Characteristics, Hazards and Mitigation of Debris Flows Along Min River after the Wenchuan Earthquake

Abstract

After the Wenchuan Earthquake, debris flows frequently occurred and became the disastrous geo-hazard following this Earthquake at the seriously hit areas. This paper focused on characteristics,hazards, change and mitigation of the debris flows along Min River. The investigation and test data showed that debris flows were characterized by various types, low triggering rainfall with over 30 mm/24 h and over 10 mm/h, the density of 2.01–2.21 t/m³, high frequency and large magnitude. Debris flow mainly appeared in the watersheds of which area and geomorphologic index (θ) was less than 10 km² and 6, respectively, accounting for 89 %, and the hazardous watersheds were featured with the area of 2–8 km² and the θ of 2–4. Moreover, debris flows occurred in simultaneity when rainfall reached 20 mm/h and produced step-dammed lakes. Debris flows and the following dammed lakes resulted in rapid change of river channel, endangered towns and frequently interrupted traffic. Debris flows, especially those from the watersheds with over 10 km²,will continuously endanger reconstruction projects and local people in the future 10–15 years before they recover normal. After analyzing the loose materials amount and the potential destructed objects, the 23 hazardous watersheds are suggested to control and prevent. Finally, the mitigation measures, including risk identification and zoning, hazards prediction, remote-monitoring and early-warning, emergency mitigation plan, integrated control and river channel dredging, are presented for debris flow hazards mitigation.