Climate change has resulted in frequent extreme rainfall events, resulting in unpredictable variations in sediment deposition and runoff in reservoirs and their catchments. In 2009, Typhoon Morakot brought lengthy, highintensity
rainfall to the Tsengwen Reservoir watershed, increasing landslides and bare areas and dumping large quantities
of sediment into the reservoir. The rainfall cycle in Taiwan remained stable after the 2009 event; however, the
Tsengwen Reservoir and its catchment continued to display variations in sediment deposition and runoff, thus warranting investigation. The present study entailed the performance of sedimentation analyses by using satellite images, light detection and ranging digital elevation models, sediment concentration records, and reports on the annual depositional volume in the reservoir. The results revealed that, as of 2020, the ratio of landslide and bare areas in the watershed had decreased, the variations in riverbed topography were minimal, the sediment concentration had returned to its pretyphoon levels, and the annual deposition into the reservoir was close to zero. This study demonstrated that the variations in sediment runoff and deposition into the Tsengwen Reservoir had returned to equilibrium.
Key Words: hysteresis, rating curve, sediment runoff, Tsengwen Reservoir