Abstract:

Since the late-Cenozoic, the strong uplift of Tibetan Plateau not only formed a large number of tectonic fractures on the southeast edge, but also generated many tectonic rift lakes due to structural stretching and compression. However, in recent years, some of the lakes started to shrink and depicted a reduction in lake depth, which has eventually exerted great influence on local ecological environment and socio-economic development. In this paper the Qionghai Lake, located on the southeast edge of the Tibetan Plateau, is selected as the study area. Based on exploring the debris flow characteristics of Guanba river in the north of Qionghai Lake, the effect of sediment deposition deriving from debris flows on Qionghai Lake is analyzed. The research shows that: (1) The scale and frequency of debris flow occurrence is higher in the Guanba River, and the primary material sources are landslide and non-point source erosion with a movable volume of 428.03×10⁴ m³. (2) The frequent occurrence of floods and debris flows are the primary cause of sediment accumulation in the Qionghai Lake, and the debris flows are controlled by the coupling effect of frequent earthquakes and heavy rainfall. It is predicted that debris flows will still occur frequently, and sedimentation disasters will become more severe in the future. (3) Since 1950, the average deposition rate was about 17.09 mm/a. In terms of current deposition rate, it is inferred that the longevity of the Qionghai Lake will be only about 600 years. (4) The comprehensive governance model with management of administrative law is proposed in the Guanba River. The results can not only provide reference bases for planning management and disaster prevention in Qionghai Lake basin, but also contribute to reveal the reason of lake shrinkage on the southeast edge of Tibetan Plateau.

Key words: Tibetan Plateau, Guanba River in Xichang, debris flows, Qionghai Lake in Sichuan, sediment deposition, tectonic rift lake