Distribution Characteristics And Hazard Assessment Of Collapse-Landslide Along The Water-Level-Fluctuating Zone Of Xiaowan Reservoir

The area of Xiaowan Reservoir(XWR)is located in the high mountain gorge with deep valley,steep terrain and thus fragile ecosystem.The XWR belongs to a typical channel high dam.Since the fully implemented of Xiaowan Reservoir in 2008,an artificial riparian zone(namely water-level fluctuations zone,WLFZ)with a vertical height of 60 m has been created.The comprehensive action of periodical submerged-exposed and storm runoff causes severe soil erosion and ecological degradation,and then makes the unstable steep bank become prone to collapses and landslides.Severe bank erosion brings a great threat to the operation safety of XWR and the people's lives and property security along the XWR.Changes of ecological and environment and geological disasters threaten the safety of lives and property along the Xiaowan reservoir and safe operation of dam.Understanding the spatial distribution characteristics of Xiaowan reservoir drawdown zone,and clear water level fluctuating zone collapse,landslide scale,density,spatial differences and influencing factors are an important premise of Xiaowan reservoir fluctuating zone potential collapse point prediction and prevention of geological disasters.Therefore,this study takes the riparian zone along the Lancang River and Heihui River belongs to Xiaowan reservoir area as the research area,based on the GF-1 and the Google Earth image data,the spatial distribution of the water fluctuating zone and collapse-landslises were analyzed by using the ArcGIS spatial analysis function.Coupling regional precipitation,geology,terrain and so on,the information model were used to evaluate the risk of collapses and landslides along the riparian zone of XWR.The following conclusions were obtained:(1)The total area of WLFZ in Xiaowan Reservoir is 87.03 km~2,with 48.46 km~2 in mainstream(Lancang River)and 38.57 km~2 in tributary(Heihui River).Three prefectures(cities)of Yunnan province is involved,including 32.84 km~2 in Dali,26.65 km~2 in Lincang and 27.54 km~2 in Baoshan,and most of which is mainly distributed in Fengqing,Changning,Yongping,and Weishan four countries.The WLFZ area mainly exists in the slope below 35 degrees and the northeast and southwest aspect.And the area distribution of the WLFZ in the elevation shows a change of the first increase,then decrease and alternation.And with the slope height becomes larger,the WLFZ area is affected by the elevation change smaller and smaller.(2)There are about 804 landslides in the water fluctuating zone of the Xiaowan reservoir,of which there are about 691 in mainstream,and 113 are tributaries.Total slip area is 1.98 km~2.The collapse and landslide are mainly distributed in the range of 1190?1240 m and below 45°,and the probability of occurrence of collapse and landslide increases with the increase of relative height and slope.The aspect distribution of the collapse and landslide is consistent with that of the water fluctuating zone.In the transition zone of flat slope to the north slope,southeast slope to the south slope.northwest slope to the north slope,the collapse and landslide are prone to change drastically and the area will suddenly increase.Riparian zone and landslides are mainly distributed in the distance less than 400 m from the river,and in the area the distance of 100 m over river,the distribution of riparian zone and landslides has a more far from the river,the smaller the area and the less the distribution trend.(3)Used the information model,the slope height,slope,slope direction,river buffer zone,vertical distribution of river,rainfall and formation evaluation index were selected,hazard assessment of Collapses and Landslides along the WLFZ of XWR is evaluated based on ArcGIS.The results show that the risk zoning map is consistent with the actual situation of Xiaowan reservoir area.Most of the highest risk areas and the higher risk areas are high elevation,high slope,closer to the river and slope aspect that is perpendicular to the Lancang River,mainly in the Silurian strata.Above average risk degree areas of the region almost all over the reservoir area of mainstream and tributaries,the distribution is very extensive.And the more prone to collapse of the high-risk sections of the river is mainly located in Wayao?Shuizhai town(Baoshan),Zhaoyang town(Baoshan),Mangshui(Changning)-Dasi(Fengqing)town,area near the dam,Niujie-Qinghua town(Weishan),Shili town(Fengqing),Da village(Zhujie town in Changning),area at the end of Heihui River in Jijie town(Yangbi).The present study results can be applied to the risk assessment of the landslide hazard in Xiaowan reservoir area,and provide the basis for the comprehensive management of the solid river bank in the riparian zone,and can provide reference for the risk assessment and control of the collapse of the other high dams in the southwest alpine gorge area.