Role of vegetation restoration in mitigating hillslope erosion and debris flows

After the 2008 Wenchuan earthquake, a large amount of loose landslide deposits was left in the stricken region. A heavy storm in 2010 turned numerous deposits into debris flows. After 2010, vegetation gradually recovered on the remnant soil deposits. During the wet seasons in 2013 and 2015, the number of debris flows decreased significantly compared with that in 2010. This paper investigates the role of vegetation in mitigating runoff induced hillslope erosion and debris flows. The study slope is near the epicentre of the Wenchuan earthquake. Three levels of vegetation restoration are considered: bare in 2010, middle level in 2013 and high level in 2015. Soil samples were taken from the landslide deposits to determine the root mass density, which is used to quantify erosion resistance parameters at different vegetation levels. Massive erosion is simulated in the 2010 case, which in turn develops into hillslope debris flows. Very little or no erosion is simulated in the 2013 and 2015 cases, which is in part attributed to the enhanced resistance to erosion by restored vegetation. A parametric study is conducted to further investigate the effectiveness of erosion reduction through revegetation.