Abstract: Surface water is a key natural resources and a restrictive element to maintain regional ecological balance and support development of social economy. River runoff is the main form of surface water resources. Variation of the both river runoff and surface water will directly influence water resources management of a basin. Based on the annual report series of water resources and the recorded runoff of 10 representative hydrometric stations on major rivers in China, the variations of the surface water resources of the ten water resources zones and recorded runoff of major rivers in China during 1956—2018 were investigated. The results show that:① The annual runoff gauged on major rivers during 1956—2018 shows a downward trend with exception of the Datong station on the Yangtze River. ② The recorded annual runoff of the Tangnaihai station on the upper Yellow River presented an insignificant decreasing trend while that gauged at the Huayuankou station on the Yellow River exhibited a significant decreasing trend. During 1980—2000 and 2001—2018, the recorded runoff at the Tangnaihai station changed by 1.8% and-5.9% as comparing to baseline in 1956—1979 while that of the Huayuankou station decreased by 26.7% and 41.0% respectively. ③ Geographically, the Yellow River could be treated as separation boundary of runoff variation trends from the north to the south of China in terms of significance level. Recorded annual runoff presented significant decreasing trends for rivers in the north to the Yellow River while that exhibited insignificant variation trends for rivers in its south. The recorded runoff in 2001—2018 decreased by more than 25% relative to the baseline of 1956—1979 for the northern China rivers, with the highest reduction of over-80% occurring in the Haihe River. ④ The average annual surface water resources of China during 1956—2018 was approximately 2 726.6 billion m3, which is 12.2 billion m3 less than that in the second water resources assessment conduced in 2004. Reduction of surface water in the Haihe River zone, Yellow River zone, and Liaohe River zone aggravated contradiction between water supply and water demand since the early 21st century.
Abstract: The construction of a large-scale water conservancy project has caused the adjustment of the scouring and silting of the downstream river channel, which has a significant impact on the ecological environment, flood control and channel transportation. Since the trial experimental impoundment of the Three Gorges Dam in 2008, the downstream erosion of Chenglingji has intensified. To explore the adjust characteristics of scouring and silting and the driving mechanism of the downstream erosion of a river channel during a water control project, the spatial evolution characteristics and transverse morphological variation of the reach from Chenglingji to Jiujiang reach were analyzed. The results show that the scouring of the low flow channel in the Chenglingji—Jiujiang reach has intensified, and the morphological changes since 2008 have mainly been concentrated in the medium flow channel, of which the proportion of the evolution volume accounts for more than 90%;the transvers changes shows scouring and incising, while a sectional view displays narrowing and deepening. On the basis of the established empirical relationship between the reach-scale medium channel dimensions and the accumulated sediment transport capacity in each discharge interval during 175 m experimental water storage period from 2008 to 2016, this paper indicates that the discharge of 29 000—31 000 m3/s at Luoshan Station and that of 31 000—33 000 m3/s at Hankou Station can be regarded as characteristic discharges corresponding to the average top levels of braided channel bars, which are of morphological significance in constraining the passing flow in the medium flow channel and guaranteeing that the water transport capacity is the strongest. The geomorphic impact of flow below the characteristic discharge was more prominent during 2008—2016;this impact resulted in the adjustment of scouring and silting being mainly concentrated in the medium flow channel. Moreover, river channel erosion has intensified because, in addition to the construction of waterway regulation projects, the volume of transported sediment with d>0.125 mm has largely diminished.
Abstract: The scientific operation of cascade reservoirs is an important means of mitigating losses from drought. In this study, a multi-spatial-temporal scale synergetic optimal operation model of cascade reservoirs is established with the goal of decreasing the severity of water shortages in the basin and optimize the spatial and temporal distribution of those shortages. An interactive and improved nested particle swarm optimization (PSO) algorithm was used to produce the model. In the outer layer, the optimal control of drought limit water level for multi-year regulating storage reservoir was realized, and in the inner layer the water storage and discharge processes of cascade reservoirs were optimized to realize the inter-annual regulation, intra-annual optimization, synergy among cascade reservoirs, and spatial coordination. The model developed in this study was applied to the cascade reservoirs in the main stream of the Yellow River during 2012—2014 to optimize drought limit water levels of the Longyangxia Reservoir and water discharge processes of cascade reservoirs to cope with the serious drought in 2014. The results show that inter-annual water supply is realized through the use of the drought limit water level in the Longyangxia Reservoir, which kept the water shortage ratios of each year between 4.9% and 5.7%. The system also kept water shortages evenly distributed across different regions at different times by optimizing the water discharge processes of cascade reservoirs. The agricultural water shortage ratios were kept between 7.0% and 11.0%, mitigating drought loss significantly.
Abstract: The formation and creeping of the density current in the Xiaolangdi Reservoir are important indices of the water scheme and sediment regulation in the Yellow River. Previous studies have focused on the theory of density current in the Xiaolangdi Reservoir, real-time tracking on the operation process, and the analysis of surveyed data; however, they did not include related research on real-time prediction of the Xiaolangdi Reservoir and the tracking analysis of latest theoretical results. In this study, a field investigation, theoretical analysis, and prediction analysis were conducted to explain the process of water and sediment inflow from the Xiaolangdi Reservoir, during the period of discharging before the flood in 2018. The formation and creeping of the density flow were observed according to boundary conditions such as reservoir operation and reservoir siltation morphology. The plunging point formula of the density flow in the reservoir was predetermined, based on the velocity distribution. The results show that, in July 2018, intense scouring in the reservoir caused a significant amount of siltation to fall at the plunging area, thereby considerable decreasing the depth of clear water. This caused the plunging point to move downstream. The position of the plunging point moved ahead of the dam with the increase in water and sediment inputs, decrease of water level before the dam, and advance of the siltation in the reservoir. The calculated and measured results reflect on the changing process. These results can be used as a reference for the preparation and post-evaluation of reservoir water and a regulation plan for sediments. The results can also provide technical support for the operation as well as planning and design of reservoirs in sediment-laden rivers.
Abstract: The Yellow River is the river with the highest sediment concentration in the world. The sediment transport of the desert-wide valley reaches in the upper Yellow River are affected by inflow, sediment and changes in topographic conditions. To research the effects of low-temperature water on sediment transport in the hyperconcentrated river, we introduced the water temperature factor to a sediment transport rate model established for the Bayangaole station. Based on the general optimization algorithm of the First Optimization platform, the sediment transport rate model was verified, and the low-temperature sediment transport effect of the hyperconcentrated river was quantified. The results show that: ① The water temperature had an influence on the sediment transport rate mainly in the low water temperature period, especially when the sediment transport rate increased obviously when the water temperature fell below 7 ℃; ② In all conditions, the sediment transport rate at a water temperature of 1 ℃ was approximately 2.5 times that at a water temperature of 25 ℃; ③ The sediment transport rate of the river at a low water temperature (5 ℃) increased by 40.7% compared to that at a normal temperature (16.6 ℃); therefore, in the Upper Yellow River, according to the sediment transport, the best time for water and sediment regulation is during the ice break-up period with low temperatures and high flow conditions. The research results are expected to provide technical support for efficient sediment transport in the low water temperature period of the Yellow River and other hyperconcentrated rivers in cold regions.
Abstract: Reverse flow has an important impact on hydrodynamic changes and water environment protection in Poyang Lake Basin. A correct understanding of the causes and conditions is of significance to clarify the function mechanism of reverse flow and study the intensity and coverage of influence of reverse flow. From the perspective of unsteady flow flood wave propagation, by analyzing the causes of reverse flow, and considering the characteristics of reverse flow when Poyang Lake is in fluviatile facies and in lacustrine facies, this paper puts forward the Yangtze River action intensity index and Poyang Lake action intensity index. On such basis, the comprehensive river-lake action intensity function is introduced. With the measured data, this paper has analyzed and studied the relational expression of the comprehensive river-lake action intensity function, as well as the occurrence conditions and quantization index for reverse flow. It is verified that the proposed reverse flow quantization index can be used to distinguish river-lake uplift and reverse flow phenomena, and predict reverse flow when Poyang Lake is either in fluviatile facies or in lacustrine facies, with improved accuracy rate in predicting the starting time, total duration and annual occurrence times of reverse flow. The results can be used to study river-lake relations and the actual engineering for comprehensive utilization of water resources in Poyang Lake Basin.
Abstract: To address the problems that the physical mechanism of the stage-discharge relationship is not clear and the uncertainty sources of estimated discharge is not adequately considered, current study used the Shijiao hydrological station of the North River basin as an example to derive the stage-discharge relationship. Based on the BaRatin model, current study evaluated the discharge measurement error and the effect of the calibration sample selection on the uncertainty of the estimated discharge. It was found that the stage-discharge relationship for the wide and shallow rectangular section of the river channel is a power function, where its coefficient can be expressed by roughness, river width, and energy slop, and the index is a constant value of 5/3. The total uncertainty of the estimated discharge decreases by 32% when considering the discharge measurement error. Doubling (Tripling) the samples drops the total uncertainty of the estimated discharge by 12% (34%). The conclusions of this study are:① The method of establishing the stage-discharge relationship here can be extended to different types of hydrological stations; ② The high water measurement error has significant impact on the calibration accuracy, and it is recommended to improve the high water flow measurement accuracy; ③ Information redundancy exists in the measured data, particularly in the low water measurements. The proposed method requires less calibration data, which can reduce the cost of discharge compilation.
Abstract: This study applied four classes of entropy-based optimization criterions for hydrometric networks, i.e., entropy-transinformation (H-T), entropy-total correlation (H-C), entropy-transinformation-total correlation (H-T1-C/H-T2-C), and transinformation index (TI), to a rainfall monitoring network in the southwest hilly area in the Taihu Lake Basin, and made comparison and assessment of the criterions. Using daily precipitation of 2007—2016 as samples, we calculated the stations' ranks with three data discretization methods respectively, then made correlation analysis of ranks, sensitivity analysis concerning the index weight of multi-objective criterions, and investigated the inter-annual variance of ranks. Results showed that ranks obtained with H-C was the most representative, the least sensitive to the index weight, and had insignificant inter-annual variance; H-T2-C was the most sensitive to the index weight, with significant inter-annual variance. H-C criterion can best reflect the basic entropy based optimization principles (increasing information content and reducing redundancy), while H-T2-C criterion can best reflect decision preferences.
Abstract: The mass exchange process across sediment-water interface (SWI) plays an important role in contaminant migration and transformation in natural waters. The mass exchange across the SWI for rough bed depends on both bed roughness and sediment permeability. By means of laboratory annular flume experiment, quantitative measurements of interfacial mass exchange flux at the SWI and its variations have been performed under the rough bed condition. A parameterization method has been adopted to analyze the dependence of effective diffusion coefficient on its main controlling parameters. The experimental results indicate that within the variation range of the present flow and sediment conditions, the effective diffusion coefficient shows an obvious piecewise variation feature from hydraulically smooth, transitional up to fully rough regimes due to the joint effect of mean flow velocity, bed roughness and sediment permeability. The dependence of the effective diffusion coefficient on its main controlling parameters can be described consistently by adopting the permeability Reynolds number. Based on an analysis of dual parameters (i.e. the roughness and permeability Reynolds numbers), the corresponding threshold values for different flow regimes have been determined to reasonably characterize the comprehensive impact of the bed roughness and sediment permeability on the interfacial mass exchange characteristics.
Abstract: Sedimentation pattern is one of the important factors affecting reservoir capacity and reservoir sediment flushing. In the near-dam area of Xiaolangdi Reservoir on the Yellow River, fine-grained muddy deposits are easy to flow like fluid. In this paper, the rheological property and flow pattern of muddy deposits were investigated. It was found out that the flow pattern of low density muddy deposits is that of Bingham flow, and its fluidity will decrease quickly when its density exceeds 1.25 g/ cm3. Base on analysis of shear stresses at interfaces between water and muddy deposits and between muddy deposits and channel bed, governing equations for the movement of muddy deposits were established. A simulation method for fine-grained sedimentation processes was developed by coupling the model for water flow and sediment transport with the model for muddy deposits movement. Calculation results indicate that sedimentation pattern of fine-grained particles in the Xiaolangdi Reservoir can be simulated accurately by considering the effect of muddy deposits movement. This investigation could improve our understanding of sediment deposition mechanisms in reservoirs, especially for fine-grained sediment.
Abstract: In order to investigate the lateral widening process of farm dike breach, a generalized physical model was constructed. Farm dikes with different soil properties in experiments were built using the soil excavated from a prototype farm dike located in the Lower Yellow River. The variation processes of hydraulic characteristics and breach widths were measured and analyzed. Experimental results show that the lateral widening mechanism during the process of dike breach was clarified by two aspects, including the lateral erosion of the dike soil below the water level, and the collapse of the dike soil above the water level. The flow velocity at breach site increased first and then decreased, with a peak value of 1.1 m/s. The water depth kept decreasing, but the decreasing rate gradually became smaller. Water depths, breach velocities and discharges, and lateral widening rates increased with an increase of inlet discharge. An empirical formula to calculate the lateral widening rate was proposed based on the analysis of factors influencing the farm dike breach, and the calculated widening process agreed well with the measured process. These results can provide experimental data not only for the research on the lateral widening process of farm dike breach, but also for the validation of numerical models.
Abstract: The aim is to solve the problem of increasing the energy dissipation rate during the flood discharge with aggravating the downstream atomization, and to explore the influence of different flip buckets on atomization of downstream. Based on the physical model test, the downstream nappe wind distribution, the splash-water distribution, the hydraulic characteristics of trajectory nappe and the scour pattern were studied. The research shows that:① The downstream nappe wind speed of the asymmetrical tongue-shaped bucket, the standard tongue-shaped bucket and the curved surface bucket are generally larger than that of continuous bucket. ② For the asymmetrical tongue-shaped bucket, on the left side of spillway axis, the splash intensity is greater than that of the right sides. the maximum difference of the rainfall intensity between the left and right sides is 5.625 g/(m2·min). but for the distribution of curved bucket is opposite, on the right sides of spillway axis, the splash intensity is greater than that of the left sides. the maximum difference of the rainfall intensity between the left and right sides is 45.125 g/(m2·min).③ With the increase of the distance between the control point and the impinging piont, the number and the volume proportion of the large water droplets decreased sharply; with the increase of trajectory angle, both the trajectory nappe width of continuous bucket and tongue-shaped bucket are increase; and the depth of scour pool decreases with the decrease of trajectory angle. ④ When adopting the flip bucket whose curved surface is attached to the proper side wall, which can reduce the atomization influence; and the erosion damage of downstream can be reduced by increasing the trajectory angle.
Abstract: To deepen the understanding of the total flow control equations for open channel flow and explore the composition and distribution characteristics of the total flow energy loss, through theoretical analysis, the total flow integral and differential model control equations describing the general characteristics of steady turbulent flow in open channel were constructed in the framework of viscous fluid mechanics theory. The model parameters can be obtained directly from the distribution of flow statistical characteristics on the flow section, thus achieving the unification of the descriptions of flow fields characteristics and total flows of turbulent flow in open channels. Besides, an explicit expression for the total flow energy loss is provided. Meanwhile, the total flow energy loss consists of viscous dissipation and maintenance of turbulence as two parts. In the composition of classified energy loss in steady uniform turbulence flow in a rectangular open channel, it is dominated by viscous dissipation part on the wall. With the increase in the distance away from the wall, the energy loss density of the part of maintaining turbulence increases rapidly, and the speed increases with the increase in the Reynolds number.
Abstract: This study investigates the hydrodynamic characteristics of a submerged horizontal circular cylinder under forced oscillation by using a 2-D two-phase flow numerical wave tank (NWT) model based on the viscous fluid theory. The calculations of the hydrodynamic forces on the circular cylinder under various liquid-phase viscosities were performed. By studying the relationship between the hydrodynamic forces and motion of the cylinder and analysing the flow fields around the cylinder, the mechanism of the viscous effects was identified. The study shows that differences between the results of the cases under different viscosities are on account of different contributions of the viscous shear forces to the total hydrodynamic forces and different influences of the vortex on the hydrodynamic forces. The considerable influences of fluid viscosity on the motion hysteresis of the vortex lead to a phase difference between the pressure forces on the cylinder under different viscosities. The phase advance phenomenon of the viscous shear forces can be explained by the fact that compared with the motion of the cylinder, the motion hysteresis of the water-particles in the higher viscosity fluid is more obvious.
Abstract: Flood events caused by the overtopping failure of earth-rock dams often lead to catastrophic disasters. Therefore, examining the cause of the dam failure and studying the subsequent flood evolution processes are extremely important for disaster prevention and mitigation. This work reviewed the phenomena and mechanism of the overtopping failure of earth-rock dams and recent researches using physical experiments and numerical simulations. The scale design of physical model test is discussed, and the research findings of dam break experiments under different scales, dam types, and experimental conditions are summarized. Research progresses of numerical simulations of dam breaks using parametric models, simplified physically-based models, and detailed physically-based models are reviewed. Advances in numerical and experimental studies of the evolution of flood caused by dam failure are highlighted. After reviewing the literature, some future research directions are proposed. They include examining the influence of river boundary conditions on dam failure and the subsequent flood propagation processes, reconciling the mechanism of the failure of heterogeneous earth-rock dams, investigating the erosion law of sediment-laden flow during dam breaks, studying the downstream scouring and silting and riverbed sediment sorting after dam failure, and evaluating the impact of dam failure on the aquatic ecosystems.
Abstract: The accurate identification of surface water pollution sources is very important for formulating remedial schemes and determining the parties responsible for sudden water pollution incidents. According to the basic principles and theories of pollution source identification, an overview of the existing methods is presented in this study, including mathematical simulation and footprint analysis methods. The mathematical simulation methods comprise direct solution methods (analytical and regularization-based methods) and indirect solution methods (simulation optimization methods, probability-based statistical methods, and coupling algorithms). The uncertainty of pollution source identification is discussed in terms of the pollution source information, observational data, surface water model, hydrodynamic conditions, and pollutant properties. The uncertainty and timeliness of surface water pollution source identification are the key factors that affect the valid application of these methods, and thus further research is needed in areas such as method coupling, improving the identification efficiency, uncertainty analysis, and determining the pollutant properties.