Breslin, S, Frazer, S & Waddell, E 2022, 'Subsidence ponded landforms and closure', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: 15th International Conference on Mine Closure
, Australian Centre for Geomechanics, Perth, pp. 1155-1168, https://doi.org/10.36487/ACG_repo/2215_85
This innovative study assessed the potential impacts (beneficial and adverse) associated with leaving subsidence-induced ponded landforms (ponded areas) in situ in comparison to reinstating free-draining landforms at Grosvenor Mine in Queensland. This included a risk-based comparison and identification of relevant post-mining land uses (PMLU) under the legislative framework of the Mineral and Energy Resources (Financial Provisioning) Act 2018.
An initial literature review identified that the most common contemporary industry standard for managing ponded areas is to reinstate free-draining landforms. However, technical studies including GoldSim water balance modelling, TUFLOW flood modelling, targeted flora and fauna surveys and groundwater, soil and geomorphology assessments determined that, in comparison to free-draining landforms, ponded areas may result in reduced erosion risk, reduced and/or differing vegetation and fauna habitat clearing, increased access to water sources for stock and native flora/fauna and reduction of sediment entering the receiving environment catchment. Ponded areas were found to reduce the average annual water volume reporting to the downstream waterways; however, the associated impact would be small in proportion to the broader regional flow in the Isaac River. The key risks of this initial study that were found to be less likely to support PMLU outcomes were associated with impacts to ecological communities as a result of long-term inundation and salt leaching in vertosol soils.
Ponded areas were shown to have the potential to support the PMLU of grazing and potentially other PMLUs, such as wetland environments. However, further site-specific monitoring and analysis is required to verify the PMLU outcomes for each individual ponded area.
Keywords: post-mining land use, subsidence ponding, innovation, closure
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