2.7.4 Streams landscape groups


The streams landscape groups in the Galilee assessment extent contain 10 landscape classes. Four landscape classes are groundwater-dependent ecosystem (GDE) streams (comprising the ‘Streams, GDE’ landscape group) and six are non-GDE streams (comprising the ‘Streams, non-GDE’ landscape group). Both GDE and non-GDE streams are widespread in the zone of potential hydrological change in the central-eastern part of the Galilee subregion, and mainly occur in the Belyando river basin (a headwater catchment of the larger Burdekin river basin). Of the 6285 km of streams in the zone, GDE streams account for 2801 km (45%) of all streams, and non-GDE streams total 3484 km. Non-GDE streams are most common in the western and southern parts of the zone.

Within the zone of potential hydrological change, annual streamflow shows a high degree of interannual variability. Flows in any 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 surface water flows occur between December and April. The streamflow regime within the zone is characterised as one of dry seasonal flows.

The dry seasonal flows of the streams within the Belyando river basin result in the ecosystems of the streams landscape groups being characterised by ‘boom–bust’ cycles. Specifically, diversity in the system is maintained by natural cycles of river flow and drying, driven by surface water inputs. Although more arid rivers further west in the Galilee subregion are driven by highly unpredictable rainfall, the ‘boom–bust’ cycle in the Belyando river basin is more predictable. Ecological processes within the zone of potential hydrological change operate in an environmental context where there is seasonally predictable summer rainfall, which produces in-channel flows (flow pulses), followed by a predictable period of drying. The drying phase is a relatively constant process in an average year uninterrupted by rainfall outside the summer period. During summers with very high rainfall, the in-channel flow is replaced by flooding. Overbank flows connect the riverine and floodplain environments during these ‘boom’ periods and primary productivity is greatly enhanced.

A combined qualitative mathematical model was developed for the two streams landscape groups. The central feature of the qualitative model was the existence and connectivity of refuge habitats. Surface water serves a key role in providing both lateral and downstream transport of detritus in the stream channel and floodplain. It also determines, through wetted area of the channel, the amount of primary production generated by algae. Detritus and algae are the principal resources that support populations of aquatic invertebrates and fishes. Surface water also plays a key role in recharging stores of deep groundwater in confined aquifers, and in turn, stores of deep groundwater can contribute to maintaining groundwater levels in near-surface (unconfined) aquifers.

Two receptor impact models were developed to examine the potential impact of the additional coal resource development on water-dependent ecosystems within the zone of potential hydrological change. The first receptor impact model focused on the response of woody riparian vegetation to changes in flow regime and groundwater. The second model examined the response of a high-flow macroinvertebrate (mayfly nymphs in the genus Offadens, family Baetidae) to changes in flow regime.

With regard to the first receptor impact model, the independent experts who contributed to the elicitation process were of the opinion that: (i) mean percent foliage cover would decrease as depth to groundwater increased, (ii) mean percent foliage cover would decrease as the number of low-flow days increased, and (iii) mean percent foliage cover would increase as the number of flood events with peak daily flow exceeding the 1983 to 2012 2-year return period increased.

Results from the second receptor impact model indicate that the experts’ opinion provides no strong evidence that either the number of low-flow days or the mean maximum spell of low-flow days have a significant effect on mean baetid density. This model also predicts that baetid density under reference conditions does not affect outcomes under different low-flow conditions in future assessment years.

Last updated:
6 December 2018
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