How long is long enough? Adopting a risk-based approach to inform drainage management in closure designs

Authors: Smedley, E; Mackenzie, S; Gregory, S Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_rep/1915_117_Smedley

Cite As:
Smedley, E, Mackenzie, S & Gregory, S 2019, 'How long is long enough? Adopting a risk-based approach to inform drainage management in closure designs', in AB Fourie & M Tibbett (eds), Mine Closure 2019: Proceedings of the 13th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1499-1508, https://doi.org/10.36487/ACG_rep/1915_117_Smedley



Abstract:
Landform design at closure has evolved from ad hoc principles, such as generic batter/berm configurations and top surface geometry, to designing structures to manage specific design rainfall events. However, there is conjecture around the application of appropriate rainfall events to inform closure designs. Design rainfall events adopted for closure may range from less than one in 100-year annual exceedance probability (AEP) to probable maximum precipitation (PMP). Often, the design rainfall events are selected on an arbitrary basis or as specified by the regulators. In accordance with standard engineering practice, defensible design criteria should be prepared prior to developing closure designs for mining landforms. Designing for extreme events (those in the order of PMP) can result in greater closure costs, increased disturbance footprint, constructability issues or a resultant increase in other post-closure risks to the environment. These negatives can outweigh the potential consequences that the design intends to manage. Although appropriate in some cases, there is a risk that extreme events such as PMP are adopted as the default design criteria. The 2016 Australian Rainfall and Runoff (ARR) guidelines and the Australian National Committee on Large Dams (ANCOLD) guidelines advocate the use of risk-based design in the management of threats posed by surface water. This is consistent with best practice mine closure planning. This paper demonstrates how a risk-based approach to drainage management can inform defensible design criteria and resultant closure designs.

Keywords: landform design, drainage management, risk assessment

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