Impact of lake expansion on the underwater topography: a case study of Lexiewudan and Yanhu Lakes on the Tibetan Plateau

With increased precipitation and meltwater, most lakes on the Tibetan Plateau have expanded rapidly. However, the impact of erosion and sedimentation following lake expansion remains unclear. Using Lexiewudan and Yanhu Lakes as examples, we created a water depth inversion model using random forest method and combined it with lake bathymetric data and Landsat images and analyzed changes in underwater topography using SRTM and ICESat-2 data. The average water depths of two lakes were 5.92 and 9.82 m, and the root mean square error of inversion values were 0.85 and 0.93 m, respectively. Results showed that the underwater topography underwent considerable changes, in which at least half of the study areas experienced large topographic changes with 2–5 m. Lexiewudan Lake had a topographic change of more than 2 m in 61.28% of the total, while Yanhu Lake made up 69.78% of the total. The erosion and sedimentation volume of Lexiewudan Lake were 0.19 and 0.03 km3 and those of Yanhu Lake were 0.38 and 0.03 km3, respectively. Extensive underwater erosion and sedimentation are closely related to the original topography. Lake water movement, sediment transport, and permafrost degradation in flooded areas may also affect changes in underwater topography.