This section describes the potential impacts on ecosystems that result from hydrological changes due to additional coal resource development. Ecosystems are represented by landscape classes, which are organised into five landscape groups that reflect their water dependencies: riverine, GDE, coastal lakes and estuaries, non-GDE vegetation and economic land use (Table 19). The basis for the landscape groups and classes is described in companion product 2.3 for the Hunter subregion (Dawes et al., 2018). Landscape classes that intersect the 3213 km2zone of potential hydrological change are considered potentially impacted due to additional coal resource development and are the focus of this section. Landscape classes that are not water dependent can be ‘ruled out’ from potential impacts. Landscape classes that do not intersect the zone are very unlikely to be impacted (less than 5% chance) due to additional coal resource development (see Section 3.4.2).
About 3,136 km (21%) of the 14,659 km of river length in the Hunter assessment extent is in the zone of potential hydrological change (Figure 30). About 1232 km of perennial streams, 1450 km of intermittent streams and 8840 km of ephemeral streams are outside the zone. Most (63%) of the stream length in the zone comprises ephemeral streams (1985 km), with a further 634 km of perennial streams and 518 km of intermittent streams (Figure 30).
Potential impacts on permanent or perennial streams and lowly to highly intermittent streams were assessed using both qualitative models and quantitative receptor impact models developed for the Hunter subregion (Table 19; also see companion product 2.7 for the Hunter subregion (Hosack et al., 2018a)), with results presented in Section 3.4.3. Most (1346 km) of the ephemeral streams within the zone are considered unlikely to be affected due to additional coal resource development and are ruled out (see Section 3.4.2; also see companion product 2.7 for the Hunter subregion (Hosack et al., 2018a)). Thus, about 1228 km of streams within the zone are considered potentially impacted. Section 3.4.3 provides an assessment of the potential impacts on and risks to the landscape classes in the ‘Riverine’ landscape group.
There are about 102 km2 of the ‘GDE’ landscape group in the zone of potential hydrological change (Figure 30). Five landscape classes in the ‘GDE’ landscape group are described by qualitative models, of which three are also described by quantitative receptor impact models. Details of these models are reported in companion product 2.7 for the Hunter subregion (Hosack et al., 2018a). These models are used to assess the potential for impacts on and risks to the landscape classes in the ‘GDE’ landscape group (see Section 3.4.4).
Receptor impact modelling converts the potentially abstract information about hydrological changes to quantities that stakeholders care about and can more readily understand and interpret. In particular, outcomes of the modelling relate more closely to their ecological values and beliefs and therefore support community discussion and decision making about acceptable levels of coal resource development (see companion submethodology M08 (as listed in Table 1) for receptor impact modelling (Hosack et al., 2018b)). Receptor impact models are not intended to make site-specific predictions but rather to quantify the range of possible responses of selected receptor impact variables to a given change in hydrology. It is beyond the scope of a BA to make precise predictions at exact locations.
Receptor impact variables represent biological components of the ecosystem that experts have chosen as indicators of ecosystem condition, and which are considered likely to be sensitive to changes in the hydrology of that system (see companion submethodology M08 (as listed in Table 1) for receptor impact modelling (Hosack et al., 2018b)). Changes in hydrology are represented in the model by hydrological response variables, chosen to reflect particular water requirements of the ecosystem. The magnitude of change in the chosen receptor impact variables to changes in one or more hydrological response variables, captured through an expert elicitation process, is an indicator of the magnitude of risk to the ecosystem as a result of hydrological perturbation. For example, a prediction that the number of riffle-breeding frog species is likely to decrease in a particular reach where zero-flow days are predicted to increase does not necessarily mean that there are riffle-breeding frogs present and that they will be impacted. Rather, it means that given the magnitude of hydrological change predicted in that reach, there is a specific risk to the habitat requirements of riffle-breeding frogs, and more generally a risk to the ecosystems represented by the landscape class the riffle-breeding frog inhabits. The receptor impact modelling results are provided at a landscape scale and should not be interpreted as exactly representing the local conditions of a particular site.
In the following sections, the results from receptor impact models should be treated as indicating the experts’ pooled knowledge as to the likelihood and magnitude of ecological impacts in an ecosystem given a known hydrological change. Results also capture the uncertainties arising from lack of knowledge, the variability inherent in landscapes across short and long distances and the variability in response pathways over short and long time frames.
Figure 30 Landscape classes in the zone of potential hydrological change
Landscape classes are shown from the ‘Groundwater-dependent ecosystem (GDE)’ landscape group and the ‘Riverine’ landscape group. The extent of the coal resource developments in the coal resource development pathway (CRDP) is the union of the extents in the baseline and in the additional coal resource development (ACRD). Groundwater-dependent ecosystems (GDEs) are exaggerated (not to scale) for clarity.
Data: Bioregional Assessment Programme (Dataset 1, Dataset 2, Dataset 3, Dataset 4)
Table 19 Length (km) or area (km2) of all landscape classes in the assessment extent and the zone of potential hydrological change, and associated qualitative models and receptor impact models
aThe ‘Lowly to moderately intermittent’ and ‘Moderately to highly intermittent’ landscape classes were collapsed into a single ‘Intermittent’ landscape class in developing the qualitative models (companion product 2.7 for the Hunter subregion (Hosack et al., 2018a)).
GDE = groundwater-dependent ecosystem, na = not applicable
Data: Bioregional Assessment Programme (Dataset 5)
