Enhancement of Sediment Routing Method of SWAT Model Considering Sediment Occurrence Trends of Rise and Fall of Streamflow

Accurate quantification of sediment occurrence in river basins is essential for establishing sediment management strategies. This study enhanced the simplified Bagnold method within the SWAT model to enhance simulation of sediment dynamics due to the rise and fall of streamflow. The sediment simulation efficacy of the enhanced Bagnold method in the SWAT was evaluated by comparison of estimated daily sediment with the original Bagnold method in the SWAT model. During the rise of streamflow, the original Bagnold method in the SWAT model yielded an R² of 0.86 and an NSE of 0.85, but these indicators declined to an R² of 0.49 and an NSE of −14.88 in simulations of sediment during the fall of streamflow. In contrast, the enhanced Bagnold method in the SWAT showed superior calibration performance, achieving an R² of 0.94 and an NSE of 0.92 during the rise of streamflow, and an improved R² of 0.68 and an NSE of 0.6 during the fall of streamflow. Notably, the enhanced Bagnold method in the SWAT provided a more accurate sediment prediction during increases in streamflow, with an overestimation of only 25.1% relative to observed data. This marks a significant improvement over the original model, which overestimated sediment by 443.5%. As shown in this study, streamflow variability (changes in rise/fall) needs to be considered in sediment simulations, enhancing model accuracy and informing effective sediment management strategy development.