1. Introduction
Creating reservoirs is known to develop and support several industries: i.e. electricity, agriculture, water transport, fisheries, recreation and tourism. At the same time, their creation leads to a fundamental restructuring of natural systems: river water flow and regime, bedload and suspended sediment yield are changed, a unique microclimate is created and landscapes are transformed (Yermolaev & Usmanov, 2014; Yermolaev et al. , 2015; Nicu et al. , 2019). The intensity of exogenous processes acting on the shore and banks increases by orders of magnitude due to the water surface area increase. This very complex of relief-forming processes (together with erosion and gravitational processes) is often called bank transformation when dealing with water reservoirs. Among all modified shores of water reservoirs in Russia, approximately 78% are destroyed by abrasion type, and the remaining 22% – by abrasion-landslide, abrasion-karst, and other types of erosion processes (Usmanov et al. , 2018; Gafurov & Yermolayev, 2020). When the banks are destroyed, a large sediment volume enters the reservoir. This leads to rapid siltation, reduction of water depths, and environmental degradation of the reservoir.
Exogenous geomorphic processes and their monitoring on the shores of water reservoirs have long been conducted (Degraff et al. , 1980). A large number of different research methods have been used for this purpose (Scaioni, 2015). Most often, the shoreline bank dynamics are evaluated, and there is limited quantitative data on the different exogenous processes, their intensity, and the particularities of soil transport on slopes. This is mainly due to poor field accessibility for making observations at the shoreline banks and for installing a reference point network (steep banks, high water level near the shore, bank collapse, crumbling, and landsliding). New opportunities for assessing the rate of shoreline modification by exogenous processes, particularly for shoreline areas that previously were difficult to access have emerged with the appearance of new instrumental methods (laser scanners, UAVs, remote sensing, etc.). Simultaneously, a large diversity of water reservoir types and natural-anthropogenic conditions shaping their banks has resulted in a specific spectrum of exogenic processes. This makes data generalization and spatial extrapolation difficult.
The objective of this study is to better understand shoreline and bank dynamics of the Kuibyshev reservoir – one of the largest reservoirs in the world. Research focuses on shoreline abrasion and landslide processes as the most significant exogenous natural hazards of bank modification. Attention to these processes has increased because a significant number of settlements, religious buildings, cattle burial grounds, and infrastructure (oil and gas pipelines, roads, power lines, etc.) located on the reservoir shores. The shoreline abrasion and landslide processes on the banks near settlements often leads to emergencies: i.e. destruction of buildings, infrastructures, communications, disturbance and total loss of (agricultural) lands bordering the reservoir. Shore transformation processes are still going on at a high rate even though the engineering project predicted the attenuation of these processes in 20 years after the reservoir creation. In this connection, it is necessary to develop effective methods to monitor these dangerous exogenous geomorphic processes. The objective of this study is therefore to assess quantitatively the rates of shoreline abrasion and landsliding using modern instrumental methods. The study sites for shoreline process dynamics were selected by the Ministry of Natural Resources and Ecology of the Russian Federation and the Federal Agency for Water Resources. These government agencies identified areas of the Kuibyshev reservoir banks with the most significant exogenous natural hazards for human settlements and infrastructure.