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

The prediction results show that additional coal resource development in the Namoi subregion can cause substantial changes in the hydrological response variables. The comparison among the 54 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 development footprint forms a large proportion of the node’s catchment.

In general, the hydrological changes are greater in the small tributaries of the Namoi River than in the model nodes along the river itself. The biggest hydrological changes occur at Namoi tributary node 25 (Merrygowen Creek), downstream of the Boggabri and Tarrawonga mines, and node 22 (Back Creek) downstream of the Maules Creek Project and the Mooki River tributary node 34 which is affected by the Watermark Coal Project.

The hydrological changes due to the additional coal resource development for the low-streamflow hydrological response variables appear to be greater than for the high-streamflow hydrological response variables. However, the uncertainty in the predicted change is greater for the low-streamflow 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 groundwater drawdown, whereas the changes to high-flow characteristics are dominated by direct interception of runoff.

The modelling results are used to define a zone of potential hydrological change for surface water in the Namoi subregion. This zone includes locations where the projected change in at least one of the nine hydrological response variables has a 5% chance or greater of exceeding a specified small threshold. The resulting zone of potential hydrological change for surface water includes those parts of the Namoi River and its tributaries downstream of and including the Mooki River, except for Baradine Creek and the uppermost nodes of Bohena Creek and the Mooki River.

Last updated:
6 December 2018
Thumbnail of the Namoi subregion

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