Modeling typhoon-induced alterations on river sediment transport and turbidity based on dynamic landslide inventories: Gaoping River Basin, Taiwan

This study examines the impacts of storm-triggered landslides on downstream sediment and turbidity responses in the Gaoping River Basin, Taiwan using the Soil and Water Assessment Tool (SWAT). Attention is given to analyzing the increased and altered baseline of suspended sediment load and turbidity after the disturbances caused by the rainfall and landslides associated with Typhoon Morakot in 2009. SWAT parameters were calibrated by the observed hydrometric data from 1999 to 2003 using the log-scale root-mean-square error (log-RMSE) and Nash-Sutcliffe Model Efficiency. Both parameter sets were applied for the simulation of suspended sediment yield and turbidity with annual updated landslide inventories for the period 2004-2012. The landslide updating mirrors the physical land-cover changes and has slightly improved the model performance, yet landslides alone cannot explain the difference between Morakot-induced and SWAT-simulated sediment discharge. The set of parameters calibrated by log-RMSE can better approximate the increased baseline and typhoon induced alterations. The results show alterations in sediment erosion and transport: (1) drastically increased the turbidity baseline and occurrence of high-turbidity; (2) altered coefficient and exponent values of the sediment rating curve; and (3) altered relationship between rainfall and induced turbidity during major rainfall events. The research in this study provides an improved modeling approach to typhoon-induced alterations on river sediment loads and turbidity.