Assessment shoreline formation of reservoirs

. The article analysis the factors influencing the reduction of reservoir useful volume, including the formation of shores, and proposes and method of their quantitative calculation. The research was provided in the South Surkhandarya reservoir. During the exploitation of the reservoir, were assessed the morphometric index of the basin and changes in a bank due to various influences. The article presented mathematical, statistical calculations of changes in erosion conditions due to displacement of the left banks of the South Surkhandarya Reservoir and changes in pressure in the strata and water saturation of the coastal layers. The proposed method of assessment and calculation will allow development measures to improve the operation of reservoirs based on the determination of morphometric parameters and prevent the formation of shores.


Introduction
One of the most important issues of integrated use of available water resources is regulation of river flow through reservoirs. In this regard, special attention is paid to the reliable and efficient use of existing reservoirs, the provision of water to consumers during the growing season, the development of improved methods for calculating the amount of sediment at the bottom of reservoirs, determining the loss of useful volume during exploitation and shoreline formation due to various impacts.
The existing reservoirs in the country are filled with mud and sediments from year to year. The useful volume is reduced due to the sedimentation in the flow of rivers, which comes to a reservoir, erosion of banks, landslides and land movement. As a result, becomes to some problems with the planned use of reservoirs, i.e. inconveniences in collecting and delivering the required water and mitigation of water demand [5,12,13,16,17,18]. In this regard, the formation of the banks of reservoirs and their quantitative assessment are relevant in the reliable and efficient use of most reservoirs currently in operation.

Methods
Researches were provided in the South Surkhandarya Reservoir and analyzed coastal changes due to various impacts during the exploitation of the reservoir. The total length of the reservoir shoreline is 60 km, of which about 4 km are cliffs. 50% of the coastline is formed from abrasive shores. Scientific research about the formation of the reservoir shores found that in the first phase of reservoir filling, the one-meter-long shoreline wash ranged from 100 m3 to 225 m 3 , while in the second phase, it ranged from 50 m 3 to 450 m 3 . Fifteen years later, this size was 5-40 m 3 . Although coastal washing was accelerated during the initial period of operation, it can be seen that this figure has declined sharply in recent years ( Figure 1). The flow degree generated by transit water discharge in the South Surkhandarya reservoirs does not significantly impact coastal erosion. However, the movement of water due to wind-induced ripples creates such a flow velocity that the result is a strong washout in the coastal and adjacent submarine zones, leading to the displacement of large amounts of ground masses [1, 2, 7, 8,].
The chemical and biological processes that happen in the reservoir area, the ripples, and the currents in the river flow gradually change the shores' natural relief and appearance in the project. Over time, the reservoir becomes shallower due to filling with sediments and the coastal areas are covered with vegetation ( Figure 2). From these observational data, we can see that the full volume of the reservoir decreases at the normal stagnant water level (NSWL), and the water surface area expands.
In the below were given mathematical-statistical calculations of changes in erosion due to the displacement of the left bank of the South Surkhandarya Reservoir and changes in pressure in the strata and water saturation of the coastal layers and a decrease in pressure there.

Results and Discussion
Results of coastal deformation bring to formation of a mobile mass, and those mass effects of reducing the volume of the reservoir and brings to rise of the reservoir water. [1,2,7,11].
The volume weight of the moving mass is expressed as follows: The volume weight of the avalanche mass is written in terms of the coordinates of the displacement limit and is given by the following multiple integral: Knowing the coordinates of the surfaces bounding the avalanche mass, it was found the curves of the boundary surface passing through the top and bottom, right and left. These curves were found using Newton or Lagrange and other approximate formulas ( Figure 3).
In the process under consideration, it was used Lagrange's interpolation formula. The same can be said for Newton's formula; one can use it too. To do this, need to write Newton's interpolation formula for the curves delimiting the avalanche mass and for

Fig. 3. Coastal displacement as a result of a sharp rise in the reservoir level
The Lagrange interpolation formula is selected by selecting the curves А В С 1 1 and СВA abscissa delimiting the avalanche mass as shown in Figure 3: We get the corresponding ordinates from the ordinates in Figure 3: We put the given coordinates in Lagrange's interpolation formula: The equation of the СВA curve looks like this: Using the coordinates of the avalanche in motion and the equations of the  Avalanche cross-sectional area of 1 1 CBB C were found with using the coordinates in By the following integral were found the moving cutting surface BA B 1 (Fig. 3).
By the following integral were found moving cutting surface

Conclusions
As a result of the research, it was found that on the left bank of the South Surkhandarya reservoir, there are cases of landslides, migration of soil. On the right bank, there is a process of shallowing due to the accumulation of debris.
One of the problems of most reservoirs currently in operation is that the reservoir can be identified using the proposed calculation method for small landslides, soil erosion and degradation, subsidence, washing, and shoreline displacement on water-buried coastal slopes. Immediate detection of emerging coastal areas provides an opportunity to develop measures to prevent them.
Suppose the reservoirs project and exploit on the basis of the above measures. In that case, they will be prevented from malfunctions and accidents, the operation of the reservoir will be further improved, and the efficient use of water from the reservoir will be achieved.