Landform evolution models (LEMs) are used to estimate potential surface water runoff and predict resulting erosion and deposition processes on a landform scale. When applied to mining landforms, LEM erosion predictions can be used to inform closure planning and to predict post-closure performance. The requirement to conduct long-term landform evolution modelling is an increasingly common regulatory condition imposed on new mining projects.
The use of LEMs to simulate the post-closure evolution of water-shedding mining landforms such as waste rock dumps is well documented. However, tailings storage facilities (TSFs) are unique landforms. TSFs often have contributing upstream catchments, long and flat (tailings beach) slopes, consist of spatially variable material types, and can be closed systems (i.e. do not release water). These factors all need to be accounted for when using an LEM to simulate a TSF.
This paper presents an approach to landform evolution modelling for TSFs, including an Australian case study using the CAESAR-LISFLOOD model to simulate the evolution of a valley-fill TSF over a 1,000-year post-closure period. Recent developments in the CAESAR-LISFLOOD LEM have significantly improved the run speed and computational efficiency of the model. The approach presented in this paper takes advantage of these improvements, incorporating the use of digital elevation models with different spatial resolutions and long-term simulations using 1,000 years of sub-daily rainfall data.
The CAESAR-LISFLOOD model can simulate the various material types present at the surface of a TSF landform, including tailings, cover material, natural soils in the surrounding catchment and embankment construction materials. As such, landform evolution modelling for valley-fill TSFs can be used to assess the extent to which erosion can compromise the water storage capacity of the closed TSF. The results of the example presented indicate that the water storage capacity of the TSF will be progressively reduced due to the sediments that are eroded and deposited within the pond area; however, not to the extent that could result in water (and potentially entrained tailings) being discharged to the environment. The results of TSF LEM could also be used to identify areas where design options could improve long-term TSF erosional stability, develop recommendations for model calibration and verification, and to assess whether erosion could result in loss of containment.
