Channel evolution triggered by a large flash flood based on sUAV at an earthquake-affected catchment

Earthquakes–induced landslides generally provide abundant loose materials at hillslopes, possiblly triggering morphological reshaping processes at river channel and riverbed during the large flash flood hydrograph and bringing huge risk to downstream. Therefore, in a Wenchuan earthquake-affected catchment, the collected hydro-meteorological data and high-precision small Unmanned Aerial Vehicle (sUAV) data were used to quantificationally analyze channel evolution by a large flash flood event on 25^th and 26^th June, 2018. It was found that the stable riverbed structure formed by the coarsening layer appeared in the tenth year after the Wenchuan earthquake. In confined channel, the layer can protect the channel and resist the drastic change after the flash flood event with only small bed elevtion from 0.2 m to 2 m. Without the protection of the coarsening layer, the change could reach 6 m in unconfined channnel. Meanwhile, more materials with deposition volume of 753,108 m³ from tributaries were generally taken to main channel,and more intense erosion with the volume of 1.010⁷ m³ mostly occurred in the downstream of tributaries. It was noted that, in the cross-section, the increased channel width could lead to the significant change with the large volume of 35 m³. Additionally, conceptual model of the generalized channel response to large flash floods was provided during multi-stage periods after the Wenchuan earthquake. It determined the rebalance processes of channel evolution in the tenth year after the earthquake. This study will contribute to understanding the post-earthquake long-term channel evolutions and could provide decision-makers of assessing the mitigation strategies for higher-magnitude flood disasters triggered by channel change in earthquake-affected watershed.