3.4.4 'Streams, GDE' landscape group


3.4.4.1 Description

The Galilee subregion includes the headwaters of six major surface water catchments: Cooper Creek – Bulloo, Diamantina, Flinders, Warrego, Burdekin and Fitzroy. Approximately 12% of all streams in the assessment extent are considered groundwater dependent (Table 19). Of the main river catchments, only the Burdekin river basin and the Cooper Creek – Bulloo river basin (Alice River) intersect the zone of potential hydrological change. Most watercourses in the zone of potential hydrological change are contained within the upper catchment of the Belyando River, part of the larger Burdekin river basin.

It is important to note the classification of streams as either groundwater dependent (‘Streams, GDE’) or non-groundwater dependent (‘Streams, non-GDE’) is based on the landscape classification approach adopted for the BA for the Galilee subregion. The methodology that underpins this classification is documented in Section 2.3.3 of companion product 2.3 for the Galilee subregion (Evans et al., 2018b). Information relating to the water source for all streams classified in the Galilee assessment extent was obtained from the Queensland Herbarium’s GDEs and shallow watertable aquifer dataset (Queensland Herbarium, Department of Science, Information Technology, Innovation and the Arts, Dataset 10). This dataset was considered fit for purpose and adopted ‘as is’ for use in the BA without additional scrutiny. However, with the recent advent of the various Digital Earth Australia products described in Section 3.2.3.3, it may be possible to revisit this original classification and enhance the accuracy of the streams classification at some stage in the future (although this could not be done for this impact and risk analysis due to operational constraints).

Almost half of the 6285 km of streams in the zone of potential hydrological change are classed as groundwater dependent (2801 km or 45% of streams in the zone) (Table 19). The ‘Streams, GDE’ landscape group includes four landscape classes that are classified based on water regime (near-permanent or temporary) and landscape position (lowland or upland). Most streams in the zone of potential hydrological change have a temporary water regime. The ‘Temporary, lowland GDE stream’ landscape class includes 2063 km of streams and ‘Temporary, upland GDE stream’ landscape class includes 478 km of streams. The zone also includes 260 km of groundwater-dependent streams with a near-permanent water regime, including 253 km classified as ‘Near-permanent, lowland GDE stream’ and about 7 km classified as ‘Near-permanent, upland GDE stream’.

Surface water – groundwater connectivity ranges from gaining or variably gaining to losing-disconnected (Figure 44). Shallow groundwater may discharge into rivers as baseflow from upward leakage from sandstone aquifers such as the Hooray Sandstone, Hutton Sandstone, Clematis Group and Ronlow beds (companion product 1.1 for the Galilee subregion (Evans et al., 2014, p. 113)).

Figure 44

Figure 44 Conceptual model of a riverine landscape in the Galilee assessment extent showing seasonal variation in streamflow and surface water - groundwater connectivity

GDE = groundwater-dependent ecosystem

Source: adapted from Queensland Department of Science, Information Technology and Innovation (Dataset 4), © The State of Queensland (Department of Science, Information Technology and Innovation) 2015

Groundwater may also discharge into springs that create outflow pools in rivers. For instance, Fensham et al. (2016) noted that where outflow from Joshua Spring and the House Springs group (both part of the larger Doongmabulla Springs complex) converge, they provide the main water source of the Carmichael River for a distance of up to 20 km (Fensham et al., 2016). The analysis of time-series Landsat data (see Section 3.2 and Section 3.5 for details) indicates that some spring pools (e.g. Moses-Keelback and Wobbly springs pools) over the last 30 years have been temporally persistent during dry periods, providing strong evidence for their groundwater dependence.

Groundwater may also be important in providing moisture for terrestrial vegetation associated with the ‘Streams, GDE’ landscape group. This includes shallow groundwater (<20 m depth to watertable) that is transpired by deep-rooted riparian trees such as river red gums and other species (Section 2.3.2 of companion product 2.3 for the Galilee subregion (Evans et al., 2018b)).

Within the zone of potential hydrological change, annual streamflow shows a high degree of interannual variability (companion product 1.1 for the Galilee subregion (Evans et al., 2014)). Flows in a given year can vary from almost no flow to major floods. Mean monthly flow is also highly variable. Flows vary between months with minimal to no flow from July to October, while most flows occur between December and April. The streamflow regime within the zone is thus characterised as one of dry seasonal flows (Kennard et al., 2010).

Despite the influence of groundwater, the ‘Streams, GDE’ landscape group within the zone of potential hydrological change is characterised by a ‘boom–bust’ ecology. Specifically, diversity in the ecosystem is maintained by natural cycles of river flow and drying, driven by surface water inputs (Sternberg et al., 2015). Although the more arid rivers further west in the Galilee subregion are driven by highly unpredictable rainfall (e.g. Cooper Creek – Bullo River), the ‘boom–bust’ cycle in the Belyando river basin is more predictable and generally follows an annual hydrological cycle (Blanchette and Pearson, 2012, 2013). Ecological processes within the zone operate in an environmental context where there is seasonally predictable summer rainfall, which produces a resource pulse that is followed by a predictable period of drying. The drying phase is relatively consistent, that is, in an average year, uninterrupted by rainfall outside the summer months (Blanchette and Pearson, 2013).

During the months of high rainfall (generally between December and April), dry rivers begin to flow and seasonally isolated water-dependent habitats (e.g. waterholes) are connected. This annual period of in-channel flow, or flow pulses, may be associated with large floods producing overbank flow (see below) or it may occur independently in response to localised rainfall (Sheldon et al., 2010). Flooding occurs at unpredictable intervals in response to periods of very high rainfall (i.e. it is not an annual occurrence). During high rainfall periods, there is overbank flow and the environment becomes a large network of interconnected river channel and floodplain habitat. Overbank floods are used to identify the ‘boom’ phase in Australia’s dryland rivers (e.g. Sheldon et al., 2010).

During the ‘boom’ phase, aquatic and terrestrial productivity is high. Dispersal of freshwater fauna occurs during this phase and important life-history stages are completed. A significant part of the aquatic fauna in this system is capable of long-distance dispersal, with animals recolonising areas from distant waterholes once movement pathways are opened by flooding. Fish are a prime example of such a group (e.g. Kerezsy et al., 2013). At the end of the wet phase, all of the waterholes are likely to be replenished and at their most ecologically productive.

Thus, the ‘Streams, GDE’ landscape group in the zone of potential hydrological change experiences annual in-channel flows each summer and floods at irregular intervals. In-channel flows are important for maintaining connectivity and dispersal of aquatic organisms; however, they do not feature the high primary productivity of overbank floods (Sheldon et al., 2010).

During the months of low or no rainfall (generally May to November) drying of the drainage system produces a series of waterholes and running reaches that have variable connectivity (Pusey and Arthington, 1996). Where the drying causes streams to cease to flow, shallow waterbodies dry out and a chain of pools, isolated pools or completely dry riverbeds result, depending on riverbed geomorphology. As conditions continue to dry, evaporation reduces the depth of each waterhole. Over time, changes to productivity and physico-chemical conditions occur, including changes to dissolved oxygen, conductivity and pH (Blanchette and Pearson, 2013). Groundwater inputs may maintain water levels in waterholes during this ‘bust’ phase.

Waterholes during low-flow or no-flow periods tend to be characterised by high turbidity and limited light penetration. Aquatic food webs in these waterholes are typically driven by energy inputs from filamentous algae that form as a highly productive band in the shallow littoral margins. Phytoplankton blooms and zooplankton may also be important parts of the aquatic food web during the ‘bust’ phase. The algae, phytoplankton and zooplankton support large populations of snails, crustaceans and fish (Bunn et al., 2003).

3.4.4.2 Potential hydrological impacts

Two receptor impact models were developed in the qualitative modelling workshops for the ‘Streams, GDE’ landscape group (companion product 2.7 for the Galilee subregion (Ickowicz et al., 2018)). One receptor impact model focused on the response of woody riparian vegetation to changes in flow regime and groundwater. The other examined the response of a high-flow macroinvertebrate (mayfly nymphs in the genus Offadens, family Baetidae) to changes in the flow regime.

For the ‘Woody riparian vegetation’ receptor impact model, the relevant hydrological response variables are:

  • maximum difference in drawdown under the baseline future or under the coal resource development pathway future relative to the reference period (1983 to 2012) (dmaxRef)
  • number of days per year with low flow (<10 ML/day), averaged over a 30-year period (LQD, subsequently referred to in this Section as ‘low-flow days’), using a modelled 10 ML/day threshold to represent a flow threshold of 1 ML/day used during the expert elicitation
  • mean annual number of events with a peak daily flow exceeding the threshold (the peak daily flow in flood events with a return period of 2.0 years as defined from modelled baseline flow in the reference period (1983 to 2012)). This metric is designed to be approximately representative of the number of overbank flow events in future 30-year periods (EventsR2.0).

For the ‘High-flow macroinvertebrate’ receptor impact model, the hydrological response variables are:

  • number of days per year with low flow (<10 ML/day), averaged over a 30-year period (LQD)
  • maximum length of spells (in days per year) with low flow, averaged over a 30-year period (LME), using a modelled 10 ML/day threshold to represent an ecological flow threshold of 1 ML/day used during the expert elicitation.

3.4.4.2.1 Groundwater

Streams classified as ‘Temporary, upland GDE stream’ in the zone of potential hydrological change are located along the western edge of the zone, upstream of the proposed Hyde Park and China Stone coal mines in the north and upstream of the proposed Kevin’s Corner, Alpha and South Galilee mines in the south (Figure 45). Streams classified as ‘Temporary, lowland GDE stream’ intersect and flow downstream of the seven proposed mines in the northern and southern parts of the zone of potential hydrological change.

Most of the groundwater-dependent streams in the zone of potential hydrological change have a temporary water regime (2541 of 2801 km). It is very unlikely that additional drawdown in excess of 0.2 m will affect more than 1597 km of streams classified as ‘Temporary, lowland GDE stream’ and 466 km of streams classified as ‘Temporary, upland GDE stream’ (Figure 46 and Table 21). None of the 260 km of groundwater-dependent streams with a near-permanent water regime are in areas where additional drawdown in excess of 0.2 m is predicted.

The median (50th percentile) estimate of greater than 2 m drawdown due to additional coal resource development is less extensive, potentially affecting 186 km, or 7% of groundwater-dependent streams in the zone (Table 21). Additional drawdown in excess of 5 m is very unlikely to affect more than 173 km of groundwater-dependent streams.

Figure 45

Figure 45 (a) 'Streams, GDE' and (b) 'Streams, non-GDE' landscape groups: location of streams in the zone of potential hydrological change in the Galilee subregion

ACRD = additional coal resource development; GDE = groundwater-dependent ecosystem

Data: Bioregional Assessment Programme (Dataset 9)

Figure 46

Figure 46 'Streams, GDE' landscape group: length (km) of groundwater-dependent streams potentially exposed to varying levels of additional drawdown in the zone of potential hydrological change

GDE = groundwater-dependent ecosystem

Data: Bioregional Assessment Programme (Dataset 1)


Table 21 ‘Streams, GDE’ landscape group: length (km) of groundwater-dependent streams potentially exposed to varying levels of additional drawdown in the zone of potential hydrological change


Landscape class

Length in assessment extent

Length in zone of potential hydrological change

Length in mine exclusion zone

Length with additional drawdown ≥0.2 m

Length with additional drawdown ≥2 m

Length with additional drawdown ≥5 m

5th

50th

95th

5th

50th

95th

5th

50th

95th

Near-permanent, lowland GDE stream

408

253

0

0

0

0

0

0

0

0

0

0

Near-permanent, upland GDE stream

52.0

6.7

0

0

0

0

0

0

0

0

0

0

Temporary, lowland GDE stream

40,798

2063

62.5

181

427

1597

56.2

162

333

15.8

75.2

151

Temporary, upland GDE stream

7,280

478

4.6

24.4

128

466

5.6

24.4

94.1

0.4

6.9

21.7

Subtotal

48,538

2801

67.0

205

555

2063

61.8

186

427

16.2

82.1

173

Some totals reported here have been rounded.

GDE = groundwater-dependent ecosystem

Data: Bioregional Assessment Programme (Dataset 1)


3.4.4.2.2 Surface water

Roughly half of the groundwater-dependent streams in the zone of potential hydrological change are not predicted to experience changes to the surface water regime (Figure 47). This includes 1095 km of groundwater-dependent streams located in the groundwater zone of potential hydrological change, but outside of the surface water zone of potential hydrological change. There are 753 km of groundwater-dependent streams in the surface water zone of potential hydrological change that are potentially impacted but not quantified. This includes parts of Bimbah, Bully, Dyllingo and North creeks and the Carmichael and Belyando rivers in the northern zone, and Sandy Creek in the southern zone (Figure 48). Potential surface water impacts could not be quantified for these streams as they were not specifically included in the surface water modelling (i.e. no model nodes were assigned to these streams).

In 2042, it is very unlikely that more than 606 km of groundwater-dependent streams will be affected by increases in modelled low-flow days in excess of 3 days per year (Figure 48 and Table 22). This includes parts of Bully and North creeks, and the Belyando and Suttor rivers, in the northern part of the zone and Sandy Creek in the southern zone. Low-flow days are predicted to increase by more than 20 days per year in a 10-km stretch of North Creek in this time period. Coal resource development is predicted to increase the number of low-flow days by more than 3 days per year along 634 km of groundwater-dependent streams by 2102. This includes parts of the Belyando and Suttor rivers in the northern zone and Native Companion Creek and the Belyando River in the southern zone (Figure 49).

Increases to modelled average annual low-flow spells of more than 3 days are very unlikely to affect more than 101 km of groundwater-dependent streams by 2042 (Figure 48). This includes parts of Bully, North and Sandy creeks (Figure 48 and Table 23). In 2102, increased average annual low-flow spells of more than 3 days are very unlikely to affect more than 648 km of modelled groundwater-dependent streams, including much of the Belyando and Suttor rivers and Native Companion Creek in the surface water zone of potential hydrological change (Figure 49).

It is very unlikely that modelled overbank flows will decrease by more than 0.1 events per year along more than 101 km of groundwater-dependent streams in the zone of potential hydrological change (Figure 48 and Table 24). This includes parts of Bully, North and Sandy creeks and the Belyando and Suttor rivers. A reduction of 0.1 events per year means one fewer overbank flow events every 10 years on average. Based on the median estimate, the number of modelled overbank flows per year is predicted to decrease by more than 0.1 along 10 km, 0.05 along 61 km and 0.02 along 121 km of groundwater-dependent streams in the 30-year period preceding 2042. Predictions in the 30-year period preceding 2102 are less extensive; median estimates of the number of modelled overbank flows per year are predicted to decrease by more than 0.02 along less than 10 km of groundwater-dependent streams in the zone of potential hydrological change (Figure 49).

Figure 47

Figure 47 'Streams, GDE' landscape group: length (km) of groundwater-dependent streams potentially exposed to changes to low-flow days per year (LQD), low-flow spells per year (LME) and recurrence of overbank flows per year (EventR2.0) in 2042 and 2102 in the zone of potential hydrological change

There are no results for the 5th percentile of any of the hydrological response variables above in 2042 or 2102. This is because, as shown in Table 22, 23 and 24, there is zero stream length that exceeds any of the specified thresholds for increases in low-flow days, increases in low-flow spells, or decreases in overbank flow events at the 5th percentile of the modelling results.

GDE = groundwater-dependent ecosystem

Data: Bioregional Assessment Programme (Dataset 1)


Figure 48

Figure 48 'Streams, GDE' landscape group: modelled (a) increase in low-flow days per year (LQD), (b) increase in low-flow spells per year (LME) and (c) decrease in overbank flows per year (EventsR2.0) in groundwater-dependent streams in 2042 in the zone of potential hydrological change

Maps show 95th percentile estimates of increases in low-flow days per year (averaged over 30 years) (LQD) and low-flow spells per year (LME) and 5th percentile estimates of decreases in overbank flows per year (EventsR2.0) to illustrate where maximum hydrological changes may occur. A reduction of 0.1 events per year means one fewer overbank flow events every 10 years.

ACRD = additional coal resource development; GDE = groundwater-dependent ecosystem

Data: Bioregional Assessment Programme (Dataset 9)

Figure 49

Figure 49 'Streams, GDE' landscape group: modelled (a) increase in low-flow days per year (LQD), (b) increase in low-flow spells per year (LME) and (c) decrease in overbank flows per year (EventsR2.0) in groundwater-dependent streams in 2102 in the zone of potential hydrological change

Maps show 95th percentile estimates of increases in low-flow days per year (averaged over 30 years) (LQD) and low-flow spells per year (LME) and 5th percentile estimates of decreases in overbank flows per year (EventsR2.0) to illustrate where maximum hydrological changes may occur. A reduction of 0.1 events per year means one fewer overbank flow events every 10 years.

ACRD = additional coal resource development; GDE = groundwater-dependent ecosystem

Data: Bioregional Assessment Programme (Dataset 9)

Table 22 ‘Streams, GDE’ landscape group: length (km) of groundwater-dependent streams potentially exposed to varying increases in number of low-flow days per year (LQD) in the years 2042 and 2102 in the zone of potential hydrological change


Landscape class

Length in zone of potential hydrological change

Length potentially impacted but not quantified

Length with increases of 3 low-flow days per year

Length with increases of 20 low-flow days per year

Length with increases of 80 low-flow days per year

Length with increases of 200 low-flow days per year

5th

50th

95th

5th

50th

95th

5th

50th

95th

5th

50th

95th

2013–2042

Near-permanent, lowland GDE stream

253

0.6

0

0

251

0

0

0

0

0

0

0

0

0

Near-permanent, upland GDE stream

6.7

0

0

0

6.7

0

0

0

0

0

0

0

0

0

Temporary, lowland GDE stream

2063

693

0

9.7

341

0

0

9.7

0

0

0

0

0

0

Temporary, upland GDE stream

478

59.3

0

0

7.5

0

0

0

0

0

0

0

0

0

Subtotal

2801

753

0

9.7

606

0

0

9.7

0

0

0

0

0

0

2073–2102

Near-permanent, lowland GDE stream

253

0.6

0

0

251

0

0

0

0

0

0

0

0

0

Near-permanent, upland GDE stream

6.7

0

0

0

6.7

0

0

0

0

0

0

0

0

0

Temporary, lowland GDE stream

2063

693

0

0

370

0

0

0

0

0

0

0

0

0

Temporary, upland GDE stream

478

59.3

0

0

6.3

0

0

0

0

0

0

0

0

0

Subtotal

2801

753

0

0

634

0

0

0

0

0

0

0

0

0

Some totals reported here have been rounded. Columns containing zero values are shown to allow consistent comparison between tables.

GDE = groundwater-dependent ecosystem

Data: Bioregional Assessment Programme (Dataset 1)

Table 23 ‘Streams, GDE’ landscape group: length (km) of groundwater-dependent streams potentially exposed to varying increases in duration of low-flow spells per year (LME) in the years 2042 and 2102 in the zone of potential hydrological change


Landscape class

Length in zone of potential hydrological change

Length potentially impacted but not quantified

Length with increases of 3 day low-flow spells per year

Length with increases of 10 day low-flow spells per year

Length with increases of 40 day low-flow spells per year

Length with increases of 100 day low-flow spells per year

5th

50th

95th

5th

50th

95th

5th

50th

95th

5th

50th

95th

2013–2042

Near-permanent, lowland GDE stream

253

0.6

0

0

0

0

0

0

0

0

0

0

0

0

Near-permanent, upland GDE stream

6.7

0

0

0

0

0

0

0

0

0

0

0

0

0

Temporary, lowland GDE stream

2063

693

0

0

99.7

0

0

0

0

0

0

0

0

0

Temporary, upland GDE stream

478

59.3

0

0

1.3

0

0

0

0

0

0

0

0

0

Subtotal

2801

753

0

0

101.0

0

0

0

0

0

0

0

0

0

2073–2102

Near-permanent, lowland GDE stream

253

0.6

0

0

251

0

0

0

0

0

0

0

0

0

Near-permanent, upland GDE stream

6.7

0

0

0

6.7

0

0

0

0

0

0

0

0

0

Temporary, lowland GDE stream

2063

693

0

0

384

0

0

0

0

0

0

0

0

0

Temporary, upland GDE stream

478

59.3

0

0

6.2

0

0

0

0

0

0

0

0

0

Subtotal

2801

753

0

0

648

0

0

0

0

0

0

0

0

0

Some totals reported here have been rounded. Columns containing zero values are shown to allow consistent comparison between tables.

GDE = groundwater-dependent ecosystem

Data: Bioregional Assessment Programme (Dataset 1)

Table 24 ‘Streams, GDE’ landscape group: length (km) of groundwater-dependent streams potentially exposed to decreases in recurrence of overbank flows per year (EventsR2.0) due to additional coal resource development in the years 2042 and 2102 in the zone of potential hydrological change


Landscape class

Length in zone of potential hydrological change

Length potentially impacted but not quantified

Length with 0.02 decrease of overbank flows (events per year)

Length with 0.05 decrease of overbank flows (events per year)

Length with 0.1 decrease of overbank flows (events per year)

5th

50th

95th

5th

50th

95th

5th

50th

95th

2013–2042

Near-permanent, lowland GDE stream

253

0.6

252

0

0

0

0

0

0

0

0

Near-permanent, upland GDE stream

6.7

0

6.7

0

0

0

0

0

0

0

0

Temporary, lowland GDE stream

2063

693

488

120

0

152

60.3

0

99.7

9.7

0

Temporary, upland GDE stream

478

59.3

8.2

1.4

0

1.7

0.9

0

1.3

0

0

Subtotal

2801

753

754

121

0

154

61.2

0

101

9.7

0

2073–2102

Near-permanent, lowland GDE stream

253

0.6

0

0

0

0

0

0

0

0

0

Near-permanent, upland GDE stream

6.7

0

0

0

0

0

0

0

0

0

0

Temporary, lowland GDE stream

2063

693

250

9.5

0

27.5

0

0

0

0

0

Temporary, upland GDE stream

478

59.3

1.7

0

0

0

0

0

0

0

0

Subtotal

2801

753

252

9.5

0

27.5

0

0

0

0

0

Some totals reported here have been rounded.

A reduction of 0.02 events per year means one fewer overbank flow events every 50 years, 0.05 is one fewer overbank flow events every 20 years and 0.1 is one fewer overbank flow events every 10 years.

GDE = groundwater-dependent ecosystem

Data: Bioregional Assessment Programme (Dataset 1)


3.4.4.3 Potential ecosystem impacts

During the receptor impact modelling process, the key hydrological determinants of ecosystem function identified by the experts are related to the existence and connectivity of refuge habitats. Here surface water serves a key role, with detritus and algae the principal resources that support populations of aquatic invertebrates and fishes. Surface water also recharges stores of deep groundwater in confined aquifers and in turn, stores of deep groundwater can contribute to shallow groundwater.

One receptor impact model focused on the response of woody riparian vegetation to changes in flow regime and groundwater. For the ‘Woody riparian vegetation’ receptor impact model, the receptor impact variable is the percent foliage cover of Eucalyptus camaldulensis and Melaleuca spp. in the streams landscape groups. Percent foliage cover is measured in a 100 m transect along the stream, extending from the stream channel to the top of the bank. The transect is at least 10 m wide, increasing to 15 m where more than a single row of river red gum is present during the reference period. The experts’ opinion provides strong evidence that:

  • mean percent foliage cover would decrease by approximately 5% if groundwater depth decreases by 5 m and all other model variables are held at their median values
  • mean percent foliage cover would decrease by approximately 10% if the number of low-flow days (LQD) increases by 100 days per year from 177 to 277 days per year and all other model variables are held at their median values
  • mean percent foliage cover would increase by less than 1% if the number of floods with peak daily flow exceeding the 1983 to 2012 2-year return period (EventsR2.0) doubled and all other model variables are held at their median values.

Uncertainty associated with these predictions increases slightly (i.e. larger credible interval) in the 30-year period preceding 2102. Interestingly, initial percent foliage cover is not a strong predictor of future values in the Galilee subregion. This is at odds with the equivalent receptor impact model in other bioregions where antecedent foliage cover has a strong effect on future foliage cover. However, percent foliage cover in the Galilee subregion is very low – the 90th percentile is approximately 30% with a mean value of about 22%. It is also important to recognise that the relatively modest changes highlighted in the summary above may still be ecologically important given the relatively low baseline condition.

Median estimates of the percent foliage cover under the baseline and CRDP futures ranged from 11% to 44% (Figure 50). Median and 95th percentile estimates of changes in percent foliage cover in the 30-year periods preceding both 2042 and 2102 indicate that there would be a less than 1% change in percent foliage cover compared to the baseline period (Figure 50). There is a 5% chance that percent foliage cover may decrease by 17% to 18% in 2042 and 2102, respectively, due to additional coal resource development.

This is consistent with the modelled changes in groundwater drawdown in excess of 5 m, which are very unlikely to affect more than 6% of groundwater-dependent streams in the zone and changes to low-flow days and overbank flows, which are predicted to affect less than 1% of groundwater-dependent streams in the zone. A change in percent foliage cover of 2% represents 10% for the median estimate of projected foliage cover of 0.2. Hence, these changes are small in terms of foliage cover, but are linked to flower production, nectar production and nectar-feeding animals in the associated qualitative mathematical models.

Figure 50

Figure 50 'Streams, GDE' landscape group: 'Woody riparian vegetation' and 'High-flow macroinvertebrate' receptor impact models showing (upper panels) modelled changes in 2042 and 2102 under the baseline and coal resource development pathway (CRDP) futures and (lower panels) difference between futures in 2042 and 2102

GDE = groundwater-dependent ecosystem

Data: Bioregional Assessment Programme (Dataset 11)

The other receptor impact model examined the response of a high-flow macroinvertebrate (mayfly nymphs in the genus Offadens, family Baetidae) to changes in the flow regime. For the ‘High-flow macroinvertebrate’ receptor impact model, the receptor impact variable is the number of mayfly nymphs (order Ephemeroptera) in the genus Offadens of the family Baetidae (Webb and Suter, 2011). Mean mayfly nymph density is the number of mayfly nymphs per m2 measured in a 2 m x 0.5 m quadrat in riffle habitat, 3 months after the end of the wet season. The experts’ opinion provides strong evidence that:

  • mean mayfly nymph density would decrease by approximately 7% if mean number of low-flow days (LQD) increases by 20 days per year and all other model variables are held at their median values
  • mean mayfly nymph density would decrease by approximately 7% if mean annual maximum spell of low-flow days (LME) increases by 20 days per year from 100 to 120 days per year and all other model variables are held at their median values.

The mayfly nymphs in the genus Offadens are known to occur in fast-flowing streams in the upper Burdekin river basin (e.g. the Cape and Campaspe rivers) to the north and north-east of the zone of potential hydrological change (Blanchette, 2012). The species can recolonise within 1 to 2 days of flows but is challenged by more than 14 consecutive low-flow days. Water depth in riffles is assumed to be more than 2 cm for this species. There is no legacy effect in terms of how mayflies respond to changing flow conditions and turbidity is not a driver for this species.

Estimates of mayfly nymph density ranged from a median value of 150 mayfly nymphs per m2 under perennial conditions to a median value slightly less than 50 mayfly nymphs per m2 under very intermittent conditions (Figure 19 in companion product 2.7 for the Galilee subregion (Ickowicz et al., 2018)). The model also predicts that mayfly nymph density under reference conditions does not influence outcomes under the different low-flow conditions in the future assessment years, which is consistent with receptor impact model predictions for other relatively short-lived species (such as Hydropyschidae larvae) in other bioregions.

Median and 95th percentile estimates of the difference in mayfly nymph density due to additional coal resource development in the 30-year periods preceding 2042 and 2102 indicate no change from abundance under the baseline (Figure 50). Results indicate a 5% chance that mayfly nymph density may decrease by up to 12 mayfly nymphs per m2 in 2042 and up to 36 mayfly nymphs per m2 in 2102 due to additional coal resource development.

Overall ecosystem risk that combines understanding from the conceptual model of causal pathways, hydrological modelling and expert opinion was estimated based on the distribution of predicted impacts due to additional coal resource development. As explained in Section 3.2.5, risk thresholds were defined for each receptor impact variable to describe areas ‘at some risk of ecological and hydrological changes’ and ‘more at risk of ecological and hydrological changes’. Assessment units where input data exist for the receptor impact modelling, but the risk thresholds are not exceeded, are considered to be ‘at minimal risk of ecological and hydrological changes’. Streams where hydrological and/or ecological modelling data were not estimated are classed as ‘unquantified risk’. The overall level of risk represents the highest level of risk determined by all relevant receptor impact variables for that assessment unit.

For the ‘Woody riparian vegetation’ receptor impact model, the risk thresholds defined here are:

  • ‘at some risk of ecological and hydrological changes’ decreases of greater than 5% foliage cover
  • ‘more at risk of ecological and hydrological changes’ decreases of greater than 10% foliage cover.

For the ‘High-flow macroinvertebrate’ receptor impact model, these are:

  • ‘at some risk of ecological and hydrological changes’ decreases of greater than 20 mayfly nymphs per m2
  • ‘more at risk of ecological and hydrological changes’ decreases of greater than 30 mayfly nymphs per m2.

The groundwater-dependent streams where there is some level of risk to woody riparian vegetation and mayfly nymph density mainly occur on parts of Sandy Creek downstream of the four proposed mines in the southern mining cluster, and along parts of the Carmichael, Belyando and lower Suttor rivers between the northern mining cluster and Lake Dalrymple (Figure 51). Receptor impact variables were not calculated for 2088 (67%) assessment units for the ‘Streams, GDE’ landscape group. Of the 1034 assessment units where receptor impact variables were calculated for this landscape group, 194 (or 19%) are considered to be ‘at some risk’ and 42 (or 4%) are considered to be ‘more at risk’. Overall, there is some level of risk to 23% of the assessment units with receptor impact modelling, and 8% of the total number of assessment units in the zone when both the quantified and unquantified changes are considered for this landscape group.

Receptor impact modelling integrates understanding from the conceptual model of causal pathways, hydrological modelling and expert opinion to estimate potential impacts to ecosystems, where receptor impact variables are considered to be useful indicators of ecosystem condition. The strength of this approach is that it provides a measure of the relative risk due to the additional coal resource development and emphasises where further attention using local-scale modelling should focus, and also where it is not needed. Prediction of changes to receptor impact variables is ultimately one line of evidence, and any assessment of risk, particularly at a local scale, needs to be considered in conjunction with the broader hydrological changes that may be experienced and the qualitative mathematical models that can describe potential cumulative impacts to ecosystems. The composite risk map for the ‘Streams, GDE’ landscape group shown in Figure 51, for instance, should thus be considered alongside the evidence provided in Figure 45, Figure 48 and Figure 49.

Figure 51

Figure 51 'Streams, GDE' landscape group: level of risk to groundwater-dependent streams due to additional coal resource development

ACRD = additional coal resource development; GDE = groundwater-dependent ecosystem

Data: Bioregional Assessment Programme (Dataset 11)

Last updated:
4 January 2019
Thumbnail of the Galilee subregion

Product Finalisation date

2018
PRODUCT CONTENTS

ASSESSMENT