TRaCK: Tropical Rivers and Coastal Knowledge

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

Bedload transport dynamics in the Mitchell River, northern Australia

TitleBedload transport dynamics in the Mitchell River, northern Australia
Publication TypeConference Participation
Year of Publication2009
AuthorsBrooks, A, J., K, Shellberg, J, Spencer, J
Keywords4: Material Budgets

Sediment transport dynamics in the large tropical rivers of northern Australia are currently poorly understood, particularly the bedload component which is notoriously difficult to measure given, amongst other things, the access issues during the wet season. Anecdotal evidence from the Mitchell River, one of the focal catchment under the Tropical Rivers and coastal Knowledge (TRaCK) program, has suggested the river has experienced sand accumulation in pools over recent decades. Traditional owners and river users are concerned about the implications of potential pool infilling on riverine ecosystems due to the potential impact on the availability of dry season remnant pool habitat. In this paper we present preliminary results from studies underway within the TRaCK program, which is attempting to determine whether there is a trend towards bedload accumulation in this river. A multiple lines of evidence approach has been adopted that incorporates analysis of Landsat archival data, historical aerial photography, field measurement using an Acoustic Doppler Current Profiler (ADCP), and OSL dating of inchannel sedimentary units. The analysis of Landsat archival data allowed us to estimate minimum river channel bed turnover by mapping the trends in the relative proportions of sand, water and vegetation from year to year. These trends when plotted up in 10km segments across the catchment provide an idea of the movement of bed material through the catchment over the period of the (30m) Landsat record and consequently the trends towards sand gain or loss in each segment. When coupled with the insights gained from a recent ADCP and field sampling trip down the flooded Mitchell River, a clearer picture of the overall bed dynamics emerges that can only be gained through such a multiple lines of evidence type approach.