Abstract
Open-cut coal mining in Queensland results in the formation of extensive saline overburden spoil-piles with steep slopes at the angle of repose (approximately 75% or 37o). These spoil-piles are generally found in multiple rows, several kilometers in length and heights of up to 50 or 60 m above the original landscape. They are highly dispersive and erodible. Legislation demands that these spoil piles be rehabilitated to minimize on-site and off-site discharges of sediment and salt into the surrounding environment. To achieve this, the steep slopes must be reduced, stabilized against erosion, covered with topsoil and re-vegetated. Key design criteria (slope gradient, slope length and vegetation cover) are required for the construction of post-mining landscapes that will result in acceptable erosion rates.A novel user-friendly hillslope computer model MINErosion 3.4 was developed that can accurately predict potential erosion rates from field scale hillslopes using parameters measured with a 3m laboratory tilting flume-rainfall simulator or using routinely measured soil physical and chemical properties. This model links MINErosion 2 with a novel consolidation and above ground vegetation cover factors, to the RUSLE and MUSLE equations to predict the mean annual and storm event erosion rates. The RUSLE-based prediction of the mean annual erosion rates allow minesites to derive the key design criteria of slope length, slope gradient and vegetation cover that would lead to acceptable erosion rates. The MUSLE-based prediction of storm event erosion rates will be useful as input into risk analysis of potential damage from erosion.MINErosion 3.4 was validated against erosion measured on 20 m field erosion plots established on post-mining landscapes at the Oakey Creek and Curragh coalmines, as well as on 120 and 70 m erosion plots on postmining landscapes at Kidston Gold Mine.
Highlights
The nature of open-cut mining is that much larger surface area is disturbed compared to underground mining
The Analysis of Variance (AOV) shows there were no differences in the steady state (SS) run-off (RO) rates between the combinations of soil, slope and vegetative
The data show clearly that stoloniferous grasses that creep over the ground surface such as sabi grass offers greater protection and reduction of erosion compared to tussocky grasses such as Rhodes grass
Summary
The nature of open-cut mining is that much larger surface area is disturbed compared to underground mining. In Australia, the deep solid overburden above the mineral or coal seam is blasted using explosives and removed mechanically using trucks & shovels or draglines. The high speed of operation using draglines results in landscapes that consist of long parallel tertiary overburden spoil-piles that are generally highly saline, dispersive and highly erodible as shown in Fig 1 [1, 2]. The height of these spoil-piles may exceed 50–60 m above the original landscape and the slopes are at the angle of repose of around 75% or 37 ̊ [3]. Legislation and public opinion require that these highly disturbed open-cut post-mining landscapes be satisfactorily rehabilitated for approved post-mining land use
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