Authors: Abramson, N; Pelletier, JD; Ananthanarayan, S; Chataut, S; Ludwick, D

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Abramson, N, Pelletier, JD, Ananthanarayan, S, Chataut, S & Ludwick, D 2022, 'Assessment and development of erosion models for landform design at BHP legacy tailings storage facilities in Arizona, USA', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: 15th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1037-1046,

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BHP has partnered with The University of Arizona (UA) and SRK Consulting, Inc. to better understand how certain reclaimed landforms in Arizona, USA maintain erosional stability post-closure while others require maintenance and repair on an annual basis to prevent rill and gully formation and subsequent exposure of underlying waste material. To give insight into the range in closure outcomes and provide the broader industry with state-of-the-art tools for future landform and cover design, we took a multi-step approach starting with a comprehensive evaluation of current models used in the mine reclamation community such as Water Erosion Prediction Project (WEPP) and SIBERIA. We applied these commonly used models to three reclaimed sites in Arizona using site-specific calibration and validation data. Continuous monitoring of runoff and erosion at eight monitoring plots across the three reclaimed sites across plot sizes spanning from 250 m2–25,000 m2, allows for site-specific calibration of the erosion models. These data were augmented by quantifying the erosion and deposition resulting from a single high-intensity rainfall event using repeat drone surveys. These novel monitoring techniques provide sediment flux and discharge measurements over seven orders of magnitude on hillslopes of up to 300 m in length. Through the evaluation of each model’s ability to successfully reproduce erosional patterns, we have identified where each model falls short in its ability to be used as a predictive tool for future landform designs. To bridge these gaps, two new models have been developed by UA using a combination of site-specific and experimental datasets: Rillgen2D and RITCH (RillInterrill Transport and Conservation of mass optimised for Hillslopes). Rillgen2D is a reduced-complexity model that requires relatively limited input data and predicts a landform’s potential erosional stability using inputs of topography, cover characteristics, and climate. RITCH is a landscape evolution model that is inspired by SIBERIA’s governing equations, but which implements a piece-wise power-law relationship between sediment flux and discharge to model both rill and interrill erosion processes. The testing of both models is currently limited to semi-arid climates and cover materials with rock armour. We seek collaborations to test these models in a wider range of climates and cover materials.

Keywords: erosion models, rilling, landform and cover design, mine closure, tailings dam, heap leach, leach dump, SIBERIA, WEPP

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