Multi-hazard scenarios and consequences in Beichuan, China: The first five years after the 2008 Wenchuan earthquake

Risk assessment for engineering construction, public safety and city planning must answer three questions: (1) What can go wrong? (2) What is the likelihood that it will go wrong? (3) What are the consequences if it goes wrong? All the three questions are difficult to answer. Often “unexpected” hazard scenarios arising from cascading effects lead to disastrous consequences because such hazards are not prepared for. During the Wenchuan earthquake in 2008 and in the subsequent five years, the Beichuan town in northern Sichuan experienced extraordinary hazards, which impacted upon every corner of the town. A systematic study of such hazard scenarios would provide the required evidence for properly answering the aforementioned questions. This paper starts with an overview of the disaster chain in the Beichuan town triggered by the Wenchuan earthquake. It then describes seven episodes of hazards in the town and the extremely severe consequences of these hazards. The hazards included a strong earthquake, multiple large landslides, dam-breaching floods, large-scale debris flows, severe sedimentation, change of river course, and flooding/scouring. The interactions among these hazards are discussed. Finally, a protocol for identifying geohazards triggered by a strong earthquake is suggested. The protocol emphasizes hazard interactions and the concept of the hazard lifecycle, and helps enhance the engineering geological practices.