Reservoir Region Research Articles

Behaviour of pile-anchor reinforced landslides under varying water level, rainfall, and thrust load: Insight from physical modelling

The stability of landslides in reservoir areas is significantly influenced by water level fluctuations and seasonal precipitation events. To mitigate these landslides, a pile-anchor (PA) structure has been developed by adding anchors to common anti-slide piles. However, limited research has been conducted on the behaviours of PA reinforced reservoir landslides under changing environmental conditions. In this study, model tests of PA reinforced landslide were carried out using a multi-field monitoring technique to investigate the behaviours of PA reinforced landslides. The study utilized the Majiagou landslide in the Three Gorges Reservoir region of China as a prototype. Three sets of model tests were conducted to simulate the three different triggers of varying water level, rainfall, and thrust load experienced by landslides in reservoir areas. Furthermore, the performance of PA structures was compared to that of pile structures to demonstrate the superiority of the PA structure reinforced landslide. The results indicated that the behaviours of PA remain consistent regardless of the three different triggers, and their general performance can be divided into three stages: stable, fast-deformed, and slow-deformed stage. The distribution of the bending moment exhibits an S-shaped curve, with the maximum bending moment near the slip surface. The maximum negative shear force in the bedrock indicates that part of the structure embedded in the bedrock can effectively resist sliding thrust. In addition, the softening effect can lead to the different responses of PA reinforced landslides under different triggers. This study may provide a deeper understanding of the behaviors of the PA reinforced landslides in response to evolving environmental conditions in reservoir areas.

Sedimentary chrysophycean stomatocysts from an alpine lake in the Three Gorge Reservoir region, central China

Sedimentary chrysophycean stomatocysts from an alpine lake in the Three Gorge Reservoir region, central China

Variation in sediment sources and the response of suspended sediment grain size in the upper Changjiang River Basin following the large dam constructions

The amount, patterns, and particle size composition of suspended sediment in the upper Changjiang Basin has been altered significantly due to the cascade reservoirs construction. A dam breach may disrupt sedimentation in the reservoir, channel erosion downstream of the dam, and the cycle of nutrients and contaminants adherent to the dam. This study is based on the long time-series field data of water discharge, sediment flux, and suspended sediment grain size of the upper Changjiang River Basin from 1973 to 2019. Four significant stepwise reduction periods in sediment load were identified by employing the M-K test, namely, 1973–1992, 1993–2002, 2003–2012, and 2013–2019. Based on the results, sediment load reduction in the upper Changjiang River (CJR) is remarkably correlated with an increase in the capacity of large reservoirs. Jialingjiang River became the largest sediment source area for upper CJR in 2013–2019. Moreover, the variation range of suspended sediment median particle size gradually narrowed with decreasing sediment load during the four periods in the upper CJR. The silt content of suspended sediment increased while clay and sand contents decreased which would maybe a factor of decreasing of P flux in the upper CJR. After the impounding of the Xiangjiaba and Xiluodu Reservoirs in the Jinshajiang River, the fining trend of suspended sediment along the main stem of upper CJR was cut off in 2013–2019, which may be ascribed to sediment management of the cascade reservoirs regulation and the sediment resuspension from the channel erosion in the river downstream. These observations can also serve as a reference for future studies about the effects of cascade reservoirs on aquatic ecology and environmental changes.

Future projections of worst floods and dam break analysis in Mahanadi River Basin under CMIP6 climate change scenarios.

This study provides a comprehensive analysis of the hydrological effects and flood risks of the Hirakud Reservoir, considering different CMIP6 climate change scenarios. Using the HEC-HMS and HEC-RAS models, the study evaluates future flow patterns and the potential repercussions of dam breaches. The following summary of the work: firstly, the HEC-HMS model is calibrated and validated using daily stage-discharge observations from the Basantpur station. With coefficient of determination (R2) values of 0.764 and 0.858 for calibration and validation, respectively, the model demonstrates satisfactory performance. Secondly, The HEC-HMS model predicts future flow for the Hirakud Reservoir under three climate change scenarios (SSP2-4.5, SSP3-7.0 and SSP5-8.5) and for three future periods (near future, mid future and far future). Thirdly, by analyzing time-series hydrographs, the study identifies peak flooding events. In addition, the HEC-RAS model is used to assess the effects of dam breaches. Downstream of the Hirakud Dam, the analysis highlights potential inundation areas and depth variations. The study determines the following inundation areas for the worst flood scenarios: 3651.52 km2, 2931.46 km2 and 4207.6 km2 for the near-future, mid-future and far-future periods, respectively. In addition, the utmost flood depths for these scenarios are determined to be 31 m, 29 m and 39 m for the respective future periods. The study area identifies 105 vulnerable villages and several towns. This study emphasizes the importance of contemplating climate change scenarios and implementing proactive measures to mitigate the peak flooding events in the Hirakud reservoir region.

Reduced-Order Models Blend Chemistry, Machine Learning for Water-Property Analysis

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 213869, “Water Digital Avatar—Where Chemistry Is Mixed With Machine Learning,” by Jesse Farrell, SPE, and Sergey Makarychev-Mikhailov, SPE, SLB. The paper has not been peer reviewed. _ Water affects almost every operation in the exploration and production industry. Until now, time-intensive laboratory tests or cumbersome third-party simulators were required to extract physicochemical properties. In the complete paper, a family of machine-learning-based reduced-order models (ROMs) trained on rigorous first-principle thermodynamic simulation results is presented. The developed ROMs that predict water properties enable automated decision-making and improve water-management work flows. The presented approach can be extended to other oilfield, chemical, and chemical-engineering applications. Introduction The properties of the water phase and all produced fluids directly influence flow assurance, three-phase flow pressure/volume/temperature modeling, and fluid-compatibility aspects across the full life cycle of the well, including during well construction, stimulation, and production operations. Modeling these systems enables one to predict, mitigate, and, in some cases, completely prevent deleterious effects in tubing, the reservoir, and near-wellbore regions. First-principle thermodynamic simulations are often considered to be ground truth in the oilfield industry and are widely used in place of time-consuming laboratory experiments. The use of rigorous thermodynamic software, however, is not always practical. In certain cases, commercial and open-source simulators are overloaded with functionality unnecessary for a task, require training of personnel, and are often difficult to incorporate into digital work flows in the cloud or to deploy at the edge on surface equipment or the downhole tools available to model changing conditions in real time. This is where ROMs find their application because they are fast, reasonably accurate, and highly customizable solutions. The authors’ scientific hypothesis was that machine-learning-based ROMs can be used to quantify the physicochemical properties and scaling tendencies of oilfield waters in place of rigorous, first-principle thermodynamic models. Methods The United States Geological Survey (USGS) Produced Waters Geochemical Database was used as the initial data source for this study. The original database contains approximately 115,000 produced-water and other deep-formation water samples collected and characterized in the United States in the past 120 years. Although the USGS database is an excellent source, the data still required cleaning and enrichment. For the first step, inconsistent, poorly populated, and outlier samples were removed, which led to noticeable data attrition and resulted in approximately 85,000 “clean” records. The enrichment phase included several manipulations and alterations of the original data. The resulting data set is not always accurate regarding individual samples but is much better populated than the original one in terms of minor ion concentrations, and is believed to be representative on a large scale.

Dam-induced flow alternations drive the regime shift towards a cyanobacteria-dominated microbiota state in the Yangtze River

While satisfying the demands of social and economic development, dams act as physical barriers affecting both abiotic and biotic factors in large rivers. These altered factors can interact with each other and gradually reshape the local ecosystem state. The reshaped state may spread downstream and affect ecosystem states on a large scale. However, the spread extent and characteristics of ecosystem states along large rivers remain understudied. To address this problem, alternative microbiota states and their responses to environmental conditions in the Yangtze River were investigated, considering the preponderance of alternative stable states theory in explaining the response of ecosystem states as well as the role of benthic microorganisms in indicating ecosystem states. In this study, flow discharge was identified as the main hydrological factor that clustered benthic microbiota into two types, and these two microbiota types were bistable and characterized by differential enrichment of the Cyanobacteria phylum. Potential analysis demonstrated that reducing flow discharge beneath a threshold (i.e., flow discharge < 12,900 m3/s) could shift benthic microbiotas to a state where benthic cyanobacteria would become the dominant species (the Microbiota State B). In the bistable region (i.e., 12,900 < flow discharge < 28,000 m3/s), both the ecological resilience and the contribution of deterministic process were found weak by relative potential depth calculations and neutral community modeling, suggesting that this region is susceptible to the microbiota state of its upstream and thus deserves more scientific attention to prevent the unfavorable state from spreading downstream. In addition, high denitrification potential at sites of the Microbiota State B was likely responsible for the low N:P ratio, further benefiting the dominance of N-fixing cyanobacteria. This study empirically showed the response of alternative microbiota states to flow gradients, and explored the distribution and characteristics of the microbiota states along the mainstream of the Yangtze River, therefore providing insights into environmental flow design and reservoir regulation of large rivers.

Runoff change and attribution analysis in a semiarid mountainous basin

Climate change and human activities are the main causes of runoff change. Exploring runoff change over time, in response to climate change and human activities, tests past effects of ecological restoration and provides a solid foundation for future decision-makers. To reduce uncertainty in our attribution analysis, we used two methods, the catchment water-energy balance equation and the geomorphology-based hydrological model (GBHM), to examine runoff change in a semiarid mountainous basin—the Chagan Mulun River Basin. The results are described as follows: (1) In the past 40 years, runoff and leaf area index (LAI) in the study area showed a significant downwards trend. (2) The two methods were consistent in terms of quantification and showed that change in the underlying surface, especially direct water abstraction, was the main reason for the reduction in runoff. Climate change had the greatest impact on runoff, which increased in the Schaake, 1990s. In other periods, climate change reduced runoff. (3) The quantitative interdecadal results of the two methods differed. The GBHM does not accurately simulate processes, such as reservoir regulation, which may cause deviation in an attribution analysis for runoff in arid and semiarid basins affected by human activities.

Study on the migration law of biogenic substances under different scheduling schemes of reservoirs

In order to study the migration process of biogenic substances in river basins under reservoir regulation and quantify the migration characteristics of nitrogen and phosphorus pollution in the middle and lower reaches of the Lancang River cascade reservoir basin. This article constructs a simulation model for the migration of biogenic substances in the Lancang River Basin based on the SWAT model, and preliminarily simulates the migration process of nitrogen and phosphorus in the basin. The results indicate that the model has good applicability in the Lancang River basin, with the NSE coefficient of 0.76 and the R2 coefficient of 0.78. Moreover, there is a roughly positive correlation between nitrogen and phosphorus production and rainfall distribution in the basin, but rainfall is not the only factor determining the distribution of nitrogen and phosphorus pollution load. By inputting different reservoir regulation schemes into the reservoir regulation module, the migration processes of nitrogen and phosphorus in various sections of the watershed under natural conditions, conventional regulation, power generation regulation, and ecological regulation schemes are calculated. The results indicate that the conventional and power generation scheduling schemes have a significant impact on the migration of total nitrogen and phosphorus in the watershed, leading to a certain retention and accumulation effect of nitrogen and phosphorus in the reservoir. However, the ecological scheduling scheme to some extent reduces the impact of reservoir scheduling on the migration of biogenic substances.

Evolution of the main channel of the Yangtze River

AbstractThe construction and operation of the Three Gorges Reservoir and the cascade reservoirs upstream have significantly altered the processes of flow and sediment in the main and tributary channels of the Yangtze River. This has led to substantial adjustments in the riverbed through erosion and deposition, thereby impacting flood protection, water resource utilization, navigation, and the aquatic environment in the Yangtze River basin. In this study, prototype measurements were used to analyze the variations in runoff and sediment load in the main channel of the Yangtze River, as well as the changes and evolution of the riverbed. Mathematical modeling was done to predict the trends in reservoir sedimentation and riverbed adjustments. The results indicate that, apart from the significantly increased runoff and sediment load in the river source region (Zhimenda station) over the past two decades, there is no clear unidirectional trend of increasing or decreasing in the main and tributary annual runoff of the Yangtze River. However, the release of reservoir outflows undergoes significant changes throughout the year due to reservoir regulation. Suspended sediment load in the upper Yangtze River has been decreasing since the 1990s, especially after the operation of the Three Gorges Reservoir and the four cascade reservoirs in the lower reach of the Jinsha River. The factors influencing flow and sediment variations include mainly climate change and human activities such as reservoir operation and soil and water conservation. The significant changes in flow and sediment conditions have disrupted the original relative equilibrium state of the main channel of the Yangtze River, leading to riverbed adjustments. The river sections in the upper reach, located within reservoir areas, have shifted from erosional state under natural conditions to accumulative state, while the middle and lower reaches have transitioned from a relatively equilibrium state to a process dominated by erosion and reconstruction. Overall, the river regime in the reservoir area and downstream of the Three Gorges Dam remains relatively stable, but there have been adjustments in some local river sections, for example, in the curved sections, particularly in the sharply curved sections downstream of the Three Gorges Dam, where gradual or abrupt chute cutoff has occurred. In the foreseeable future, the river channel downstream of the Three Gorges Dam will remain in an unsaturated state regarding sediment transport. The process of river channel erosion will persist for a long time and have far‐reaching consequences. Some long straight sections, multiple bifurcation sections, and sections with large curvature are expected to undergo certain adjustments in the river regime, necessitating continuous observation, long‐term monitoring, and timely river management and channel governance.

Optimal Scheduling of Reservoir Flood Control under Non-Stationary Conditions

To improve reservoir flood control and scheduling schemes under changing environmental conditions, we established an adaptive reservoir regulation method integrating hydrological non-stationarity diagnosis, hydrological frequency analysis, design flood calculations, and reservoir flood control optimization scheduling and applied it to the Chengbi River Reservoir. The results showed that the peak annual flood sequence and the variation point of the annual maximum 3-day flood sequence of the Chengbi River Reservoir was in 1979, and the variation point of the annual maximum 1-day flood sequence was in 1980. A mixed distribution model was developed via a simulated annealing algorithm, hydrological frequency analysis was carried out, and a non-stationary design flood considering the variation point was obtained according to the analysis results; the increases in the flood peak compared to the original design were 4.00% and 8.66%, respectively. A maximum peak reduction model for optimal reservoir scheduling using the minimum sum of squares of the downgradient flow as the objective function was established and solved via a particle swarm optimization algorithm. The proposed adaptive scheduling scheme reduced discharge flow to 2661 m3/s under 1000-year flood conditions, and the peak reduction rate reached 60.6%. Furthermore, the discharge flow was reduced to 2661 m3/s under 10,000-year flood conditions, and the peak reduction rate reached 65.9%.

The role of precise management in mitigating non-point source nitrogen pollution of a reservoir region: Environmental profits and economic benefits

Non-point source pollution is a worldwide water environment pollution problem, which could be effectively solved with the concept and method of precision management. In this study, an integrated optimization decision system (IODS) was developed for supporting precise management of non-point source nitrogen pollution under multiple uncertainties. Several kinds of methods were innovatively coupled into the IODS, including material flow analysis (MFA), Gumbel copula model (GCM), path analysis (PA), and interval multi-objective chance constraint programming (IMOCCP). The IODS could (i) identify the main sources of non-point source pollution through the MFA; (ii) estimate the pollution status of different zones within the entire watershed using the GCM and PA; (iii) incorporate the pollution sources and pollution status to the IMOCCP as decision variables and development scenarios (i.e., S1 to S3), respectively. The settlement of the IMOCCP model could provide targeted optimal solutions to zones of different pollution status, with minimized non-point source nitrogen pollution and maximized economic benefit. Our research demonstrates great advantage of precise management in obtaining more environmental profits and economic benefits. Specifically, the precise management makes the system benefit increased by about [89.86%, 96.10%], [87.35%, 95.00%], and [28.23%, 60.40%] from S1 to S3, respectively. While the nitrogen loading decreased by about [23.40%, 81.84%], [66.51%, 145.72%], and [385.05%, 623.16%], correspondingly. This work may offer inspiration and guidance for the practice of precise management in mitigating the non-point source pollution.

An insight into wax/asphaltene deposition behavior in the wellbore regions of gas condensate reservoirs

Wax/asphaltene deposition has been an important problem in the gas condensate reservoirs development. The cold plate device is designed to reveal the effect of operating conditions on the wax/asphaltene deposition behavior. The characteristic of wax/asphaltene deposition with well conditions is determined. The results show that when the temperature difference was considered, the growth rate of wax deposition thickness in the operation period was that stabilizing first, rising again, and then slowing down. However, the temperature and hydrogen bonding interaction significantly affects the asphaltene deposition process. The asphaltene deposition rate was stable at the beginning period of operation, then increased significantly, and decreased gradually after reaching the peak value of 21.61 g/cm2·h. An identification diagram of the wellbore deposition location is established. Increased deposition surface area of the cold plate structural design ensures qualitative and quantitative characterization of wax/asphaltene deposition traits. The real well fluids components were employed in the experiments to obtain critical conditions for wax/asphaltene deposition which approximated actual production conditions. This diagram facilitates the reliable identification of wax/asphaltene removal areas in the wellbore during production. This study provides a comprehensive understanding of the wax/asphaltene deposition behavior, which helps the gas condensate well operation safety and efficiency.

The Improved Reservoir Module of SWAT Model with a Dispatch Function and Its Application on Assessing the Impact of Climate Change and Human Activities on Runoff Change

Climate change and human activities significantly impact the hydrological cycle, particularly in regions with numerous large-scale reservoirs. Recognizing the limitations of the reservoir module in the original SWAT model, this study presents an improved reservoir module based on a dispatch function to enhance runoff simulation. Its performance is validated by simulating daily runoff in the Jinsha River Basin, China. The scenario simulation approach is employed to quantitatively analyze the influences of climate change and human activities on runoff. And downscaled Global Climate Models (GCMs) are utilized to predict runoff for the next three decades. The results show that (1) the improved SWAT model outperforms the original model in runoff simulation; (2) during the test period, reservoir regulations caused a reduction of 26 m3/s in basin outlet runoff, while climate change led to an increase of 272 m3/s; and (3) future changes in basin outlet runoff over the next 30 years exhibit a high level of uncertainty, ranging from −5.6% to +11.0% compared to the base period. This study provides valuable insights into the hydrological impacts of climate change and human activities, highlighting the importance of incorporating an improved reservoir module in hydrological modeling for more accurate predictions and assessments.

Floodwater utilization potential assessment of China based on improved conceptual model and multi-reservoir basin assessment method

Floodwater resource utilization is an important way to alleviate the water resources shortage in China. The quantitative assessment of the floodwater utilization potential under the current engineering conditions is vital for implementation of floodwater resource utilization. However, the imperfect conceptual model of floodwater utilization potential, the limited availability of reservoir engineering data, and the lack of universal assessment method that directly considers the reservoirs regulation capacity pose a major challenge to assessment of floodwater utilization potential in China. This study improves the universality of the previous conceptual model of floodwater utilization potential by analyzing the differences and connections of floodwater resources potentials under different states of utilization. The floodwater utilization potential assessment method for river basin with multi-reservoir was also proposed based on our previous assessment method for single reservoir controlled basin. The assessment method was used to evaluate the floodwater utilization potential of the first- and second-level water resources regions in China based on the reanalyzed monthly runoff data (1902 ∼ 2014) and large and medium-sized reservoirs data (as of 2015). Results indicate that the annual average total floodwater utilization potential of China was calculated as 668.62 billion m3 under the current reservoir regulation capacity, accounting for 34.05% of the total floodwater water resources in China. The study demonstrated that the frequency curve of floodwater utilization potential can provide a better understanding of the states of floodwater utilization, and the assessment method. Strategies for long-term floodwater utilization and flood control planning in different regions of China were also provided to government in our study.

Reservoir operation affects propagation from meteorological to hydrological extremes in the Lancang-Mekong River Basin

Hydrological extremes intensified by meteorological extremes are threatening water security in the Lancang-Mekong River Basin (LMRB), and reservoir operation may mitigate hydrological extreme through regulating hydrological processes during meteorological extreme. However, the capacity of reservoirs in modulating propagation from meteorological extremes to hydrological extremes has seldom been quantified. This study adopted the VIC-Reservoir hydrological model to assess the impact of reservoir operation on the propagation at multi-timescales in the LMRB. The Standardized Precipitation Index and Standardized Streamflow Index were adopted to characterize meteorological extreme and hydrological extreme, respectively, on a range of timescales. The results indicate that reservoir operation has effectively delayed the propagation from meteorological to hydrological extremes during the period of 2008–2016 with rapid reservoir development in the LMRB, compared with the period of 1984–2007 with natural condition. The transmission process of extreme events with a duration of no more than 6 months has been suppressed during the reservoir impact period. However, the influence of reservoir regulation on long-term extreme events that last more than 12 months is generally low. In the upstream basin where reservoir impact is largest, reservoirs can exert a weak mitigation effect on long-term dry extremes. This study provides quantitative assessment of the role of reservoirs in regulating propagation between meteorological and hydrological extremes in the LMRB, and facilitate decision making for the management of water hazards under changing environment.

The role of human activities in the weakening of the propagation relationship between meteorological and hydrological droughts in the Heihe River Basin

AbstractMeteorological droughts could propagate into hydrological droughts and cause agricultural and societal damage. However, the quantitative impact of human activities on the drought propagation has not been well understood. Based on the precipitation and streamflow observational data and hydrological model simulations during 1961–2013, this study analysed the drought propagation characteristics and quantified the impact of human activities on the propagation in the upper and middle reaches of Heihe River Basin. The matched meteorological and hydrological drought events indicated that the drought propagation was characterized by a lagged onset, weakened drought severity and reduced development and recovery speeds. In the upstream area, the correlations between meteorological and hydrological droughts were significant, and human activities had a negligible impact on the drought propagation. In contrast, the impact from human activities was significant in the midstream area, and the effect was two‐fold. Specifically, human activities (e.g., reservoir regulation) reduced the propagation probability of one or several meteorological droughts propagating into a hydrological drought by 16%. Meanwhile, human activities had remarkable effects on long‐lasting and extreme hydrological droughts through reducing their duration and severity by 18% and 37% respectively. On the other hand, the occurrence probability of mismatched drought events, that is, meteorological droughts without causing hydrological droughts and hydrological droughts without preceding meteorological droughts, increased by 34% due to human interventions. Human activities also accelerated the development speed of slowly developing hydrological droughts. In addition, human activities increased the mean duration and severity of moderate hydrological droughts by 32% and 18%. The results are expected to provide scientific bases for understanding the formation and development process of hydrological drought and improving drought forecasting under global change.

Assessing the impacts of reservoirs on downstream hydrological frequency based on a general rainfall-reservoir index

When large reservoirs are built and put into operation, the downstream hydrological processes will be altered significantly, and ecology and agricultural irrigation water of the basin will be affected to some extent. The reservoir index (RI) and the sediment trapping efficiency (TE) of reservoirs are defined to quantify the reservoir impacts on the water flow and sediment by considering the static storage capacity. However, the regulating effect of reservoirs on hydrological variables is not only related to static storage capacity, but also to dynamic reservoir operation. Thus, in this paper, a general rainfall-reservoir index (GRRI) is developed by coupling reservoir regulation indicator (RR, including RI and TE) and effective rainfall affecting the dynamic operation of reservoirs, and the GRRI is used as the covariate to carry out the nonstationary frequency analysis of flood (Q) and annual sediment load (S) at Gaochang (GC) station in Min River, Wulong (WL) station in Wu River, Ankang (AK), Huangjiagang (HJG) and Huangzhuang (HZ) station in Han River, and Cuntan (CT) station on the main stream of the upper Yangtze River. It is found that Q and S at six stations have obvious changes induced by reservoirs, the mean of Q decreases by 22.8%–60.6%, and S drops by 47.7%–89.5% after the change-point of time series. The nonstationary probability distribution models with GRRI as the covariate have better fitting effects than nonstationary models with RR as the covariate. With the incorporation of the impacts of effective rainfall, the GRRI can more accurately capture the occurrence of nonstationarity in the downstream hydrological frequency. These results might be helpful for exploring the impact mechanism of the reservoir regulation on the downstream hydrological variables as well as ecological management of basin.

Variable drivers of surface turbulence under condition of stratified density currents in a tributary bay of Three Gorges Reservoir

Surface turbulence has a direct impact on thermal stratification and important ecological process. The dissipation rate of turbulent kinetic energy (ε), a key parameter to quantify turbulence, also significantly affects the hydrodynamic and biochemical processes. Continuous measurements of high-frequency surface (0.50 m depth) flow velocity, meteorological data, water level and water temperature conducted in Xiangxi Bay (XXB) of the Three Gorges Reservoir (TGR) during summer (2019/6/17–2019/6/24) and winter (2019/12/29–2020/1/4) observational period, have been used to explore the variability of surface turbulence and its possible driving factors. The results show that a two-layered flow structure was clearly visible in summer. The surface water flowed from downstream to upstream (surface intrusion currents), with an average longitudinal velocity of 0.05 m/s and 0.02 m/s during summer and winter observational periods, respectively. Meanwhile, the longitudinal velocity also showed periodic fluctuations at three different time scales, with periods of 1.80 h, 20 min and 1–3 s, respectively. The 1.80 h fluctuation was caused by the flow oscillation driven by daily discharge regulation of TGR. In addition, the surface turbulence dissipation rates varied from 10−8 W/kg to 10−4 W/kg in summer, and from 10−9 W/kg to 10−4 W/kg in winter. In XXB, the movement of surface intrusion currents is an important factor that dominates and maintains the surface turbulence, while the contribution of atmospheric forcing (wind shear and convective cooling) accounts for 27.17 % in summer but 58.95 % in winter. The diurnal water level regulation of reservoir and wind variations are co-driving forces for the diurnal differences of surface turbulence during the observational periods. Therefore, the atmospheric forces and reservoir regulation together determine the variability of surface turbulence. This study will help to deepen the understanding of the hydrodynamic process of large regulated riverine reservoirs.

Altitudinal variations in water and sediment composition of 47 lakes in the Three Gorges Reservoir region and its adjacent regions: implications for watershed environmental management

Altitudinal variations in water and sediment composition of 47 lakes in the Three Gorges Reservoir region and its adjacent regions: implications for watershed environmental management

Optimizing environmental flow based on a new optimization model in balancing objectives among river ecology, water supply and power generation in a high-latitude river

Environmental flow plays an important role in maintaining the health of river ecosystems and aquatic habitats. Although ecological regulation of environmental flow has attracted the attention of scientists, managing the world's reservoir-regulated rivers to better meet the needs of human being and ecosystems is a complex social challenge. To address the above issues, we constructed a model for optimizing reservoir operation based on a balance in achieving multi objectives among environmental flow, water supply and power generation (EWP). The model was solved using an intelligent multi-objective optimization algorithm (ARNSGA-III). The developed model was demonstrated in a large reservoir, Laolongkou Reservoir in the Tumen River. The results showed that the reservoir altered environmental flows mainly in terms of flow magnitude, peak, times, duration and frequency, which result in a sharp decrease in spawning fish, and degradation and replacement of vegetation along the channels. In addition, the mutual feedback relationship between the objectives of environmental flows, water supply and power generation is not static, but varies over time and space. The constructed model based on Indicators of Hydrologic Alteration (IHAs) can effectively guarantee the environmental flow at daily scale. In detail, the river ecological benefit increased by 64% in wet year, 68% in normal year, 68% in dry year after optimizing regulation of reservoir, respectively. This study will provide a scientific reference for the optimizing of the management in other rivers affected by dams.