INSTRUMENTAL OBSERVATIONS OF BANK EROSION IN SMALL AND MEDIUM-SIZED RIVERS IN UDMURTIA

Abstract

The paper presents the results of channel displacement studies for 2003–2023 at 8 key sites located on small and medium-sized rivers of Udmurtia. In each case, the average and maximum width, area, and volume of erosion were determined using tacheometric survey and unmanned aerial vehicles. For medium-sized rivers with an order of 9.1–14.0 (according to A. Scheidegger's methodology), maximum erosion rates were 5.96–6.15 m/year. The length of the eroded areas varied between 115 and 533 m. The height of the investigated bank scarps ranged from 3.5 m on the Siva River to 5.6 m on the Cheptsa River. For small rivers (order 6.1–9.0), the largest scour values vary from 2.26 m (Lumpun River) to 8.14 m (Kyrykmas River). The length of eroded sections ranges from 48–110 m on the Lumpun River to 55–330 m on the Nylga River. The average height of the eroded scarp on these rivers varies from 2.5 m (Nylga River) to 8.8 m (Lumpun River). In the long-term dynamics of washouts on the Cheptsa River (2 sites) and the Kyrykmas River, one can clearly see a positive (upward) trend with maximum washouts in 2012–2014, 2019, and 2021. The studies established a very close correlation between the maximum width, area, volume of washouts on the Cheptsa River (Adam village) and the Siva River (Metlyaki village) and the maximum annual flow rates of the rivers for the period from 2004 to 2015. The location of eroded areas within bends of different types is characterized by local peculiarities; more often they are confined to areas with the highest steepness.