Determination of the maximum flow of the river with anthropogenic factors

. This study was aimed to determine the anthropogenic and natural factors affecting hydrological regime of rivers, reliability and safety of hydroelectric facilities. The work of the Uchkurgan hydroelectric complex before and after the commissioning of the Toktogul reservoir with a hydroelectric power station is considered. The observations were conducted over a period of 92 years. A significant decrease in the unevenness of the average long-term water flow has been established for various periods. A homogeneity graph was built, which showed the periods of influence of anthropogenic factors in 1975 and 1990. The following scenarios for determining the maximum water discharges were considered: local water consumption regime, commissioning of the Toktogul reservoir, and energy mode. The estimated verification flow of 0.01% security satisfies the design capacity of the hydroelectric complex of 2720 m 3 /s..


Introduction
The founder of the application of the theory of reliability and safety in hydro-reclamation and hydrotechnical science is considered to be Mirtskhulava [1].According to his works, the issues of reliability and safety of the operation of hydroelectric facilities are considered [2][3][4].The main reasons for failures in the operation of water intake in hydroelectric facilities are called erosion of the downstream, silting of the upstream in front of the galleries, deviation of the flow from the waterworks, deformation of individual elements and hydrological aspects [5][6][7].Approximate methods are proposed for assessing the reliability of elements and foundations of water intake in hydroelectric facilities and other irrigation and drainage structures.A number of methods [8], recommendations [9][10][11], provisions [12] for assessing and ensuring the safety of hydraulic structures have been developed.Lentyaev and Smirnov [13] indicated that hydrographs for different service life of a structure, when calculating the depth of local erosion, and taking into account cavitation phenomena.Zolotov and Ivashenko [14] studied a sample including 2132 cases of accidents and damage to the dams over the world, including 1148 accidents.Based on the analysis three main forms of dam failure were identified: overflow over the crest, strength (stability) damage, and seepage strength damage [18,19].Bobkov et al (1999) [17] noted that the conditions for skipping flood flows largely determine the level of safety of operation of a hydroelectric complex.According to ICOLD data, 25% of all dam failures are caused by water overflowing over their crest due to insufficient capacity of spillways.
It is necessary to refine the values of the estimated discharge flows, taking into account the data of hydrological and meteorological observations carried out during the operation of the hydroelectric complex.It is advisable to adjust these costs at least once every 10 years for class I and II hydroelectric facilities, the design of which includes a lower provision for estimated costs, and at least once every 5 years for all other hydroelectric facilities, as well as after each flood with a flow rate close to estimated.
Vasilevsky et al. [18] were analyzed the operation of the Volga-Kama cascade of 14 large hydroelectric facilities from the condition of skipping the estimated waste flows.
It is noted that this condition may not be feasible due to: insufficient hydrological knowledge of the area at the time of determining the estimated flow rates, changes in the operating conditions of the hydroelectric complex, restrictions on the passage of flow rates in the downstream (courage, development of floodplain lands, construction, etc.) operability of mechanical equipment.
Oliver et al. [19] devoted to the study of issues of modeling scenarios for managing the regime, water quality, and its changes during operation.
In the studies of Bakiev et al. [20] assessed the current state of silting in the channel reservoir of the Tuyamuyun hydroelectric complex and, using GIS technologies, developed ways to increase the useful capacity [21][22][23].
In the dissertation of Fisenko [24], the development of safety criteria for a mediumpressure hydroelectric complex is given, taking into account the time factor, silting of the drainage with manganese and channel processes.
Bondarenko and Belokonev [25] noted that reservoir hydroelectric facilities are technologically dangerous objects.The authors of the danger emanating from waterretaining structures to the hydrological, hydraulic, structural, filtration and channel.It is noted that 30% of emergencies arise due to the hydraulic aspect of safety, namely due to an incorrect assessment of the capacity of culverts.From this point of view, the Yumaguzinsky hydroelectric complex on the river Belaya in the Republic of Bashkortostan was analyzed.
Issues of water safety and safety of hydraulic structures are in the focus of attention of world organizations [26][27][28][29][30]. Hydrological calculations are carried out using normative documents [31].The paper proposes a 3H-EMC modeling procedure for determine the ecological flow in the Sperchios River in Central Greece [32].The study considers a method for determining the maximum discharges for the Wronka gauging station located at the mouth of the Warta River in Poland [33].The expediency of using GIS technologies in solving the problem, taking into account flood zones, has been established [34,35].The paper investigates both natural and anthropogenic factors affecting water quality in rural and urban areas.All these studies do not consider changes in the water management situation, an increase in irrigated areas, the reconstruction of water intake facilities, the construction of a cascade of water storage facilities, the transition to an energy regime, etc.

Methods
In regulatory documents, the parameters of probability distribution curves are recommended to be determined in accordance with normative documents.Since the site of the hydroelectric complex under consideration is located on the high-mountain river Naryn, the hydrological features of high-mountain rivers, the characteristics of the probability distribution curves for maximum water discharges are recommended to be determined in accordance with the guidelines for determining the estimated maximum water discharges.In modern hydrology, it is proposed to determine the calculated values of the river discharge by constructing a graph of the uniformity of the observed discharges, where one can clearly trace the beginning of the period of influence of anthropogenic factors.
To do this, the years of observation are arranged from beginning to end, in ascending order, and the expenditure of the first year is added to the second year of observation, and so on.Every five years, the calculated amount is entered opposite that year.Arranging the years along the ordinate, and the sum of the costs along the abscissa, we obtain a uniformity graph and, at the fault points, we determine the influence of anthropogenic factors on the domestic flow of the river.

Results and Discussion
Determination of the statistical parameters of the maximum flow of the Naryn river by the graphical-analytical method was carried out in the following sequence: -in the value of the actual series of observations x we arrange in descending order and for each member of the series the empirical security is determined by the formula: Where: mserial number of members of the statistical series; nthe total number of members -in values x and m P are plotted on the cell of probabilities and a security curve is drawn on them, which best corresponds to the actual data.
Based on three points ( % 5 x , % 50 x , % 95 x ) removed from the curve, the coefficient of skewness is determined: -according to the skewness coefficient S, the difference of normalized deviations ( % 95 % 5
-further, the standard deviation is calculated: To determine the costs max Q of any given supply, we find the asymmetry coefficients s C built in relative ordinates, i.e. in the form of normalized deviations.
The natural regime of the rivers of Central Asia changes significantly from anthropogenic impact.The words of V.L. Schultz, who said that each new stage in the development of economic activity will be characterized by a different variance of the annual flow, have not lost their relevance.
With the independence of the Central Asian countries in 1990.The Toktogul reservoir is operated in an energy mode with high discharges in the winter season, which creates certain difficulties in the operation of the underlying structures.Figure 1 shows the comparative hydrographs of average annual discharges at the station Uchkurgan for various periods of time.The observation period includes 1910-1918 and 1925-2007, and the longer the series of observations, the higher the probability of a small error in the calculations.But it must be taken into account that on rivers with a cascade arrangement of hydroelectric facilities, the calculated maximum water flow for the hydroelectric complex under consideration should be determined taking into account its location in the cascade, the capacity of the upstream hydroelectric complex at FBL and NBL, and also taking into account the operating mode of hydraulic structures and reservoirs of the cascade.
The results obtained for the Naryn river in the alignment of the Uchkurgan hydroelectric complex is shown in Table 1, 2  For these two scenarios, we also perform the entire sequence of calculations and obtain the results are shown in Table 3. Calculations show that the data obtained for different periods of observation differ greatly from each other.The results obtained are scattered over a wide range, and what development scenario should we consider when further substantiating the reliability of the entire hydroelectric complex in terms of the passage of extreme flood waters.
Indeed, all three development scenarios are closely related to the commissioning of the Toktogul reservoir.It will remain the main regulating water body for the entire Naryn basin, as a result of which, when calculating the underlying objects, the culverts and the mode of its operation should be taken into account.The first scenario includes a period of domestic flow of the river, without regulation by large reservoir capacities, which creates a catastrophic flow of 0.01% security.Also, this scenario is unacceptable, due to the fact that the Toktogul reservoir and the cascade of hydroelectric power plants located above the Uchkurgan hydroelectric complex are not able to transform the flow rate of more than 3600 m 3 /s.Hydroelectric power plants operate on regulated irrigation releases during the growing season (up to 800 m 3 /s) and energy during the low-water period (up to 650 m 3 /s).
If in the second scenario the reservoir was operated in the irrigation mode, then in the third scenario there is a transition to the energy mode.The hydrograph of the river during these periods, losing its maximum peak, takes on a more even appearance.Also, for the entire period of operation of the reservoir, the maximum water flow in the alignment of the Uchkurgan hydroelectric complex above 2000 m 3 /s was not observed.In both cases, the calculated verification flow of 0.01% security satisfies the design capacity of the hydroelectric complex of 2720 m 3 /s.

Conclusions
 New water management conditions associated with a change in the water use pattern, an increase in irrigated areas, and transition of the Toktogul reservoir to an energy mode of operation, lead to an increase in maximum water consumption during winter period and sharp daily water fluctuations in the Naryn River.
 The considered three scenarios for determining the maximum discharges showed that they are all closely related to the commissioning of the Toktogul reservoir.It will remain the main regulating water body for the entire Naryn basin, as a result of which, when calculating the underlying objects, the culverts and the mode of its operation should be taken into account.Proceeding from this, the maximum flow rate of the hydroelectric complex is assumed to be 2720 m+/sec.

E3S
Web of Conferences 410, 05030 (2023) https://doi.org/10.1051/e3sconf/202341005030for individual areas, we s C find the deviation of the ordinates of the binomial supply curve from the middle  

Fig. 1 .
Fig. 1.Hydrographs of the average annual water discharges of the Naryn River at the station Uchkurgan for various periods.Note: 1925-1952 -before the design of the Uchkurgan hydroelectric complex; 1990-2007 -after the commissioning of the Toktogul reservoir.

Fig. 2 .
Fig. 2. Graph of the flow uniformity of the Naryn River at the site of the hydrometeorological station UchkurganFor these two scenarios, we also perform the entire sequence of calculations and obtain the results are shown in Table3.

Table 1 .
. Calculation of the uniformity of the maximum discharges of the Naryn river after the design of the Uchkurgan hydroelectric complex

Table 2 .
Calculation of the homogeneity of the maximum discharges of the Naryn River after the design of the Uchkurgan hydroelectric complex as a sample of 5 years

Table 3 .
Determination of the maximum discharges of the Naryn River of low security for different periods of observation, m 3 /s