Material Activity in Debris Flow Watersheds Pre- and Post-Strong Earthquake: A Case Study from the Wenchuan Earthquake Epicenter

The 2008 Wenchuan earthquake released vast quantities of loose material, significantly influencing post-earthquake material dynamics, particularly through recurrent debris flow disasters that posed long-term threats to the earthquake-affected area. To explore the transport and involvement of loose materials in debris flow events within earthquake-affected basins, this study focuses on a representative area near the Wenchuan epicenter, creating a multi-temporal database of active landslides and channel materials pre- and post-earthquake, quantitatively assessing material transport and source replenishment in debris flow basins, and categorizing debris flows based on channel material activity, post-earthquake historical activity, and sustainability of activity. This study revealed that pre-earthquake material activity was concentrated in the watershed’s upper regions, while post-earthquake materials were progressively transported from the central to the lower regions, with many small co-seismic landslides ceasing activity. The supply area ratio from active landslides capable of recharging debris flows, i.e., those connected to channels, consistently remained at approximately 72%, with the peak area of channel material activity comprising approximately 2.5% of the total watershed area. Channel material activity areas serve as valuable indicators for hazard assessment in regions lacking historical debris flow data, with the watershed area predominantly determining the sustainability of post-earthquake debris flow activity.