4.2. Observations at site 2.
Landsliding was initiated at this site after the Kuibyshev reservoir filling in 1957, as shown in the archive images (Figure 10). On the 1958 image at the shore scarp foot small erosion forms of rill type can be observed. The 1985 image shows the slope transformation due to abrasion and landslide processes along the bank front, reaching the gully’s left bank in the eastern part of the site. In 1987, the shoreline scarps began to take a circular shape, and later on, the upper part of the slope was transformed by landslide processes. In the lower part, a landslide body is formed, which is gradually eroded due to abrasion by wave erosion.
The digitized scarp lines for different periods – (i.e.1958-1975, 1975-1985, 1985-1987, 1987-1993, 1993-2002, 2002-2019) were analyzed to calculate the rate of landslide scarp retreat in DSAS. This is primarily due to the change in the slope’s horizontal shape and transition into a cirque type of landslide. The plan shape of the scarp line was gradually changing from a line to an arc, which would introduce distortions when making measurements in the DSAS module. Therefore, it was decided to plot lines perpendicular to the baseline of the corresponding period separately.
In general, the average rate of landslide slope retreat varies in the range of 1-2 m/year throughout the study period (Table 7). The period of 1985-1987 stands out as a landslide block moved downslope, and subsequently, the landslide changed to the cirque type and the scarp retreat rate decreased (Figure 11). The analysis of the landslide scarp retreat rate between 2002 and 2019 was conducted from the 2002 line because of the stabilization of the plan shape of the landslide scarp in subsequent years. This is partly due to the excavation works to improve the surrounding area, which leads to a reduction of the landslide scarp retreat rate to 0.84 m/year in 2019 which transferred the landslide to the moderately hazardous landslide category (Ragozin & Burova, 1993).
It should be noted that the study in 2002-2006 was carried out according to the state program, the aim of which was to analyze the landslide processes on both sites and to evaluate their hazard for nearby inhabited and uninhabited constructions. As a result of this study, several recommendations for landslide control measures were formulated. At Site 1, following the recommendations made, shore protection constructions were installed, which made it possible to stabilize the landslide processes above it completely. Unfortunately, a shore protection dam was not installed along the slope’s entire length (see Figure 2), which made it impossible to stabilize the entire landslide section. At Site 2, shore protection and improvement works were not organized until 2018-2019. When the camping base was constructed, approximately one-third of the landslide cirque was reduced, which also resulted in a reduction of the landsliding intensity (Figure 11).