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Sustainable Landscape Design for Coal Mine Rehabilitation

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Published: May 10Project Number: C18024

Get ReportAuthor: Rob Loch | Landloch Pty Ltd

Until recently, successful mine site rehabilitation in the NSW Coalfields has focused on introduced pasture with intermittent tree lots. With changes in community expectations, greater emphasis has been placed upon landforms and vegetation that are relatively "natural" in appearance and self-sustaining, taking due consideration of maintaining native ecosystems, wildlife corridors, biodiversity, and native plantation forestry.

 

Historically, the landform design component of rehabilitation has been plagued by a number of issues. For instance, maintenance of drainage line stability is critically important, as waterways carrying concentrated flow on steep slopes are expensive to construct and maintain and expensive to repair if they fail.

 

This project compared waste dump landform design outputs using (a) existing landform guidelines; (b) the Water Erosion Prediction Program (WEPP) runoff and erosion model; and (c) dedicated landform design software (Geofluv). The three landform design approaches were applied at two mine sites in the NSW Hunter coalfield, for landforms sheeted with local topsoil. Landforms developed using the three design methods were then assessed for erosion risk using the SIBERIA landform evolution model, with the impacts of varying vegetation cover for each landform design also being evaluated to assess the importance of cover in ensuring the stability of the designed waste dumps.

 

Material characterisation is essential in the Hunter environment, where most landforms rely heavily on establishment of vegetation to achieve erosion stability. Sodic soils are common, and make stabilisation of landforms difficult as they typically produce high rates of runoff and erosion, and are extremely difficult to vegetate. Consequently, the effective management of these sodic soils is crucial for achieving stable and sustainable landforms.

 

Using measured erodibility parameters within WEPP gave a relatively simple landform design that achieved the lowest predicted erosion rates. Importantly, the WEPP runoff and erosion modelling process had the advantage of providing explicit information on potential runoff and erosion rates and clear identification of priorities for the rehabilitation and landform stabilisation process. The modelling-based approach to landform design included comprehensive cover material characterization and consideration of fertiliser and amendment requirements to achieve optimal soil conditions for revegetation.

 

Complex landform designs were developed using the GeoFluv landform design software, with designs based on a range of observed landform parameters. The GeoFluv approach is predicated on the proposition that stable, natural landforms used to derive its input parameters will have erosion characteristics identical to those of the mine wastes used in landform construction. This crucial assumption within GeoFluv can be difficult to satisfy in relatively ancient landscapes such as in Australia, where soils are strongly differentiated in terms of both landscape position and depth in the soil profile, and topsoils placed on constructed landforms may have significantly higher erodibility. Consequently, the GeoFluv approach generated landforms with the highest erosion potential.

 

However, although all landform designs varied in their estimated erosion potential, they were all shown to be stable if well vegetated, demonstrating that soil management to maximise vegetation establishment and growth is a crucial component of landform rehabilitation in this area.

 

Landform design for minesites in the Hunter Valley can be further challenged by limitations to landform footprint, reducing design options and forcing increases in slope gradient, irrespective of the approach used.

 

The range in landform rehabilitation costs is often dictated by the way in which a waste dump has been initially constructed. If the initial construction does not consider rehabilitation requirements, then final shaping may require large volumes of material to be moved, resulting in considerably higher costs for rehabilitation. For example, the correct initial spacing of lifts can drastically reduce the costs of final shaping, by reducing the distances and volumes of materials to be moved. As well, the costs of rehabilitation and maintenance operations are generally not considered and are not well documented. Nonetheless, there is evidence that ineffective rehabilitation can create quite significant costs for repair, and some additional cost or effort to achieve consistently stable landform rehabilitation would generally be economically justified.

The report illustrates the importance of a comprehensive approach to rehabilitation planning, with landform design being an essential component of planning, rather than a standalone activity. In practice, landform design should be influenced by the requirements for vegetation establishment, and equally, vegetation strategies should take account of the requirements for landform stabilisation and efficient hydrologic function.

 

This report illustrates a range of alternative approaches to the planning and design of minesite landforms. Most importantly, it demonstrates the importance of planning.

 

 

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