Channel aggradation decelerates downstream sweep erosion in Daan river Gorge, Taiwan

Abstract Downstream sweep erosion (DSE), rapid erosion at gorge entrances where wide channels narrow into confined gorges, drives rapid bedrock gorge removal. However, sediment can both enhance erosion through abrasion and decelerate it by channel aggradation, yet the role of sediment dynamics in modulating DSE efficiency remains poorly understood. We used SfM-MVS photogrammetry with aerial photographs and UAV imagery from 2009 to 2025 to quantify upstream gorge retreat and sediment-driven feedbacks in Taiwan’s Daan River Gorge. DSE-driven gorge retreat rate decreased dramatically from 11.5 m/yr (2009–2014) to 0.7 m/yr (2014–2016) due to channel aggradation, before partially recovering to 1.5 m/yr (2016–2025) following alluvial bar scouring. High sediment flux initially enhanced erosion through the tool effect but later inhibited it by forming bars that deflected flow and shifted impact angles from perpendicular to parallel. This cyclic mechanism extended gorge lifespan from ~ 50 years to 182–208 years, though removal remains faster than the ~ 470-year tectonic recurrence. These findings demonstrate that sediment can strongly regulate gorge evolution and transient topography persistence in the Daan River Gorge.