Slingerland, N & Dressler, S 2022, 'Evaluating construction tolerances and tailings dam shape for closure using the CAESAR-Lisflood landscape evolution model', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: 15th International Conference on Mine Closure
, Australian Centre for Geomechanics, Perth, pp. 1117-1130, https://doi.org/10.36487/ACG_repo/2215_82
Variability in landform construction for closure has long been an uncertainty: downstream tailings dam slopes are designed with precision, while the earth moving equipment that build them vary in their ability to accurately replicate designs. As such, performance outcomes of the closure landform can be tied to the equipment used and/or operator experience, for better or worse. Unintended surface variations can lead to concentrations of surface water flow, gully formation, and excess erosion of the landform surface. A key concern is therefore how much variability in construction, or ‘surface roughness’ is acceptable, and does this level of acceptability change based on the complexity of the landform being constructed?
While many closure landscapes seek to maximise surface roughness and micro-topography for the associated microclimatic and biodiversity benefits, a concern with respect to surface roughness at closure, particularly on steep slopes, is that too much may lead to excess erosion. Controlling factors lend this problem well to investigation using a landscape evolution model (LEM); in this case the CAESAR-Lisflood LEM.
Using four different downstream sand dam designs with identical overall dimensions, one digital elevation model (DEM) of each was created with (a) low surface roughness and with (b) high surface roughness. A standardised precipitation database, grain size distribution, and parameters were used for all LEM simulations, such that variations due to surface roughness could be isolated. LEMs are often used to test computer-generated designs (i.e. smooth contours with no surface roughness), as well as existing landforms whose surfaces are replicated using light detection and ranging (LiDAR)-based DEM inputs (i.e. surfaces with substantial roughness). These two extremes have not previously been compared but have implications for the way LEM inputs are generated and assessed, the assumptions made during design, and for the degree of precision required in closure earthworks construction.
Results of the LEM testing indicate landform-scale topography provides superior erosion mitigation compared to micro-topographic variations, and that geomorphic landform designs are more resilient to surface variations than traditional designs, providing greater ‘room for error’ during construction.
Keywords: CAESAR-Lisflood; construction tolerance; erosion; landscape evolution model; tailings dam; risk assessment; surface roughness
Al-Mamun, M & Small, A 2018, ‘Revision of guidance on landforms in CDA Mining Dams Bulletin – a companion paper with additional details’, Proceedings of the CDA 2018 Annual Conference, Canadian Dam Association, Quebec.
Coulthard, TJ, Lewin, J & Macklin, MG 2005, ‘Modelling differential catchment response to environmental change’, Geomorphology, vol. 69, pp. 222–241.
Coulthard, TJ, Macklin, MG & Kirby, MJ 2002, ‘A cellular model of Holocene upland river basin and alluvial fan evolution’, Earth Surface Processes and Landforms, vol. 27, pp. 269–288.
Hancock, GR, Coulthard, TJ & Lowry, J 2016a, ‘Predicting uncertainty in sediment transport and landscape evolution – influence of initial surface conditions’, Computers & Geosciences, vol. 90, pp. 117–130.
Hancock, GR, Coulthard, TJ, Martinez, C & Kalma, JD 2011, ‘An evaluation of landscape evolution models to simulate decadal and centennial scale soil erosion in grassland catchments’, Journal of Hydrology, vol. 398, pp. 171–183.
Hancock, GR, Lowry, J & Coulthard, TJ 2016b, ‘Long term landscape trajectory; can we make predictions about landscape form and function for post-mining landforms?’, Geomorphology, vol. 266, pp. 121–132.
International Council on Mining & Metals 2021, Global Industry Standard on Tailings Management, International Council on Mining & Metals, London, pp. 1–40.
International Commission on Large Dams 2013, ‘Sustainable Design and Post-Closure Performance of Tailings Dams’, Bulletin 153, International Commission on Large Dams, Paris.
Lowry, J, Narayan, M, Hancock, GR & Evans, KG 2019, ‘Understanding post-mining landforms: Utilising pre-mine geomorphology to improve rehabilitation outcomes’, Geomorphology, vol. 328, pp. 93–107.
Martinez, C, Hancock, GR & Kalma, JD 2009, ‘Comparison of fallout radionuclide (caesium-137) and modelling approaches for the assessment of soil erosion rates for an uncultivated site in south-eastern Australia’, Geoderma, vol. 151, pp. 128–140.
Saynor, MJ, Lowry, J & Boyden, JM 2019, ‘Assessment of rip lines using CAESAR-Lisflood on a trial landform at the Ranger Uranium Mine’, Land Degradation & Development, vol. 30, no. 5, pp. 504–514.
Slingerland, N, Zhang, F & Beier, NA 2022, ‘Sustainable design of tailings dams using geotechnical and geomorphic analysis’, CIM Journal, vol. 13, pp. 1–15.
Welsh, KE, Dearing, JA, Chiverrell, RC & Coulthard, TJ 2009, ‘Testing a cellular modelling approach to simulating late-Holocene sediment and water transfer from catchment to lake in the French Alps since 1826’, Holocene, vol. 19, no. 5, pp. 785–798.
Wischmeier, WH & Smith, DD 1978, ‘Predicting rainfall erosion losses—a guide to conservation planning’, Agriculture Handbook No. 537, US Department of Agriculture.
World Bank & International Finance Corporation 2002, ‘It’s Not Over When It’s Over: Mine Closure Around the World’, Mining and Development Series, Washington.