Assessing tailings dam long-term failure risk using computer based Landform Evolution Models

Tailings are a by-product of the processing of minerals. Tailings can be highly erodible and transportable via fluvial processes and are commonly stored in tailings dams which are a feature of many mine sites. These dams and their impounded material will become permanent geomorphic features in the post-mining landscape. The question examined here is - can tailings dams ever be walk-away structures? Tailings dams can fail by both catastrophic and gradual failure. Catastrophic failure occurs when there is a large scale rapid structural failure of the dam wall. Gradual failure occurs over time by slow infilling of the dam and the erosion of the dam wall. This can lead to overtopping of the dam wall and gully incision and failure of the wall and release of sediment to the environment. To understand failure modes and risk profile, computer based Landscape Evolution Models (LEMs) can be used. LEMs have become common tools to quantify risk for mine waste rock dumps and waste repositories. LEMs provide detailed information on erosion rates, type of erosion and where erosion is likely to occur. They inform long-term behaviour which allows designs to be tested and improved. Here they are used to assess tailings dams where the strengths and weaknesses of different tailings dams designs are examined across a range of climates and material settings. The results show that if well-designed and assuming a well understood climate, a dam can be sufficiently robust to last centuries. However, failure can occur under different climate settings. Modelling also demonstrates that upon failure water quality will be affected for many centuries post-breach if no remedial work is conducted. Longer term, the 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.