Effects of mining - bauxite hydrology
Alcoa of Australia mines bauxite for the production of alumina from Western Australia's Darling Range extending from east of Perth to Collie. These operations occur on Mineral Lease 1SA, granted by the State Government under the Alumina Refinery Agreement Act 1961. Mineral Lease 1SA currently covers 7,129 square kilometres, and Alcoa clears, mines, and rehabilitates an average of 600 hectares of regrowth forest each year. Alcoa's operations are overseen by the Mining and Management Program Liaison Group (MMPLG). The MMPLG is chaired by the Department of Industry and Resources on behalf of the Minister for State Development. The Department of Water sits on the MMPLG and also chairs and administers the Bauxite Hydrology Committee — a subcommittee of the MMPLG that oversees the aspects of mining and rehabilitation that have implications for water supply in Perth's Water Supply Catchments.
The Bauxite Hydrology Committee, formerly the Bauxite Subcommittee, is charged with providing technical advice and recommendations to the MMPLG on hydrology and stream zone ecology relating to Alcoa's bauxite mining operations, and reviewing related research. The committee's objectives are to:
- Minimise salinity risks associated with mining in the intermediate rainfall zone, where clearing of the natural vegetation could cause secondary salinity if not properly managed, and
- Minimise impacts of mine rehabilitation on catchment water yields and riparian ecosystems caused by high water use of dense, regrowth forests. This issue has exacerbated the severe decline in water inflow to Perth's water supply dams experienced in recent years due to the drying climate.
The Joint Intermediate Rainfall Zone Research Program (JIRZRP), running since the 1970s includes detailed monitoring of surface water, groundwater and salinity as well as analysis and modelling. It is the primary mechanism by which intermediate rainfall zone risks are monitored and managed. Regular reviews of Alcoa's mine rehabilitation completion criteria, the development of 'hydrologically considerate' rehabilitation, and collaboration with other efforts within the state to mitigate stream declines are the main mechanisms for minimising mine rehabilitation impacts on streamflows.
31 Mile Brook (2010), reforestation after bauxite mining in the Canning River Catchment of South-Western Australia.
Photograph by Keren Raiter.