- Bioregional Assessment Program
- Gloucester subregion
- 3-4 Impact and risk analysis for the Gloucester subregion
- 3.3 Potential hydrological changes
Potential hydrological changes were derived for the two futures considered in bioregional assessments (BAs): the baseline and the coal resource development pathway (CRDP).
The groundwater zone of potential hydrological change is defined as the area with a greater than 5% chance of exceeding 0.2 m of drawdown in the regional watertable due to additional coal resource development (as predicted by numerical groundwater modelling). It consists of an area of 88 km2 around Stratford mine, Rocky Hill mine and the Gloucester Gas Project Stage 1, and an additional 12 km2 around Duralie mine.
The surface water zone of potential hydrological change is defined as the area in which the change in any one of the eight surface water hydrological response variables exceeds the specified threshold. It includes all modelled reaches that are within the assessment extent except for those in the Barrington River, Booral Creek and the Karuah River below Booral Creek. Additionally, it includes three unmodelled reaches in the Gloucester river basin: Sandy Creek (a tributary of the Gloucester River), Avondale Creek (a tributary of the Avon River), and an unnamed tributary of the Avon River.
The combined groundwater and surface water zone of potential hydrological change in the Gloucester assessment extent covers an area of 250 km2 and 242 km of stream network.
It is very likely that an area of 19 km2 will experience at least 0.2 m of drawdown, and it is very unlikely that more than 100 km2 will experience drawdowns of this magnitude, due to additional coal resource development. It is very unlikely that more than 16 km2 exceeds 2 m of drawdown, and very unlikely that more than about 4 km2 exceeds 5 m of drawdown.
The potential impacts due to additional coal resource development on surface water flow regimes are summarised using three hydrological response variables: low-flow days, high-flow days and annual flow. Low-flow days are likely to increase at a number of locations across the assessment extent. The median change is less than the interannual variability observed under the baseline; however, there is at least a 5% chance that changes will be comparable to or greater than the interannual variability seen under the baseline. Similar, although slightly smaller in both area and magnitude, reductions in the number of high-flow days are modelled. The reduction in annual flow is smaller again in both area and magnitude and is unlikely to move the system out of the range of interannual variability seen under the baseline.
Potential changes in hydrology could lead to changes in water quality (although water quality was not modelled). Several regulatory requirements are in place in NSW to minimise potential water quality impacts from coal resource development. Potential impacts on water quality due to additional coal resource development are considered unlikely in the Gloucester subregion, as no development is permitted to discharge mine water off site. Modelled predictions of baseflow reductions are small and, if anything, are expected to result in small decreases in stream salinity.
Potential hydrological changes due to additional coal resource development are summarised using hydrological response variables based on results from regional-scale surface water and groundwater modelling, reported in companion product 2.6.1 (Zhang et al., 2018) and companion product 2.6.2 (Peeters et al., 2018) for the Gloucester subregion. These hydrological response variables have been defined to represent the maximum difference between the CRDP and baseline for groundwater drawdown and a range of streamflow characteristics. They have also been used to define the zone of potential hydrological change – the focal extent for the impact and risk analysis (Section 3.3.1).
Potential changes in groundwater and surface water within the zone of potential hydrological change are presented in Section 3.3.2 and Section 3.3.3, respectively. Areas more at risk of hydrological changes, and hence potentially adverse impacts, due to additional coal resource development are identified. Local scale information is needed to refine the assessment of risk and determine the appropriate management response in these areas. While changes in water quality were not part of the hydrological modelling, the potential for changes in water quality due to additional coal resource development in the Gloucester subregion is considered in Section 3.3.4.
Additional hydrological response variables have been defined for input into the landscape class qualitative models and receptor impact models (companion product 2.7 for the Hunter subregion (Hosack et al., 2018b)), and for quantifying potential impacts on economic assets. They represent key water dependencies in these systems and are based on average differences over 30-year and 90-year periods. Changes in these variables are presented as part of the impact and risk analysis in Section 3.4 and Section 3.5.
Product Finalisation date
- 3.1 Overview
- 3.2 Methods
- 3.3 Potential hydrological changes
- 3.4 Impacts on and risks to landscape classes
- 3.5 Impacts on and risks to water-dependent assets
- 3.6 Commentary for coal resource developments that were not modelled
- 3.7 Conclusion
- Contributors to the Technical Programme
- About this technical product