Distribution and prevention of dammed lakes triggered by Wenchuan Earthquake

Wenchuan earthquake induced large-scale of collapses and landslides which blocked river channels and brought about quantities of dammed lakes. The number and the scale of dammed lakes are extremely rare in the world. Besides the backwater of the dammed lakes can flood the road traffic, villages and farmland on the upstream, it can severely threaten the safety of the people's lives and properties on the downstream. Once the dammed lakes burst out, they can cause severe flood disaster. Therefore, it is urgent to monitor the dammed lakes, study their distribution and analyze their development by means of remote sensing (RS) and geography information system (GIS) after the earthquake. In this paper, 145 high-resolution images were processed and 31 severely-afflicted counties were studied through RS monitoring and field investigation. By the time of May 28,2008, 257 dammed lakes existing more than 14 days were identified and there were 34 dammed lakes with capacity of more than 100 000m(3). Based on these conditions, the distribution and development of dammed lakes were discussed and the findings showed that: (a) The dammed lakes induced by Wenchuan earthquake mainly scatter in Beichuan, Wenchuan, Shifang, Mianzhu and Anxian counties, and there exist 154 dammed lakes in these regions, which is 59.92 percent of the total. (b) 95.3 percent of the dammed lakes are within 10km of three major fault zones of Longmen Mountains and the relationship between the number of dammed lakes and their distance to fault zone accords with the law of logarithmic decrement. (c) Most of dammed lakes are distributed in the upper reaches of Minjiang River, Tuojiang River, Jianjiang River and Fujiang River, etc. in rosary. (d) The distribution of dammed lakes in the study areas is dominated by seismic intensity, lithology, slope and altitude. In the next 5-10 years, collapses, landslides and debris flows in the study area will occur frequently and severely and they are likely to block river channels and form dammed lakes. As rainy season comes, the risk of dammed lakes forming and bursting is increasing. So it is necessary to reinforce the real-time monitoring of dammed lakes, make risk assessment and formulate the emergency countermeasures.