Mulligan, DR, Doley, D, Baumgartl, T & Lynch, KM 2008, 'The Role of Vegetation in Mine Waste Cover Systems with Particular Reference to Australian Mine Rehabilitation', in AB Fourie, M Tibbett, I Weiersbye & P Dye (eds), Mine Closure 2008: Proceedings of the Third International Seminar on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 727-738, https://doi.org/10.36487/ACG_repo/852_68
(https://papers.acg.uwa.edu.au/p/852_68_Mulligan/)
Abstract: Vegetation can potentially assist in limiting the ingress of water into rock dumps or tailings storage 
facilities, an attractive potential when the geochemical characteristics of such waste materials indicate that 
water ingress should be minimal in order to reduce long-term impacts and liabilities. However, the presence 
and/or necessity for vegetation can present potential conflicts for cover design and management as the cover 
system objectives are often to minimize the amount of cover material required and to establish a low-cost but 
effective means of removing water from above the waste to reduce the likelihood of deep drainage. 
Due to the physical nature and heterogeneity of particle sizes and sorting characteristics of many cover 
materials used, the distribution patterns of water infiltration into constructed profiles may be very irregular, 
with penetration to depth (and thus potentially the underlying waste material or impervious capping layer) a 
high probability in zones of higher hydraulic conductivity. This irregularity of water distribution will also 
result in heterogeneous patterns of vegetation distribution and growth, especially in low rainfall 
environments. 
Although actual evapo-transpiration can account for up to 90% of annual rainfall at some locations, 
vegetation is unlikely to dry cover material completely or prevent water percolation through the root zone 
during high intensity precipitation events, especially if vegetation distribution and infiltration patterns are 
irregular. In humid environments, a seasonal water table is likely to develop, making lateral water discharge 
from within the cover essential, and the integrity of any impervious capping layer (if present over the waste 
as a part of the design) capable of preventing penetration by plant roots. In semi-arid environments, a thick 
cover of benign rock may prevent infiltrating water from ever reaching the impervious capping layer, 
provided plant roots can penetrate the wetting zone and extract all of the water. Trees have many shallow 
ephemeral roots and fewer roots that may penetrate more than 20 m but they require permanent water for 
survival. Grasses on the other hand may have a root biomass that fluctuates more between seasons and their 
dense root systems may be more effective than those of woody plants in removing water from the surface 
horizons. 
Detailed site physical and plant physiological data enable soil and plant water balance and plant growth 
models to predict temporal variations in vegetation cover, but site heterogeneity requires the use of two- or 
three-dimensional models. There is also the need to increase the capacity to model and quantify the 
contribution of vegetation to the hydrological processes occurring in cover systems. This paper reviews the 
information that provided the background and context for a current major research program involving three 
Australian universities, Canadian collaborators and nine mining company sponsors. Among other goals, this 
project seeks to increase the understanding of the role of vegetation in cover performance, and the extent of 
variation in the function and performance of covers over time due to cover construction design, climate, soil 
physical and chemical changes, and the likely effects of vegetation changes. All sources of variability must 
be considered in cover design, and if site and species characteristics are well understood, the extent of 
variation can be indicated clearly and unreal expectations concerning the role and impact of a vegetative 
cover can be avoided. 
The Role of Vegetation in Mine Waste Cover Systems with Particular Reference to  D.R. Mulligan et al. 
Australian Mine Rehabilitation