Development Characters And Hazard Assessment Of Debris Flow In Kala Area In Muli County, Sichuan

Hazard assessment of debris flow is an important part of risk management,providing a powerful guarantee for people’s lives and hydropower development in disaster area. As one of the most favorable development bases in China, Yalong river is a debris flow active zone, especially in Kala area, the middle reaches of Yalong river. According to the statistics, there are six typical debris flow gully in this area, which caused severe damage to the people’s lives and hydropower facilities. On August 5, 2012, a large-scale debris flow occurred due to the barrier dam broken in Jiaer gully. The debris flow had loosened pier on the Jiaer bridge and swept a excavator away, which is the most serious debris flow. Therefore, the hazard assessment of debris flow has important scientific value and practical significance.In this paper, selecting single gully and regional as debris flow hazard assessment respectively, based on the analysis of the development characteristics of debris flow, we come up with a model that combined extension theory and combination weighting. The model was applied to access the hazard degree of six debris flow gullies. What’s more, combined information-theoretic method with GIS database, we finished the regionalization of debris flow danger degree.Thesis research content in the following areas:(1) Kala area is a zone with high mountainand deep valley, and have the basic conditions for the formation of debris flow. The conditions include lots of gully with high longitudinal slope, rich landslide source and concentrated rainfall. The area is in a high prototype subtropical climate, where rainfall is concentrated from June to September, and the precipitation intensity is up to 29 mm/h. The elevation of the basin range from 1500~3000m. The topography is steep, and the longitudinal slope range from 130 to 400 per thousand. The slope on the left bank of Yalong river are sunny and escarpment slope, where the rock had received strong weathering, which is good for accumulation of collapse and freeze-thaw. As a result, there are 10 sites collapse. However, the slope on the right bank of Yalong river are shady and bedding slope, where mankind activity is intense and 7 sites landslide are developed.(2) As a debris flow active zone, in spatial terms, the gully debris flow occurs on the left bank of Yalong river, which has the characteristics of bigger basin, bigger scale, lower numbers, and higher maturity. However, the slope mudflow occurs on the right bank of Yalong river, which has the characteristics of smaller basin, smaller scale, higher numbers, and lower maturity. While in time terms, debris flow broke out during the rainy season, namely June to September in Kala. Moreover, the development of debris flow are under the control of Qianbo fault which makes a supply to landslide and mudflow.(3) For gully debris flow, the Jiaer gully has long history. Relative difference of altitude in this basin can achieve 2890 m, and the Longitudinal slope is 183.9‰. Several parts in the gully are blocked by debris of rockfall. The total provenance of Jiaer gully is 143.52×104m3,of which 36.78×104m3 is active. Dammed lakes can be seen in the gully, which contain large amount of water. A diluted debirs flow of medium-large scale may burst in the gully under the effect of extreme large amount of rainfall. However, for slope mudfolw, the Yeli gully has a short history. Relative difference of altitude in this basin can achieve 1290 m, and the Longitudinal slope is 396.97‰. The gully is blocked by loose debris of landslide, whose scale is 130×104m3,of which 30×104m3 is active, and a viscous debris flow of small scale may appear caused by heavy rain.(4) By means of combined extension theory and combination weighting, we come to the conclusion that of all the gullies are medium danger, except for Jiaer, the high danger gully.(5) By means of combined GIS and information-theoretic method, we come to the conclusion that the hazard on the right bank is higher than the left bank. Besides, the Yanggou gully on the left bank and the landslides(Xiatianzhen, Shangtianzhen, Kala) on the right bank are high danger areas, namely, the debris flow is likely to break out in this area.