Computer simulations of runoff and erosion are a key element in the design of stable waste dump outer batter profiles. The Water Erosion Prediction Project (WEPP) model is used to develop erosionally stable landform batter surfaces. Although the WEPP model has been widely validated elsewhere, there is a perceived need to similarly validate the model for mine site conditions. Erosion monitoring data collected on landforms for which model parameters are known can be used for two primary purposes: a) to demonstrate that erosion rates are consistent with site targets; and b) to validate and more precisely calibrate the erosion model used in landform design, enabling continuous improvement in the design process. Model validation techniques are discussed and validation data for several landforms are presented. In general, cumulative erosion rates measured since completion of construction show good agreement with predicted erosion rates. The data have provided validation of the landform design process used; confidence in the surface stability of existing landforms that have been constructed; refinement and improvement in the design process; and a means for continual improvement in landform rehabilitation methods.
Berms remain a persistent feature in waste dump landform designs as they are perceived to provide the benefits of reduced slope length, protection against future batter erosion by partitioning the slope with level or backsloping berms, and reduced flow velocity. Underpinning this rationale is the belief that the berms will be a permanent and unchanging feature that controls erosion over the long term. These assumptions are not true. Berms begin to evolve immediately after their construction by trapping sediment and having a beneficial effect over the short to medium term. Longer term, berms fill with sediment and overtop. The time it takes to overtop depends on the material, the size of the berm, and the climate. Once a berm is breached, previously hydraulically disconnected batter sections become a connected flow network that delivers large volumes of runoff from upper slopes to lower slopes that were never designed to withstand them. This process can be caused, or contributed to, by poor quality construction techniques.
The rehabilitation of mined landscapes has reached a significant crossroad. There are rising regulatory and community expectations and financial costs, but operational success has made very slow progress across the mining and minerals sectors. The history of rehabilitating mined landscapes is relatively short, with prescriptive approaches encouraged by the introduction of the US Surface Mining Control and Reclamation Act in 1977. During these four decades, the goalpost of closure standards has shifted from non-pollution in the 1980s, sustainable land use since 1990s, to 'resilient ecosystems', in response to the society's acceptance of climate change and uncertainties. In the meantime, operations at mine sites have been largely resorting to 'environmental engineering' (or briefly referred to as 'engineering') thinking and approaches to reconstruct and rehabilitate mined landscapes for economic and natural land uses. The continuation of 'engineering' from mining into rehabilitation is because this mindset is conducive to 'engineering' methods which are prescriptive and definitive in operational process, such as land contouring, topsoil sheeting, and seed sowing, fertilisation, drainage installation, and slope stabilisation. In contrast, the transition into 'ecological' thinking is much needed to design and create new ecosystems at an operational level. 'Ecological' methods are descriptive and characteristics of undefined operational requirements and associated risks in the short/intermediate term. In many cases, agroecosystems (e.g. pastures) have been adopted as post-mining land use of mined landscapes, such as coal mines in central Queensland. Agroecosystems at remote mine sites may not be sustainable due to high energy requirements to improve and maintain the productive capacity for economic outcomes in landscapes with inherently infertile soils and low rainfall. Nor are they 'resilient' due to the lack of ecological diversity and functional redundancy. In other cases, the goal is to restore the mined landscapes back to seemingly 'original' ecosystems, based on comparing short-term ecological features with non-disturbed 'reference sites', while disregarding the loss of regolith structure and landform diversity after mining.
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