3.4.4.1 Description
The ‘Non-floodplain or upland riverine’ landscape group, excluding the Pilliga region, encompasses those landscapes that are typically located away from the broader, floodplain and alluvium landscapes along the Liverpool Plains and Castlereagh-Barwon IBRA subregions (SEWPaC, 2012). Within the zone of potential hydrological change, the upland stream network consists of predominantly minor tributaries to Back Creek (eastern portion of the zone), minor tributaries to the Mooki River and Coxs Creek in the southern portion of the zone and forms most of the stream network in the eastern portion of the Pilliga region. Most of the stream network in the zone of potential hydrological change is classified as ‘Temporary upland stream’ reflecting the highly intermittent and/or ephemeral nature of surface water flow across much of the upland riverine network. The non-riverine landscape classes within this group include remnant vegetation in the riparian zone along the stream channel (‘Upland riparian forest GDE’ landscape class, less than 0.1% of the zone of potential hydrological change), groundwater-dependent vegetation across different landforms (‘Grassy woodland GDE’ landscape class, approximately 1% of the zone) and non-floodplain wetlands (‘Non-floodplain wetland’ and ‘Non-floodplain wetland GDE’ landscape classes, 0.2% and 0.1% of the zone, respectively (Table 23). Further background description of this landscape group is provided in Section 2.7.4 of companion product 2.7 for the Namoi subregion (Ickowicz et al., 2018).
Table 23 Area (km2) and/or length (km) of landscape classes in the ‘Non-floodplain or upland riverine’ landscape group within the entire assessment extent and the non-Pilliga region of the zone of potential hydrological change
The percentage of each landscape class’ contribution to the total area of the zone of potential hydrological change is also given.
na = ‘not available’
Data: Bioregional Assessments (Dataset 2)
3.4.4.2 Potential hydrological impacts
The key hydrological determinants of ecosystem function identified by experts in the qualitative modelling workshops (see Section 2.7.4 in companion product 2.7 for the Namoi subregion (Ickowicz et al., 2018)) have been interpreted as a set of hydrological response variables for each landscape class (Table 24). Hydrological response variables were assigned for two separate components of the upland riverine system based on recognised ecohydrological linkages between water regime and ecosystem health. Firstly, changes in the projected foliage cover in the riparian zone were modelled based on maximum groundwater drawdown and changes in the frequency of overbank flows (Table 24). Secondly, changes in assemblages of macroinvertebrates in instream pool habitats and changes in presence of tadpoles were modelled using attributes of zero flow, annual number of zero-flow days and annual maximum zero-flow spells (defined in Table 24).
3.4.4.2.1 Groundwater
Changes in maximum drawdown along upland streams identified as ‘Upland riparian forest GDE’ were very small with intersected areas exposed to 5% chance of drawdown greater than 0.2 m in the zone of potential hydrological change (Table 25).
Table 24 Summary of the hydrological response variables and corresponding receptor impact variables used in the receptor impact models for the ‘Non-floodplain or upland riverine’ landscape group, together with the corresponding qualitative model (signed digraph) that describes the ecosystem linkages among different components
The proportion of landscape classes with surface water modelling is also provided.
a‘Non-Pilliga’ as used here refers to those parts of the zone of potential hydrological change that fall outside of the ‘Pilliga region’.
See Section 2.7.4 in companion product 2.7 for the Namoi subregion (Ickowicz et al., 2018) for further details.
na = not applicable
Table 25 Area (km2) of landscape classes in the ‘Non-floodplain or upland riverine’ landscape group (non-Pilliga) potentially exposed to varying levels of baseline drawdown and drawdown due to additional coal resource development in the zone of potential hydrological change
The area potentially exposed to ≥0.2, ≥2 and ≥5 m baseline drawdown and additional drawdown is shown for the 5th, 50th and 95th percentiles. Baseline drawdown is the maximum difference in drawdown (dmax) under the baseline relative to no coal resource development. Additional drawdown is the maximum difference in drawdown (dmax) due to additional coal resource development relative to the baseline. Areas within mine pit exclusion zones are excluded from further analysis.
Data: Bioregional Assessment Programme (Dataset 2)
3.4.4.2.2 Surface water
Only 20% of the upland riverine landscape classes had surface water modelling data available (Table 24). For those upland riverine classes where modelling data was available a total of 8.1 km are exposed to a 50% chance of increases in zero-flow days greater than 3 days during the 2013 to 2042 simulation period. Only two upland riverine landscape classes, ‘Temporary upland stream’ and ‘Temporary upland stream GDE’, are exposed to a 50% chance of increases in zero-flow days greater than 20 days (2.2 km and 2.6 km, respectively) for the 2013 to 2042 simulation period (Table 26). For the 2073 to 2102 simulation period, the increase in zero-flow days is similar, with the ‘Temporary upland stream’ and ‘Temporary upland stream GDE’ landscape classes exposed to a 50% chance of increases in zero-flow days greater than 20 days (2.2 and 2.6 km, respectively; Table 26). Further, there are 22.3 km of the upland riverine landscape classes exposed to a 50% chance of increases in zero-flow days greater than 3 days during this period (Table 26, Figure 34).
Both ‘Temporary upland stream’ and ‘Temporary upland stream GDE’ landscape classes are exposed to a 50% chance of annual maximum zero-flow spells increasing greater than 10 days during the 2013 to 2042 simulation period (2.2 and 2.6 km, respectively; Table 27). For the 2073 to 2102 simulation period, there are similar stream reaches having a 50% chance of annual maximum zero-flow spells increasing greater than 10 days for the ‘Temporary upland stream’ and ‘Temporary upland stream GDE’ (Table 27, Figure 35).
Only a very small area (0.3 km2) of the ‘Upland riparian forest GDE’ landscape class has a 5% chance of one less overbank flow event every 50 years (during the 2013 to 2042 simulation period), indicating a very small potential impact on this landscape class based on the surface water modelling results (data not shown).
Table 26 Length (km) of landscape classes in the ‘Non-floodplain or upland riverine’ (non-Pilliga) landscape group potentially exposed to an increase in zero-flow days for two different simulation periods: 2042 and 2102, in the zone of potential hydrological change
The length potentially exposed to ≥3, ≥20 and ≥80 days increase in zero-flow days for the 30-year simulation period compared to the baseline period (1983 to 2012) is shown for the 5th, 50th and 95th percentiles. Areas within mine pit exclusion zones are excluded from further analysis.
Data: Bioregional Assessment Programme (Dataset 2)
The extent of the coal resource developments in the coal resource development pathway (CRDP) is the union of the extents in the baseline and the additional coal resource development (ACRD).
Data: Bioregional Assessment Programme (Dataset 1)
Table 27 Length (km) of landscape classes in the ‘Non-floodplain or upland riverine’ (non-Pilliga) landscape group potentially exposed to an increase in annual maximum zero-flow spells for two different simulation periods: 2042 and 2102, in the zone of potential hydrological change.
The length potentially exposed to ≥3, ≥10 and ≥40 days increase in the length of the maximum zero-flow spell during the 30-year simulation period compared to the baseline period (1983 to 2012) is shown for the 5th, 50th and 95th percentiles. Areas within mine pit exclusion zones are excluded from further analysis.
Data: Bioregional Assessment Programme (Dataset 2)
The extent of the coal resource developments in the coal resource development pathway (CRDP) is the union of the extents in the baseline and the additional coal resource development (ACRD).
Data: Bioregional Assessment Programme (Dataset 1)
3.4.4.3 Potential ecosystem impacts
The potential for ecosystem impacts on those areas classified as ‘Non-floodplain or upland riverine’ within the zone of potential hydrological change was estimated using three separate receptor impact models (see Table 24). To gauge an overall indication of ecosystem risk across this landscape group, the results of these receptor impact models were aggregated. This was done using the differences for each receptor impact variable (average number of families of aquatic macroinvertebrates, projected foliage cover of riparian vegetation dominated by C. cunninghamiana and the probability of presence of tadpoles from the Limnodynastes genus) between the CRDP and baseline futures that were derived for each assessment unit where model data were available. The risk thresholds used for defining risk and the associated terminology are identical to that applied to the receptor impact variables assigned to the landscape classes in the ‘Floodplain or lowland riverine’ landscape group (Section 3.4.3.3).
The composite of all receptor impact models is presented in Figure 36, whereby the highest level of risk determined from one or more receptor impact variables for any assessment defines the overall level of risk for that assessment unit. Only a small area on or adjacent to Maules Creek was identified as being ‘more at risk of ecological and hydrological changes’ (Figure 36), and therefore worthy of more emphasis in any subsequent follow up with local analyses and monitoring. These follow-up assessments should also consider other suitable locations where modelling data were unavailable. Analogous to the ‘Floodplain or lowland riverine’ landscape group, a more detailed and local consideration of risk needs to consider the specific values at the location that community are seeking to protect (e.g. particular assets), and bring in other lines of evidence that include the magnitude of the hydrological change and the qualitative mathematical models.
There was a considerable proportion (80%) of the potentially impacted landscape classes in this group where ecological impacts could not be quantified due to a lack of surface water modelling data (Table 24 and Figure 36). While much of these unquantified areas are upstream of the areas of coal resource development, this current analysis only applies to a limited extent of the upland riverine landscape classes. The subsequent sections describe the specific results of each model that contribute to the observed location and magnitude of risks described here.
The level of risk: ‘at minimal risk of ecological and hydrological changes’ (‘at minimal risk’), ‘at some risk of ecological and hydrological changes’ (‘at some risk’) and ‘more at risk of ecological and hydrological changes’ (‘more at risk’) is presented for different assessment units where the receptor impacts are modelled for the different landscape classes. Remaining assessment units for the relevant landscape classes in the ‘Non-floodplain or upland riverine’ landscape group without receptor impact modelling and surface water modelling are also shown (green). Extent captures areas with ‘at some risk’ or ‘more at risk’ assessment units.
Data: Bioregional Assessment Programme (Dataset 5)
3.4.4.3.1 Upland riverine
The receptor impact model for upland riverine landscape classes modelled the relationship between cease-to-flow hydrological response variables (zero-flow days and maximum zero-flow spells) and two receptor impact variables: average number of families of aquatic macroinvertebrates in edge habitat and the probability of presence of tadpoles from the Limnodynastes genus (L. dumerilii, L. salmini, L. interioris and L. terraereginae) (see Table 24).
There were no detectable differences in predicted mean changes in either average number of families of aquatic macroinvertebrates or the probability of presence of tadpoles across the upland riverine landscape classes between the baseline and CRDP futures across the different percentile simulation periods (2042 and 2102) (Figure 37a and c). However, an assessment of the modelled changes in the number of families of aquatic macroinvertebrates or the probability of presence of tadpoles at a given assessment unit identified locations across the extent of the lowland riverine landscape classes that are at risk due to coal resource development (Figure 37b and d). Declines in the average number of families of aquatic macroinvertebrates due to additional coal resource development were similar between simulation periods and ranged from approximately –12 families at the 5th percentile to approximately –3 families at the 50th percentile (Figure 37b). An increase in the average number of families of aquatic macroinvertebrates was observed at the 95th percentile (Figure 37b). Changes in the probability of tadpoles ranged from approximately –0.7 to –0.2 between the 5th and 50th percentile and was greater for the simulation period to 2042 (Figure 37d).
Box and whisker plots of modelled (a) average number of families of aquatic macroinvertebrates and (c) probability of the presence of tadpoles in 2042 and 2102 in upland riverine landscape classes under both baseline and coal resource development pathway (CRDP) futures. Differences in (b) average number of families of aquatic macroinvertebrates and (d) probability of the presence of tadpoles between CRDP and baseline futures for each assessment unit containing upland riverine landscape classes.
The relevant thresholds used to delineate changes in the receptor impact variable associated with ‘at some risk of ecological and hydrological changes’ and ‘more at risk of ecological and hydrological changes’ are indicated by the orange and red dashed horizontal lines.
Data: Bioregional Assessment Programme (Dataset 5)
3.4.4.3.2 Upland riparian forest GDE
The receptor impact model for the ‘Upland riparian forest GDE’ landscape class was based on the relationship between the effect of changes in groundwater drawdown and the frequency of overbank flows on projected foliage cover in the riparian trees (dominated by C. cunninghamiana) (see Table 24).
Projected foliage cover estimates between the baseline and CRDP were similar across different model percentiles and ranged from 0.09 to 0.47 from the 5th to 95th percentiles, respectively (Figure 38a). There were only a small number of assessment units where projected foliage cover was predicted to decline at the 5th percentile, and no assessment units at the 50th percentile for either simulation period (2042) (Figure 38b). The limited change in this receptor impact variable is consistent with the associated hydrological response variables, where very small parts of the ‘Upland riparian forest GDE’ landscape class were exposed to changes in additional groundwater drawdown or the frequency of overbank flows.
(a) Box and whisker plots of projected foliage cover for 2042 and 2102 in upland riparian forests in under both baseline and coal resource development pathway (CRDP) futures. (b) Difference in projected foliage projected cover between CRDP and baseline futures for each assessment unit containing ‘Upland riparian forest GDE’ classes
Data: Bioregional Assessment Programme (Dataset 5)
