Abstract: As the secondary disaster after the megaquake on May 12,2008, a heavy debris flow broke out on August 13, 2010 in Wenjiagou village with its one-time discharge amount up to 4.6 million cubic meters and maximum depth of gully bed downcutting over 70 meters. This catastrophic debris flow, together with complex geological conditions, makes it challenging to select and design the control scheme. Based on analysis of the formation and source of the debris flow, we demonstrated the effects and limitations of control schemes involving drainage, obstructing, source consolidation, flow cutoff and diversion. Through comparison, we proposed the scheme of separating the upstream water flow with middle stream stone by flow diversion tunnels. The project consisted of diversion tunnel, catch basin, diversion dike, and screening grids at the bottom of the catch basin. The project was proved to be effective through rainfalls of 165mm, 130mm, 182.4mm in 2011. This research provides a new approach and could be referential for the control over large-scale debris flow.

Key words: debris flow, separation of stone and water, prevention project, geohazard, diversion tunnel