Section summarises prediction results of hydrological changes for nine hydrological response variables due to the modelled additional coal resource development. The hydrological changes on each model node were generated from among 3000 replicates of the model runs using randomly selected parameter sets.

The prediction results show that the additional coal resource development in the Hunter subregion can cause substantial changes in the hydrological response variables. The comparison among the 65 model nodes shows that for the hydrological response variables that characterise high-streamflow conditions, the relative hydrological changes are particularly evident at model nodes where the footprint forms a large proportion of the node catchment.

In general, the hydrological changes are greater in the small tributaries of the Hunter River than in the model nodes along the river itself. The biggest hydrological changes (flow reductions of up to 80%) occur at nodes 7 to 9 (Loders Creek, including Doctors Creek), which enter the Hunter River just upstream of Singleton, and at nodes 52 (Dry Creek) and 55 (unnamed creek) in the vicinity of Muswellbrook. The catchments of nodes 7 to 9 include the Bulga and Mount Thorley–Warkworth mines, while the catchments of nodes 52 and 55 include the Bengalla and Mount Pleasant mines. The prediction that the biggest hydrological changes occur downstream of multiple mine developments highlights the cumulative nature of potential hydrological changes, particularly on low-flow characteristics.

The hydrological changes due to the additional coal resource development on the low-streamflow hydrological response variables appear to be slightly larger than those on the high-streamflow hydrological response variables. However, the uncertainties in the predicted change and the timing of the maximum change are greater for the low-streamflow hydrological response variables.

The results suggest that changes to low-flow characteristics are caused by a combination of the instantaneous effect of interception from the additional mine footprints and the cumulative effect on baseflow over time caused by watertable drawdown, while the changes to high-flow characteristics are dominated by direct interception of runoff.

Last updated:
18 January 2019
Thumbnail of the Hunter subregion

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