Excessive flow turbulence poses a threat to the development of drifting fish eggs, leading to mortality or developmental malformations and ultimately depleting early fish resources. Currently, there is a scarcity of quantitative studies investigating the effects of flow turbulence on the entire process of drifting fish egg development, from fertilized egg division to hatching. In this paper, the effects of different flow turbulence conditions (FTCs), including turbulent kinetic energy and shear stress, and action times on different stages of fish egg development were quantitatively explored using a transverse-oscillating-grids turbulence tank. Empirical formulas were established to predict the proportion of normal fish egg development under different FTCs within a selected range. The research findings provide a quantitative basis for protecting early fish resources, mitigating the biological invasion of specific fish, constructing fish-breeding facilities, and ensuring safe transfer and transportation.

The Jingjiang Sandbank (JJS) is located on the bank of the tidal reach in the Yangtze River. It experiences a periodic evolution process of increase, split, migration, and dissipation, which affects the current direction, fish habitat, navigation safety, etc. In this paper, the periodic evolution of the JJS is investigated based on 17 field bathymetric measurements of the river from 1999 to 2017. Firstly, six cycles of the evolution process of the sandbank are described, and the evolution pattern of the split detached bar and the main body of the sandbank are analyzed according to the migration tracks of the detached bars and the historical volume-change of the JJS, respectively. Then an empirical orthogonal function (EOF) is conducted on the historical measurements of the bathymetry. The first four eigenfunctions correspond to the time-averaged bathymetry, the long-term change of the pattern of bathymetry, the periodic change of the JJS, and the downstream migration of the split detached bar, and the periodic change of the rip at the back of JJS. It is pointed out that the construction of two waterway regulation projects might have changed the evolution pattern of the JJS permanently.

The Yellow River, a critical water resource, faces challenges stemming from increasing water demand, which has led to detrimental effects on hydropower generation and ecological balance. This paper will address the complex task of balancing the interests of hydropower generation, water supply, and ecology within the context of cascade reservoirs, specifically Longyangxia and Liujiaxia reservoirs. Employing a systemic coupling coordination approach, we constructed a multi-objective synergetic model of the upper Yellow River in order to explore synergies and competitions among multiple objectives. The results reveal that there is a weak competitive relationship between hydropower generation and water supply, a strong synergy between hydropower generation and ecology, and a strong competitive relationship between water supply and ecology. The Pareto solution set analysis indicates a considerable percentage (59%, 20%, and 8% in wet, normal, and dry years, respectively) exhibiting excellent coordination. The probability of excellent coordination decreases with diminishing inflow. The optimization scheme with the highest coupling coordination demonstrates significant improvements in power generation, water supply, and ecological benefits in the upper Yellow River without compromising other objectives, fostering the sustainable operation of hydropower generation, water supply, and ecology in the upper Yellow River.

The flow dynamics adjacent to spur dikes exhibit turbulence and complexity, often resulting in the formation of scouring pits in the riverbed nearby. In regions downstream characterized by robust riverbed mobility, the vulnerability of riprap spur dikes stems from the instability of the upper riprap induced by these scour pits. Current research on scour pits primarily focuses on singular runoff conditions, with a limited exploration into the formation and traits of these scour pits under the combined influence of runoff and tidal currents. This study delves into the formation process and features of scour pits adjacent to submerged riprap spur dikes shielded by flexible mattresses, considering the impact of both runoff and tidal forces, using flume model tests in the tidal zone of the lower Yangtze River as a reference. Our findings reveal that the scour pits at the forefront and rear of riprap spur dikes undergo cyclic scouring and silting influenced by the runoff and tide current’s duration and intensity. The maximum scour depth observed ranges from 60% to 90% of that during runoff alone, contingent upon the ratio of maximum flow velocity at flood tide and ebb tide (denoted as e). This law can be quantitatively elucidated through the concept of the average effect of flow on the riverbed scouring and silting in a unit time (denoted as E). A formula to calculate the maximum scour depth of riprap spur dikes under both runoff and tidal current scenarios, along with a slope formula describing the maximum scour depth relative to the spur dike toe are proposed in this study. These formulations offer versatility across varying flow conditions. Subsequently, we establish an evaluation index pertinent to the safety operation of spur dikes based on the latter formula. This research contributes to a more comprehensive understanding of scour pit dynamics adjacent to spur dikes, especially under combined runoff and tidal influences. The proposed formulae and evaluation index hold promise in enhancing the assessment and maintenance practices for these critical riverbank structures.

Due to water scarcity in the Yellow River basin, the existing operations for the Longyangxia and Liujiashan cascade reservoirs are insufficient to meet the demands of multiple objectives. This study establishes a coupled coordination model considering hydropower generation, water supply, and storage capacity at different periods during the year. At the same time, the model quantifies the impact of scheduling strategies on multiple objectives and determines the optimal operation for reservoirs at different periods. The results indicate that the scheduling strategy of the Longyangxia reservoir dominates the changes in hydropower generation, water supply, and storage capacity. Specifically, during the ice flood control period, the scenario of continuous release from Longyangxia and continuous storage at Liujiaxia achieves 1.26 billion kWh of hydropower generation, with a water supply shortage rate of 8.67%; During the non-flood period, releasing water from Longyangxia in April and May and storing it in June while Liujiaxia continuously releases water results in 4.68 billion kWh of hydropower generation and a shortage rate of 1.61%. During the flood control period, continuous storage at Longyangxia and controlling the water level of Liujiashan within flood control limits, with storage in September and release in October, achieves 5.65 billion kWh of hydropower generation and a shortage rate of 0%.

Sediment adsorption in rivers is a crucial pathway influencing the migration and transformation of biogenic substances at the water–sediment interface, thereby playing a significant role in the eutrophication process of aquatic systems. This study quantitatively investigates the individual contributions of initial nutrient concentration, sediment concentration, and sediment particle size on nitrogen and phosphorus adsorption through generalized laboratory experiments. Comparative analyses were conducted on the adsorption characteristics and mechanisms of phosphate (PO₄ ³ ⁻) and ammonium (NH₄⁺), and the adsorption response to varying sediment concentrations was further examined. Results indicate that the contribution rates of initial concentration, sediment concentration, and particle size to PO₄ ³ ⁻ adsorption were approximately 0.71, 0.23, and 0.06, respectively; while for NH₄⁺ adsorption, these were 0.67, 0.27, and 0.06, respectively. The Sediment Concentration Adsorption Model (SCAM) was subsequently developed to elucidate the adsorption mechanism modulated by sediment concentration. The concept of The Adsorption Critical Sediment Concentration (ACSC) was introduced, identifying it as the threshold at which the adsorption mechanism transitions, along with a description of its calculation method. This study provides quantitative guidance and practical reference for optimizing adsorption systems, contributing to pollutant regulation and removal engineering in riverine and lacustrine environments.