Post-Earthquake UnstableSediment Hazards in MountainWatersheds: Case Study from the 2024 ML 7.2 HualienEarthquake, Taiwan

Abstract

On 3 April 2024, an M_L 7.2 earthquake struck eastern Taiwan, triggering 18.2 ha of new landslides in the DF174 watershed (292 ha). Roughly 270,000 m³ of unstable sediment stored on upstream. Loose slope material transformed into debris flows that endangered downstream villages and the culvert bridge. This study integrated field surveys with remote sensing: SAR-based change detection and InSAR track sub-centimeter slope deformation, while repeating UAV survey. UAV-derived DTM differencing indicates ~188,000 m³ (≈70%) of the unstable sediment was deposited downstream, causing channel aggradation, overflow and confluence siltation. Using RAMMS, debris flow simulations under design rainfall scenario show that the 50-year event would rapidly aggrade the riverbed, inundate the culvert, bury the bridge, and potentially block the mainstream—posing extreme threats to downstream school. Mitigation scenarios suggest that lowering the spillway crest of the check dam and constructing additional dams substantially reduce debris-flow risk. Medium- to long-term resilience measures include installing solar-powered CCTV and radar-based, non-contact water-level gauges; conducting periodic dredging paired with UAV photogrammetric surveys to support early warning and community protection; and maintaining InSAR/satellite surveillance of residual unstable sediments upstream.