Normal Water Level Research Articles

Evaluation navigation controlled gate of aging spillway on cavitation damage.

High-speed flow of clean water or water with sediment released from aging spillways may cause abrasion and cavitation on the concrete surface gradually. The occurrence of irregularities on the concrete surface can exacerbate the erosion problem. Which might jeopardize the safety of dams constantly, hence the rehabilitation efforts become urgent tasks in dam safety projects. This study employs a 3D Computational Fluid Dynamics (CFD) model to quantitatively analyze the cavitation risk on the aging concrete surface of the Chay 5 spillway in Ha Giang, Vietnam, under various operation scenarios. There are two standards used to measure cavitation: the cavitation index (σ) which indicates the danger due to the drop of pressure in rapid flow, and the new gasification index (β) which takes into consideration the formation and collapse of bubbles behind asperities. Three extreme flood cases may not result in potential cavitation because both σ and β exceed critical thresholds. Regarding the six controlled gate scenarios with normal water level, the σ profiles are approximated 1,0 showing a low likelihood of cavitation damage while the β values are smaller than 0.8, indicating a considerable risk of cavitation. Besides, the opening height of 100 cm poses the greatest risk of creating severe cavitation erosion in the concave area and slope portion. The flip bucket experienced the most vulnerable cavitation when the opening height is 400 cm. In addition, an approach to spillway surface rehabilitation involving specialized mortars has been presented. For aging conveyance structure, gasification index (β) takes into account irregularities surface, providing a more comprehensive assessment of the likelihood of cavitation damage than cavitation index (σ). After rehabilitation with anti-shrinkage high abrasion resistance mortar, the entire spillway surface is smooth. This allows for reducing the cavitation risk and improvement of life service thereof.

Development of a distributed hydrological model combined with sediment transport calculations and its application to a medium-scale basin in northeast China

Abstract An accurate assessment of sediment transport can assist land and resource managers in any region. The primary objective of this study was to develop a distributed hydrological model for calculating rainfall-runoff coupled with sediment transport to provide a practical method for estimating sediment transport in western Heilongjiang Province, China. The Alun River Basin, which has typical meteorological and hydrological characteristics of western Heilongjiang Province, was chosen as the study area. A sediment transport calculation module was developed based on physically based formulas for the suspended load and bedload, which was coupled with a numerical model of the physical distributed rainfall-runoff process. The model’s ability was validated by comparing the sediment sampling survey results of the particle size group distribution (PSGD) in the flow and the corresponding value of the model calculation results for a control case. The root mean square error (RMSE) and the mean absolute error (MAE) were mostly <10%. The model was used to calculate the rainfall-runoff combined with sediment transport in 2016, and the results indicate that the primary form of sediment transport was as suspended load. The suspended load accounted for over 90% of the total sediment transport caused by the maximum flood peak, and the suspended load accounted for over 80% during the period of normal water level across the selected sections. The sediment transport process was dominated by the runoff process. The contribution of the monthly sediment transport in winter to the annual total value was mostly <1%; while in the rainy season, the contribution of the monthly sediment transport to the annual total value was >15%. The results provide a basis for the assessment of sediment transport and the development of a numerical platform for modeling hydrological processes coupled with land surface processes in western Heilongjiang Province, China.

Flood risk assessment of a small river with limited available data

Flood risk modeling of small watercourses is challenging when only limited input data are available. Therefore, this study assessed the flood characteristics of a small river (Tarna River: entire watershed-C, upper-VS, middle-TMS, and lower section-TOS) from 1990 to 2019. The assessment focused on modeling, model calibration, and validation using feature event-based time-series data in data-scarce environments. We showed that since the 2000s, the number of high-water levels above 250 cm, and the frequency of three flood types had increased. Flood simulation results showed the largest flooded area in the TMS section, followed by the VS, and then the TOS. The outcomes from the VS, TMS, and TOS sections did not exhibit superior performance compared to the C area. Models performed well for larger flood events, with Kling Gupta Efficiency corresponding well to NRMSE and Nash-Sutcliffe efficiency metrics. Accordingly, flood events characterized by the longest duration and high-water levels yielded outstanding results across all areas, followed by moderate flood events with good accuracy. Normal water level events exhibited significant deviations from the reference across all sections. In summary, despite the event-based modeling challenges in data-limited environments, such models can still mitigate potential flood events and improve decision-making processes.

Native macrophyte community response to water-level manipulation for an invasive species

Disturbance regimes related to water level fluctuation play an important role in the structuring of aquatic macrophyte communities. In managed systems, winter water level drawdowns have shown promise in controlling populations of nuisance macrophytes, however, drawdowns may have unintended negative consequences on erosion, fauna, and non-target plant species. The Chippewa Flowage, located in Sawyer County, WI, has implemented targeted winter water level drawdowns with the goal of reducing nuisance levels of Myriophyllum spicatum. To evaluate the effects of water level drawdowns on Myriophyllum spicatum and the native macrophyte community, we conducted repeated full lake surveys of aquatic macrophytes at 2018 points under drawdown and normal water level management in 2005/06, 2015, and 2017. We supplemented these efforts with downscaled surveys in 2007, 2010, and 2016. Surveys revealed a statistically significant decline in both Myriophyllum spicatum occurrence and abundance, and average macrophyte abundance during active drawdown management. Kernel distributions of change in point-specific c-value between the two time periods showed a significant increase under drawdown conditions, and a decrease under normal management (D = 0.41, P ≤0.0001). Drawdown management appeared to successfully control Myriophyllum spicatum abundance and allowed for improvements in the floristic quality of the macrophyte community but resulted in reduced macrophyte abundance overall.

Some solutions to improve the efficiency and environmental safety of reservoir use

Abstract Flood and landslide control and unhindered management is a global problem worldwide. In high-water years, it is advisable to control the volume of water in reservoirs, taking into account such factors as increased loads on them, due to siltation and sedimentation of soils. In particular, in years with hydrological security of more than 75%, it is necessary to direct the main part of floods and mudflows into the lower stream, for this it is recommended to keep the water level as close as possible to the level of useless volume in high water, and water pumps should operate at full capacity during the passage of floods and downpours. In years when the water consumption of the water source is above 75%, the months of April and May are considered sufficient to create water reserves in high streams. Also, in years when the water consumption of the water source is less than 50%, it is necessary to collect mudflows and floodwaters to create the necessary water supply. In such conditions, it is recommended to carry out the dynamics of stopping water discharge at high temperature as follows. It is advisable to distribute the useless volume of water between the precipitation zones of dense flow and the normal water level in the upper boeuf. Based on this, it is necessary to install “Hydraulic posts” on the upper reaches of reservoirs, with the help of which it is possible to control the transformation of water flows.

PENANGANAN BANJIR DAERAH ALIRAN SUNGAI BABON KOTA SEMARANG

Floods are natural disasters that we often encounter during the rainy season. Apart from there are also tidal floods which are caused by global warming, this problem occurs in the city of Semarang, especially North Semarang, specifically the north coast of the Java Sea. Floods that occurred in 2021 in the city of Semarang include Starting from Genuk, Kaligawe, Satsiun Tawang, Tanjungmas, Karangayu, the flood disaster was caused by high rainfall, while tidal floods caused high tides and inundated roads and houses of residents on the north coast of Semarang city. To handle this problem, the government Currently we have made embankments, namely making embankments including the Sringin River which is equipped with a ponpa, Tenggang River, Babon River, Semarang River, Banger River, and others. These embankments are equipped with pumps so that when the water from upstream to downstream is high, the water is pumped. to the sea, the aim is to find out one of the annual discharges of the river, namely the Babon, and to find out the tamping capacity of the Babon River Longstorage. Apart from that, there is a method for handling tidal floods, namely using the Babon River Longstorage which is equipped with a pump, if there is high tide which inundates roads and houses. residents then the pump is turned on, whereas if the water recedes and does not inundate residential areas then the pump is turned off. Flood control analysis is calculated using the HEC-RAS program simulation using a return period of 50 years. Based on calculations using the HEC-HMS program. The flood discharge is 2,529 m3/sec. The high tide elevation is + 1.67 m, while the normal water level is -0.5 m.

Study Comparative Stability of Dam Body with Geomembrane Core Material using GeoStudio Application

The availability of embankment material and the quality of the material is one of the problems in planning a dam, especially impermeable material which must be watertight. With the GeoStudio application, the dam will be modeled to observe the stability of the dam, especially against landslides and seepage. Modeling I is modeled with core zone material using upstream borrow clay material and modeling II using downstream borrow clay material. Modeling III and IV used the same core material with the addition geomembrane material between the transition zone and the upstream filter. The geomembrane was added to observe and compare the effect of use on the stability. The weir body was analyzed under conditions when the weir body was completed, flood water level, normal water level, low water level and rapid drawndown water condition. Modeling III with upstream borrow clay material and geomembrane between the transition zone and upstream filter is the design with the best stability with the most critical avalanche safety factor of 2.459 downstream of the weir under flood water level conditions. The seepage discharge downstream of the weir is 0.0017 m³/dt/m and the maximum seepage discharge is 0.0026 m³/dt/m under flood water level conditions.

Design of the Jlantah Reservoir Mini-Hydro Power Plant, Karanganyar Regency, Central Java Province

An increase in the number of electricity users in Jatiyoso District, Central Java, has occurred in the last few years. In 2020 there were 12,773 families using electricity in Jatiyoso District, where there has been an increase of 79 families using electricity compared to 2019. This increase in electricity demand should be balanced with an increase in sources of electrical energy for the community. Therefore, Jlantah Mini-hydro Power Plant is expected to become a source of electrical energy for the local community. The normal water level of the reservoir is planned at an elevation of +691.00 MASL and the elevation of the intake structure at +661.00 MASL. The total dead storage of the reservoir is 1.66 million and the total effective storage is 9.16 million. The powerhouse elevation planning is carried out by analyzing the 100-year return period of flood in the river around the powerhouse. The powerhouse is planned at an elevation of +624.00 MASL. The turbines used in the powerhouse are 2 turbines. Turbine 1 with HLA550-WJ-55 series and turbine 2 with HLA678-WJ-50 series. The average power generated in a normal year (2013) is 516.44 kW with a total energy of 4.47 GWh. The construction cost of the Jlantah PLTM is estimated at IDR 18,795,716,076.00 with normal annual income (2013) of IDR 4,060,935,522. With this income, the NPV value is IDR 4,461,454,224, IRR is 12.96%, BCR is 1.24, and PBP is 12.78 years, so this project is said to be economically feasible.

Investigating the Impact of Large Lakes on Local Precipitation: Case Study of Lake Urmia, Iran

Large lakes face considerable challenges due to human activities and climate change, impacting local weather conditions and ecosystem sustainability. Lake Urmia, Iran’s largest lake and the world’s second-largest saltwater lake, has undergone a substantial reduction in water levels, primarily due to drought, climate change, and excessive irrigation. This study focuses on the potential repercussions on local climate conditions, particularly investigating the impact of moisture sources, evaporation from lake surfaces, and evapotranspiration from agricultural activities, on local convection rainfall. The prevailing westerly winds in the basin suggest a hypothesis that this moisture is transported eastward within the basin, potentially leading to local precipitation as it ascends to higher altitudes near the eastern basin border. To validate this hypothesis, climate data from 1986 to 2017 from the Sarab meteorological station (east of the lake basin, influenced by local precipitation) and Saqez meteorological station (south of the basin, unaffected by local precipitation) were analyzed. The impact of lake water level reduction was assessed by categorizing data into periods of normal lake conditions (1986–1995) and water level reduction (1996–2017). Additionally, the MSWEP global precipitation product was used to examine the precipitation distribution in the entire basin over the entire period and sub-periods. The findings indicate Lake Urmia’s significant influence on convective rainfall in the eastern basin, especially during the summer. Despite decreasing lake levels from 1996 to 2017, convective rainfall in the eastern basin increased during the summer, suggesting intensified agricultural irrigation, particularly in hot seasons.

Ecological problems and ecological restoration zoning of the Aral Sea

The Aral Sea was the fourth largest lake in the world but it has shrunk dramatically as a result of irrational human activities, triggering the “Aral Sea ecological crisis”. The ecological problems of the Aral Sea have attracted widespread attention, and the alleviation of the Aral Sea ecological crisis has reached a consensus among the five Central Asian countries (Kazakhstan, Uzbekistan, Tajikistan, Kyrgyzstan, and Turkmenistan). In the past decades, many ecological management measures have been implemented for the ecological restoration of the Aral Sea. However, due to the lack of regional planning and zoning, the results are not ideal. In this study, we mapped the ecological zoning of the Aral Sea from the perspective of ecological restoration based on soil type, soil salinity, surface water, groundwater table, Normalized Difference Vegetation Index (NDVI), land cover, and aerosol optical depth (AOD) data. Soil salinization and salt dust are the most prominent ecological problems in the Aral Sea. The Aral Sea was divided into seven first-level ecological restoration subregions (North Aral Sea catchment area in the downstream of the Syr Darya River (Subregion I); artificial flood overflow areas downstream of the Aral Sea (Subregion II); physical/chemical remediation area of the salt dust source area in the eastern part of the South Aral Sea (Subregion III); physical/chemical remediation areas of severe salinization in the central part of the South Aral Sea (Subregion IV); existing water surface and potential restoration areas of the South Aral Sea (Subregion V); Aral Sea vegetation natural recovery area (Subregion VI); and vegetation planting areas with light salinity in the South Aral Sea (Subregion VII)) and 14 second-level ecological restoration subregions according to the ecological zoning principles. Implementable measures are proposed for each ecological restoration subregion. For Subregion I and Subregion II with lower elevations, artificial flooding should be carried out to restore the surface of the Aral Sea. Subregion III and Subregion IV have severe soil salinization, making it difficult for vegetation to grow. In these subregions, it is recommended to cover and pave the areas with green biomatrix coverings and environmentally sustainable bonding materials. In Subregion V located in the central and western parts of the South Aral Sea, surface water recharge should be increased to ensure that this subregion can maintain normal water levels. In Subregion VI and Subregion VII where natural conditions are suitable for vegetation growth, measures such as afforestation and buffer zones should be implemented to protect vegetation. This study could provide a reference basis for future comprehensive ecological management and restoration of the Aral Sea.

Attempts to reduce cavitation phenomena at the Ciawi Dam inlet conduit using CFD Modeling

The conduit bottom outlet is prone to cavitation damage on its channel surface, and one preventive measure is the installation of air ventilation. This research aims to grasp flow characteristics comprehensively, predict cavitation likelihood at the intake, and assess the impact of a ventilation pipe’s installation. Utilizing Computational Fluid Dynamics (CFD), the study modeled flow dynamics, focusing on velocity and pressure variables. The Ciawi bottom outlet intake was meticulously modeled at a 1:1 scale under normal water level conditions, and model accuracy was validated through physical testing by BHGK. The research includes two series: Series 0 (intake without ventilation pipe) and Series 1 (intake with ventilation pipe), with gate opening heights varied at 25%, 50%, 75%, and 100% for both series. Simulation results show that in Series 0, potential cavitation damage is indicated at a 75% gate opening in sections 3 and 4 with a cavitation index of 0.11. Series 1, featuring ventilation pipe installation, demonstrated positive outcomes, eliminating potential cavitation damage in the inlet bottom outlet, with all cavitation indices surpassing 0.2. This study provides crucial insights for preventing cavitation damage in conduit bottom outlets through the strategic deployment of ventilation systems.

Delayed coastal inundations caused by ocean dynamics post-Hurricane Matthew

Post Hurricane Abnormal Water Level (PHAWL) poses a persistent inundation threat to coastal communities, yet unresolved knowledge gaps exist regarding its spatiotemporal impacts and causal mechanisms. Using a high-resolution coastal model with a set of observations, we find that the PHAWLs are up to 50 cm higher than the normal water levels for several weeks and cause delayed inundations around residential areas of the U.S. Southeast Coast (USSC). Numerical experiments reveal that while atmospheric forcing modulates the coastal PHAWLs, ocean dynamics primarily driven by the Gulf Stream control the mean component and duration of the shelf-scale PHAWLs. Because of the large spatial impact of the post-hurricane oceanic forcing, the coastal hazards are not limited to a direct hit from a hurricane but can be detected throughout the USSC where the oceanic processes reach.

Assessment of groundwater reservoir and the influence of its characteristics on water dynamic control.

Groundwater reservoirs play an important role in regional water volume balance. In order to ensure the efficiency of a groundwater reservoir and obtain its maximum value, it is necessary to figure out its characteristics, such as minimum water level, normal water level, and maximum water level. The characteristics not only determined the storage capacity but also influenced the water allocation and utilization. Therefore, this paper took a groundwater reservoir built in an alluvial fan as an example to assess its storage capacity and the influence on water dynamic control. The alluvial fan was located in the front of Lao River, where there were an alluvial-diluvial fan, groundwater storage space, and natural impervious boundary. Therefore, it was an ideal place for constructing a groundwater reservoir. Through theoretical analysis and numerical simulation, the storage capacity was determined, and the influence of groundwater reservoir characteristics on water dynamic control was analyzed. On this basis, the water-supply method in the research area was confirmed. This paper will present a new method for repairing the groundwater system and protecting the ecological environment.

Developing a stochastic hydrological model for informing lake water level drawdown management

Winter drawdown (WD) is a common lake management tool for multiple purposes such as flood control, aquatic vegetation reduction, and lake infrastructure maintenance. To minimize adverse impacts to a lake’s ecosystem, regulatory agencies may provide managers with general guidelines for drawdown and refill timing, drawdown magnitude, and outflow limitations. However, there is significant uncertainty associated with the potential to meet management targets due to variability in lake characteristics and hydrometeorology of each lake’s basin, making the use of modeling tools a necessity. In this context, we developed a hydrological modeling framework for lake water level drawdown management (HMF-Lake) and evaluated it at 15 Massachusetts lakes where WDs have been applied over multiple years for vegetation control. HMF-Lake is based on the daily lake water balance, with inflows simulated by a lumped rainfall-runoff model (Cemaneige-GR4J) and outflow rate calculated by a modified Target Storage and Release Based Method (TSRB). The model showed a satisfactory performance of simulating historical water levels (0.53 ≤ NSE ≤ 0.86), however, uncertainties from meteorological inputs and TSRB determined lake outflow rate affected the result accuracy. To account for these uncertainties, the model was executed stochastically to assess the ability of study lakes to follow the Massachusetts’ general WD guidelines: drawdown by Dec 1 and fully refilled by Apr 1. By using the stochastic HMF-Lake, the probabilities of each lake to reach the drawdown level by Dec 1 were calculated for different drawdown magnitudes (1–6 ft). The probability results suggest it was generally less possible for most of study lakes to achieve a drawdown of 3 ft or more by Dec 1. Moreover, we employed the stochastic model to derive the annual latest refill starting dates that ensure a 95 % probability of reaching the normal water level by Apr 1. We found starting a refill in March for drawdowns up to 6 ft was feasible for most of study lakes. These results provide lake managers with a quantitative understanding of the lake’s ability to follow the state guidelines. The model may be used to systematically evaluate current WD management strategies at state or regional scales and support adaptive WD management under changing climates.

Mapping Algal Blooms in Aquatic Ecosystems Using Long-Term Landsat Data: A Case Study of Yuqiao Reservoir from 1984–2022

Water eutrophication poses a dual threat to ecological and human well-being. Gaining insight into the intricate dynamics of phytoplankton bloom phenology holds paramount importance in comprehending the complexities of aquatic ecosystems. Remote sensing technologies have gained attention for mapping algal blooms (ABs) effectively, but distinguishing them from aquatic vegetation (AV) remains challenging due to their similar spectral characteristics. To address this issue, we propose a meticulous three-step methodology for AB mapping employing long-term Landsat imagery. Initially, a multi-index decision tree model (DTM) is deployed to identify the vegetation signal (VS) encompassing both AV and ABs. Subsequently, the annual maximum growth range of AV is precisely delineated using vegetation presence frequency (VPF) in conjunction with normal and low water level imagery. Lastly, ABs are accurately extracted by inversely intersecting VS and AV. The performance of our approach is thoroughly validated using the interclass correlation coefficient (ICC) based on a Gaofen-2 Panchromatic Multi-spectral (GF-2 PMS) image, demonstrating strong consistency with notable values of 0.822 longitudinally, 0.771 latitudinally, and 0.797 overall. The method is applied to Landsat images from 1984 to 2022 to quantify the spatial distribution and temporal variations of ABs in Yuqiao Reservoir—a significant national water body spanning a vast area of 135 km2 in China. Our findings reveal a pervasive and uneven dispersion of ABs, predominantly concentrated in the northern sector. Notably, the intensity of ABs experienced an initial surge from 1984 to 2008, followed by a subsequent decline from 2014 to 2022. Importantly, anthropogenic activities, such as fish cage culture, alongside pollution stemming from nearby industrial and agricultural sources, exert a profound influence on the dynamics of water eutrophication. Fortunately, governmental initiatives focused on water purification exhibit commendable efficacy in mitigating the ecological burden on reservoirs and upholding water quality. The methodological framework presented in this study boasts remarkable precision in AB extraction and exhibits considerable potential in addressing the needs of aquatic ecosystems.

SUITABLE BOUNDARY LOCATION IDENTIFCATION FOR RAINFALL-RUNOFF AND SURGE MODEL COUPLING TO EVALUATE COMPOUND FLOOD HAZARDS IN COASTAL REGIONS

Flooding in many coastal regions is exacerbated due to complex interactions of multiple flood drivers such as rainfall-runoff and coastal surge which can occur simultaneously or sequentially during storm events, leading to compound flooding hazards. The Texas Gulf Coasts (USA) are especially vulnerable from compound flooding due to frequent occurrence of tropical storms which bring strong winds to drive storm surge and heavy rainfall to generate inland flooding. Large scale studies {Coastal Texas Restoration and Protection Study (CTX, 2021), Texas General Land Office’s Texas River Basin Study, Base Level Engineering Study} are being conducted by state and federal agencies for flood hazard assessment and for development of mitigation and abatement strategies for reducing this risk and increasing community resilience. Traditionally, large scale storm surge models do not account for runoff contributions to water levels in the interior of their domain. Riverine models for their part use either normal depth or mean high water levels to assign downstream boundary conditions within tidally influenced area, thus ignoring effects of storm surge. In this Planning Assistance to States (PAS) study, located in the Lower Clear Creek and Dickinson Bayou watersheds (Texas, USA), we have evaluated rainfall-runoff and storm surge interactions to determine suitable locations to use as model boundary conditions for exchanging data between rainfall-runoff and surge models under compound flooding conditions.

Study on the anti-floating water level of the underground structure's comprehensive anti-floating

A significant amount of groundwater is in the underground rock and soil, which can exert buoyancy force on the underground structure. In severe cases, this can result in damage, such as cracking of basement walls and arching of floors. Single-using passive anti-floating measures cannot actively reduce the water load of the underground structure when a sudden high water level occurs. Single-using active anti-floating measures may cause environmental problems, and the reliability and durability of the system are difficult to guarantee. This paper adopted the comprehensive anti-floating method of active and passive combination, and the water level distribution function was established based on the measured data of the groundwater depth. The relationship between the normal water level (NWL) and the failure probability of passive anti-floating, which is the starting probability of active anti-floating (SPAA), was obtained. Then, according to the soil properties of the substrate where the active anti-floating system was located, the design service life of the building, the building function, and how the active anti-floating system affected the surrounding environment, assess the harm caused by exceeding the NWL, select the appropriate SPAA, and determine the NWL, which is the anti-floating water level (AWL) of passive anti-floating. Conventional passive anti-floating measures control groundwater below the NWL. When the water level exceeds the NWL, active anti-floating measures of active pressure relief are adopted. Whether groundwater rises or falls, it will not cause structural anti-floating failure. Reasonably selecting the anti-floating program and AWL ensure the underground structure's anti-floating effect to achieve a balance between its safety and economic viability. The new method was theoretically analyzed using measured one-year groundwater depth data from an observation well in Beijing's Fangshan District.

The influence of water level hydrodynamics on potential changes in the morphology of a mountain reservoir shore zone

This study evaluates the influence of water level fluctuations in a mountain reservoir on potential changes in the morphology of its shore zone. The analysis was carried out in the Czorsztyn reservoir on the upper Dunajec river (located in the upper Vistula Basin within the Polish Carpathians). The spatio-temporal distribution of water levels in the Czorsztyn reservoir was analysed using Fourier spectral analysis, Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN), and predictive models. The results indicate that the actual range of water levels in a mountain dam reservoir that can have an impact on the morphology of the shore zone is much narrower than its theoretical range. Over the multi-year distribution of daily water levels in the reservoir, four quasiperiodic, overlapping cycles were identified (0.5-year, 1-year, 1.9-year, and 3.8-year cycles); these cycles are expected to have the greatest impact on the intensity of changes to the morphology of the reservoir’s shore zone. Predictions of water levels in the reservoir were carried out using STLForecaster, TBATS, ThetaForecaster, ExponentialSmoothing, and EnsembleForecaster models. The forecasting results suggest that the reservoir will be subjected to slight but statistically significant changes in its water levels in the following years. Furthermore, the frequency of high water levels close to normal water levels is expected to increase, that may consequently lead to morphological changes of the shore zone and instability of the reservoir slopes. The results of the study can be useful in predicting the effects of environmental changes within dam reservoirs as important elements of infrastructure for effective water resources management.

Modal Analysis of Chushandian Gravity Dam

This article uses the finite element software ABAQUS to establish a three-dimensional finite element model based on the overflow dam section 12 # ~15 # and surface outlet dam section of the Chushandian gravity dam. The stress and displacement distribution of the 12 # ~15 # dam section of the Chushandian gravity dam under normal water storage level are analyzed; On this basis, modal analysis is conducted on the 12 # ~15 # dam section to study the impact of the dam's own modal conditions on the normal operation of the dam. The research shows that: (1) Under the condition of normal height water level, there is a small tensile stress at the dam heel, and the compressive stress at the dam toe is within the normal range. There is significant stress at the intersection of the upper curved part of the overflow dam and the transverse joint. The dam body strength meets the requirements and can be considered safe for the reservoir. (2) Modal analysis of the model reveals that significant deformation can occur at the right side of the dam crest during lower frequency vibrations. With the increasing frequency, the easily deformed parts of the dam are still at the top of the dam, and the displacement of the easily deformed parts is increasing. The position of the easily deformed parts is moving along the Dam axis, and the deformation direction of the easily deformed parts will change regularly.

Current Hydrological Regime of the Volga Reservoirs

The study is focused on variations of air temperature in the basin of the Volga reservoirs, the total inflow into the water bodies, their water exchange, water level and temperature, and the heat content of water mass in open-water period under various climate conditions. The object of the analysis is the long-term series of hydrometeorological data processed by statistical methods. It is shown that the present-day air temperature has increased by 1.3‒1.8°C compared with the period before 1976. The rate of warming was on the average 0.50°C/10 years. The volume of annual inflow increased by 12.4%. Three low-water and 4 high-water phases were identified in the reservoirs of the Upper Volga, including 29–31 low-water, 25–31 high-water, and 8–16 medium-water years. During the low-water phases, the volume of inflow into the reservoirs is 10–28% less than the long-term average, while in high-water years, it is 4–20% higher. The coefficient of water exchange in the reservoirs decreased or increased by 5–13% relative to the values obtained earlier. An increase in the winter and a decrease in the spring inflow were recorded in the reservoirs of the Upper Volga and in the Kuibyshev Reservoir. A tendency toward an increase in the normal annual water level was observed in the reservoirs in the upper part of the Volga and in the Kuibyshev Reservoir, while in the lower Volga, the normal annual level somewhat decreased. In low-water phases, the reservoir levels were on the average 17 cm below and in the high-water phases, 10 cm above the normal annual value. An increase in air temperature during the warm season in the reservoir water areas, on the average by 1.2°C, led to a synchronous increase in the temperature of the water mass by 1.1°C. At the same time, the heat content of the water mass of the reservoirs increased, on the average, by 24% in the upper part of the Volga and by as little as 2–11% in its lower part