In September 2016, Typhoon Meranti triggered a large-scale slope failure upstream of Hongye Village, Taitung, Taiwan. The resulting debris flow inundated residential areas, causing extensive property damage. Thus, two questions remain: (1) How can such events be accurately reconstructed? and (2) Are there more effective check dam arrangements that mitigate risk without exacerbating downstream impacts? Therefore, the necessity and effectiveness of check dam mitigation structures are determined under varying debris flow magnitudes in this study. Using the iRIC Morpho2DH two-dimensional numerical model, a Baseline Case was calibrated through back-calculation, achieving a coverage index (CI) of 0.694 and a mean deposition thickness error below 20%. These results indicate good agreement with the observed post-event data. The observations show that (1) debris flow behavior and deposition extent are highly sensitive to key parameters such as the static sediment concentration, liquid behavior sediment ratio, and debris flow source volume; and that (2) check dams offer limited benefits in small-scale debris flows where sediment remains within the channel. In contrast, under large-scale debris flows, check dams may induce localized overflow and increase downstream deposition, potentially creating new hazards. This study demonstrates that iRIC Morpho2DH is a robust tool for evaluating debris flow dynamics and mitigation strategies, offering a foundation for evidence-based planning and risk-informed engineering design in mountainous hazard-prone regions.
Feng et al. (Sat,) studied this question.