Conventional mine rehabilitation in Central Queensland often involves flattening slopes, applying limited topsoil, fertilising, and establishing pasture for grazing. However, a long-term trial near Moranbah suggests an alternative approach.
Since the early 1990s, a rock-clad slope has been established without topsoil or formal drainage structures, yet it has supported vegetation for decades while remaining largely resistant to erosion.
A study co-authored by Brendan Roddy, Principal of Landform and Soils, and Peter Berghofer from BHP Mitsubishi Alliance Australia, indicates that, when woodland is the intended land use post-mining, focusing on landform stability and utilising available site materials may provide a viable alternative worthy of further exploration.
Why revisit conventional rehabilitation approaches, and what makes this trial different?
Traditional grazing rehabilitation often relies on substantial topsoil, fertilisers, and engineered drainage. However, in Central Queensland, topsoil can be scarce and vulnerable to erosion before vegetation is established. This trial adopted a different approach: a thick layer of locally sourced sandstone rock was placed over problematic spoil without any topsoil. The surface was deliberately left rough and aerially seeded, focusing on native trees and shrubs. The slope included gradients of approximately 23% to 40% and did not depend on conventional contour banks or spine drains.
How has the rock-clad landform performed, and why might the design work?
More than 20 years after establishment, the area was reported to support a self-sustaining vegetated surface, with no visible signs of broad-scale erosion observed during inspections in 2023. The coarse rock helps protect the underlying sodic and dispersive spoil, as it is much more difficult for stormwater to move across the rough surfaces compared to fine soil. The depth and permeability of the rock may also help keep the spoil relatively dry. Additionally, the mounds and furrows of the rough surface can store and disperse rainfall, creating microsites where water, sediment, seeds, and organic matter can accumulate. However, some local material movement and a strong presence of Buffel grass remain important limitations.
Does this mean topsoil and conventional drainage are no longer needed?
No, this case study does not provide a universal replacement for conventional rehabilitation. It demonstrates that alternative designs can be effective under specific materials, climate conditions, and post-mining land-use objectives. A low-fertility rocky surface may also create conditions suitable for native species adapted to tougher substrates, but further research is necessary to understand rock properties, cover depth, infiltration, vegetation growth, erosion behaviour, and how to strengthen native ground cover.
What is the broader lesson for mine closure?
Begin with the long-term outcome rather than defaulting to legacy practices. If the goal is to create a safe, stable, and sustainable woodland rather than grazing land, the optimal rehabilitation design may look quite different. Long-term trials like this one can help the industry test its assumptions, make more strategic use of available site materials, and design stability into the landscape from the outset.
