The cumulative impacts of coal and coal seam gas (CSG) developments in the Gloucester subregion are presented in terms of separate groundwater and surface water balances for two locations over three future periods.
In the Avon river basin, the impact of additional coal resource developments at the open-cut Stratford and Rocky Hill coal mines and the AGL CSG development is a reduction in the mean annual surface water outflow of 1105 ML/year between 2013 and 2042. Smaller reductions are predicted for the subsequent two 30-year periods to 2102 (717 and 712 ML/year). This is primarily due to the retention of surface runoff on the mine sites rather than a decrease in baseflow due to groundwater extraction (median baseflow reductions vary from 90 to 81 ML/day over the 90-year period). This change in outflow is less than 2% of the baseline coal resource development (baseline) flow and is within the uncertainty of the predicted surface water outflow.
In the Mammy Johnsons river basin, the period from 2043 to 2072 experiences on average the biggest reduction in surface water outflows (186 ML/year) as a consequence of additional coal resource development (Duralie Coal Mine). This reduction persists through the subsequent 30-year period. These reductions are dominated by the retention of surface runoff on the mine sites rather than the baseline responses due to groundwater extraction. This change in outflow represents less than 0.3% of the baseline flow and is within the uncertainty of the predicted surface water outflow.
The lack of constraint on the magnitude of upward flow of groundwater from deeper layers into the alluvium is identified as a major gap in the ability to estimate the water balance. The prediction interval between 10th and 90th percentiles is very wide, indicating that there is insufficient data to constrain this term in the model. It is therefore not possible to provide a reliable estimate of this water balance term with the current modelling.
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- 2.5.1 Methods
- 2.5.2 Water balances
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