2.7.5.1.1 Overview
The ‘Floodplain, terrestrial GDE’ landscape group contains two landscape classes within the zone of potential hydrological change of the Galilee subregion: ‘Terrestrial GDE’ and ‘Terrestrial GDE, remnant vegetation’ (see Section 2.3.3 of companion product 2.3 for the Galilee subregion (Evans et al., 2018b)). The first landscape class comprises non-remnant vegetation whereas the second landscape class comprises remnant vegetation. The classification does not distinguish between artesian and non-artesian groundwater sources. The zone contains 2358 km2 of ‘Terrestrial GDE, remnant vegetation’ compared to 75.2 km2 of ‘Terrestrial GDE’ (Figure 24). These two landscape classes are type three GDEs following the typology of Richardson et al. (2011). These are terrestrial GDEs that rely on the subsurface expression of groundwater on a permanent or intermittent basis to maintain growth or to avoid water stress and adverse impacts on condition (Eamus et al., 2006; Richardson et al., 2011).
In the landscape classification adopted here, these landscape classes would be broadly defined as groundwater-dependent vegetation assemblages (mostly woodlands or shrublands) that occur on floodplains but are not associated with palustrine, lacustrine or riparian wetlands. Floodplains are broadly defined as a collection of landscape and ecological elements exposed to inundation or flooding along a river system (Rogers, 2011). Within the Lake Eyre Basin, floodplains are considered to be alluvial plains that have an average recurrence interval of 50 years or less for channelled or overbank streamflow (Aquatic Ecosystems Task Group, 2012). Patterns of flooding and drying are a key driver of spatial and temporal variability in vegetation in these areas (Capon et al., 2016).
Companion product 2.3 for the Galilee subregion (Evans et al., 2018b) identified two high-level conceptual models relevant to this landscape group: GDEs: alluvia – lower catchment; and GDEs: alluvia – closed drainage systems (Figure 25). These conceptual models are presented and discussed in more detail in DSITI (2015). Here, a brief description is given for context. The floodplains are commonly underlain by sediments deposited in fluvial (riverine) environments. The alluvial aquifers that support these groundwater-dependent landscape classes are formed from particles such as sand, silt and/or clay deposited within channels or on floodplains as a result of highly intermittent flooding processes. Floodplains in the lower parts of catchment areas tend to be much wider and deeper than alluvial floodplains that occur in higher parts of the catchments.
Climatically, areas occupied by the ‘Floodplain, terrestrial GDE’ landscape group are water limited, annual rainfall is low (about 300 mm/year) and evaporation is high (greater than 2000 mm/year) (companion product 1.1 for the Galilee subregion (Evans et al., 2014)). Low and sporadic rainfall coupled with high evaporative demand suggest that groundwater may be a more reliable source of water for the landscape group than surface water (Eamus et al., 2006). Several processes, acting either individually or in combination, control recharge into these alluvial aquifers including direct infiltration of rainfall, inundation by floodwaters or discharge from surrounding water-bearing rock types (Figure 25).
GDE = groundwater-dependent ecosystem
Data: Bioregional Assessment Programme (Dataset 1)
GDE = groundwater-dependent ecosystem
Source: adapted from Queensland Department of Science, Information Technology and Innovation (Dataset 2), © The State of Queensland (Department of Science, Information Technology and Innovation) 2015
2.7.5.1.2 Hydrological regimes and connectivity
Understanding the connectivity of groundwater in the zone of potential hydrological change is complicated both because the Galilee subregion contains a series of stacked groundwater systems and by a paucity of data in some areas. The groundwater systems are described in detail in companion product 2.1-2.2 (Evans et al., 2018a) and Section 2.3.2 of companion product 2.3 (Evans et al., 2018b) for the Galilee subregion and are summarised below to provide context.
Shallow groundwater systems in alluvial sediments that underlie floodplains may take the form of perched aquifer systems isolated from the regional watertable, or in groundwater systems that are connected with deeper aquifers that are not in the alluvial sediments. The degree of connection between deeper aquifers and shallow aquifers in alluvial sediments is governed by a number of factors including variations in hydraulic head (pressure) in the different aquifer systems, and whether sedimentary layers in alluvial deposits impede upward groundwater movement from underlying aquifers. If there is sufficient hydraulic head in underlying aquifers and a connective pathway exists, then groundwater may discharge from underlying aquifers into overlying aquifers in alluvial sediments. This may occur if there is not a sufficiently competent aquitard (e.g. thick clay-rich layers) to impede upwards groundwater flow. Aquifers that may have potential to discharge to overlying alluvial sediments in the zone of potential hydrological change (within the Burdekin river basin) include the: Clematis Group, Dunda beds (the more permeable upper part of the Rewan Group), upper Permian coal measures and Joe Joe Group.
Potentiometric mapping of different aquifer systems outlined in companion product 2.1-2.2 for the Galilee subregion (Evans et al., 2018a) suggests that areas where there is potential for discharge from deeper aquifers to overlying alluvium include where the:
- Clematis Group and Dunda beds aquifers occur near-surface under shallow cover of the Moolayember Formation, or where these units directly underlie alluvium in the Carmichael River valley (e.g. in the vicinity and downstream of the Doongmabulla Springs complex)
- Belyando River floodplain is underlain by the upper Permian coal measures and/or the Joe Joe Group, in particular in the vicinity of the confluence of the Carmichael River and the Belyando River (this includes the Mellaluka Springs complex and Albro Springs).
Further information about the variability of the depth to the watertable in the zone of potential hydrological change (i.e. the standing water level observed in groundwater bores) is provided in Section 3.4.1 of companion product 3-4 for the Galilee subregion (Lewis et al., 2018).
Connection between surface water features and shallow groundwater in floodplain environments will vary depending on local geological conditions (e.g. distribution of sand-rich sediments in the floodplain), hydrogeological characteristics (e.g. flow system dynamics), and climatic events. For instance, after high rainfall events groundwater levels can rise to a point resulting in temporary discharge to streams. During drier periods groundwater levels can fall to a point where the reverse process may occur, with surface water recharging shallow groundwater.
Regardless of aquifer configuration and connectivity, vegetation can draw from groundwater if the watertable, or capillary zone that can form above the watertable, comes within reach of a plant’s root system (generally within 20 m of the surface). The majority of vegetation that forms the ‘Floodplain, terrestrial GDE’ landscape group is likely to source groundwater from alluvium and Cenozoic sediments. As a result, GDEs connected to regional groundwater systems within the zone of potential hydrological change may be impacted by changes in groundwater due to additional coal resource development (for example, from drawdown or reduced recharge) across a broad area.
2.7.5.1.3 Ecological processes
The water requirements and the degree of groundwater dependency of the vegetation that occupies the ‘Floodplain, terrestrial GDE’ landscape group will depend on a number of factors including:
- age and rooting distribution of plants and how this enables access to the watertable
- depth to the watertable, and any spatial and temporal (seasonal) variation in watertable levels
- groundwater quality.
Vegetation within the ‘Floodplain, terrestrial GDE’ landscape group will typically use deep roots to access groundwater in the capillary zone above the watertable via capillary action or hydraulic lift. A baseline assumption with the physiology of Australian plants is that they can access groundwater to a depth to 10 m (D Eamus, 2016, pers. comm.). This value is supported by research that found the mean maximum rooting depth across 11 species of sclerophyllous trees to be 12.6 m ± 3.4 m (standard error) (Canadell et al., 1996). However, some tree species have roots that can access water at much greater depths. As an example of the potential of eucalypt roots to access water at depth, Eucalyptus marginata roots in south-western Australia are reported to reach depths of 40 m by Dell et al. (1983).
It is generally assumed that groundwater dependency of vegetation will change seasonally with rainfall and be greatest at times of seasonal rainfall deficit. There is empirical support for this viewpoint. For example, in eucalypt woodland along the Condamine River, southern Queensland, the frequency of deep subsurface water use was greatest in the late dry season (Gow et al., 2016).
The depth to the watertable is an important factor in determining the volume of water discharged through GDEs. In the Galilee subregion, the average depth to standing water level of 250 bores in the ‘Terrestrial GDE, remnant vegetation’ landscape class is 20.9 m below surface, with a wide range of 152.5 to 3.3 m depth below surface. The bores from which the measurements were taken cover a variety of aquifer systems including: alluvial sediments (49 bores); Paleogene sediments (43 bores); other types of Cenozoic sediments (25 bores); Hooray Sandstone (20 bores); Clematis Group aquifer (7 bores); upper Permian coal measures (9 bores); Wallumbilla Formation (24 bores); and Winton-Mackunda Formation aquifer (40 bores). In the ‘Terrestrial GDE’ landscape class (i.e. non-remnant vegetation GDEs) the average depth to groundwater across 17 bores is 33 m below surface, with a range of 90 to 4 m depth below surface.
Currently, there is little published information on either the amount of water used by GDEs or the physiology of GDEs. Similarly, there is a knowledge gap in terms of information on root depth of vegetation within GDEs and on responses to changes in depth-to-groundwater (Eamus et al., 2015). This information, if it were available, would be invaluable in assessing the potential impacts of groundwater drawdown on GDEs.
2.7.5.1.4 Vegetation
Within the Galilee subregion’s zone of potential hydrological change, the ‘Floodplain, terrestrial GDE’ landscape group supports over 85 regional ecosystems (REs). There is considerable uncertainty related to the water regime required to support many of these REs. However, the nature of the dependency on groundwater is likely to vary among and within vegetation communities, as a function of groundwater availability, depth and quality (companion product 2.1-2.2 for the Galilee subregion (Evans et al., 2018a)).
The distribution of the most widespread vegetation assemblages, represented by REs, within the ‘Floodplain, terrestrial GDE’ landscape group is shown in Figure 26. The majority of these REs have Eucalyptus or Corymbia or Acacia species as dominant/co-dominant in the upper storey. Specifically, eucalypt woodlands dominate the alluvial river and creek-flat land zone. Eucalyptus brownii or E. coolabah woodlands and open woodlands dominate the alluvial plains. Acacia woodlands, including A. cambagei are also common on the alluvial plains. Smaller areas of Corymbia woodlands are associated with alluvial plains. The most widespread REs in the ‘Floodplain, terrestrial GDE’ landscape group within the zone listed in order of decreasing area (expressed as a percentage of the zone) (Figure 26) are:
- RE 10.3.28 ‘Eucalyptus melanophloia or E. crebra woodland to open woodland on sandy alluvial fans’ (4.31%)
- RE 10.3.6 ‘Eucalyptus brownii woodland to open woodland on alluvial plains’ (2.89%)
- RE 11.3.3 ‘Eucalyptus coolabah woodland on alluvial plains’ (1.90%)
- RE 11.3.5 ‘Acacia cambagei woodland on alluvial plains’ (1.68%)
- RE10.3.27 ‘Eucalyptus populnea woodland to open woodland on alluvial plains’ (1.47%)
- RE 11.3.2 ‘Eucalyptus populnea woodland on alluvial plains’ (0.97%)
- RE 11.3.10 ‘Eucalyptus brownii woodland on alluvial plains’ (0.91%)
- RE 11.3.7 ‘Corymbia spp. woodland on alluvial plains’ (0.42%)
- RE 10.3.14 ‘Eucalyptus camaldulensis and/or E. coolabah woodland to open woodland along channels and on floodplains’ (0.34%)
- RE 10.3.4 ‘Acacia cambagei low open woodland to low woodland on alluvial plains’ (0.31%)
- RE 10.3.3 ‘Acacia harpophylla and/or Eucalyptus cambageana low open woodland to open woodland on alluvial plains’ (0.26%).
Canopy cover in these woodlands and open woodlands tends to be sparse, with sparse or scattered understories, dominated by grasses such as Aristida spp. and Triodia spp.
GDE = groundwater-dependent ecosystem
Data: Bioregional Assessment Programme (Dataset 1, Dataset 3)
Two threatened ecological communities occur within the ‘Floodplain, terrestrial GDE’ landscape group. ‘Brigalow (Acacia harpophylla dominant and co-dominant)’ is listed under the Commonwealth’s Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) as an ‘Endangered’ ecological community. This ecological community is predicted to occur widely in the eastern half of the Galilee subregion zone of potential hydrological change (Department of the Environment and Energy, 2017a). The vegetation types that make up the brigalow ecological community mostly occur on acidic and salty clay soils. Within the zone these are mostly on deep cracking clay soils. Gilgai may be present in these areas. The dominant landform on which this ecological community occurs is flat to gently undulating clay plains that are not associated with recently deposited alluvium. It is also present on gently undulating areas on fine-grained sedimentary rocks.
‘Weeping Myall Woodlands’ is listed under the EPBC Act as an ‘Endangered’ ecological community. The ecological community is predicted to occur widely in the south-eastern section of the zone (Department of the Environment and Energy, 2017b). It occurs on flat areas or shallow depressions on alluvial plains. Such areas are not associated with river channels and are rarely flooded. The soils are black, brown, red-brown or grey clay or clay loam (Commonwealth of Australia, 2009). The ‘Weeping Myall Woodlands’ ecological community is likely to be present in the ‘Floodplain, terrestrial GDE’ landscape group within the zone.
2.7.5.1.5 Flora and fauna
The ‘Floodplain, terrestrial GDE’ landscape group provides potential habitat for a range of threatened plant and animal species. These are detailed below.
The potential habitat of the koala (Phascolarctos cinereus) occurs within the zone of potential hydrological change. Koalas that occur in Queensland, NSW and the ACT are considered as a combined management unit that is listed nationally as ‘Vulnerable’ under the EPBC Act (Department of the Environment and Energy, 2017c). Koalas in the remainder of Australia are not listed as threatened. The koala is also listed as ‘Vulnerable’ under Queensland’s Nature Conservation Act 1992 (Nature Conservation Act). Within the zone of potential hydrological change of the Galilee subregion, koala habitat occurs in the ‘Floodplain, terrestrial GDE’ landscape group. Koalas in semi-arid environments, including the zone, inhabit forest and woodland dominated by Eucalyptus species in riparian and non-riparian areas. Important food and habitat trees for koalas in semi-arid Queensland include Eucalyptus camaldulensis, E. populnea, E. crebra, E. tereticornis, E. melanophloia, E. tessellaris and Melaleuca bracteata (Gordon et al., 1988; Ellis et al., 2002). Apart from E. camaldulensis, which is largely restricted to the riverine landscape groups, many of the other important food and habitat trees of koalas are dominant components of the regional ecosystems within the ‘Floodplain, terrestrial GDE’ landscape group (E. populnea, E. tereticornis, E. melanophloia).
The ornamental snake (Denisonia maculata) occurs within the Galilee subregion zone of potential hydrological change. The species is listed as ‘Vulnerable’ under both the EPBC Act and the Nature Conservation Act (Department of the Environment and Energy, 2017d). Within the zone, it occupies the ‘Floodplain, terrestrial GDE’ landscape group. The ornamental snake is considered to be water-dependent as it feeds almost exclusively on frogs. It occurs in riparian vegetation along watercourses, on the margins of wetlands including lakes and swamps and in terrestrial vegetation that is likely to be groundwater-dependent. The latter category includes woodland and open woodland of coolibah (Eucalyptus coolabah), poplar box (E. populnea), brigalow (Acacia harpophylla), gidgee (A. cambagei) and blackwood (A. argyrodendron) (Department of the Environment and Energy, 2017d). The REs in which it has been found all have clay soils. These REs include 11.4.3, 11.4.6, 11.4.8 and 11.4.9 (Department of the Environment and Energy, 2017d).
Dunmall’s snake (Furina dunmalli) potentially occurs within the zone. The species is listed as ‘Vulnerable’ under both the EPBC Act and the Nature Conservation Act (Department of the Environment and Energy, 2017e). In Queensland, the range of Dunmall’s snake is mostly within the Brigalow Belt region to the east of the zone. Dunmall’s snake inhabits terrestrial vegetation. The two main types of environment in which it occurs are:
- forest and woodland on black alluvial cracking clay and clay loams dominated by brigalow (Acacia harpophylla), other acacias (A. brownii, A. deanei, A. leiocalyx), cypress (Callitris spp.) or bulloak (Allocasuarina luehmannii)
- open forest and woodland on sandstone-derived soils dominated by blue spotted gum (Corymbia citriodora), ironbarks (Eucalyptus crebra and E. melanophloia), white cypress (Callitris glaucophylla) and bulloak (Allocasuarina luehmannii).
The species seems unlikely to be water-dependent. The potential range of the species within the Galilee subregion zone of potential hydrological change includes the ‘Floodplain, terrestrial GDE’ landscape group.
The yakka skink (Egernia rugosa) is a threatened lizard that occurs within the Galilee subregion zone of potential hydrological change. It is listed as ‘Vulnerable’ under both the EPBC Act and the Nature Conservation Act (Department of the Environment and Energy, 2017f). The species occurs in woodland and open forest dominated by a range of trees including Acacia, Eucalyptus, Casuarina and Callitris. Yakka skinks are burrowing animals that occur in colonies or small groups (Chapple, 2003). Within the zone the yakka skink is likely to occupy sand plains, clay and clay loam plains, sandstone rises and minor pediments and vegetation fringing watercourses and stream channels and on alluvial plains. Therefore, it is expected to occupy all the landscape groups within the zone with the exception of the ‘Springs’ landscape group. The water-dependency of the species is poorly understood.
The southern subspecies of the squatter pigeon (Geophaps scripta scripta) is listed as ‘Vulnerable’ under both the EPBC Act and the Nature Conservation Act (Department of the Environment and Energy, 2017g). It is a granivorous bird that occurs through much of the zone. It was recorded during surveys as part of the environmental impact statements for five of the proposed coal mine developments in the zone. From north to south these are China Stone, Carmichael, Kevin’s Corner, Alpha, and China First. The squatter pigeon (southern) forages and breeds in a range of open-forest, woodland and open-woodland vegetation types that have a grassy understory. It depends on surface water as it needs to drink on a daily basis and, as a consequence, foraging and nesting sites are located within 3 km of a water source. Water sources used by the species include rivers, lakes and artificial sources such as farm dams (Department of the Environment and Energy, 2017g). Therefore, the squatter pigeon uses water available in the ‘Floodplain, terrestrial GDE’ landscape group.
The red goshawk (Erythrotriorchis radiatus) is listed as ‘Vulnerable’ nationally (EPBC Act) and ‘Endangered’ in Queensland (Nature Conservation Act). The range of this species includes small areas of the Galilee subregion zone of potential hydrological change. The species can be considered to be water-dependent because of the nest sites it uses. Nests are constructed in tall trees (mean height of 31 m) that are located within 1 km of, and often beside, permanent water. Water sources include rivers, swamps and pools (DERM, 2012). Given this nesting preference, the red goshawk is mostly likely to occur within the riverine landscape groups and the ‘Floodplain, terrestrial GDE’ landscape group within the zone.
The southern subspecies of the black-throated finch (Poephila cincta cincta) is classified as ‘Endangered’ nationally (EPBC Act) and in Queensland (Nature Conservation Act). This threatened species occurs throughout the Galilee subregion zone of potential hydrological change and adjacent areas (Vanderduys et al., 2016). The black-throated finch was located during surveys as part of environmental impact statements and subsequent surveys at Carmichael (nine locations) and China Stone (eight locations) coal mine developments. The black-throated finch occupies grassy woodland within the zone. It is surface water dependent. The finch feeds mostly on the ground on a range of grass seeds. It occupies several vegetation assemblages within the ‘Floodplain, terrestrial GDE’ and ‘Non-floodplain, terrestrial GDE’ landscape groups. Important Res for the black-throated finch in the zone are listed below (based on GHD, 2012; Vanderduys et al., 2016):
- RE 10.3.6 ‘Eucalyptus brownii woodland to open woodland on alluvial plains’
- RE 10.3.28 ‘Eucalyptus melanophloia or E. crebra woodland to open woodland on sandy alluvial fans’
- RE 10.5.1 ‘Eucalyptus similis and/or Corymbia brachycarpa and/or Corymbia setosa low open woodland on sand plains’
- RE 10.5.5 ‘Eucalyptus melanophloia woodland to open woodland on sand plains’. This is the dominant RE where the black-throated finch occurs on the Carmichael mine lease (GHD, 2012)
- RE 10.7.11 ‘Eucalyptus melanophloia low open woodland on ferricrete’.
The species also occurs in non-remnant vegetation (GHD, 2012).
