How landslide sediments are transferred out of an alpine basin: Evidence from the epicentre of the Wenchuan earthquake.

• The first decadal time series analysis is carried out after the 2008 M s 8.0 Wenchuan earthquake. • Field investigations and experimental approaches evaluate landslide sediment transfer processes along hillslopes. • The decadal dynamic transfer process of landslide sediment in the channel was quantified. • The landslide sediment transfer process may last 20–50 years or longer to return to the pre-earthquake level. The Wenchuan earthquake and subsequent strong rainfall triggered extensive mass wasting, which caused sufficient landslide sediment to be continuously transferred out of the alpine basin. Effective sediment management in earthquake areas requires a full understanding of how landslide sediment is transferred out of alpine basins. In this study, field investigations and remote sensing interpretations indicated that the bedrock or hillslope surface materials were transferred downstream of the hillslope through falls, slides, fall slides, slide falls, and slide flows. Subsequently, field investigations and box model tests showed that the loose landslide sediment was transferred to the channel mainly through three typical processes (erosion driven by torrents or debris flow, saturation, and surface runoff), which occurred simultaneously in the first several years after the Wenchuan earthquake. However, surface runoff erosion was the main transfer process in the following period. Using the number and area of effective landslides, the length and area of landslide sediment in channels, and the effective basin as indicators, we present observational evidence of the landslide sediment transport process based on a remote sensing image time series from 2005 to 2018. The trends of the indicators suggested that the sediment transfer process in the alpine basin was intense during the first 5 years after the Wenchuan earthquake; then, it gradually weakened without the influence of extreme rainfall, but it may last 20 years or longer before returning to the pre-earthquake level. [ABSTRACT FROM AUTHOR]