Coal is extracted using either open-cut or underground (longwall) mining methods. The coal mines in the Surat Basin are all open cut, as illustrated in the diagram. The excavation of coal results in a mine pit exposing coal seams that intersect with the water table. This causes groundwater to seep or inflow into the pits, decreasing the groundwater in areas near the mine. For safe operation of the mine, the water is pumped out and discharged away from the pit. This process is called dewatering.
In the Surat Basin coal mines, the drop generally extends to about 5 kilometres.
If the volume of water flowing into the pit is very high, water bores may be drilled around the mine pit to aid dewatering. In the Surat Basin this type of depressurisation is not required because pit inflows are very low in volume.
Reduction in water level can also cause some loss of groundwater from aquifers above and below the coal seams. Geological faults, if present, may provide additional pathways or barriers for the impacts of coal mining to spread.
This video shows impacts from coal mining on groundwater and how impacts can be predicted.
Last updated: 31 Oct 2023