TRaCK: Tropical Rivers and Coastal Knowledge

Science and knowledge that governments, communities, industries for sustainable use of Australia's tropical rivers and estuaries

Double the dirt eroding into the Mitchell River Catchment? Tropical Rivers and Coastal Knowledge (TRaCK) present research findings at Mareeba

Double the dirt eroding into the Mitchell River Catchment? Tropical Rivers and Coastal Knowledge (TRaCK) present research findings at Mareeba

Are river channels and waterholes along the Mitchell River filling up with sand and dirt? Where is this sediment coming from? And is erosion increasing?

These are some of the questions concerning those using and managing the waterways and land in the Mitchell River Catchment in Northern Queensland. The Tropical Rivers and Coastal Knowledge (TRaCK) program has been researching the answers to questions such as these since 2008 and will be reporting back today [2/9/10] to interested state and local water and land managers about their findings so far.  "There are no simple answers to some of these questions," says TRaCK researcher, Dr Andrew Brooks from Griffith University.  "We found that the Mitchell River transports a lot of sand, silt and clay each year - we measured more than a quarter of a million tonnes of sand moving along the bed and a similar amount of fine sediment moving in suspension down the river in a single day during February 2009.

"We also found that the Mitchell River can change its course very quickly.  For example, the main river channel can shift 100 metres sideways and individual pools several kilometres long can be completely filled up with sediment in a single wet season.

"If that pool was your favourite fishing hole, then this might be cause for considerable concern. However, we have also shown that at the same time new pools of a similar size will form elsewhere.

Researchers found that despite river channel changes in the past few decades, there appeared to be no significant increase in sediments.  But the story appears to be different when looking at 100 years or more.

"We found that most of the erosion into rivers comes from alluvial gullies or "breakaways" as they are known locally, that have developed over the last 130 years on the floodplains adjacent to the main river channels," says Dr Brooks.

Such gullies cover less than 0.5 per cent of the landscape, but they generate two thirds of the river's sediment load.

"This is a very important finding, because it highlights how different these northern Australian savanna rivers are compared to the rest of Australia," says Dr Brooks.  "Alluvial gullies are found along most of the Gulf Rivers as well as many rivers in the Northern Territory.

"Our modelling of the sediment in the Mitchell shows that erosion appears to have doubled since European settlement, largely due to the increased erosion from these alluvial gullies, but we still need to fully check this out."

TRaCK researchers are not yet sure of the full implications of their findings, but they're looking forward to discussing these results with water and land managers in the northern Gulf today.

Other TRaCK researchers will be discussing how river landscapes can be classified for better management, the effects of floods on the Norman River estuary, and findings about the natural food webs in the Mitchell and Flinders Rivers.

"All of our research is about providing knowledge to help managers and users of northern rivers to make the best possible decisions about any river development or conservation actions," says Ruth O'Connor, TRaCK Knowledge and Adoption Coordinator.

TRaCK receives major funding for its research through the Australian Government's Commonwealth Environment Research Facilities initiative; the Australian Government's Raising National Water Standards Program; Land and Water Australia; the Fisheries Research and Development Corporation and the Queensland Government's Smart State Innovation Fund.

For interviews: Dr Andrew Brooks, phone 0427 232 709; Ruth O'Connor, phone 0434 315 430

For media assistance and photos: Jenni Metcalfe, phone 0408 551 866, ; OR Bill Sokolich, phone 0439 665 202.