Authors: Mengler, FC; Gilkes, RJ


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Mengler, FC & Gilkes, RJ 2006, 'Thresholds, Triggers and Time ⎯ Erosion Risk on Evolving Reclaimed Landforms after Bauxite Mining in the Darling Range, Western Australia', in AB Fourie & M Tibbett (eds), Mine Closure 2006: Proceedings of the First International Seminar on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 587-597,

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Some rehabilitated bauxite mines in southwestern Australia have accelerated gully erosion while the majority have little erosion. Anecdote suggests that gully erosion in rehabilitated forest is controlled by slope gradient but not all steep areas erode and conversely, some gentle slopes do. Mining companies aim to achieve erosion behaviour in rehabilitated areas similar to that of the surrounding forest - where large gullies are rare. We surveyed 26 eroding and erosion-prone rehabilitated hillslopes and developed descriptive models to predict the occurrence of gully erosion. A model of gully triggers implies that triggers and threshold effects are as influential as slope gradient and length in determining both the occurrence and severity of gully erosion. Many pre-existing triggers that predispose critical parts of a landscape to gully erosion activate only under threshold-excess conditions. Pinched concavities (thalwegs), shallow topsoil and gravel cover, erodible subsoil, high groundwater level, misplaced fauna habitats and irregular rehabilitation boundary edges are common erosion triggers. Slope angle and slope length, upslope catchment area, landscape position, soil storage and infiltration capacity, and rainfall (duration and intensity) are threshold variables. Many of these triggers and some thresholds can be identified and hence mitigated at the pre-mining stage. Topographic thresholds for gully erosion determined by the relationship between the critical slope (Scr) and contributing area (A) at Boddington, Huntly and Willowdale bauxite mines are: Scr = 0.2A-0.39, Scr = 0.05A-1.66 and Scr = 0.02A-1.59. Additionally, at the minimum catchment area for gully incision (0.3 ha), critical pre- mining slopes are 14° for Boddington, 10° for Huntly and 6° for Willowdale. Landforms exceeding these conditions may need site-specific designs to mitigate gully erosion risk. The rate of cumulative erosion and gully development measured by erosion pins on selected hillslopes closely follows the trend of cumulative precipitation at least during the first three seasons of rehabilitation growth. After this time, most gullies reach stasis. Cumulative erosion of non-mined, natural slopes also closely follows cumulative precipitation but at much lower rates (about 30 times lower than gullied sites). A proposed model of site erosion potential versus contributing area suggests that sites with the biggest gullies are above a threshold separating low- and high- state erosion. The effect of fire and maturity on the stability of gullied, rehabilitated sites is unknown.

Bodnár, F. and Hulshof, J. (2006) Soil crusts and deposits as sheet erosion indicators in southern Mali. Soil Use and
Management 22, pp. 102–109. DOI: 10.1111/j.1475-2743.2006.00010.x.
Davenport, D.W., Breshears, D.D., Wilcox, B.P. and Allen, C.D. (1998) Viewpoint: sustainability of pinon–juniper
ecosystems—a unifying perspective of soil erosion thresholds. Journal of Range Management 51, pp. 231–240.
Gerrard, A.J. (1981) Soils and Landforms. George Allen and Unwin Ltd. London, 219 p.
Haigh, M.J. (1977) Use of erosion pins in the study of slope evolution. British Geomorphological Research Group
Technical Bulletin 18, pp. 31-49.
Hancock, G.R and Evans, K.G. (2006) Channel head location and characteristics using digital elevation models. Earth
Surface Processes and Landforms (in press) DOI: 10.1002/esp.1285.
Horton, R.E. (1933) The role of infiltration in the hydrological cycle. Trans. American Geophys. Union 14, pp. 446-
Loch, R.J. and Silburn, D.M. (1996) Constraints to sustainability — soil erosion. In L. Clarke and P.B. Wylie (eds)
Sustainable Crop Production in the Sub-tropics: an Australian Perspective. QDPI.
MacDonald, L.H. and Huffman, E. L. (2004) Post-fire soil water repellency: persistence and soil moisture thresholds.
Soil Science Society of America Journal 68, pp. 1729–1734.
McFarlane, D.J., Davies, R.J. and Westcott, T. (1986) Rainfall erosivity in Western Australia. In Proceedings of the
Hydrology and Water Resources Symposium, Griffith University, Brisbane. Institution of Engineers, Australia,
Barton, ACT, pp. 350-354.
Mengler, F.C. and Gilkes, R.J. (2007) Landscape, soil surface and management practices control gully erosion on steep
rehabilitated landforms after bauxite mining in the Darling Ranges, Western Australia. Catena (in prep.).
Moore, I.D., Burch, G.J. and Mackenzie, D.H. (1988) Topographic effects on the distribution of surface soil water and
the location of ephemeral gullies. Transactions of the American Society of Agricultural Engineers 34, pp. 1098-
Parkner, T., Page, M.J., Marutani, T. and Trustrum, N.A. (2006) Development and controlling factors of gullies and
gully complexes, East Coast, New Zealand. Earth Surface Processes and Landforms 31, pp. 187-219.
Thresholds, Triggers and Time ― Erosion Risk on Evolving Reclaimed
Landforms after Bauxite Mining in the Darling Range, Western Australia
F.C. Mengler, R.J. Gilkes
596 Mine Closure 2006, Perth, Australia
Poesen, J. (1986) Surface sealing as influenced by slope angle and position of simulated stones in the top layer of loose
sediments. Earth Surface Processes and Landforms 11, pp. 1-10.
Poesen, J.W., Torri, D. and Bunte, K. (1994) Effects of rock fragments on soil erosion by water at different spatial
scales: a review. Catena 23, pp. 141-166.
Renard, K.G., Lane, L.J., Foster, G.R. and Laflen, J.M. (1996) Soil Loss Estimation. In M. Agassi (ed) Soil Erosion,
Conservation and Rehabilitation. Marcel Dekker, New York, pp. 169-202.
Tromp-van Meerveld, H.J. and McDonnell, J.J. (2006) Threshold relations in subsurface stormflow 2. The fill and spill
hypothesis. Water Resources Research 42, 11 p. W02411, .
Valentin, C., Poesen, J. and Yong, L. (2005) Gully erosion: Impacts, factors and control. Catena 63, pp. 132-153.
Vandaele, K., Poesen, J., Govers, G. and van Wesemael, B. (1996) Geomorphic threshold conditions for ephemeral
gully incision. Geomorphology 16, pp. 161-173.
Wainwright, J., Mathys, N. and Esteves, M. (2006) Gully erosion in mountain areas: processes, measurement,
modelling and regionalization. Earth Surface Processes and Landforms 31, pp. 133-134. DOI: 10.1002/esp.1318.
Landform Stability
Mine Closure 2006, Perth, Australia 597

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