Abstract:

Lengzi gully is the first order branch of Anning River.There is a largesize landslide in the gully,which provides debris flows with sufficient loose materials.To study the debris flow hazard characteristics,researches were conducted on the formation conditions and development trend of debris flows in the gully based on the field survey,and the countermeasures for debris flow mitigation were also proposed.Results indicated that the debris flows are characterized by low viscous, high frequency,largesize and severe risks.The densities of debris flows were 21 t/m3 of 100year return period,20 t/m3 of 50year return period and 19 t/m3 of 20year return period and the corresponding peak discharges were 12768,8171 and 3818 m3/s,respectively.In normal situation,the frequencies and scales of debris flows will decrease gradually in Lengzi gully.But if strong earthquake or heavy rain happens in this area,largesize debris flows will occur,which will largely block the main river and cause serious harm to upstream and downstream.Accordingly,we suggest that the debris flow control projects should be laid and stability monitoring and warning system of landslide and both sides’ slopes of the gully should also be conducted in the valley