Using a landform evolution model to model the effect of extreme rainfall events on the geomorphic stability of a rehabilitated landform

Authors: Lowry, J; Saynor, M; Hancock, GR; Coulthard, T

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DOI https://doi.org/10.36487/ACG_repo/2415_02

Cite As:
Lowry, J, Saynor, M, Hancock, GR & Coulthard, T 2024, 'Using a landform evolution model to model the effect of extreme rainfall events on the geomorphic stability of a rehabilitated landform', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2024: Proceedings of the 17th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 59-70, https://doi.org/10.36487/ACG_repo/2415_02

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Abstract:
Ensuring long-term erosional stability is crucial to successful rehabilitation of post-mining landforms. Landform evolution models (LEMs) are being used to assess landform stability in mine closure and relinquishment applications through their ability to predict the extent of erosion and gully development that may occur under a range of climatic and other environmental scenarios. Here we use the CAESAR-Lisflood LEM to assess the potential impact of extreme rainfall events on a conceptual rehabilitated landform design of the Ranger uranium mine in the Northern Territory of Australia. Rehabilitation of the Ranger mine requires the isolation of buried tailings for a period of at least 10,000 years. CAESAR-Lisflood was used in this study as it can model the impact of specific rainfall events over periods of thousands of years. Data from the largest recorded rainfall events at the Ranger mine (~800 mm in 72 hours at Jabiru Airport in February 2007) and in the Northern Territory (600 mm in 24 hours in January 2020 at Dum In Mirrie Island near Darwin) were used to generate different rainfall scenarios for extreme rainfall events at different recurrence intervals and rainfall intensities. Different rainfall scenarios were then modelled for simulated periods of up to 10,000 years to determine whether rainfall-induced gully erosion could expose buried tailings under a hypothetical worst-case scenario. Varying the intensity and frequency of extreme rainfall events in model simulations resulted in different predictions on the extent and depth of gully erosion and sediment transport for each catchment. The results reflect the influence of both the landform design and the impact of extreme rainfall events on the landform itself. This information has been provided to landform designers to assist in optimising the final design of the rehabilitated Ranger landform so that tailings will not be exposed within the 10,000-year period.

Keywords: landform, erosion, modelling, rainfall, climate change, CAESAR-Lisflood

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