Probability assessment of river blocking by debris flow associated with the Wenchuan Earthquake

Abstract

This paper assesses the probability of the main stream in the Dujiangyan–Wenchuan reach of the Minjiang River becoming blocked by debris flows in response to the Wenchuan Earthquake of 12 May 2008, on the basis of analyses of remote sensing data and ground investigations. Background information of debris flow gullies was developed from field investigations and high-resolution remote sensing image interpretation, and was used to estimate the maximum discharge per unit width by means of the revised model of debris flow magnitude according to the situation after the Earthquake. Based on improved discrimination equations of river blocking induced by debris flow, 29 debris flow gullies were evaluated and classified as four probability levels: extreme high, high, moderate and low. The results show that most of the debris flow gullies were at or over moderate hazard level, accounting for 72.4% of the total area. The present results provide a scientific basis for the prevention, elusion and mitigation of debris flow hazards and will contribute to the reconstruction of an earthquake prone area.