Integrating catchment, waterway and environmental risk to support a pit lake closure strategy

Authors: Hardie, R; Sims, A Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2615_15

Cite As:
Hardie, R & Sims, A 2026, 'Integrating catchment, waterway and environmental risk to support a pit lake closure strategy', in AB Fourie, G Boggs, J Heyes & M Tibbett (eds), Mine Closure 2026: Proceedings of the 19th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1-13, https://doi.org/10.36487/ACG_repo/2615_15



Abstract:
The rehabilitation of large open cut coal mines presents complex, interdependent challenges where void filling strategy, water resource management, environmental protection and long-term landform stability must be assessed together and reconciled with adjacent mine closure proposals. The Hazelwood Rehabilitation Project in Victoria provides a nationally significant case study demonstrating how complex closure elements and large volumes of technical assessment can be integrated into a coherent risk narrative that supports pit lake filling strategy, regulatory decision-making and management commitments under contemporary environmental and water governance frameworks. The project involves the transformation of the former Hazelwood mine void into a pit lake, supported by extensive earthworks, decommissioning of legacy infrastructure, and restoration of altered waterways. As part of the EES process, the catchments, rivers and wetlands assessment was used to separate existing approval settings from project elements requiring approval, align modelling platforms, base cases and project descriptions across technical disciplines, and trace project impact pathways through risks, impacts, mitigation measures and residual commitments. Integrated modelling and risk assessment demonstrated that the alternative scenarios can be delivered with limited and manageable impacts on downstream rivers, wetlands and the Gippsland Lakes system. Faster filling reduced the duration of altered flow conditions and therefore some ecological exposure, while connected configurations offered potential benefits for fill time and flood behaviour but introduced additional regulatory, operational and contingency requirements. This paper highlights practical lessons for mine closure planning where the central challenge is integrating extensive technical assessments into a defensible chain of reasoning from assumptions to consequences to commitments. The key lessons are that approval questions need to be separated from optimisation choices, technical disciplines need a common assessment platform, and impact pathways need to be carried through consistently from project activity to residual risk and management commitment.

Keywords: lessons, mine closure planning, water resource management, waterways, wetlands

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