Cascade hydropower stations frequently lead to supersaturated total dissolved gases (TDGs), harming aquatic organisms. In deep reservoirs, thermal stratification and upstream inflow slow TDG release. Using a two-dimensional model of Baihetan Reservoir, we found: (1) thermal stratification remains intact but deepens with increasing inflow; (2) the thermocline restricts supersaturated water movement; and (3) after inflow stops, stratification persists and TDG recovery varies by depth. Overall, the reservoir’s thermal structure critically influences supersaturated water transport and distribution, providing insights into TDG management in deep reservoir operations.

The threat of dissolved gas supersaturation to fish has become an important ecological risk associating with the operation of high dams. Enhancing flow turbulence and increasing mass transfer area are effective measures to promote the release of the supersaturated gas, which can be achieved by application of stepped spillways. This paper reports a preliminary study on the relationship between the mitigation of dissolved gas supersaturation in stepped spillway flows and their hydraulic and self-aeration properties. In this work, we focused on the transition flow regime on a 45° sloping stepped spillway, with the ratio of critical depth to step height 0.70 < dc/h < 1.13. The gas saturation was measured along the stepped spillway together with the characteristics of flow aeration, including the distributions of void fraction, bubble count rate, and specific air-water interfacial area. The results show that, within the range of transition flow conditions, the bubble count rate and air-water interfacial area increase with decreasing flow rate, and the enhancement of air-water mass transfer promotes the release of supersaturated gas from water flow. These experimental data are useful for quantitative analysis and theoretical modelling of correlation between the mass transfer area in turbulent multiphase flow and the supersaturated gas release efficiency in dissolved gas supersaturated water.

The total dissolved gas (TDG) supersaturation caused by high dam discharges pose significant ecological risks to aquatic organisms inhabiting downstream river systems, thereby representing a critical concern in hydropower development. Aquatic vegetation zones, distinguished by their characteristic low-flow regimes and intricate vegetative structures, function as essential habitats for aquatic biota. Consequently, it is imperative to examine the dissipation dynamics of supersaturated TDG within these aquatic vegetation zones. Previous studies have conceptualized the dissipation of supersaturated TDG as a process involving liquid-gas interfacial transfer, solid wall adsorption, and the internal dissipation. While, the factors influencing the internal dissipation coefficient and its quantitative characterization remain inadequately elucidated, resulting in an incomplete understanding of the overall supersaturate TDG dissipation process. To address this gap, flume experiments and numerical simulations were conducted in the present study. The determinants affecting the internal dissipation coefficient were identified. Findings indicate that the internal dissipation coefficient exhibits a positive correlation with water depth. Under equivalent vegetation densities, scenarios characterized by elevated flow velocities and increased turbulence intensities correspond to higher internal dissipation coefficients. Moreover, for consistent flow conditions, an increase in vegetation density is associated with an augmented internal dissipation coefficient. Through multiple regression analysis, a predictive formula for the internal dissipation coefficient was derived. This research advances the quantitative understanding of supersaturated TDG dissipation in vegetated flow environments and provides a theoretical foundation for subsequent investigations in this research field.

Riparian zones provide essential food sources, including litter, invertebrates, and organic detritus. In this study, the downstream reach of the Xiangjiaba Dam on the Jinsha River was selected using the water level corresponding to the 90% water level frequency derived from daily discharge data from 2013 to 2025 as a reference, samples were collected at ten elevations in the riparian zone corresponding to different water level frequencies. The variation patterns of litter, invertebrates, organic detritus, and soil total carbon (STC) at different elevations were systematically analyzed during both the normal and high flow periods. Meanwhile, carbon and nitrogen stable isotope analyses were conducted to determine the food sources of the representative fish species Rhinogobio typus. The results indicated a significant differentiation pattern of food resources along the elevation in the riparian, with high-value zones of litter, invertebrates, organic detritus, and STC forming near the water level. Based on normalization analysis, areas with a normalized mean value exceeding 0.80 were defined as the "High Food Availability Zone," corresponding to the elevation range associated with water level frequencies of 20%similar to 1% (2-year return flood level). The riparian zone within this water level fluctuation range serves as a key energy subsidy area. Stable isotope results showed that terrestrial sources contributed 57.3% in July, an increase of 12.9% compared to May, indicating an enhanced role of terrestrial resources in fish food sources under high-flow conditions.

Landslide-induced waves are primarily controlled by granular dynamics during landslide–water impact. While particle size, velocity, and volume are recognized influences, the role of internal grain arrangement and segregation remains less clear. This study employs a coupled CFD-DEM model to investigate how vertical permutation of three fixed grain fractions and layered configurations affect surge generation and propagation. Simulations using three particle sizes (1, 3, and 5 mm) in six initial arrangements reveal that fine particles dominate leading wave formation through efficient momentum transfer, yielding an overall wave height growth of 5.22% and a maximum local growth rate of 2.42%. Grain size segregation governs deposit morphology, with larger particles migrating preferentially along the flow direction. Increasing still-water depth systematically shifts surge characteristics from strongly nonlinear, high-amplitude shallow-water waves to more linear, longer-wavelength, smaller-amplitude deep-water features. Energy dissipation, which is linked to reduced equivalent water depth, decreases wave celerity with propagation distance. The model reproduces granular collapse experiments with a relative error below 5%, confirming that granular segregation critically controls surge dynamics and providing a refined framework for simulating natural landslide-generated waves.

River intakes are critical to national water supply networks and water resource utilization, but intake operations in river channels can cause entrainment effects that lead to the loss of early fish resources and disrupt functional ecological connectivity between key habitats. This study investigated the Jingangtuo intake on the Yangtze River using 28 larval flow events recorded between 2021 and 2022. Each event lasted about 4 d on average and showed a strong positive correlation with flood duration. Based on these observations, a larval drift model was developed by coupling an Eulerian concentration diffusion method with a Lagrangian particle-tracking approach. The model simulated larval passage time and behavior near the intake during different events. Results indicated that at river discharges of 5,700 to 13,100 m3/s, larval passage time ranged from 3.8 to 5.0 h, with a 1,000 m3/s increase reducing passage time by 0.16 h. Nonuniform upstream larval distribution—shaped by flow field heterogeneity—markedly affected downstream movement. Higher larval densities in the main channel led to a 0.5-h reduction in passage time. To reduce entrainment risk, a tiered ecological scheduling strategy was proposed, integrating real-time larval flow monitoring with dynamic response timing, shutdown durations, and optimized monitoring layouts. This approach ensures sufficient early warning and operational flexibility. The study provides a theoretical and practical basis for ecological intake operation and protection of early-stage fish.

The construction of cascade dams in the upper Yangtze River has severely impacted indigenous fish resources. Current hydro-ecological operations primarily focus on fish spawning but ignore other critical life stages, such as juvenile rearing, resulting in limited recovery of adult fish. To solve this problem, we develop an innovative Hydrology-Food Web Model (HFM) for the mainstem reach downstream of Xiangjiaba Dam (XJB), the lowermost mega-dam in the upper Yangtze mainstem, to simulate the relationships between the annual dynamics of XJB discharge and the production of basal ecological groups (prey) and fish in the downstream reach. HFM exhibits satisfactory predictive performance owing to three key features: 1) its framework incorporates the requirements of all life history stages of two major fish groups, i.e., indigenous fish producing pelagic and adhesive eggs; 2) ecological group models are built based on biologically perceptive spatiotemporal scales and hydro-ecological mechanisms, ensuring high predictive accuracy; 3) a structurally simplified yet mechanistically robust food web model effectively integrates basal group models to predict fish production. Using HFM, we can assess environmental flows for the reaches downstream of XJB, satisfying hydrological needs of both fish spawning/hatching and basal groups (primarily floodplain plants). Our model provides a more comprehensive and ecologically realistic tool for river management. It is applicable to ecological operation and biodiversity restoration in regulated rivers worldwide. The main innovations include: 1) advocating for environmental flows assessments targeting entire life cycles of most species within protected groups; and 2) establishing two principles for hydrology-biology model development—matching model’s spatiotemporal scales to biological perception and employing mechanism-driven quantitative modeling.

Daily hydropower regulation and mainstem backwater generate complex hydrodynamic conditions in the Min River estuary, posing significant challenges to navigation safety. To analyze the impact of mainstem backwater on tributary navigation safety, this study focuses on the lower Min River reach affected by backwater from the Jinsha River. A depth-averaged 2D hydrodynamic model is established, and a water level difference parameter is used to construct the stage-discharge relationship at the estuary based on long-term measured water level and discharge data. Indicators including backwater distance, water surface slope, hydrodynamic axis migration, flow velocity, and cross-flow are used to delineate navigation risk zones. The results indicate the following: (1) The backwater intensity and extent are primarily governed by the mainstem and tributary discharges and by the distance from the estuary. High discharge and water levels produce significant backwater effects and reduced flow velocity. Empirical formulas for backwater length under various discharge conditions are established to support navigation decision-making, with RMSE values ranging from 0.42 km to 0.92 km. (2) Variations in estuarine water level induce oscillations in the hydrodynamic axis. When the upstream discharge is 900 m3/s and the estuarine water level is 258.4 m, the maximum oscillation amplitude reaches 20.33 m. (3) During periods of medium and low water, the reach exhibits significant navigation-obstructing behavior, with high-risk zones concentrated in Tongluowan, Yangjiaoshi, and other shoals 5-8 km being found from the estuary. (4) Under the design discharge condition, the minimum estuarine water level required to ensure adequate channel depth, appropriate flow velocity, and manageable ship resistance for safe navigation is 267.96 m. This study provides a scientific basis for navigation safety and channel regulation in the Min River estuary and similar reaches affected by mainstem backwater, thereby supporting sustainable waterborne transport.

Fish kills at Neotropical hydroelectric power plants, particularly those driven by total dissolved gas (TDG) supersaturation, are difficult to diagnose and quantify due to data scarcity and rapid carcass decomposition. This study proposes a novel framework to address these challenges by (1) inferring TDG saturation from more readily available Dissolved Oxygen (DO) data, using thermodynamic principles and (2) estimating true daily mortality through a Bayesian multistate model that accounts for decomposition stages and catchability. Applied to a fish kill event at an Amazonian dam, the models showed that TDG levels can be accurately inferred from DO data and that direct carcass counts severely underestimate the magnitude of mortality events due to low detection probabilities. Furthermore, these results revealed a significant temporal lag between the actual mortality peak and carcass recovery. This integrated methodology offers a robust framework for quantifying impacts, expanding monitoring capacity, and supporting more rigorous environmental licensing processes in the Neotropical region.

Black-odorous water pollution has gained widespread attention, particularly due to the accidental discharge of chromium (Cr), which increases the risk of ecosystem function loss and complicates treatment processes. In this study, a strain capable of tolerating high Cr concentrations while simultaneously removing Cr(VI), COD, and NH3-N under micro-oxygen conditions was isolated from an urban river and identified as Providencia burhodogranariea T91. The detoxification mechanisms for Cr(VI) involved reduction, adsorption, and chemotaxis, as revealed by SEM, FTIR, XPS, and transcriptional analyses. RNA-seq and qRT-PCR results consistently indicated that genes related to Cr(VI) reduction (LpDH), denitrification (nirk) and chemotaxis (cheR, cheA and cheY) were up-regulated. In the in-situ channel experiment, the T91 strain demonstrated TN degradation rates ranging from 29.8% to 42.9%, with the dominant bacterial population shifting to Bacilli. A mathematical turbulence model based on in-situ channel experiments was developed, revealing that the best removal effect of T91 occurred at a flow velocity of 0.005m/s, with a removal rate of 24.39%. This study provides valuable insights into the simultaneous removal of Cr(VI), NH3-N, and COD under high Cr concentration stress and offers a low-energy, biotechnological solution for the treatment of Cr-containing wastewater of polluted natural rivers.

During dam discharge, supersaturated total dissolved gas (TDG) is generated in the plunge pool and transported downstream for a long distance. Fish living in supersaturated TDG water may suffer from gas bubble disease and even death. Investigating the transport time of supersaturated TDG helps to predict better the downstream impact range and duration of TDG supersaturation and then facilitate mitigation measures for fish in time. From another perspective, it also contributes to optimizing flood discharge management and enhancing the effectiveness of ecological management strategies. This is essential for improving the effectiveness of ecological management strategies. This study utilized a laterally averaged numerical model to investigate the factors influencing the supersaturated TDG transport time in a large deep reservoir. The Baihetan (BHT)–Xiluodu (XLD) hydropower stations were selected as the research object. Simulations under various BHT–XLD joint operation strategies were conducted to analyze the supersaturated TDG transport time in the XLD Reservoir. It is revealed that the transport time of supersaturated TDG is associated with the discharge flow and reservoir characteristics. A power function relationship was identified between the transport time and the transport distance as well as the discharge flow. The relationship among the transport time, water depth, and total volume follows a linear function. Furthermore, a quantitative relationship between the transport time and these four influencing factors was established. The results provide a scientific basis for the accurate prediction of the supersaturated TDG transport process in large deep reservoirs and the formulation of effective regulation and early warning schemes.

Hydropower development is one way to efficiently harness the energy of rivers. However, damming limits the upstream reproductive behavior of migratory fish, and fish passage facilities are now an important means of restoring connectivity. Flow velocity is an important factor for fish to perceive the environment and maintain swimming behavior. The reservoir in front of the dam has become a near-hydrostatic environment that significantly changes the river properties. Reduced velocity may make it difficult for fish released into the reservoir area by fish passage facilities to find the flow direction, reducing their migratory success rate. This paper takes the Wudongde reservoir as an example and uses numerical simulation to analyze the characteristics of the flow field in the reservoir at different flow levels. It takes the induced velocity of fish as the threshold value to analyze the river sections in the reservoir affected by the reduced velocity. The results show that the flow velocity in the reservoir area decreases significantly from the end of the reservoir to the front of the dam; the flow velocity in the main reservoir is more homogeneous in the direction of water depth, and the tributary estuaries present non-uniform distribution. Under the conditions of low flow (February), medium flow (May), and high flow (August), a certain range of the river section is below the induced velocity of the fish (0.2 m/s), and the suitable locations for migratory fish stocking are located in the upper part of Wudongde Dam, 102, 96, and 38 km, respectively. The results provide technical references for the selection of release sites for fish passage facilities in high dams and large reservoirs, and are of great significance for the protection of water ecology in the dam-built river reaches.

The Fish Habitat Comprehensive Suitability (FHCS) indicator plays a pivotal role in evaluating fish spawning and egg hatching behavior. Assessments of fish spawning and egg hatching suitability have traditionally relied on deterministic outcomes from single- or multi-factor hydrological designs. However, considering the uncertainty of riverine environments, the FHCS and its components, including the fish spawning weighted suitability area (WUA) and the potential number of eggs hatching (Negg), should be viewed as random variables that follow specific probability distributions. To address this, an FHCS assessment method combining a mechanism model with a Bayesian network (BN) model was developed to evaluate the FHCS of four major Chinese carps (FMCCs) in the Xunjiang River, China. The mechanism model provided foundational data essential for constructing the BN. The BN model was then employed to determine the values of key factors, such as Weighted Usable Area (WUA) and egg viability (Negg), which were subsequently used to calculate the FHCS of the study area. The results of the study were obtained using the mean of the 94 % confidence intervals of the BN model parameters. The results showed that the suitable spawning period for FMCCs at the Dongta spawning ground was 68 days in 2022, compared to just 7 days in 2023. The suitable hatching period for eggs was 65 days in 2022 and only 7 days in 2023. The FHCS assessment for the study area revealed that the period of fish habitat suitability was 57 days in 2022. However, due to the brief duration of favorable flow conditions in 2023, there were no overlapping time intervals suitable for both spawning and hatching. This underscores the critical role of comprehensive suitability assessments for fish spawning and egg hatching, offering more precise and scientifically grounded tools for fish conservation.

Withdrawal of fish eggs and larvae through a river intake (entrainment) may damage the river's early fish resources. To investigate how the hydraulics (flow velocities, directions, and magnitudes) around and within the water intake structure influence entrainment, this study focused on a typical river-pump intake. A turbulence model was developed based on the Euler-Lagrange method and the variable of helicity was introduced to define the zone of the river from which water is withdrawn and organisms are entrained. The process of simulated hydraulics on organism withdrawal was validated by physical experiments using artificial fish eggs under various river flow and intake flow conditions. The simulated results indicated that when the intake-to-river flow ratio ranged from 3 to 7 parts per thousand, the width of the planar entrainment area was approximately 1.2 to 1.4 times the width of the intake structure, and the entrainment quantity of fish eggs and larvae accounted for 0.12% to 0.49% of the incoming flux. The entrainment quantity increased with the intake flow to the river flow ratio. The absolute helicity threshold under different conditions ranged from 0.004 to 0.047 m/s2, which was inversely proportional to the intake flow rate and unaffected by river flow and water depth. An optimized intake structure design with stepped side walls was promoted, which can minimize the impact of river sedimentation and reduce the fish entrainment quantity by an average of 11%. This research provides valuable insights for water intake safety and fish resource protection.

Supersaturated total dissolved gas (TDG) resulting from dam discharge can cause gas bubble disease in fish, threatening aquatic ecosystems. Reservoir operations influence the transport of supersaturated TDG, yet the underlying mechanisms remain incompletely understood. This study utilizes the TDG generation and transport model to evaluate the impacts of various operational strategies, including upstream discharge duration, upstream sluice discharge operation, and downstream water level variation, with case studies of the Baihetan (BHT) and Xiluodu (XLD) hydropower stations. The findings indicate that reducing the upstream BHT discharge duration lowers both the peak TDG saturation and its duration. Compared to the gradual closure process of sluices, a gradual opening process of sluices shortens the period of elevated TDG saturation. Additionally, decreases in downstream water levels accelerate TDG saturation reduction and shorten its persistence. The study also proposes an optimized operational strategy, assessing its impact on fish risk before and after optimization.

Microbial coalescence plays a crucial role in shaping aquatic ecosystems by facilitating the merging of neighboring microbial communities, thereby influencing ecosystem structure. Although this phenomenon is commonly observed in natural environments, comprehensive quantitative comparative studies on different lifestyle bacteria involved in this process are still lacking. The study focuses on 16S rRNA Amplicon Sequence Variants (ASVs) at the Jinsha River hydropower stations (Wudongde [WDD], Baihetan [BHT], Xiluodu [XLD], Xiangjiaba [XJB]), specifically examining free-living (FL) and particle-attached (PA) bacteria. Minimal differences in microbial composition were observed across water layers (surface, middle, and bottom). Analyses of overlapping ASVs, Bray-Curtis dissimilarity, and the SourceTracker algorithm revealed a significant difference in the coalescence ability of FL and PA bacteria, particularly in the surface water of XJB (FL: 31.1% ± 2.0%, PA: 27.6% ± 2.5%, p < 0.05). The coalescence of FL bacteria was primarily influenced by the mixing of adjacent water layers, while PA bacteria exhibited significant geographical variations across water layers (p < 0.05), displaying lower coalescence compared to FL bacteria. Using a cohesion metric, 12 keystone species in PA bacteria were identified and 7 in FL bacteria. Proteobacteria and Bacteroidetes were the most abundant phyla at the keystone species in PA and FL bacteria, respectively. The abundance of keystone ASVs decreased with distance in PA bacteria, whereas FL bacteria showed the opposite trend. At the genus level, Brevundimonas and Chryseobacterium were identified as keystone species in both lifestyles. Moreover, the impact of community coalescence on the stability tends to exhibit differences downstream in cascade stations. This study provides novel insights into the dynamic variations of microbial communities with diverse lifestyles in stratified aquatic environments and assesses the impact of dam construction on microbial coalescence and the alteration of keystone species.

The riparian zone is a crucial interface between the aquatic and terrestrial components of river ecosystems. Organic matter deposited here can serve as an important food source for aquatic organisms, earning it the name of detritus bait. The construction of hydrological facilities has altered the flow rhythms of rivers, reducing the inundated area of banks and the frequency of flow velocity changes, which in turn negatively affects the ecological stability of the river. Given these reasons, it is crucial to understand the distribution characteristics of debris bait on riparian and the recharge pattern to rivers under flow impacts. The physical properties intrinsic to the debris in question were examined in order to ascertain their influence on the dynamics of debris transport through natural sampling methods. The distribution patterns of debris on natural river banks were investigated using density separation. A quantitative experimental model was designed based on the results of natural investigations to analyze the response characteristics of debris in-stream recharge to hydrodynamic structures at different flow velocities. The results indicate that the debris distribution is influenced by the background soil situation and flow effect. The soil layer immediately adjacent to the surface of the bank has a higher recharge effect. The main period for riparian debris recharge occurs at the onset of changes in flow rate. Furthermore, there is a positive correlation between the flow velocity and the quantity of debris entering the river. The findings of this study offer valuable insights into the replenishment of river bank debris bait under the current conditions, with implications for the ecological management of rivers undergoing hydropower development.

High dam discharge can lead to total dissolved gas (TDG) supersaturation in downstream rivers, causing fish to suffer from bubble trauma and even mortality. Focusing on the Datengxia hydropower station in the Xijiang River basin, we conducted in-situ experiments to explore the tolerance patterns of economic fish species, including Ctenopharyngodon idella, Hypophthalmichthys molitrix, and Cirrhinus molitorella, under the influence of TDG supersaturation at different compensation depths. Moreover, the development and recovery patterns of bubble trauma and the swimming ability of fish exposed to TDG supersaturated water were investigated. In-situ experiments showed that TDG supersaturation ranged from 112.2 % to 125.2 %, averaging 118.3 % at the experiment site. The results revealed that compensation depth is favorable in fish avoidance of TDG supersaturation. The survival rate of the experimental fish at the surface was lower than for those at the 0-3 m water depth. The survival rates of Ctenopharyngodon idella, Hypophthalmichthys molitrix, and Cirrhinus molitorella at the surface were only 30 %, 47.5 %, and 70 %, respectively, while at the 0-3 m water depth, the survival rates were 97.5 %, 87.5 %, and 87.5 %, respectively. Additionally, the survival rate of fish was related to their preferred water depth. The bubble trauma scores of the experimental fish in TDG supersaturated water significantly increased with exposure time and significantly decreased after recovery in freshwater. The relative and absolute critical swimming speed (U crit ) of Ctenopharyngodon idella ranged from 10.91 to 12.98 BL/s and 83.3-102.9 cm/s respectively, and there were no significant changes in the U crit with increasing TDG supersaturation exposure.