A physically-based multi-hazard risk assessment platform for regional rainfall-induced slope failures and debris flows

Abstract

Rainfall-induced slope failures and debris flows are two major hazards in mountainous areas. A physically-based multi-hazard risk assessment platform for regional rainfall-induced slope failures and debris flows has been developed in this study. The platform enables prompt assessment of risks posed by regional rainfall-induced slope failures and debris flows across multiple catchments, which is required in landslide risk management in a large area. It considers the contribution of slope failures to debris flows and the scenario of a location impacted by multiple slope failures or debris flows or both. The contribution of slope failures to debris flows is considered by adding the increased amount of channel deposit from slope failures to the source material of debris flows. The platform is applied to a highway near the epicentre of the 2008 Wenchuan earthquake. The platform predicts the impact areas and runout distances of regional debris flows reasonably well. The risk assessment results indicate that both slope failures and debris flows pose a great danger to travellers along the road shortly after the earthquake due to the presence of a large amount of loose landslide deposits on steep terrains. The materials from the slope failures triggered during a storm substantially increase the channel deposit volume, leading to significantly increased debris flow volume and risk. A multi-hazard risk assessment approach is necessary to consider the scenario of a location impacted by multiple slope failures or debris flows or both, since assessing risks of slope failures and debris flows separately may underestimate the risk.