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Base Flow Rivers

Groundwater is a vital component of flow in most streams or rivers. This flow is termed 'Baseflow'. It provides a permanent water source suppoting a range of habitats such as surface flow, flow within the subsurface of sand and gravel bed streams, and permanent pools. The presence of this baseflow enables a far greater diversity of biota to exist than possible in temporary streams. This includes surface vertebrates such as fish, amphibians and reptiles, surface and subsurface invertebrates communities, macrophytes, and terrestrial/riparian vegetation.

Groundwater base flow in sand and gravel–bed rivers and streams also support a specialised community of invertebrates termed the 'hyporeos' that exist below the river bed in the hyporheic zone. This zone represents the transition or mixing zone between the surface waters and the deep groundwaters. The fauna found in these environments can include surface macroinvertebrates with many insects and groundwater faunas containing Crustacea, Oligochaeta (worms), flatworms and micro crustaceans. The hyporheic zone also acts a nursery and refuge for stream invertebrates during periods of drought. As the community composition of organisms present within the hyporheic zone is dependent on the surface water/groundwater connectivity it can be used a direct indicator of change in loosing and gaining streams and the condition of the river system in general. In turn this relationship has implications for the management of water resource and as a monitoring tool for climate change.

"We recommend that all development applications and EIS adopt the WA protocols for sampling stygofauna, as assessments will be consistent with those in other states."