TRaCK: Tropical Rivers and Coastal Knowledge

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A catchment sediment and nutrient budget for the Daly River, Northern Territory

TitleA catchment sediment and nutrient budget for the Daly River, Northern Territory
Publication TypeReport
Year of Publication2010
AuthorsRustomji, P, Caitcheon, G
Date Published12/2010
InstitutionCSIRO Water for a Healthy Country National Research Flagship
KeywordsDaly River, model, nutrients, primary production, sediments, water quality

This report presents a catchment sediment and nutrient budget for the Northern Territory’s Daly River catchment. A catchment sediment or nutrient budget accounts for the major sources, transport pathways and sinks of sediments and nutrients within a catchment. The SedNet and ANNEX models have been used in this case; these models have been widely applied in tropical Queensland settings and elsewhere in Australia.

The model predicts budgets for fine sediment readily transported in suspension, and dissolved and particulate nutrients. The model has been calibrated which is critical to obtaining realistic model results. The model was consequently able to predict erosion intensity moderately well for two of the three load estimate stations, was able to correctly predict the dominant tributary contributions, and predicted surface-soil to be a minor component of the transported load.

The calibrated model predicts 503 kt per year of fine sediment export from the catchment. Bank erosion is predicted to be the main sediment input term. Bank erosion also contributes strongly to the sediment load exported from the catchment. Sediment deposition upon floodplains accounts for approximately 81% of the catchment sediment supply. Areas strongly contributing to sediment export from the catchment are predominantly located in the north-west of the catchment (including the Douglas River) and along the stems of the major channels. The high rate of bank erosion is likely a product of a shift to wetter conditions since 1996, resulting in systematic channel widening along at least the main stem of the Daly River, however this remains to be confirmed by more detailed field investigations.

The modelled nutrient budgets indicated 855–1369 and 178 t/yr of nitrogen and phosphorus export respectively. In the case of phosphorus this is approximately evenly split between dissolved and particulate phosphorus, though nitrogen may comprise a particulate-dominated load, depending on model parameterisation. The spatial pattern of nutrient contribution to catchment export is again dominated by input from the north-west of the catchment.