Modelling sediment transport and the relative dominance of sediment sources in agricultural catchments with the SWAT+ model

Abstract Purpose Greater understanding of the contributions from different sediment sources and their linkages to the downstream suspended sediment load (SSL) is essential to advancing knowledge of catchment sediment transport dynamics and informing sediment management. Implementation and uncertainty-based analysis of integrated catchment hydrologic and sediment models can provide valuable insights into sediment sources and their relative dominance at the catchment scale. Materials and methods The SWAT+ model is calibrated and validated for prediction of monthly SSL in two agriculture-dominated catchments; the River Owenabue (143 km 2 ) and River Bandon (598 km 2 ) catchments in County Cork, Ireland. Using the behavioural parameter sets identified via the Sequential Uncertainty Fitting (SUFI-2) procedure, sediment fluxes from different sources are analysed at the catchment scale. Results SWAT+ modelled median 95PPU values for riverbed, terrestrial and bank erosion sediment fluxes in the Owenabue Catchment were 3,984, 382 and 262 t yr − 1 , respectively. SWAT+ modelled median 95PPU values for riverbed, terrestrial and bank erosion sediment fluxes in the Bandon Catchment were 14,544, 1,246 and 5,606 t yr − 1 , respectively. The SWAT+ model predicted the largest sediment fluxes from riverbed erosion in both catchments. Conclusion The results of this study indicate the importance of in-channel sediment sources within the SWAT+ models of the catchments and their role as a long-term control on catchment sediment transport dynamics. The approach presented in this paper advances modelling and understanding of sediment sources, transport processes and associated uncertainty in agricultural catchments.