Marine and Freshwater Research Marine and Freshwater Research Society
Advances in the aquatic sciences

A preliminary typology of Australian tropical rivers and implications for fish community ecology

W. D. Erskine A F , M. J. Saynor B C , L. Erskine D , K. G. Evans B E and D. R. Moliere B

A Centre for Sustainable Use of Coasts and Catchments, School of Applied Sciences, University of Newcastle – Ourimbah Campus, PO Box 127, Ourimbah, NSW 2258, Australia.

B Hydrological and Ecological Processes Group, Environmental Research Institute of the Supervising Scientist, GPO Box 461, Darwin, NT 0801, Australia.

C School of Earth and Geographical Sciences, University of Western Australia, Crawley, WA 6009, Australia.

D School of Geosciences, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia.

E School of Engineering and Logistics, Charles Darwin University, Darwin, NT 0909, Australia.

F Corresponding author. Email:

Marine and Freshwater Research 56(3) 253-267
Submitted: 4 May 2004  Accepted: 7 March 2005   Published: 3 June 2005


Australian tropical rivers are dependent on highly seasonal rainfall and runoff between November and April. They also transport low sediment and solute loads, except where catchments have been disturbed by mining, grazing and cropping. Aquatic habitats or channel units are the physical template influencing fish communities. Pools provide dry-season refuges for fish and channels provide pathways for movement between refuges when streamflows are re-established. A preliminary geomorphological typology of Australian tropical river reaches (excludes estuaries) is proposed that defines nine distinct river types: (1) bedrock rivers (upland channels and gorges); (2) bedrock-confined rivers; (3) avulsive rivers; (4) meandering rivers (confined meandering, laterally migrating unconfined and laterally stable unconfined); (5) straight rivers; (6) floodouts; (7) island- and ridge-anabranching rivers; (8) co-existent mud-braided and anabranching rivers; and (9) extensive freshwater wetlands and billabongs. Many of these have not been recognised overseas and are unique. Channel units differ greatly between river types and contribute to distinctive fish communities in different river types. As expected, fish diversity decreases upstream because of less diverse habitat and natural barriers to fish movement at steps, falls and turbulent cascades and rapids. Fish kills occur in most years and are caused by several different factors that reduce dissolved oxygen.

Extra keywords: anabranching, avulsion, billabongs, channel units, fish kills, fish migration, floodplain stripping, refuges, river reaches, river types, wetlands.


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