Predicting the long-term erosional stability of valley fill tailings dams using a computer-based landscape evolution model

Authors: Hancock, G; Coulthard, TJ Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2215_74

Cite As:
Hancock, G & Coulthard, TJ 2022, 'Predicting the long-term erosional stability of valley fill tailings dams using a computer-based landscape evolution model', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: Proceedings of the 15th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1013-1024, https://doi.org/10.36487/ACG_repo/2215_74



Abstract:
Tailings are commonly stored in ‘tailings dams’ where the particulate component can settle out and such dams are a feature of many mine sites. As they impound water and sediment, tailings dams can be at risk from both catastrophic and gradual failure, especially if unmanaged. Therefore, in many post-mining landscapes, tailings dams will be permanent features. A fundamental question for their management is, can tailings dams ever be walk-away structures? Catastrophic failure occurs when there is a large-scale rapid structural failure of the dam wall suddenly releasing large quantities of water and sediment. Further, over time, there will be the increased risk of gradual failure by the slow infilling of the dam and the erosion of the dam wall. This occurs where water overtops the dam wall and then incises through the wall due to a loss of freeboard in the dam, a situation which is more likely in legacy tailings dams where they have been filled, vegetated and abandoned. This work demonstrates how a computer-based landscape evolution model (CAESAR-Lisflood) can be used to assess a hypothetical tailings dam failure risk for the gradual failure situation. Using a conceptual setting, our findings demonstrate that given average climate conditions, a dam can be sufficiently robust to last centuries. CAESAR-Lisflood also can model runoff and here the assessment includes modelling of water quality both during mine operation and post-breach. Tailings can be contained if there is maintenance and/or an increase in the dam wall height over time or a more robust dam wall constructed to manage extreme events. However, erosion and infill will continue to reduce the integrity of a more robust structure over time. Therefore, it is highly likely that tailings dams will require continued monitoring and maintenance.

Keywords: CAESAR-Lisflood, mine closure, dam closure, environmental risk, water quality

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