2. Study area
The Kuibyshev reservoir, built on the Volga River, is the largest in
Eurasia and the third-largest in the world, after Volta (Ghana) and
Smallwood (Canada) reservoirs. It is located in the central part of the
Middle Volga basin at the intersection of the forest and forest-steppe
landscape zones of the Volga uplands and the Low Volga (Yermolaev, 2017)
(Figure 1). The geographic coordinates of the reservoir’s borders are
56°10’ - 53°30’ N, 47°30’ - 49°30’ E. There are three orographic regions
within its basin: Volga Upland, Vyatka Predkamye, Low Volga. The
research was conducted within the Volga Upland at the right side of the
reservoir; its banks are steep and precipitous. Absolute heights are
175-215 m in the north and 250-270 m in the south. The maximum altitudes
are confined to the Zhigulevskiy Mountains (349 m).
The reservoir was formed on October 31, 1955 following the Volga River
damming by Kuibyshev hydroelectric complex. The reservoir reached its
full reservoir level (FRL) of 53 m a.s.l. during the 1957 high waters.
Its total capacity is 57.3 km3, its water surface area
equals 6150 km2 and its total length along the Volga
river is 510 km and 280 km along the Kama river. Its width varies
between 2 and 27 km with a maximum of 38 km at Kamskoe Ustye. Average
water depth is 9.4 m, maximum – 41 m. The length of the coastline is
2604 km, minimum navigation level is 49.00 m. The reservoir is a
seasonal flow regulation storage: the average annual conditional
coefficient of water exchange is 4.3.
The inflow and outflow discharges are asynchronous, and their ratio
determines the reservoir filling and drawdown. The reservoir fills up to
the maximum level during spring floods, while in autumn and winter the
level is at its lowest position. The annual amplitude of level
fluctuations is about 6 m. The average runoff velocity in the reservoir
is 2-10 cm/sec, depending on the value of transit flow and the live
cross-sectional area. The morphological structure of the reservoir is a
system with lake-like expansions. This reservoir serves several economic
sectors: i.e. energy, water transport, agriculture, fisheries,
industrial and municipal water supply.
Two sites on the right bank of the Kuibyshev reservoir near Kamskoe
Ustye village (Republic of Tatarstan) were selected to evaluate the
intensity of shoreline abrasion and landsliding. The sites were selected
based on their representativeness in terms of
geological-geomorphological and landscape conditions for the study area.
In addition, the economic aspect was taken into account since there is a
threat of partial destruction of the buildings and infrastructure
facilities according to the state authorities of the Russian Federation.
At site 1 not only landsliding but also abrasion processes at
the shoreline have developed. The site is located on the right bank 30 m
upstream of the Volga river pier (Figure 2).
The landslide and abrasion process acting on the bank are observed here.
In the upper part of the slope, composed of heavy and middle
deluvial-solifluction loams, collapse and sliding of earth blocks of
different volumes towards the shoreline occur. At the foot of the
abrasion ledge in some places, there are outcrops of the Kazanian age
deposits, i.e. clayey-melty gray pack of rocks of the upper Permian
system.
The landslide has a frontal shape, its length is 32.0 m and its width is
55 m (total area is 1760 m²). An abrasion scarp has formed in the lower
part of the slope with traces of landslides and washout. In aslope
profile, the landslide body itself is well identified in the upper part
with a head scarp and in the lower part a terrace-shape section. The
beach is 2.5-5.0 m wide and is composed of sand-and-shingle material.
The abrasion section at the lower part of the slope erodes and
collapses; soil blocks slide through cracks to the shoreline where they
are eroded by water. Wavebreaking caves are practically absent. Other
exogenous processes are acting on the slope in addition to the dominant
landslide process. There are rills and ephemeral gullies in the upper
part of the slope and gravitational processes (collapse and crumbling)
in the middle and lower part. However, they are of subordinate
importance in terms of active slope processes.
At site 2, a large landslide cirque has formed as a result of
mass movement processes. Here, the landslide-abrasion type of coastal
escarpment is observed. Due to changes in groundwater outflow caused by
water level rise, a sliding landslide develops (Figure 3), forming a
large landslide cirque.
The upper part of the landslide processes led to the destruction of the
old cemetery. Landslide length is 173 m and its width is 110 m (total
area is 13900 m²). The height of the landslide edge is 14,7 m, the
steepness is 90 degrees. The body of the landslide is hilly and
canopy-shaped. The upper landslide scarp is close to the buildings.
The lower northern part of the landslide body is affected by very active
slope subsidence of the earth block type. The slope is composed of
deluvial-solifluction loams with the vertical type of clastic-block
structure, blocks with shrub and woody vegetation are collapsing along
the cracks.
The height of the blocks is 5-6 m, width up to 7-8 m. The soil surface
of the old cemetery is deformed due to cracking and subsidence. The
landslide bodies are located further down the slope, moving towards the
Volga at low speed; their hilly surfaces are overgrown with willow,
american maple, saltbush, common nettle and coltsfoot. Behind the edge
of this landslide body is the landslide cirque. Its southwestern cliff
destroys the old cemetery. Numerous human remains emerge from a depth of
1.5-2 m in the landslide escarpment. In the lower part of the slope, an
abrasion scarp with traces of breakwater caves can be observed.
In 2018 to the south of the study Site 2, a shore reconstruction was
carried out to organize a recreational area near the camping base
(Figure 4). As a result of excavation works and re-organization of
access roads to the camping base pier, the south-eastern part of the
studied landslide cirque and landslide body was leveled and sodded
(Figure 4b). As a result, this fragment of the landslide ledge was
excluded from further analysis. However, the works carried out to
improve the sloping area did not reduce the intensity of geomorphic
processes, and the works on slope stabilization had to continue.