The Study on the Potential Debris Flow Triggered by Wenchuan Earthquake:A Case Study of the Guanshan Gully in the Upper Reaches of Minjiang River

After the Wenchuan earthquake,a lot of potential debris flow gullies are activated as active debris flow gullies because of the earthquake.These debris flow gullies will be in the active period for a long time in the future.The debris flow outbreak scale and frequency increase obviously,which threatens life and property safety of the people in the disaster area and influences the reconstruction of the disaster area.This paper takes Guanshan gully in the upper minjiang river as an example to discuss about the cause,starting mode and damage of the potential debris flow triggered by the earthquake preliminarily.The Guanshan gully can be defined as a typical potential debris flow gully through the interpretation of remote sensing image before the earthquake and aerial image after the earthquake.The Guanshan gully changes from a potential debris flow gully into an active and high-frequency debris flow gully.The cause is that the earthquake results in many collapses and landslides in the basin,which provides rich material sources for the debris flow.Through estimation,there are 2 landslides,21 collapses and 7.8 million m3 loose solid materials in the Guanshan gully.The starting mode of the debris flow in the Guanshan gully is that under the condition of precipitation,the landslides in the upper basin turn into debris flows,then with the acceptance of the materials runoff scoured from the two-side slope surface,the debris flows scour the loose materials in the gully bed strongly to increase debris flow scale at the same time,therefore harmful debris flows are formed.If the rainstorm frequency of P equals to 1% or 2%,the blockage caused by debris flows has more possibility.Once debris flows block the main river,the blockage backwater and outburst flood will threaten the safety of people's life and property in the upper and lower river.at the same time,debris flow will threaten the safety of 213 provincial road.