TRaCK: Tropical Rivers and Coastal Knowledge

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

Fine sediment sources in the largely undisturbed, tropical, low relief catchment of Darwin Harbour, Australia

TitleFine sediment sources in the largely undisturbed, tropical, low relief catchment of Darwin Harbour, Australia
Publication TypeConference Participation
Year of Publication2009
AuthorsNawaz, M, Wasson, R, Ahmad, W, Parry, D, Sattar, F
Keywords5: Foodwebs and biodiversity, chain of ponds, channel and sheet erosion, Dambo, sediment sink, top soil tracers

Fine sediments, organic matter, nutrients and metals are currently transported from catchment to the Harbour. These are the materials of future concern for the Harbour’s environment and its ecological setup. Channel sources dominate because of the higher erosion rates of channel walls as compared to the hillslopes and dambos (unchannelled valley floors). Identification and quantification of these fine sediment sources play a key role in the landscape management and water quality protection planning. The catchment has highly erodible soils due to high rainfall erosivity associated with low soil surface cover and high rainfall. Although recent sediment sources modelling at sub-catchment scale addresses such conditions, it does not take into account, dambos and discontinuous channels (chain of ponds). Hillslope surfaces, dambos and discontinuous channels affect sediment delivery because channels are small and relatively short. This paper describes the sequence of hillslopes, dambos, discontinuous channels, continuous channels and estuaries in the catchment. The paper also reports the top soil tracers 210Pbex and 137Cs based identification and quantification of fine sediment sources and describes the role of dambos and chain of pond as sediment sinks in the catchment. Results show that the concentrations of the 210Pbex and 137Cs in the rivers are on an average five times lower than the hillslope samples. This implies that approximately 20% of the creek and river sediment comes from sheet erosion, and the remainder from channel erosion of the material that contain no or very low if any top soil tracer. The possible reasons for this are the sediment trapping by dambos and ponds and on the other hand the higher erosion rate of channel walls.