Amplification Mechanism and Hazard Analysis for Zhouqu Giant Debris Flow

A giant debris flow occurred in Zhouqu County, Gannan Tibetan Autonomous Prefecture, Gunsu Province, in the evening of 7 August 2010, causing 1765 deaths and missing, with enormous property losses. It ruined 4321 houses and caused 22,667 homeless. The stricken area at Sanyanyu debris flow was 50.0 hm including 3 hm urban area and 47 hm farmland. A dammed lake 2 km in length was formed in Bailongjiang River by the debris flow deposit with 8~10 m high, which blocked the river. The main urban area of Zhouqu city was inundated for one month. This tragic catastrophe raises a topic that how a giant debris flow develops from a relatively small original one in source area and what methodology can be used to identify whether a building is in danger or not. In order to understand this issue, a detailed field survey had been carried out in catchments of Sanyanyu and Loujiayu. The field survey revealed that flood in upstream eroded the debris barriers and unconsolidated soil bed in channel and developed into debris flow. The laboratory physical experiments indicated that the major mechanism of giant natural debris flows formation is scale amplification caused by cascading landslide dam failures. Another process of scale amplification is that debris flow schleps sediment from erodible channel bed. At last, a numerical technique will be developed to simulate danger area and momentum of debris flow. Based on the results of dynamic simulation, a method of hazard assessment will be established for identifying dangerous area. Hope this methodology can serve for urban management in mountainous villages and townships.