Designing for the long term: a risk-based approach to stormwater management at mine closure

Authors: Cleven, S Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2615_99

Cite As:
Cleven, S 2026, 'Designing for the long term: a risk-based approach to stormwater management at mine closure', 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. 1-17, https://doi.org/10.36487/ACG_repo/2615_99



Abstract:
Effective stormwater and waterway design is fundamental to achieving safe, stable and sustainable mine closure outcomes. As operational controls are progressively removed, closure landscapes must perform over extended design lives, often in the presence of residual geotechnical, environmental and public safety risks. This paper presents a structured, risk-based framework developed for rehabilitation of the Hazelwood mine site to guide the selection of design life and minimum design flow events for surface water infrastructure. The framework integrates corporate risk matrices with hydrologic and geomorphic design processes to ensure that stormwater assets are proportionate to the consequence of failure. Consequence categories – including public safety, environmental harm, cost, legal and reputational impacts – are linked to likelihood thresholds over defined design life criteria, such as operational and post-closure phases. These likelihood thresholds are translated into annual exceedance probability (AEP) design events, enabling consistent and transparent derivation of minimum design criteria across diverse landform and drainage settings. A spatial classification of ‘surface water management unit types’ was developed based on discharge location (internal pit, internal terminal, or external receiving waters of the Latrobe catchment) and underlying material (e.g. ash, coal, overburden, in situ soils). This classification directly informs consequence ratings for erosion-related failure and, in turn, the required design event. The approach aligns with Australian Rainfall and Runoff (ARR) guidance, including climate change adjustments to rainfall intensity (Ball et al. 2019). Testing across multiple design domains, illustrated through the West Field Western Batter (WFWB) domain worked example, demonstrated that the framework improves consistency and defensibility of closure designs without imposing unnecessary conservatism. By explicitly linking risk appetite to hydraulic performance criteria, the methodology supports transparent trade-offs between capital cost, long-term maintenance and residual risk. The framework provides a scalable model for other mine sites transitioning to closure, offering regulators and operators a practical pathway to risk-informed, climate-resilient water management.

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