Development and implementation of a state and transition successional model for Ranger mine closure (Northern Territory, Australia)

Authors: Grant, CD; Grant, NL; Parry, ML Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2315_079

Cite As:
Grant, CD, Grant, NL & Parry, ML 2023, 'Development and implementation of a state and transition successional model for Ranger mine closure (Northern Territory, Australia)', in B Abbasi, J Parshley, A Fourie & M Tibbett (eds), Mine Closure 2023: Proceedings of the 16th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, https://doi.org/10.36487/ACG_repo/2315_079



Abstract:
Energy Resources of Australia Ltd (ERA) has owned and operated the Ranger uranium mine since the commencement of operations in 1980. The former Ranger mine has been one of Australia's largest uranium mines, producing in excess of 132,000 tonnes of uranium oxide over 40 years. Operations ceased in early 2021 2021 and ERA’s focus is now on the rehabilitation of the Ranger Project Area. The overall goal for rehabilitation is outlined in the Environmental Requirements (ER) namely “The company must rehabilitate the Ranger Project Area to establish an environment similar to the adjacent areas of Kakadu National Park such that, in the opinion of the Minister with the advice of the Supervising Scientist, the rehabilitated area could be incorporated into the Kakadu National Park”. State and Transition (ST) models are non-linear conceptual models, which organise information about ecosystem change (Bestelmeyer et al. 2017). Grant (1997, 2006, 2009) proposed that ST models could be utilized to identify desired and deviated states for areas rehabilitated after mining to drive management towards an identified end state. The development of a ST model for Ranger rehabilitation commenced in 2018 and has been ongoing since. The objective of this paper is to present the latest version of the Ranger ST model and outline the next steps in its development. The revised Ranger ST model identified the end state as a mixed savanna woodland, in line with the ERs. Seven desired states were identified along the desired trajectory at 0, 1-2, 5, 10, 15, 25+ and 50+ years. The abiotic and biotic characteristics of all states (desired and deviated) were described in detail based on existing information and expert input. Fourteen deviated states were also identified across the successional trajectory. Deviated states were characterised by significant erosion, weed or Acacia domination, high seedling mortality, lacking understorey or the overstorey being dominated by non-eucalypts. Triggers and associated actions were identified for all deviated states including remedial surface works, weed control, re-planting/seeding, prescribed burning and physical/chemical removal. Qualitative completion criteria have been developed and signed-off by internal and external stakeholders for Ranger rehabilitation. The desired states have incorporated relevant characteristics related to these criteria. Further work is being undertaken to identify SMART (Specific, Measurable, Attributable, Realistic and Time-framed) metrics associated with the qualitative completion criteria and these will subsequently be incorporated into the ST model. An ArcGIS Project is currently being developed as the repository for monitoring data to spatially demonstrate whether rehabilitated areas are in desired or deviated states, and drive the maintenance and management programs required to meet defined completion criteria. The development of the Ranger ST model has been a journey over the last five years. The ability to present complex successional development pathways in a simple model has assisted in obtaining alignment with the diverse range of external stakeholders with significant interests in the closure of Ranger. As rehabilitation of Ranger ramps up over the next few years, the ST model will be a critical management tool that facilitates driving rehabilitated areas along the desired successional trajectory towards the identified desired end state, through early identification of deviated states, and rapid maintenance and management intervention to ultimately drive relinquishment.

Keywords: state and transition model, ranger, desired/deviated states, end state, maintenance, management, rehabilitation

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