The sources and dispersal of sediment within a large flood plain complex

Abstract

Knowledge of sediment sources and their dispersal across the landscape is essential for understanding the dynamics of flood plain ecosystems. This is important for flood plain management because rates of upstream catchment erosion are predicted to increase considerably throughout much of inland Australia. In this study, the provenance and dispersal of sediment across a large lowland flood plain complex are investigated. A range of non-soluble geochemical elements were used in a Bayesian mixing model to determine the source and dispersal of very fine sand and clay sized particles across the lower Balonne flood plain in SE Australia. These two sediment fractions were chosen because they are the dominant material present within this flood plain complex. The relative contribution of the two main sediment sources differed for each of the sediment fractions. Clay sized particles were predominantly derived from the Maranoa catchment, whereas the very fine sand was derived from the Condamine catchment. In terms of the dispersal of these sediment fractions from the two main sources, very fine sands were dispersed relatively uniformly across the Lower Balonne flood plain, whereas the clay sized sediment was restricted to the main flow channels that dissect this flood plain. These spatial patterns are contrary to that expected in terms of the dispersal ability of sediment across flood plain surfaces and result from the complex hydrology of the flood plain surface along with the timing of flow events originating from the two tributaries.