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INFLUENCE OF CLIMATIC CONDITIONS ON THE MAXIMUM FLOWS OF WATER
DISCHARGED INTO THE LOWER WATER RESERVOIR
B.F.Khikmatov,
Civil Protection Institute Ministry of Emergency Situations
Republic of Uzbekistan,
B.R.Rapikov
National University of Uzbekistan named after Mirzo Ulugbek,
Abstract:
The article is devoted to studying the dependence of the maximum flow rates of water
discharged into the lower pool through reservoir dams on weather and climatic conditions, using
the Tokhtogul reservoir as an example. For this purpose, a statistical assessment of the
relationship between air temperature and maximum water flows discharged from the Tohktogul
reservoir in the autumn and winter seasons into its lower pool (
r = 0.911 ± 0.008
) was
carried out and a regression equation for this relationship was obtained. As a result, it was
possible to predict the maximum water flows of the Naryn river in the autumn-winter seasons
depending on air temperature.
Keywords:
reservoir, dam, tailwater, maximum water flow, air temperature, flood, assessment.
I. Introduction
Currently, specialized scientific centers worldwide are paying significant attention to
studying hazardous hydrological processes, particularly the breaching of dam reservoirs under
various influencing factors. When reservoirs are operated in an energy-driven mode, especially
during autumn and winter seasons, the discharge of maximum water volumes from dam
reservoirs into downstream sections increases, leading to hazardous hydrometeorological
phenomena such as floods and mudflows [1,11,14,15,16]. Moreover, disasters associated with
peak river discharges of different origins have become more frequent in recent years. These
events cause substantial material and moral damage to various economic sectors and the
population, and, in some cases, result in human casualties [3,7,10,12]. Therefore, current
research focused on assessing the hydrometeorological and socio-economic dependencies of
maximum water discharges from reservoirs operating in energy-driven modes is of great
relevance.
II. Research Objectives and Tasks
The primary objective of this study is to examine the impact of weather conditions on the
maximum water discharges released into downstream sections of reservoirs operated in an
energy-driven mode, using the Toktogul Reservoir as a case study. To achieve this objective, the
main tasks of the study include analyzing the daily peak water discharges from the Toktogul
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Reservoir dam into the downstream section, statistically evaluating their dependence on air
temperature, and developing practical recommendations based on the obtained results.
The Toktogul Reservoir and the daily peak water discharges released from its dam into
the downstream section have been chosen as the
research object
. The study focuses on
analyzing the hydrometeorological and socio-economic dependencies of water discharges from
the reservoir, which constitutes the subject of this research.
III.Main Results and Discussion
The emergence of this extraordinary situation is directly linked to the Toktogul Reservoir
and its operation in an energy-driven mode. Over the past decade, the neighboring Kyrgyz
Republic has primarily operated the Toktogul Reservoir for energy production purposes [11,15].
Consequently, the current hydrograph of the Naryn River has transformed into an almost
complete inverse of the hydrograph that represents its natural water regime (Figure 1).
During the winter months, due to increased electricity demand, the Toktogul Hydropower
Station operates at its maximum capacity. As a result, the peak water discharges in the Naryn
River also occur in the winter months, as illustrated in Figure 4. In this graph, the water inflows
(labeled as "Inflow") represent data provided by the Kyrgyz National Energy Holding Company,
while the water outflows (labeled as "Outflow") correspond to measurements taken at the
"Uchkurgan" hydrological station of UzHydromet.
Fig. 4. Changes in the inflow and outflow elements of the
Tokhtogul reservoir during the year (2020)
Therefore, the main reason for the discrepancy between the hydrographs shown in Figure
1 is the sharp drop in air temperature during the winter months, which in turn leads to an
increased demand for electricity generation. To meet this demand, the volume of water released
Inflow
Outflow
day
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from the reservoir dam into its downstream section must be significantly increased. Below, we
discuss the hydrometeorological aspects of this process.
To achieve the research objective, we utilized air temperature data from the Uchkurgan
agrometeorological station, administered by UzHydromet, located along the Naryn River.
Information on the water discharges from the Toktogul Reservoir dam was obtained from the
engineering service of the Kyrgyz National Energy Holding Company, as previously noted.
Using these hydrometeorological data, chronological graphs of water discharges and air
temperatures were plotted for September–December 2022 and for January–February 2023, when
the extraordinary conditions arose [2].
As can be seen from the resulting graph, an inverse relationship exists between the
average daily water discharges released from the Toktogul Reservoir into the downstream
section and fluctuations in air temperature: when air temperature decreases, the volume of water
released to the downstream section increases (Figure 2).
Fig. 2. Changes in air temperature (t) and water flow rates (Q) discharged through the
dams of the Tokhtagul reservoir (autumn-winter season, 2022-2023)
Based on this graph, the variations in air temperature and the volume of water released
from the reservoir dam into the downstream section were analyzed. Specifically, from January
11 to January 21, 2023, the average daily air temperature in the region dropped sharply (to as
low as -10 °C), and during nighttime hours, it fell below -20 °C. As a result, the demand for
electricity increased, prompting the Toktogul Hydropower Station to operate at full capacity.
This situation led to an increase in the volume of water discharged from the reservoir into the
downstream section, with average daily peak flow rates reaching up to 1000 m³/s. Notably, this
flow rate remained at approximately 1000 m³/s from January 12 through January 28, a span of 17
days.
Flow rate discharged through the Tokhtagul
reservoir
Air temperature
Days
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It was precisely this scenario—namely, several consecutive days of maximum,
unchanging discharge from the reservoir dam—that caused significant damage to the banks of
the lower reaches of the Naryn River, specifically the section flowing through Naryn District of
Namangan Province in Uzbekistan. It should be emphasized that this study relied on average
daily flow data. In reality, instantaneous peak flow rates (i.e., measured at specific moments)
likely exceeded 1000 m³/s.
To enhance the practical significance of the results, a statistical evaluation was performed
on the relationship between the average daily peak discharges from the Toktogul Reservoir
during autumn–winter seasons and the average daily air temperatures (Figure 3).
Fig. 3. Dependence of the maximum water flows released from the Tokhtagul
reservoir in the autumn-winter seasons on air temperature, 2022-2023.
Based on the above graph, a statistical assessment was made of the relationship between
two variables, namely the average daily maximum water discharges (Q
max
) released from the
reservoir during the autumn–winter season of 2022–2023, and the corresponding air
temperatures (t) recorded on those dates. The regression equation expressing the relationship
between these variables was obtained in the following form:
Q
мах
=− 21.73t + 822.6
,
(1)
where: Q
max
— average daily maximum water discharges; t — air temperature.
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The accuracy of this regression equation was evaluated using the simple correlation
coefficient. Its value was determined to be
r ± σ
r
= 0,911 ± 0,008
. These figures indicate that
the derived relationship can be reliably used in practice. In particular, using the above regression
equation, it is possible to forecast the maximum water discharges in the Naryn River during the
autumn–winter seasons based on air temperature data. Most importantly, given that the
information on average daily water discharges is provided by the Kyrgyz National Energy
Holding Company and air temperature data are measured by UzHydromet in accordance with
standard requirements, one can draw a positive conclusion regarding the reliability of the study’s
results.
IV. Conclusion
In recent decades, the growth of average daily water discharges up to their maximum
values released from the Toktogul Reservoir dam—operating in an energy-driven mode—has led
to frequent occurrences of destructive phenomena such as floods and inundations along the banks
of the Syr Darya and Naryn Rivers. No one can rule out the possibility that such adverse
hydrological events may also occur downstream from other large reservoirs in Tajikistan, such as
the Nurek Reservoir or the Rogun Reservoir (the latter still under construction). This situation
underscores the necessity of continuing research in this field in a systematic manner.
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