Geomorphic Response Of Dam Events In The Yalong River

The southeast margin of qinghai-tibet plateau is the qinghai-tibet plateau crustal deformation and earthquake,one of the strongest region is the geological research hotspots,Yalong River basin is located in the southeast margin of qinghai-tibet plateau region,the terrain ups and downs is bigger.Mountains and valleys are interlaced.Dry and wet seasons are distinct.Because of abundant rainfall and steep terrain,this area is prone to landslides and debris flow blocking the river and becomes the typical study area of damming events.The dammed lake affected the longitudinal section of the river mainly through the sedimentation,the barrier to the erosion of the river,and the strong erosion to the downstream of the dam after the lake outburst.It is helpful to understand the evolution process of fluvial geomorphology in the Yalong River Basin to analyze the barrier events by using the reconstruction of Yalong Lake and fluvial geomorphology parameters.In this paper,the influence of dam events on river elevation profile in Yalong River Basin is discussed in detail to reveal the geomorphic evolution mechanism of this region.In this study,the distribution and size of 34 dams in the Yalong River basin were obtained by remote sensing interpretation and partial field investigation,and a detailed age and scale reconstruction of the Yuting ancient landslide dam lake formed by a typical dam was carried out.At the same time,the 12.5m Also DEM was used for river digital terrain analysis,and Topo Toolbox was used to extract river geomorphic parameters such as longitudinal profile,crack point and steepness index(k_sn)of the main trunk stream of Yalong River,Liqiu River,Litang River and Xianshui River.Further dams and rivers profile,river knickpoint,k_sn value and spatial overlay,and combining with the slope in the basin,the basin area,faults,lithology and other factors,taking Xianshui River with no weir dam distribution as the control,the influence of weir dam on the elevation profile of the main trunk stream of Yalong River,Liqiu River and Litang River was analyzed,and the causes of river splits were preliminarily discussed.The research conclusions are as follows:(1)Based on the photoluminescence dating of the sedimentary samples and the analysis of the sedimentary characteristics of the landslide lake,combined with the results of field investigation,it can be preliminarily determined that the Yuting ancient landslide lake was a landslide lake,formed about 7.9ka ago and ended about2.9ka ago,and the ancient landslide lake lasted for 5ka;The lake inundated from the north of Shade Village to the Laha Village at the Yuting Landslide.The lake covers an area of 6.47×10⁶ m² and has a reservoir capacity of 1.54×10⁷m3.(2)The spatial superposition results of the weir dam and the longitudinal profile,the river break point and the river break point show that the spatial correlation between the weir dam and the longitudinal profile,the high value of k_sn and the river break point is significant in the Yalong River basin.Compared with the debris flow barrier dam,the landslide dam has a more obvious influence on the longitudinal profile of the river,and has a better spatial correspondence with the high value of k_sn,so it is easier to form the river crack point.(3)Dammed events,lithology,faults and other factors may form river fissure points.Under the support of the upstream accretion and downstream erosion,the maximum impact of the dam on the longitudinal profile of the river can reach 596 m(Yuting landslide),and the influence of the dam should be considered in the inversion of the tectonic activity information by using the river fissure point.