The impact and risk analysis investigated how hydrological changes due to additional coal resource development may affect ecosystems, such as wetlands, rivers or groundwater-dependent ecosystems. These ecosystems were classified into landscape classes (Box 6; Section 2.3.3 in Dawes et al. (2018)) which were categorised into five landscape groups:
- ‘Riverine’
- ‘Groundwater-dependent ecosystem (GDE)’
- ‘Estuarine’
- ‘Non-groundwater dependent ecosystem (Non-GDE)’
- ‘Economic land use’.
The impact and risk analysis (Box 7) focused on landscape classes that intersect the zone of potential hydrological change (Box 4). Any ecosystem or asset wholly outside of this zone is considered very unlikely to be impacted due to additional coal resource development.
For potentially impacted ecosystems within the zone, receptor impact models (Box 8) were used to translate predicted changes in hydrology into a distribution of ecological outcomes that may arise from those changes. These models used indicators of the health of the ecosystem, such as taxa richness, or canopy cover of vegetation, to assess the potential ecological impacts of hydrological changes.
The natural and human-modified ecosystems in the subregion were classified into 20 landscape classes (Table 3 and Figure 9 in Dawes et al. (2018)) to enable a systematic and comprehensive analysis of potential impacts on, and risks to, the water-dependent assets nominated by the community. The landscape classification was based on the subregion’s geology, geomorphology, hydrogeology, land use and ecology. These landscape classes were aggregated into five landscape groups, based on their likely response to hydrological changes. Definitions for landscape classes and landscape groups for the Gloucester subregion are available online at environment.data.gov.au/def/ba/landscape-classification/gloucester-subregion.Box 6 Understanding the landscape classification
Box 7 Analysing impact and risk
Potential impacts to water-dependent ecosystems and assets were assessed by overlaying their location on the zone of potential hydrological change (Box 4) to identify the hydrological changes that a particular asset or ecosystem might experience.
- Outside this zone, ecosystems and assets are very unlikely to be impacted by hydrological changes due to additional coal resource development.
- Inside this zone, ecosystems and assets are potentially impacted.
Within the zone, not all water-dependent ecosystems or assets will be affected, as this depends on their reliance on groundwater or surface water. Hydrological changes due to additional coal resource development may be large, but within the range of natural seasonal and climatic variability, and so may not affect water-dependent ecosystems or assets. Alternatively, small changes may affect sensitive ecosystems that have a strong reliance on groundwater or surface water.
For ecological assets, the assessment considered the potential impact to the habitat of the species, not potential impacts to the species themselves.
Ecosystems that fall within the mine pit exclusion zone are likely to be directly impacted, but as estimates of drawdown are unreliable, the degree of impact is not possible to quantify. Similarly, the surface water modelling close to mine pits (Figure 11) cannot quantify the degree of impact on some streams.
Figure 13 Landscape classes in the zone of potential hydrological change
Groundwater-dependent ecosystems (GDEs) are exaggerated (not to scale) for clarity. Landscape classes in the ‘Estuarine’ landscape group are not shown because they are not water dependent.
Data: Bioregional Assessment Programme (Dataset 12, Dataset 13, Dataset 15); NSW Office of Water (Dataset 14); ABARES (Dataset 16)
Ecosystems
Which ecosystems are very unlikely to be impacted?
Potential impacts due to additional coal resource development are ruled out for all of the 139 km2 of ‘Native vegetation’ landscape class in the assessment extent, as it is not groundwater dependent. All estuarine ecosystems, 7.05 km2 of the 10.3 km2 of groundwater-dependent ecosystems, and 67 km of the 344 km of streams lie outside the zone of potential hydrological change, and so are very unlikely to be impacted.Key finding 5
Most ecosystems in the zone of potential hydrological change (246 km2 or 99%, see Table 14 in Post et al. (2018)) are classified as non-groundwater-dependent vegetation and economic land use (Figure 13). Non-groundwater-dependent vegetation is not considered water dependent for the purposes of bioregional assessments. While some economic land use classes such as irrigated agriculture are water dependent, impacts on economic assets are not evaluated by landscape class. Instead, economic assets are assessed by analysing changes in the availability of groundwater or surface water, and against specific management thresholds. This is explained further in Section 3.5 of Post et al. (2018) and in ‘What are the potential impacts of additional coal resource development on water-dependent assets?’
The following ecosystems in the south of the assessment extent are outside the zone of potential hydrological change and thus impacts are very unlikely:
- the estuarine reaches of the Karuah River
- 1.1 km2 of freshwater wetlands
- 65 km of perennial streams and 3 km of intermittent streams, mainly along the Karuah River.
There are no springs in the Gloucester subregion.
Which ecosystems are potentially impacted?
There are 242 km of streams and 3.3 km2 of groundwater-dependent ecosystems in the zone of potential hydrological change (Table 1). Modelled hydrological changes are likely to lead to minimal ecological impacts in intermittent and perennial gravel/cobble streams. It is very likely that modelled drawdown under the 3.3 km2 of groundwater-dependent ecosystems is less than 2 m.Key finding 6
Riverine ecosystems
Receptor impact models (Box 8) were built to predict how hydrological changes (as measured by a suite of hydrological response variables) might result in changes to the ecological condition of intermittent and perennial gravel/cobble streams, which make up about 75% of the subregion’s streams. The zone of potential hydrological change includes 78 km of the 81 km of intermittent gravel/cobble streams and 133 km of the 175 km of perennial gravel/cobble streams in the assessment extent (Table 1). Perennial gravel/cobble streams are found along the Gloucester River in the north, and along the Karuah and Mammy Johnsons rivers in the south. Most intermittent gravel/cobble streams are found in the Avon River, a major tributary of the Gloucester River, and its tributaries. Within the zone, only 3% of perennial streams and 2% of intermittent streams were reported as being in good condition (Figure 31 of Post et al. (2018)).
Overall, modelling suggests it is unlikely that perennial gravel/cobble streams will experience large changes in groundwater drawdown, changes in baseflow index, or increased zero-flow days (averaged over 30 years) as a result of additional coal resource development. Small‑decreases in the frequency of overbench and overbank flows are possible for short reaches. An increase in zero‑flow days (averaged over 30 years) may occur in short sections of intermittent gravel/cobble streams due to additional coal resource development but large lengths of stream are not expected to experience changes.
Outputs of receptor impact models suggest that these modelled hydrological changes will have a minimal impact on the chosen indicators of ecological condition (Box 8). Details can be found in Section 3.4.3.3 of the impact and risk analysis (Post et al., 2018).
Groundwater-dependent ecosystems
The water requirements of groundwater-dependent ecosystems in the subregion are poorly understood and the frequency, timing and duration of groundwater use are uncertain. Therefore, receptor impact models were not developed. Instead, qualitative models were developed for forested wetlands, wet sclerophyll forests and dry sclerophyll forests. These models predicted that groundwater drawdown would have negative impacts on all vegetation-related variables, including overstorey and understorey (ground layer) cover, and recruitment.
There are 3.3 km2 of groundwater-dependent ecosystems in the zone of potential hydrological change (Table 1), of which 0.4 km2 is in the mine pit exclusion zone (Table 23 in Post et al. (2018)). Modelling of the additional coal resource developments indicated a 5% chance of about 1.1 km2 of groundwater-dependent ecosystems being subject to a drawdown of between 0.2 and 2 m. Most of the impact would be in forested wetlands. No groundwater-dependent ecosystems were modelled to be subject to more than 2 m of drawdown. These qualitative models did not, however, predict the magnitude or likelihood of potential ecological impacts.
Table 1 Extent of each landscape class in the assessment extent and in the zone of potential hydrological change, and the landscape classes that have qualitative and/or receptor impact models
The extent of each landscape class is either an area of vegetation (km2) or length of stream network (km). See Table 14 in Post et al. (2018) for results for the ‘Non-GDE’ and ‘Economic land use’ landscape groups.
aDefinitions for landscape classes and landscape groups for the Gloucester subregion are available at http://environment.data.gov.au/def/ba/landscape-classification/gloucester-subregion.
na = not applicable
Data: Bioregional Assessment Programme (Dataset 1)
Explore potential impacts on ecosystems in more detail on the BA Explorer, at http://www.bioregionalassessments.gov.au/explorer/GLO/landscapes. Conceptual modelling, product 2.3 (Dawes et al., 2018) Impact and risk analysis, product 3-4 (Post et al., 2018) Assigning receptors to water-dependent assets, submethodology M03 (O’Grady et al., 2016) Receptor impact modelling, submethodology M08 (Hosack et al., 2018a) Analysing impacts and risks, submethodology M10 (Henderson et al., 2018) Impact and risk analysis database (Dataset 1) Landscape classification (Dataset 17) Landscape class spatial overlay by assessment unit (Dataset 18)FIND MORE INFORMATION
Box 8 Receptor impact models
Receptor impact models translate predicted changes in hydrology into ecological outcomes that may arise from those changes. Applying receptor impact models across ecosystems allows a better understanding of how changed hydrological conditions may impact water-dependent assets within those ecosystems at specified points in time.
To assess potential ecological outcomes:
- Experts first choose receptor impact variables, characteristics that serve as indicators of the ecological condition of an ecosystem. These are specifically chosen to be representative of a landscape class. For each indicator, experts also choose one or more hydrological response variables, chosen because the indicator is sensitive to changes in those hydrological response variables.
For example, in the Gloucester subregion, for perennial gravel/cobble streams three indicators (bolded) were chosen to predict changes that are sensitive to the following hydrological response variables:
- percent canopy cover: overbench flow, overbank flow, groundwater drawdown
- mean abundance of caddisfly larvae: baseflow index, number of zero-flow days (averaged over 30 years)
- mean abundance of eel-tailed catfish per 100 m of stream length: baseflow index, number of zero-flow days (averaged over 30 years).
For intermittent gravel/cobble streams in the Gloucester subregion, the indicator (bolded) and hydrological response variable were:
- richness of hyporheic taxa in a 6 L sample of stream water: number of zero-flow days (averaged over 30 years). (Hyporheic taxa are the organisms found where surface water and groundwater mix below the bed of a stream.)
- Hydrological models are used to quantify changes in the hydrological response variables.
- Receptor impact models are used to predict changes in the indicator for a landscape class that result from the changes in hydrological response variables. The changes in the indicator reflect the magnitude of potential ecological impacts for that ecosystem.
