Assessment of failure and success of preventing damages of debris flows caused by landslide in Laogan Ravine, Yunnan, China

Laogan Ravine is a tributary of Xiaojiang River which is a branch of the Ya ngtse River in North-eastern Yunnan province, China. The railway from Dongc huan to Kunming, a highway and Tuanjie irrigation canal pass through the lo wer reach of the Laogan Ravine. During 70's through 80's, debris flows occu rred frequently in the Laogan Ravine and created great damages to the railw ay, highway and the irrigation canal, total economic losses was 19.5 millio n Yuan. On July 26, 1985 a large debris flow overturned a bus and killed 12 passengers, silted up the open railway tunnel and highway bed with total 4 10m long. The Road Department and Railway Department of Dongchuan city used many methods separately to prevent debris flow damages but they were all n ot in success. Therefore, development and enlargement of debris flow in Lao gan Ravine became a key blocking section of traffic not only for Dongchuan city but also for north-eastern Yunnan province therefore Laogan Ravine deb ris flow control was a great issue for the development of Dongchuan city. I n 1991, area approach was used to control debris flow in Laogan Ravine. The area approach consisted of 2 main dams with total height of 17.5m, 1080 m draining channel, 60 long catch drain, 4 fixing-bed dams, 155 m long protec tion dyke, 8 check dams and afforestation of 160 ha. This debris flow contr ol project was completed in 1994 with total investment of 1.372 million Yua n. Since then, debris flow has not occurred in the Laogan Ravine.