments in the scale and professionalism of the engineering and revegetation approaches to erosion control as part of the response to Great Barrier Reef ecosystem threats,” she said.

“The typical erosion control sites are now much larger than those tackled several years ago, and the level of rigor to complete the requirements has also increased. The recent programs have developed the capacity of natural resource managers and the local economic activity in Reef catchments.”

Timeline of Gully remediation in the Burdekin catchment, clockwise from top left. A: the scarp height varied from 2m up to more than 4m. B: Topsoil was stockpiled, and tunnel erosion was excavated. The gully landform was reshaped C: The finished landform surface was capped with crushed gravel, fertile soil, compost and grass seed. Rock check dams were installed to control runoff. D: Ground cover is now protecting the soil surface.Photographs by Damon Telfer

Big obstacles remain in terms of improving water quality in the Great Barrier Reef

The fourth mass coral bleaching event since 2016 developed over the late summer of 2022. It was the first to occur in a La Niña year. Heat stress across the Reef reached levels where widespread bleaching was confirmed by aerial and in-water bleaching surveys. However, the heat stress did not reach levels where extensive mortality is expected.

The increased frequency and extent of bleaching events remains concerning. Each year, the Reef is at increased risk of widespread coral bleaching due to climate change, which means time for recovery is becoming shorter.

Hard coral cover in the southern region has also decreased from 2021, due to predation by crown-of-thorns starfish. The Crown-of-thorns Starfish Control Program continues to work in all three regions of the Reef to cull starfish down to non-outbreak levels.

CSIRO Environmental Management group leader Dr Rebecca Bartley said improving the resilience of coral is a huge multi-disciplinary research area and needs to consider many threats.

“It makes sense that coral that has been hit by multiple stress factors like bleaching, crown-of-thorns starfish and poor water quality is going to struggle,” she said.

“That’s why it’s important that we support multiple efforts to improve all the stressors, including water quality and climate change.”

Looking towards the future

The Reef Water Quality Report Card was released by the Australian and Queensland governments in April 2022.

This report card includes the results of the water quality improvements regarding soil erosion and sediment loss and the methods, which are set out in the toolbox. CSIRO also contributes to the report card through eReefs modelling.

It shows continued improvement of the quality of water flowing onto the Reef with key reductions in dissolved nitrogen levels and fine sediments.

The report card also shows that long-term work with communities, business, farmers, landholders and industry groups in Reef catchments is improving water quality and delivering results that protect the values of the Reef.

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