Estimating the debris-flow magnitude using landslide sediment connectivity, Qipan catchment, Wenchuan County, China

In an earthquake disturbed basin, the earthquake-induced landslides' connectivity with debris-flow channels determines the landslide sediment volume that is transported into debris flows, and the debris-flow magnitude as well. In this study, the index of sediment connectivity (IC) was used to analyze the evolution of landslide sediment transport capacity. A normalized IC was developed to quantify the movable volume of the landslide sediment available for debris flows. Combined with a landslide empirical relationship, sediment connectivity calculation, particle model, and numerical algorithm, two debris-flow events after the 2008 Wenchuan earth-quake were simulated for the Qipan catchment. The results show good agreement between the simulated and observed debris-flow magnitudes of peak discharges, inundated areas, and depths with approximately 9% average error, which indicates that the normalized landslide connectivity index is suitable for estimating the movable volume. Moreover, the IC and landslide characteristics (area and location) showed significant negative correlations, indicating that the spatial connectivity of landslide sediment generally decayed over time, with a corresponding reduction in debris-flow magnitude.

Automated summary

In a seismic basin, the connectivity between earthquake-induced landslides and debris-flow channels plays a crucial role in determining the sediment volume transported into debris flows and the magnitude of the debris flows. This study developed a normalized index of sediment connectivity to analyze the evolution of landslide sediment transport capacity. By simulating two debris-flow events, the results showed a good agreement between the simulated and observed debris-flow magnitudes, indicating the suitability of the normalized landslide connectivity index for estimating the movable volume. Additionally, a negative correlation was found between the sediment connectivity index and landslide characteristics, suggesting a decay of spatial connectivity over time and a corresponding reduction in debris-flow magnitude.