关键词: 岷江上游, 泥石流, 堰塞湖, 潜在危害, 判识

Abstract:

The Wenchuan earthquake caused numerous landslides and collapses that provided abundant loose solid materials for future mobilization as debris flows. The formation conditions for debris flows were changed consequently. Debris flows will be very active for a long time in the affected area. Their secondary disaster, barrier lake, is beginning to appear. Therefore, it is urgent to identify those debris flow gullies which are potential to form barrier lakes following the environmental changes caused by the earthquake. This paper selected the upper Min River from Yinxiu to Wenchuan as study area, analyzed the changed formation conditions of debris flows and the damages of a typical debris flow barrier lake, and interpreted the loose solid materials from TM satellite images and aerial photographs. Then, the identification factors were selected and classified based on the factor independence analysis. At last, the fuzzy matter-element extension theory was used to construct a model to identify potential barrier lakes. The potential future increase in debris flow activity relates directly to the great increase in loose materials. The interpretation results indicated that the area of the landslides and collapses caused by the earthquake is 39.40 km², accounting for 6.97% of the total study area. Assuming 55% of the landslide and collapse area were their deposition area and the average deposition depth was 10 m, the volume of the loose solid materials can be estimated as 2.13×10⁸m³ which was sufficient for debris flow formation. Based on the factor independence analysis, the volume of the loose solid materials per unit area, the discharge ratio between the debris flow gully and the main river, the slope gradient of debris flow channel, the main river width, and the included angle between the debris flow gully and the main river were determined as identification factors. According to the multi-factor comprehensive identification, among the 55 first-grade gullies, 17 gullies have high probabilities for potential debris flow barrier lakes, 15 have moderate probabilities, and 23 gullies have low probabilities. The most likely debris flow gullies for forming barrier lakes mainly distribute in the middle-to-lower reaches of the study area (Yingxiu Town to Caopo Town), and those with moderate and low probabilities are mainly distributed in the upper reaches of the study area (Caopo Town to Wenchuan County). In addition, among the 17 potential debris flow gullies with high probabilities, 4 gullies already yielded barrier lakes during the 2008-2010 rainy seasons. The remaining debris flow gullies will produce barrier lakes in the future with high probability.

Key words: Upper Min River, debris flow, barrier lakes, potential damages, identification