Assessing the long-term geomorphic stability of a rehabilitated landform using the CAESAR-Lisflood landscape evolution model

Authors: Lowry, JBC; Coulthard, TJ; Hancock, GR Download Paper

DOI https://doi.org/10.36487/ACG_rep/1352_51_Lowry

Cite As:
Lowry, JBC, Coulthard, TJ & Hancock, GR 2013, 'Assessing the long-term geomorphic stability of a rehabilitated landform using the CAESAR-Lisflood landscape evolution model', in M Tibbett, AB Fourie & C Digby (eds), Mine Closure 2013: Proceedings of the Eighth International Seminar on Mine Closure, Australian Centre for Geomechanics, Cornwall, pp. 611-624, https://doi.org/10.36487/ACG_rep/1352_51_Lowry



Abstract:
The ability to accurately predict the stability of post-mining landscapes through time scales ranging from decades to thousands of years is a critical element in the assessment of closure designs for uranium mines. In this paper, the CAESAR-Lisflood Landscape Evolution Model (LEM) is used to simulate and assess the geomorphic stability of a conceptual rehabilitated landform of the Ranger Uranium Mine in the Northern Territory, Australia. Crucially, this is the first time that the CAESAR-Lisflood model has been applied to an entire conceptual rehabilitated mine landform. Following construction of the landform and subject to environmental conditions, erosion features such as gullies may erode containment structures, potentially leading to the exposure and transport of encapsulated radioactive material. Further, erosion may lead to increased sediment loads and the transport of other mine-related contaminants off site and into downstream waterways. The CAESAR-Lisflood LEM requires several data inputs to run simulations to assess these processes. Particle size distribution and rainfall data were obtained from field measurements on the Ranger lease, and the Bureau of Meteorology. A digital elevation model (DEM) of the conceptual rehabilitated landform of the mine, which was used to simulate changes to the landform surface under a variety of model scenarios, was generated through the integration of landform design plans supplied by mine operator, Energy Resources of Australia (ERA), with a high resolution LiDAR DEM of the surrounding undisturbed environment. For the purposes of this study, the CAESAR-Lisflood model was modified to enable the differential consolidation of areas representing capped pits on the landform to be modelled. Model scenarios run by CAESAR-Lisflood included the effect of vegetated /unvegetated and consolidated/ unconsolidated surfaces over simulated time periods of 45 and 1,000 years. The 45-year scenarios were used to assess the stability of the landform in the period after the initial construction of the landform once all consolidation had occurred. The 1,000-year scenarios were used to assess the longer-term stability of the landform. Several simulated scenarios identified the potential for large-scale erosion to occur on the landform, potentially exposing buried contaminants. Initial model results provide a guide to areas of improvement in both landform design and the enhancement of the modelling software. The results from simulations of the conceptual landform provide increased confidence that the CAESAR-Lisflood LEM will be able to correctly predict the evolution of a rehabilitated landform once it has been constructed.

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