All landscape classes are described in companion product 2.3 (Dawes et al., 2018) for the Gloucester subregion. Landscape classes potentially impacted by the additional coal resource development were identified as those that intersect the modelled zone of potential hydrological change. The zone of potential hydrological change was derived from the combination of a modelled groundwater drawdown zone and its downstream surface water network (see Section 3.3 of companion product 3-4 for the Gloucester subregion (Post et al., 2018)). The groundwater drawdown zone is defined as having a 5% probability of exceeding a 0.2m drawdown in the watertable aquifer. The surface water network downstream of this groundwater-drawdown zone was identified and a buffer of 150 m placed around it. A 150 m buffer was considered sufficient to capture any off-stream surface water impacts given the geomorphology of the Gloucester subregion. Any 500 m x 500 m assessment units (companion submethodology M08 (as listed in Table 1) for receptor impact modelling (Hosack et al., 2018)) that intersect the groundwater drawdown zone or the buffered surface water network are included in the zone of potential hydrological change. The total area of the zone of potential hydrological change is 250 km2. The zone of potential hydrological change is conservative and is designed to focus attention on those landscape classes that may be subject to hydrological changes, and at the same time identify areas and landscape classes beyond the zone where impacts are very unlikely (less than 5% chance).
All BA landscape classes in the ‘Economic land use’ landscape group are in the zone of potential hydrological change (Figure 6), as is the ‘Native vegetation’ landscape class in the ‘Non-GDE’ landscape group. These comprise the vast majority (98.6%) of the area inside the zone of potential hydrological change (Table 5). There are 3.5 km2 of GDEs in the zone, classified as wet or dry sclerophyll forests, rainforests or forested wetlands (Table 5). There are 242 km of river within the zone of potential hydrological change, which are overwhelmingly (88%) dominated by perennial and intermittent streams with a gravel/cobble substrate (Table 5).
Table 5 Length or area of each landscape class within the zone of potential hydrological change in the Gloucester subregion
Also indicated are whether the landscape classes are represented in the qualitative model and the receptor impact model (RIM).
GDE = groundwater-dependent ecosystem
Data: Bioregional Assessment Programme (Dataset 1)
2.7.2.1.1 ‘Riverine’ landscape group
Landscape classes in the ‘Riverine’ landscape group within the zone of potential hydrological change were identified and their lengths tabulated (Table 5). The total length of landscape classes within the ‘Riverine’ landscape group in the zone of potential hydrological change is approximately 242 km, the majority of which (88%) is either perennial or intermittent streams with gravel/cobble substrate. Hence, the receptor impact modelling described in Section 2.7.3 for the ‘Riverine’ landscape group focuses on the ‘Perennial – gravel/cobble streams’ and ‘Intermittent – gravel/cobble streams’ landscape classes. Rivers in the vicinity of coal resource development are intermittent in the north of the assessment extent and perennial in the south of the assessment extent (Figure 6).
The remaining streams within the non-estuarine region of the Gloucester subregion are a mixture of high gradient bedrock confined streams and transitional and lowland fine streams. High gradient bedrock confined streams are upstream of any development and lack a connection to the lowland regional groundwater aquifers; hence there is little potential for development to directly impact on these streams. Alterations to flow in the intermittent lowland streams could result in reduced opportunities for fish passage between lowland and upland streams (Thorncroft and Harris, 2000).
2.7.2.1.2 ‘Groundwater-dependent ecosystem (GDE)’ landscape group
The total area of all landscape classes in the ‘Groundwater-dependent ecosystem (GDE)’ landscape group within the zone of potential hydrological change is 3.3 km2, the majority of which (90%) is either ‘Forested wetlands’ or ‘Rainforests’ landscape classes. Rainforests are concentrated in the southern part of the assessment extent and are mainly associated with perennial streams while forested wetlands are concentrated in the northern part of the assessment extent and are mainly associated with intermittent streams. Rainforests are closely allied with wet sclerophyll forest. Wet sclerophyll forests are characterised by a tall, open, sclerophyllous tree canopy of Eucalyptus spp. and an understorey of soft-leaved shrubs, ferns and herbs, many of which are in common with rainforest species. More than 30% of crown cover of emergent, non-rainforest species (including eucalypts, brushbox and turpentine) results in a classification of wet sclerophyll forest rather than rainforest (DECC, 2007).
Qualitative mathematical models for the ‘Dry sclerophyll forests’ and ‘Forested wetlands’ and ‘Wet sclerophyll forests’ landscape classes are presented in Section 2.7.4. A qualitative model for rainforests was not developed owing to its small area within the subregion and lack of proximity to coal resource development.
2.7.2.1.3 ‘Estuarine’ landscape group
Landscape classes in the ‘Estuarine’ landscape group were not present in the zone of potential hydrological change.
2.7.2.1.4 ‘Non-GDE’ landscape group
A substantial area (54 km2) of the zone of potential hydrological change is within the ‘Native vegetation’ landscape class of the ‘Non-GDE’ landscape group. As this class lacks a dependence on water other than rainfall, it was not expected to be impacted by development through groundwater or surface water mediated pathways, and no receptor impact model was developed for this landscape group.
2.7.2.1.5 ‘Economic land use’ landscape group
In the ‘Economic land use’ landscape group, the majority of the zone of potential hydrological change is within the ‘Dryland agriculture’ landscape class (170 km2). A further 23 km2 is within the other landscape classes of the ‘Economic land use’ landscape group. Potential impacts on these landscape classes are not assessed.
Figure 6 Zone of potential hydrological change for the Gloucester subregion
Distribution of landscape classes is shown for (a) the ‘Riverine’ landscape group and (b) for the ‘Groundwater-dependent ecosystem (GDE)’, ‘Non-GDE’ and ‘Economic land use’ landscape groups. For clarity, the ‘Riverine’ landscape group has been simplified to ‘Perennial’ or ‘Intermittent’. The vast majority of stream length has a gravel/cobble substrate (Table 5).
GDE = groundwater-dependent ecosystem
Data: Bioregional Assessment Programme (Dataset 2)
