Evolution and migration patterns of sediments in an earthquake-affected catchment in Wenchuan, Sichuan Province, China

Earthquakes of magnitude often contribute to changes in sediment availability, and those available sediments, once entrained by runoff, can lead to catastrophic debris flow events. Effective management of debris flow events in seismic areas relies on monitoring the changes in available sediments at the catchment scale and the movement mode of available sediments at the sedimentary deposits scale. For this reason, the present study integrates satellite remote sensing images, terrestrial 3D laser scanner, and field experiments to establish a monitoring framework across diverse spatial scales. This approach reveals the evolution and migration patterns of available sediments in the typical debris flow catchment Cutou gully in the Wenchuan earthquake area since the 2008 earthquake disaster. Accordingly, we can illuminate how sediment evolution responds to different disaster events and clarify the sediment migration patterns before and during debris flow disasters. It is found that the seismic events led to an increase in sediments available for mobilization within Cutou gully. For the available sediments involved in the debris flow, since some of the loosely consolidated active material sources were carried away by the debris flow, following the debris flow, they were more stable compared to those not involved in the debris flow. Available sediments migrated from the upper slopes with higher elevation to the debris flow channel with lower elevation due to surface runoff before and during the debris flow. Localized collapse at the toe of the sedimentary deposits occurred continuously in a retrogressive manner, mainly due to lateral erosion of the channel bank, which complements the magnitude of the debris flow.