The dominant erosion processes supplying fine sediment to three major rivers in tropical Australia, the Daly (NT), Mitchell (Qld) and Flinders (Qld) Rivers

• Published in: Geomorphology (Amsterdam, Netherlands) Vol. 151-152; pp. 188 - 195
• Main Authors: Caitcheon, Gary G., Olley, Jon M., Pantus, Francis, Hancock, Gary, Leslie, Christopher
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.05.2012; Elsevier
• Subjects: 137Cs; bank erosion; cesium; Channel erosion; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geomorphology, landform evolution; gully erosion; Isotope geochemistry; Isotope geochemistry. Geochronology; land management; Landuse management; Marine and continental quaternary; planning; prediction; probability; Probability density function; rain; rill erosion; rivers; Sediment sources; sediments; soil; Surficial geology; Tropics; watersheds; wet season; Northern Territory; Queensland; Queensland Australia; Australia; Northern Territory Australia; Sediment sources; Probability density function; Landuse management; Channel erosion; Tropics; 137Cs; tributaries; gullies; sediment sources; Australasia; fine-grained materials; Cs; drainage basins; water resources; land use; soils; rivers; models; density; Cs-137; probability; investment; concentration; rills; planning; sediment transport; channels; management; prediction; soil erosion; landform evolution
• ISSN: 0169-555X; 1872-695X
• DOI: 10.1016/j.geomorph.2012.02.001

The tropics of northern Australia have received relatively little attention with regard to the impact of soil erosion on the many large river systems that are an important part of Australia's water resource, especially given the high potential for erosion when long dry seasons are followed by intense wet season rain. Here we use 137Cs concentrations to determine the erosion processes supplying sediment to two major northern Australian Rivers; the Daly River (Northern Territory), and the Mitchell River (Queensland). We also present data from five sediment samples collected from a 100km reach of the Cloncurry River, a major tributary of the Flinders River (Queensland). Concentrations of 137Cs in the surface soil and subsurface (channel banks and gully) samples were used to derive ‘best fit’ probability density functions describing their distributions. These modelled distributions are then used to estimate the relative contribution of these two components to the river sediments. Our results are consistent with channel and gully erosion being the dominant source of sediment, with more than 90% of sediment transported along the main stem of these rivers originating from subsoil. We summarize the findings of similar studies on tropical Australian rivers and conclude that the primary source of sediment delivered to these systems is gully and channel bank erosion. Previously, as a result of catchment scale modelling, sheet-wash and rill erosion was considered to be the major sediment source in these rivers. Identifying the relative importance of sediment sources, as shown in this paper, will provide valuable information for land management planning in the region. This study also reinforces the importance of testing model predictions before they are used to target investment in remedial action. ► We apply sediment tracing to three northern tropical catchments in Australia. ► A new method for using 137Cs data is developed. ► 90% of the sediment along the main channels originates from subsoil erosion. ► The primary source of sediment to tropical rivers in Australia is subsoil erosion.