3.7.2 Future monitoring

Post-assessment monitoring is important to test and (in)validate the risk predictions of the Assessment. At the highest level, monitoring efforts should reflect the risk predictions, and focus the effort where the changes are expected to be the largest. However, it is important to place some monitoring effort at locations with lower risk predictions so as to confirm the range of potential impacts and identify unexpected outcomes.

The BA of the Hunter subregion has identified that potential hydrological or ecosystem impacts due to additional coal resource development are likely in a small number of catchments within the subregion. Groundwater monitoring effort should be concentrated in the five discrete drawdown zones. In most cases, it is the hydraulic properties of the aquitards that determine impacts at the surface from stresses at depth. Nested piezometers that can monitor the changes in hydraulic gradients between layers are required to determine impacts at the surface from mining-induced stresses. The Sydney Basin – North Coast groundwater source has the largest number of bores where ‘make good’ provisions might apply and would be expected to be a focus of the groundwater monitoring to determine impacts from mining. Monitoring changes in hydraulic gradients between geological layers below the Jilliby Jilliby Creek, Tuggerah Lake and South Macquarie Lake water sources, where potential changes in streamflow from mining at Wallarah 2 and Mandalong Southern Extension have generated considerable concern, would permit early detection of mining-induced changes and more timely management responses.

Results from the surface water modelling would seem to suggest that Wyong River, Loders Creek, Saddlers Creek, Wollar Creek and two unnamed creeks near the Mount Pleasant and Mount Thorley–Warkworth coal mines should be considered for future streamflow monitoring. Given similar levels of drawdown in Dora Creek to Wyong River, it should also be considered for future streamflow monitoring. However, local information on, for example, stream condition, habitat value, recovery potential and existence of other stressors, is needed to determine actual priorities. Monitoring of the Goulburn and Hunter rivers should continue given the potential for changes in baseflow. The Singleton, Muswellbrook, Jerrys and Wyong River water source areas may warrant monitoring given potential changes in water availability.

There are also lengths of stream that are noted as potentially impacted because risk predictions are not made in some cases (e.g. because it is not sensible to interpolate from the stream model nodes used) whose impacts could be quantified through monitoring streamflow, ideally with as much lead in time as possible before new developments commence.

Seven mining proposals identified as additional coal resource developments were not included in the surface water and/or groundwater modelling. Streamflow monitoring may be necessary in Mannering, Morans, Stockton, Wallarah and Wyee creeks given potential changes in flow regime that may arise from the Mandalong Southern Extension development, and in the Wyong River catchment due to changes from the new West Muswellbrook mine. Monitoring of groundwater levels and hydraulic gradients in the vicinity of the proposed West Muswellbrook mine area, which was not modelled in this BA, would contribute to understanding the risk to Wybong Creek flows from this development.

To accompany the hydrological monitoring, monitoring of changes in select ecosystem indicators in potentially at risk streams and GDEs is recommended. The large uncertainties reflected in the receptor impact models from the expert elicitations can be reduced through collecting data on measurable ecosystem components that are sensitive to changes in hydrology (two of the criteria for selection of the receptor impact variables by experts for receptor impact modelling). How frogs, hyporheic invertebrate populations, Hydropsychidae larvae and/or tree canopies respond to changes in water availability and flow regime in different environments and the extent to which changes in these ecosystem components propagate through to other components of the ecosystems they occupy require greater understanding.