A decadal evolution of landslides and debris flows after the Wenchuan earthquake

Abstract

The 2008 Wenchuan earthquake triggered numerous coseismic landslides. The loose materials were retained on steep terrains and deep gullies as well as in river channels, which increased higher flooding hazard and geo-hazard (landslides and debris flows) risks in the area. In this paper, between 2008 and 2016 we monitored landslides and debris flows occurred during rainfall, especially the high rainfall amounts in 2013, which caused serious damage to reconstructed villages. The changes over time aids in understanding long-term landscape evolution in the investigated area impacted by major earthquakes as well as in regions with comparable settings. With the aid of a GIS platform combined with field investigations, we continuously tracked the area and movement paths of the loose deposit materials in all the debris flow gullies and coseismic landslides in the study area. And then the spatial and temporal evolutionary patterns of these movements as well as the evolution under different triggering factors were analyzed using the terrain and precipitation information from the past nine years. The results showed that both the area and number of coseismic landslides decreased over time and that the deposited materials moved to areas of lower elevation and lower slope. In addition, the new landslides occurred more easily in areas of low elevation and high slope during periods of normal rainfall. Under the high rainfall, many new landslides and expansion processes occurred easily at high altitudes, providing loose materials for debris flows. Although the overall geoenvironment in the earthquake-stricken area has a recovering tendency, the outburst of hazards triggered by future extreme rainfalls is still expected and this kind of fluctuating cycle may last for an unexpectedly longer period.