- Bioregional Assessment Program
- Hunter subregion
- 3-4 Impact and risk analysis for the Hunter subregion
The impact and risk analysis for the Hunter subregion is a regional overview of potential impacts on, and risks to, water resources and water-dependent ecological, economic and sociocultural assets. Hydrological and ecosystem changes due to coal resource development are quantified and impacts that are very unlikely (less than 5% chance) are ruled out.
Results of regional-scale hydrological modelling indicate potential risks to Wyong River and Saddlers, Loders and Wollar creeks due to additional coal resource development. More detailed local-scale information is required to determine the level of risk and potential impacts.
The Hunter subregion is just over 17,000 km2 and is located north of Sydney, NSW. The Hunter subregion straddles three of the five coalfields that make up the Sydney geological basin: mainly the Hunter and Newcastle coalfields and part of the Western Coalfield.
The impact and risk analysis considered two potential coal resource development futures:
- baseline coal resource development (baseline): a future that includes all coal mines and coal seam gas (CSG) fields that were commercially producing as of December 2012. In the Hunter subregion, this includes 42 mining operations, comprising 22 open-cut mines and 20 underground mines
- coal resource development pathway (CRDP): a future that includes all coal mines and CSG fields that are in the baseline as well as the additional coal resource development (those that were expected to begin commercial production after December 2012). In the Hunter subregion, the additional coal resource development includes 22 proposals, including 4 new open-cut coal mines, 2 new underground coal mines and 16 expansions to baseline mining operations. As of May 2015, there is no CSG production in the Hunter subregion, nor any proposals for CSG development in the future.
The difference in results between CRDP and baseline is the change that is primarily reported in a bioregional assessment (BA). This change is due to the additional coal resource development.
Zone of potential hydrological change
The zone of potential hydrological change covers an area of 3213 km2 (19% of the assessment extent). The zone is the union of the groundwater zone of potential hydrological change and the surface water zone of potential hydrological change:
- The groundwater zone of potential hydrological change is defined as the area with at least a 5% chance of exceeding 0.2 m of drawdown in the regional watertable. In the Hunter subregion, it spans an area of 2441 km2 and comprises five discrete drawdown areas.
- The surface water zone of potential hydrological change incorporates a total stream length of 1228 km where a change in any one of the nine surface water hydrological response variables has at least a 5% chance of exceeding its specified threshold. The thresholds can be generally described as at least a 5% chance of a 1% (or 3 day) or greater change in a flow volume or frequency.
The zone was used to rule out potential impacts on ecosystems and water-dependent assets within the Hunter assessment extent. Water resources and water-dependent assets outside the zone are very unlikely to be impacted.
Potential hydrological changes
Results from regional groundwater modelling show cumulative drawdowns of greater than 0.2 m due to additional coal resource development is very likely (greater than 95% chance) at distances of up to 5 km from mine sites and very unlikely to occur at distances exceeding 20 km.
Results of the groundwater modelling of drawdown extent suggest it is:
- very likely that an area of at least 528 km2 exceeds 0.2 m of drawdown and very unlikely that more than 2441 km2 exceeds 0.2 m of drawdown (Figure 19 and Table 8)
- very likely that an area of at least 121 km2 exceeds 2 m of drawdown and very unlikely that more than 927 km2 exceeds 2 m of drawdown (Figure 19 and Table 8)
- very likely that an area of at least 35 km2 exceeds 5 m of drawdown and very unlikely that more than 524 km2 exceeds 5 m of drawdown (Figure 19 and Table 8).
When drawdown predictions are constrained using local information, the range of predicted drawdown extent can be reduced. For example, drawdown extents predicted around Wallarah 2 based on local hydrogeological information are predicted to be smaller than extents based on the regional parameter set (Section 3.3.2).
Changes in streamflow regimes due to additional coal resource development were assessed using three hydrological response variables, which characterise the low-flow and high-flow parts of the flow regime, as well as total flow (Table 6).
The largest flow regime changes are modelled to occur downstream of multiple mine developments, reflecting the cumulative nature of potential hydrological changes. Results of regional-scale modelling suggest large changes in flow regime are possible as a result of additional coal resource development in Loders Creek, Dry Creek and two unnamed creeks near the Mount Pleasant and Mount Thorley–Warkworth coal mines. Dry Creek and the unnamed creeks are small and the hydrological changes are localised. The Hunter Regulated River, into which these creeks flow, is not very sensitive to changes from these creeks (Section 3.3.3).
Wollar Creek, Saddlers Creek and the Wyong River are modelled to have relatively large hydrological changes at the 50th percentile. Wollar Creek, Saddlers and Loders Creek do have a hydrological effect on the Goulburn and Hunter rivers into which they flow. However, changes in baseflow to the Goulburn and Hunter rivers due to groundwater drawdown could be more significant than changes in tributary inflows on Goulburn River and Hunter River flows (Section 3.3.3.).
Results for the Hunter Regulated River show that decreases in mean annual flow of between 1% and 2% are very likely. These changes need to be interpreted with caution, since the Australian Water Resources Assessment river model (AWRA-R) has not been constructed to specifically represent operational management of releases from Glenbawn and Glennies Creek storages.
The potentially large changes in hydrology predicted in the Wyong River reduce considerably when the regional results are constrained using local information. The small chance of at least 200 or more low-flow days per year based on the regional analysis becomes a small chance of at least 7 additional low-flow days when the baseflows from the groundwater model are based on local hydrogeological data.
Generally, the modelled changes are small relative to the interannual variability due to climate, especially for high-flow (Figure 27) and annual flow (Figure 28) days. There is a chance that changes in low-flow days could significantly impact the values associated with streams near all the mining areas, with smaller intermittent and perennial streams close to Central Hunter and Lower Hunter additional coal resource developments particularly at risk (Figure 24). Areas identified as at risk of large hydrological changes require further investigation using local-scale information.
Any change in hydrology could result in changes in groundwater and/or stream water quality but this was not modelled. However, the implications for stream salinity in the Hunter subregion were considered in light of the modelled hydrological changes due to additional coal resource development, salinity hazard mapping and existing regulatory controls (Section 3.3.4). Some of the streams identified as at risk of potentially large hydrological changes, such as Loders Creek and Saddlers Creek, are naturally highly saline, and this would be expected to influence the management response to the predicted hydrological changes.
A range of regulatory requirements are in place in NSW that are intended to minimise potential water quality impacts from coal resource development. For example, in the Hunter Regulated River, a salinity trading scheme manages mine and industry discharges to the river to acceptable levels. Modelling results suggest there will be negligible impact on the number of high-flow days when discharge is permitted under the scheme.
Changes in stream salinity cannot be ruled out. Groundwater is typically more saline than surface runoff. This suggests that reductions in baseflow are more likely to lead to decreases in stream salinity, while reductions in catchment runoff could lead to increases in salinity. The actual effects depend very much on local conditions and relative changes in surface water and groundwater components of the streamflow.
Impacts on, and risks to, landscape classes
The impact and risk analysis investigates how hydrological changes due to additional coal resource development may affect ecosystems at a landscape scale. In the Hunter subregion these ecosystems are classified into landscape classes and aggregated into five landscape groups: ‘Riverine’, ‘Groundwater-dependent ecosystem (GDE)’, ‘Coastal lakes and estuaries’, ‘Non-GDE vegetation’ and ‘Economic land use’.
The vast majority (3012 km2 or 94%) of the zone of potential hydrological change includes the ‘Non-GDE vegetation’ landscape group, which is not water dependent, and the ‘Economic land use’ landscape group.
Estimates of overall ecosystem risk integrate understanding from the conceptual model of causal pathways, hydrological modelling and expert opinion. The strength of this approach is that it provides a measure of relative risk and emphasises where attention should focus, and also where it should not. In the Hunter subregion estimates for overall ecosystem risk were informed by six receptor impact models in five landscape classes.
‘Riverine’ landscape group
Permanent or perennial streams – Potentially large hydrological changes are possible along reaches of the Wyong River, and possibly Dora Creek, in the Macquarie-Tuggerah lakes basin, with potential for adverse ecological impacts. Results from receptor impact modelling, which predicts changes in the probability of presence of riffle-breeding frogs and densities of riffle-dwelling caddisfly larvae (Hydropsychidae), suggest that instream habitats of these streams could be impacted. However, when local hydrogeological information is used to constrain the hydrological change predictions in this area, the likelihood of potentially significant changes in instream habitat is low. Elsewhere in the subregion, it is very unlikely that instream habitats of permanent or perennial streams are impacted (Section 22.214.171.124.1).
Lowly to highly intermittent streams – Potentially large hydrological changes are possible in Saddlers and Loders creeks in the Hunter Basin. Results from receptor impact modelling, which predicts changes in the probability of presence of riffle-breeding frogs and richness of invertebrate hyporheic taxa, indicate a risk of adverse impacts upon instream habitats in these intermittent systems. Instream habitats of other intermittent streams near all additional coal resource developments are also potentially impacted, but the hydrological changes in these streams were not modelled. Local information is needed to determine the actual risk, having regard to stream condition, habitat diversity, other catchment stressors and recovery potential. (Section 126.96.36.199.2).
‘Groundwater-dependent ecosystem (GDE)’ landscape group
Wet sclerophyll forests and dry sclerophyll forests – Overall, the modelled results suggest little detectable impact on the condition of wet sclerophyll forests and dry sclerophyll forests in the Hunter subregion due to additional coal resource development. Results from receptor impact modelling, which predicts changes in projected foliage cover, suggest there is a 5% chance that 10 to 15 km2 of mainly dry sclerophyll forests in the Macquarie-Tuggerah lakes basin may be subjected to adverse ecological impacts, although risk is much reduced when the groundwater modelling result are constrained by local hydrogeological information (Section 188.8.131.52.1).
Forested wetlands – Nearly all the riverine forested wetlands in the Hunter and Goulburn basins are potentially subject to drawdown of less than 2 m, and about 2.6 km2 of the coastal forested wetlands are potentially subject to drawdown of more than 2 m (Section 184.108.40.206.1.). Results from receptor impact modelling, which are based on predicted changes in projected foliage cover, suggest little likelihood of impacts on riverine forested wetlands along unregulated rivers in the Hunter river basin. The model is not considered appropriate for application to the regulated river. Riverine forested wetlands along the Goulburn River are identified as more at risk, but the significance of this risk can only be determined through more local information (Section 220.127.116.11.2). The ecological impact on the coastal forested wetlands in the Macquarie-Tuggerah lakes basin was not represented in the receptor impact model.
Rainforests – Most communities are unlikely to be impacted, because if they are dependent on groundwater at all, it is local groundwater sources. The exception are the riparian rainforests of the Wyong River catchment, which, given they occupy the same landscape position as the ‘Forested wetland’ landscape class (i.e. alluvium along perennial streams), are likely to have a dependency on streamflow and alluvial groundwater. They are potentially impacted by changes in groundwater levels and streamflow due to the proposed Wallarah 2 and Mandalong Southern Extension developments, but are not explicitly represented in any of the qualitative or quantitative models developed for the landscape classes.
Freshwater wetlands – Experts were uncertain about the groundwater dependencies of these systems and their sensitivity to potential hydrological changes from underground coal mining higher up in the catchment. It was thought that tidal fluctuations influence water levels in the lagoons and that any drawdown would be compensated by the inflow of seawater intrusion, leading to no change in water levels, but potential changes in salinity of the wetland water. Given the lack of certainty about the key driving processes, a quantitative model was not developed for this landscape class. The potential for ecological impacts on this landscape class is a knowledge gap.
Semi-arid woodlands, heathlands and grassy woodlands – These landscape classes are very unlikely to be impacted because they are located almost exclusively outside the zone of potential hydrological change.
Springs – This landscape class is represented by four assets within the water-dependent asset register for the Hunter subregion. None of these four assets intersects the zone of potential hydrological change. This landscape class is considered very unlikely to be impacted by additional coal resource development.
Impacts on, and risks to, water-dependent assets
The Hunter subregion has 1652 ecological assets in the assessment extent. The 921 ecological assets outside the zone are considered to be very unlikely (less than 5% chance) to be impacted due to additional coal resource development in the Hunter subregion.
Out of the 731 assets in the zone of potential hydrological change 210 are identified as being ‘more at risk of hydrological changes’ because all or part of the area where the assets occur is within one or more of the potentially impacted landscape groups and there is a greater than 50% chance of the modelled hydrological change exceeding the defined threshold for the relevant landscape class (Section 18.104.22.168). These assets include:
- One endangered ecological community (EEC), the Hinterland Spotted Gum EEC, where 3.6 km2 is in the zone and of this 1.3 km2 is associated with wet and dry sclerophyll forests (Figure 70).
- Twenty-three potential habitats of species listed by the state or Commonwealth including the regent honeyeater (Anthochaera phrygia), swift parrot (Lathamus discolor) and koala (Phascolarctos cinereus). Some species, including migratory species such as the black-faced monarch (Monarcha melanopsis), cattle egret (Ardea ibis), fork-tailed swift (Apus pacificus), great egret (Ardea alba) and satin flycatcher (Myiagra cyanoleuca), have very large potential distributions that cover most, or all, of the zone and use a variety of landscape classes beyond the potentially impacted classes.
- Potential habitats of three state-listed species: green-thighed frog (Litoria brevipalmata), red-crowned toadlet (Pseudophryne australis) and wallum froglet (Crinia tinnula). These all have extensive potential distributions across 2150 to 3170 km2 of the zone.
- Three Important Bird Areas within the zone that were associated with potentially impacted GDE landscape classes: 134 km2 of the Greater Blue Mountains Important Bird Area, associated with 1.5 km2 of forested wetlands; 112 km2 of the Lake Macquarie Important Bird Area, associated with 5.0 km2 of wet and dry sclerophyll forests and 3.8 km2 of forested wetlands; and 395 km2 of the Mudgee-Wollar Important Bird Area, associated with 1.0 km2 of wet and dry sclerophyll forests and 10.1 km2 of forested wetlands.
- Five protected areas listed in the Collaborative Australian Protected Areas Database (CAPAD) were associated with potentially impacted GDE landscape classes, and include 3.6 km2 of the hinterland spotted gum endangered ecological community, which is associated with 1.3 km2 of wet and dry sclerophyll forests and 1.5 km2 of forested wetlands.
Impacts on economic assets were assessed in terms of changes in water availability, reliability of supply and potential for invoking ‘make good’ provisions under the NSW Aquifer Interference Policy.
There are 123 economic assets in the zone of potential hydrological change. Five groundwater and 19 unregulated and alluvial surface water sources were identified as being potentially impacted due to additional coal resource development.
There are 3831 water supply bores and surface water extraction points in the zone of potential hydrological change. Just over half are associated with the Hunter Regulated River water source, 32% with unregulated and alluvial water sources and 15% with non-alluvial groundwater (Section 22.214.171.124, Figure 73).
Decrease in mean annual water availability is very likely to exceed 5 GL/year in the Hunter Regulated River at Greta (less than 1% of mean annual flow), but very unlikely to exceed 12 GL/year (1.6% of mean annual flow). In unregulated and alluvial water sources, there is a 5% chance of reductions in water availability of 3 to 6 GL/year in the Singleton, Muswellbrook, Jerrys and Wyong River water sources.
Potentially significant changes in reliability of supply (as indicated by change in number of cease-to-pump days) are possible for some creeks in the Singleton, Jerrys and Muswellbrook water sources, and in the Wyong River. In the Wyong River, the median change over the three 30-year periods is modelled to be between 6 and 8 days, with a 5% chance of 145 days per year in 2043 to 2072). Modelling with local-scale information indicates that the changes are more likely to be towards the lower end of this range (Section 126.96.36.199).
Of the 1450 bores in the zone, 170 have at least a 5% chance of drawdowns exceeding 2 m. Of these, 159 are on mining and exploration leases. There is at least a 5% chance that the drawdown due to the additional coal resource developments will exceed 2 m at 11 of these bores that include non-mining water supply sources: Sydney Basin – North Coast groundwater source (7) and Jilliby Jilliby Creek (2), Tuggerah Lake (1) and South Macquarie Lake (1). Five of these bores have a 50% chance of drawdowns exceeding 2 m (Section 188.8.131.52, Figure 74).
There are 67 water-dependent sociocultural assets within the zone of potential hydrological change; 45 of these are built infrastructure and were not assessed and 22 are reserves or national parks. The reserves and national parks overlap with 13 km2 of potentially impacted GDEs.
There are three National Heritage-listed areas within the zone of potential hydrological change in the Hunter subregion as well as 137 km2 of the Greater Blue Mountains World Heritage Area. Any impact on these assets is predicted to be minor (Section 3.5.4).
There are two Indigenous sites within the zone of potential hydrological change in the Hunter subregion:
- Register of National Estate-listed Swansea Heads Area – Lambton Parade, Swansea Heads – not predicted to be impacted by additional coal resource development
- Register of National Estate-listed Bobadeen Area (Hands on the Rock Shelter) – Cassilis Rd, Ulan – requires site-specific study for assessment of potential impact.
To demonstrate how BA data can be used to assess potential impacts on a particular asset, malleefowl (Leipoa ocellata), Section 3.5.5 provides an analysis. This analysis found that there is little chance of any impact of additional coal resource development on the ‘potential distribution of Malleefowl (Leipoa ocellata)’.
Monitoring is important to evaluate the risk predictions of the assessment. Monitoring efforts should reflect the risk predictions, with the greatest effort directed to areas where changes are expected to be the largest and local-scale information supports the regional-scale assessment of risk. Monitoring in locations with lower risk predictions can help to confirm the range of potential impacts and identify unexpected outcomes.
Suggested priorities for groundwater monitoring based on potentially impacted bores are the Sydney Basin – North Coast, Jilliby Jilliby Creek, Tuggerah Lakes and South Lake Macquarie water sources. In addition, groundwater level monitoring for the area west of the proposed West Muswellbrook Project is recommended before its development.
Future surface water monitoring should focus on streams identified as potentially at risk from large changes in flow regime and include the Wyong River and nearby Dora Creek and possibly Loders Creek, Saddlers Creek and Wollar Creek. Streamflow and groundwater monitoring could be of value in Mannering, Morans, Stockton, Wallarah and Wyee creeks given potential changes in flow regime that may arise from the proposed Mandalong Southern Extension Project and Wallarah 2. Monitoring of the Goulburn and Hunter rivers should continue, given potential changes in baseflow. Additional streamflow monitoring in the Wybong river basin would help to assess potential impacts from the proposed West Muswellbrook Project.
Gaps and opportunities
There are opportunities to build on this assessment and address science gaps and include future coal resource developments. For example, seven mining proposals identified as additional coal resource developments as at September 2015 were not included in the surface water and/or groundwater modelling. Based on proposal details, the Austar underground, Chain Valley underground and Mount Arthur open-cut developments were considered unlikely to result in significant hydrological change (Section 3.6). The non-modelled Mandalong underground, West Muswellbrook open-cut, Wambo underground and Wilpinjong open-cut additional coal resource developments could increase the regional impact. The potential impacts are explored in Section 3.6 of this product.
The assessment is regional and cumulative, and provides an important frame for local-scale environmental impact assessments of new coal resource developments, and the local geological, hydrogeological and hydrological modelling that support them (Section 3.7.4). There are opportunities to tailor the BA modelling results for more local analyses, for example:
- combining detailed local geological information with the groundwater emulators developed through BA
- considering alternative coal resource development pathways.
There are specific opportunities for improvement:
- incorporating additional geophysical, well and bore data
- improved characterisation of hydraulic properties of sedimentary rocks
- improved mapping of depth to groundwater, and its spatial and temporal variation
- mapping groundwater depths outside of alluvial layers to build understanding of interactions between changes in groundwater availability and the health and persistence of groundwater-dependent vegetation
- incorporating feedback mechanisms in more closely coupled surface water and groundwater models to reduce predictive uncertainty
- more extensive sets of surface water model nodes to improve the interpolation of surface water hydrological response variables
- reviewing vegetation mapping in the subregion, and undertaking field-based studies to assess condition, determine degree of groundwater dependence and sensitivity to changes in groundwater levels
- identifying the spatial location of water-dependent assets valued by the local Indigenous communities.
The full suite of information, including information for individual assets, is provided at www.bioregionalassessments.gov.au. Users can explore detailed results for the Hunter subregion using a map-based interface in the BA Explorer, available at www.bioregionalassessments.gov.au/explorer/HUN.
- 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 are not modelled
- 3.7 Conclusion
- Contributors to the Technical Programme
- About this technical product