Underwater mass movements on seasonally inundated banks of the Votkinsk Reservoir (Kama River, Russia)

Abstract

The paper presents a study conducted at a monitoring site near the village of Galyovo on the right bank of the Votkinsk reservoir. The research focuses on the processes of mass movement of fine and clastic material, including the destruction of rockfall slopes and the displacement of debris. The following methods and results were employed. Observations were conducted on the destruction of rockfall slopes, primarily composed of siltstones undercut by abrasion. The peculiarities of debris displacement were also noted. High-precision tacheometric surveying in non-reflective mode was used to determine the rates of slope failure. This method allowed for accurate measurements of slope movement. The rates of debris displacement were calculated by analyzing images obtained from drones and conducting topographic surveying. Mass measurements of the debris position were used to quantify the displacement rates. For the first time, the rates of slow mass movement of material delivered to the shoal due to bank destruction were determined and quantified. The main contribution to the volume of loose material entering the reservoir at the monitoring site was caused by weathering of high slopes. The rate of slope retreat was determined to be 14—15 cm/year, resulting in an input of colluvium of 6.6—7 m3 per linear meter per year. In the seasonally submerged areas of the shallow coastal zone, sediment transport was found to be related to various processes, including wave activity and mass movement of material in underwater conditions. The study recorded the displacement of sediments lining the shallow coastal zone before the formation of seasonal ice cover, with sliding distances of 15—20 meters by the beginning of spring water discharge. The movement of boulders was also observed, mainly in the range of 10—20 cm/year. It was noted that mass displacement of fine sediments in the summer was compensated by the input of products of crumbling, collapse, and bank abrasion. The data obtained from this study can be used to assess the role of various processes in the shallow water of the reservoir and calculate the rate of siltation of the reservoir. This information is valuable for understanding and managing the geomorphological dynamics of the coastal area and the reservoir.