Debris flow forecast based on soil-water coupling mechanism: a case study in Aizi gully watershed

On 28 June 2012, a huge disastrous debris flow occurred in Aizi gully watershed which is situated in Ningnan County, Sichuan Province, China. This debris flow event not only resulted in 40 people being dead or missing, but also seriously affected the construction process of Baihetan Hydropower station. With the aim of reducing the influence of the debris flow on local economy development and people’s life, a field investigation and remote sensing interpretation were carried out to explore the whole condition of this area, including the amount of loose deposits, topography conditions and rainfall amount, etc. We concluded that the loose materials, rainfall conditions and topography still satisfied the conditions for debris flow initiation. In the future, under intensive rainfall a large scale debris flow could probably occur in this area, which would pose a grave threat to the safety of the residents. To reduce the risk posed by future debris flows in Aizi gully watershed, a soil-water coupling model was employed to calculate the mixture density, and evaluate the occurrence probability of the debris flow, and assess the corresponding warning grade. On the basis of the results of model calculation, combined with the real-time rainfall condition, timely forecast information can be issued. This in turn can significantly facilitate disaster mitigation and prevention, and the potential disaster of debris flow in Aizi gully can be minimized.