Alteration of habitat following subsidence due to longwall mining as a key threatening process - fact sheet
'Alteration of habitat following subsidence due to longwall mining' has been listed by the NSW Scientific Committee as a key threatening process under the Threatened Species Conservation Act 1995.
What is longwall mining and how does it cause subsidence?
Longwall mining is an underground coal mining technique which involves removing a portion of an underground coal seam. Longwall mining can cause the land above the mined-out coal seam to destabilise and collapse - this is known as subsidence.
The extent of subsidence is influenced by various factors, including the width and depth of the longwall mine, topography, the type of overlying rock layers, the design of the mine and the location of the mine. These factors vary from site to site, so the amount of subsidence - and its subsequent impacts - also varies.
What is alteration of habitat?
The specific area or environment in which a plant or animal lives is called its habitat. A habitat provides all the basic requirements for survival. Alteration of habitat refers to a change in the structure or function of habitat, making it potentially unsuitable for the organism to live in. Subsidence due to longwall mining has been recognised as causing habitat alteration. Species and ecological communities that depend on aquatic and semi-aquatic habitats are particularly susceptible to the impacts of subsidence.
Subsidence due to longwall mining can cause deformation of ground surfaces as well as cracking of valley floors and creeklines. This can affect natural water flow regimes and water quality, depending on such factors as the width of the crack, riverbed steepness, the riverbed material and the presence of organic matter. Subsidence can also destabilise cliff faces.
In turn, these impacts can lead to the alteration of species habitats and changes to the ecological function of communities. Effects can be temporary or long-term. When water flows are altered, there can be permanent effects on the functioning of ecosystems in localised areas, which may be exacerbated in drought conditions.
Why list 'alteration of habitat following subsidence due to longwall mining' as a key threatening process?
The NSW Scientific Committee in its final determination concluded that alteration of habitat following subsidence due to longwall mining:
- adversely affects two or more threatened species, populations or ecological communities, or
- could cause species, populations or ecological communities that are not threatened to become threatened.
What species, populations and ecological communities are particularly affected?Threatened species and ecological communities are known to occur in areas affected by subsidence due to longwall mining, and their habitats are likely to be altered by subsidence and mining-associated activities. Species include the following:
- Blue Mountains water skink
- giant dragonfly
- broad-headed snake
- Epacris hamiltonii
- eastern pygmy possum
- giant burrowing frog
- stuttering frog
- large-footed myotis.
Endangered ecological communities identified in the listing include the following:
- Genowlan Point Allocasuarina nana heathland
- O'Hares Creek shale forest
- shale/sandstone transition forest
- Newnes Plateau shrub swamp in the Sydney Basin Bioregion.
Subsidence associated with longwall mining can significantly affect the water balance of upland or hanging swamps. Even though subsidence may be detected within a few months of a mining operation, related changes in vegetation can occur over a longer time period.
Mining subsidence can also destabilise slopes and escarpments. Changes to cliff line topography can change the availability of roosting sites for bats and nest sites for cliff-nesting birds.
What are the implications of the listing?
The Department of Environment and Conservation is required to develop strategies for mitigating or managing the adverse effects of this threatening process on our native wildlife. The mining industry and wider community will be invited to contribute to the development of these strategies.
Strategies may include:
- reviewing existing policies, regulatory and non-regulatory regimes
- preparation of impact assessment guidelines.
A number of actions are currently underway to address the environmental impacts caused by subsidence. The actions include the development of subsidence management plans as required under the Mining Act 1992 (administered by the Department of Primary Industries). DEC is on the inter-agency committee that reviews these plans. The effectiveness of these actions will be taken into account when DEC is considering the need for a threat abatement plan.
What does the listing mean for the mining industry?
This listing does not change the current laws regulating longwall mining activities. However, the listing will lead to increased responsibility for - and consideration of - the biodiversity impacts of subsidence caused by longwall mining.
Longwall mining activities will continue to be regulated under the Mining Act 1992. The environmental regulation of the industry is shared with DEC, the Department of Lands, and the Department of Infrastructure, Planning and Natural Resources.
More information
Page last updated: 17 March 2009
