Abstract:Based on an analysis of impacts of hydropower development on the ecological environment, research progress in ecological protection measures during hydropower station construction and operation is summarized, including construction of fish passage facilities, establishment of fish proliferation and release stations, methods for determination of ecological flow downstream of dams, and ecological operation of cascade reservoirs, and the disadvantages of the ecological protection measures in cascade hydropower development are illustrated. Accordingly, the ideas of cooperative determination of the water head in river cascade hydropower development and the ecological water head are discussed. Furthermore, the concept, implications, and principle for definition of the ecological water head are presented based on natural river habitats, natural ecosystems, and species protection, and a comprehensive optimization method is proposed for ecological water head planning.

Abstract:Rainfall with time and space distribution is regarded as muster of infinitely great “drop of rainfall” from the view of random theory. Infiltration, evapotranspiration and flow concentration for rainfall of a point located in the watershed can be handled by hydrodynamics. The collective expression of infinitely great “drop of rainfall” with space distribution, i. e. , formations of runoff yield and flow concentration of watershed can be handled by probability theory. The above-mentioned idea not only resolves the runoff yield of watershed affected by space variations of rainfall and underlying surface condition, but also reveals physical nature of watershed instantaneous unit hydrograph(IUH), i. e. , proportionality and superposition of watershed flow concentration. Finally, a method for determining space distribution of flow concentration velocity is put forward.

Abstract:In this paper, we compare the changes of reservoir storage capacity, the increase of irrigation area, and evolution of water utilization structure between China and the USA, and compare the data of water resources exploitation of China with those of several major countries. We conclude that China's total water utilization volume will continuously increase in the next 20 years, driven by the rigid growth of agricultural water utilization, household water utilization, and ecological water utilization. We also present the countermeasures and suggestions, which include strengthening the water resources exploitation, carrying out large-scale western route projects of the South-to-North Water Diversion Project, improving the utilization efficiency of water resources in the northwestern regions, and making overall plans for the ecological water utilization in the northwestern regions, in order to achieve multiple-win outcomes involving the land and water resources exploitation in western China, poverty alleviation, and the improvement of the ecological environment.

Abstract:In order to analyze the influence of land use and land cover changes on runoff regimes, a distributed hydrological model in the Jinghe Basin was built based on the SWAT model. The synthetic influence of climate change and human activities on the hydrological processes in the study area was also investigated. The results show that, before 1996, land use and land cover changes were the main human activities affecting hydrological processes; under those influences, inter-annual fluctuations of runoff were stable, showing a significant positive skew. At the intra-annual scale, the main influence was runoff in dry seasons, and the flow was more uniformly distributed than before. Meanwhile, the concentration ratio of runoff decreased, and the concentration period lagged and tended to be stable. The analysis of the physical causes of the runoff change indicates that land use and land cover changes lead to decreasing evapotranspiration, a decreasing amount of rainfall intercepted by the canopy and litter layer, and increasing infiltration in the basin, all of which cause the increase of the baseflow and surface runoff in the channel, leading to new variations of hydrological processes. The results also show that the runoff increased after 1996 due to climate change, and the main human activities changed from single land use and land cover type to land use and land cover coupled with other water-related activities. Also water-related activities, rather than climate change and land use and land cover changes, became the principal factor in the variation of hydrological processes.

Abstract:In order to investigate the relationships among the sudden variation positions of vertical distributions of turbulent statistical parameters, the zero-plane displacement, and the penetration height, laboratory flume experiments with submerged rigid vegetation were carried out. Aluminum cylinders were used to simulate rigid vegetation and laser Doppler velocimetry(LDV)was utilized to measure the flow fields. The characteristic heights, determined by longitudinal velocity, Reynolds stress, local drag coefficient distribution, respectively, and the penetration height are discussed to compare their relative positions and analyze the effects of vegetation density and submergence on them. Experimental results show that, under high-density conditions, velocity along the vertical direction nearly remains constant, the gradient of Reynolds stress is low near the bed, and the sudden increase positions of the gradients of velocity and Reynolds stress distribution can be easily determined because distinct variations of their distribution patterns exist at certain heights. The influence of submergence on these characteristic heights is not obvious. Compared with other characteristic heights, the one determined by Reynolds stress is most approximate to the penetration height. Moreover, penetration height increases with the increase of vegetation density and submergence. Penetration height has a linear relationship with the zero-plane displacement.

Abstract:As the current standard NB/T 35023—2014 “sluice design specification” involves stilling basin with rectangular cross section, excluding stilling basin with trapezoid section, energy dissipation calculation for stilling basin with trapezoidal cross section were studied on the basis of the classical hydraulics theory and numerical analysis. The analytical formula of shrinking depth and the equation of conjugate depth after hydraulic jump of stilling basin with trapezoidal cross section were derived. Using theory of high-order equation, simple iterative formulas for conjugate depth after hydraulic jump of stilling basin with prismatic trapezoidal cross section and diffused trapezoidal cross section were given, respectively. Finally, the calculation formulas for depth and length of the stilling basin with trapezoidal cross section were obtained according to the energy dissipation equation. Calculation results of a practical project validate the proposed formula has high accuracy.

Abstract:In order to study the influence of jet spacing on the hydrodynamic and dilution characteristics of dual jets, the velocity and concentration fields of dual jets were studied in stagnant, crossflow, and wave environments using particle image velocimetry(PIV)and planar laser induced fluorescence(PLIF). The axial and cross-section vertical velocity, jet trajectory, and concentration fields were analyzed when the jet spacing varied between 5D, 10D, and 15D, where D is the inner diameter of the jet nozzle. The results indicate that, in a stagnant environment, the decay of the axial velocity for the dual jets with small jet spacing is slow compared with that of a single jet, while it grows faster with the increase of jet spacing and gradually resembles that of the single jet; in a crossflow environment, the shielding effect and entrainment decrease with larger jet spacing, enhancing the bending and lowering the ascending height of jets; and in wavy conditions, there is a dependent high concentration area in the middle of two jet holes with small jet spacing and contour lines grows to be bulge-shaped with larger jet spacing. To reduce the influence of spacing on initial dilution, it is advised that the jet spacing should be larger than 10D in crossflow and wave environments.

Abstract:In order to investigate the influences of initial defects, such as the internal tiny cracks, on the concrete strength, concrete was considered to be a four-phase composite composed of coarse aggregate, mortar matrix, interfacial transitional zones(ITZs), and initial interfacial defects at the meso-level, and a numerical model for mesoscale modeling of concrete, considering initial interfacial defects, was developed to predict the uniaxial tensile strength of concrete. The influences of the initial interfacial defect distribution and the amount of defects on the uniaxial tensile strength of concrete are discussed. Results show that the initial interfacial defect distribution has little influence on the uniaxial tensile strength, while the amount of initial interfacial defects has a large influence on the concrete strength. Results also indicate that the uniaxial tensile strength decreases with the increase of the amount of initial interfacial defects. When the volume fraction of initial interfacial defects in the transition zone increases from 10% to 50%, the uniaxial tensile strength of samples in comparison to the strength of samples without defects decreases from 94% to about 60%.

Abstract:In order to ensure that the chloride ions concentration of the water from a reservoir with high-salinity sediment reaches the standard(less than 250mg/L), the effects of high-salinity sediment, the main source of chloride ions, on the water quality of the reservoir were studied during the periods of layout design of reservoir gates and operation of the reservoir, using the Beitang Reservoir in Tianjin City as an example. To determine the optimal layout of gates from alternative schemes and to simulate the water salinization in the operation period of the reservoir, a three-dimensional hydrodynamic and water quality model was established, with the release of chloride ions from the high-salinity sediment considered. The results show that the water quality is directly influenced by the spatial layout of the inflow and outflow gates. It is put forward that the scheme with the inflow gate located in the southwestern corner and with the three outflow gates open at the same time is the optimal scheme, in which there is nearly no static region and the water quality will reach the standard after eight days. In the static period of the reservoir, the release rate of chloride ions from the sediment is positively correlated with the salt content in the sediment, and the concentration of chloride ions in the reservoir will exceed the standard at the 55th day after the release under the most unfavorable conditions.

Abstract:In order to evaluate the influences of the bank boundary condition and the river dynamic condition on bank stability, through quantification of qualitative indices and standardization of quantitative indices, comprehensive evaluation functions for bank stability during the dry period and the flood period were created based on the hierarchical framework model and weight coefficients of the factors of bank failures, and a comprehensive evaluation method for bank stability, considering many factors, was put forward. The results of stability evaluation of three reach banks with different soil properties, bank boundary conditions, and river dynamic conditions show that the comprehensive evaluation function and method are suitable for bank stability evaluation.

Abstract:The bearing capacity of a pile foundation in Zhanjiang group structural clay under vertical loads was studied based on in situ model tests. In single pile in situ model tests, six groups of pile models with the same material and diameter but different depths in soil were selected, and the slow maintained load method was used. The load-settlement curve, axial force distribution along the pile shaft, and side friction varying with the depth in soil of single piles were obtained. Under vertical loads, the load-settlement curves of all six groups of single pile models in the Zhanjiang group structural clay show sharply declining trends, with yielding points occurring at the ultimate limit state, and the vertical ultimate bearing capacity increases with the length-diameter ratio of the single piles; under constant loads, with the increase of the length-diameter ratio, the settlement at the pile top gradually decreases at a slowly decreasing rate; under large loads, the decreasing rate of resettlement at the top of super-long piles, according to the load-settlement curve, is almost zero, and there exists an effective pile length; and under a constant level of loads at the pile top, the proportion of the pile end resistance to the total load at the pile top gradually decreases with the increase of the length-to-diameter ratio, with the maximum value decreasing from 29.8% to 0.8%, while the side frictions of single piles with different depths in soil under ultimate loads change little, with a stable value of about 40kPa.

Abstract:A two-dimensional(2D)viscoelastic boundary element, VS2D2Bar, was developed based on the open source finite element package OpenSees. The applicability of the 2D viscoelastic boundary element was verified with a numerical example, and it was applied to the seismic response analysis of a gravity dam. Numerical results demonstrate that the peak dynamic response of the dam body according to the viscoelastic boundary element model greatly decreases in contrast to that obtained from the massless foundation model with fixed boundary conditions. As a result, the radiation damping effect of the infinite foundation should be considered in seismic response analysis of gravity dams. The results also show that OpenSees is applicable to the seismic response analysis of gravity dams. With a high efficiency in programming and debugging, OpenSees can be easily extended to the static and dynamic analysis of complex hydraulic structures.

Abstract:Using a triangular fuzzy number to express the difference degree coefficient might lead to a large error when the connection components show a broad peak distribution characteristic. The optimal interval of the difference degree coefficient was determined, the difference degree coefficient was formulated with the trapezoidal fuzzy numbers, and an assessment method using the connection number based on trapezoidal fuzzy numbers was developed through analysis of the relationship between the difference degree coefficient and grade standard threshold. The method was applied to vulnerability assessment of the water resources system in the Chaohu Basin. The results show that the confidence interval of the vulnerability grade in the water resources system in the Chaohu Basin is ［2.89,3.44］ with a 75% confidence level. This method can not only obtain the confidence interval of the evaluation grade and effectively avoid the error induced by the broad peak of the difference degree coefficient, but also determine the priorities of vulnerability grades in different sub-regions using the expectation-variance method

Abstract:Runoff, tides, riverbed morphology, and water intake influence saltwater intrusion in the Qiantang Estuary. Of these factors, runoff and tides are the decisive factors that determine whether the salinity at the intake exceeds the standard. Based on the main factors in saltwater intrusion, key issues in predicting the salinity-resisting discharge were analyzed, and a quantitative relationship regarding the response of the standard-exceeding time to the runoff and tidal range was established. A model for predicting the salinity-resisting discharge was built, and computational methods for parameters in the model were proposed. The prediction model was applied in the prediction of minimum salinity-resisting discharge in the Qiantang Estuary from 2012 to 2014. The validation results show that reservoir operation based on the predicted discharge can satisfy the salinity-resisting demand of Hangzhou City, and a discharge sufficient to resist saltwater intrusion must be guaranteed not only during spring tides but also during mid-and neap tides.

Abstract:In order to examine the effect and possible influence of the implementation of two-bank regulation of the wandering lower Yellow River, through summary of the background of implementation and the expected effect, project and social environmental problems regarding two-bank regulation are analyzed. Although the flood control situation in the lower Yellow River Basin is improved, there exist some problems, such as the insufficient sediment transport capacity of the wandering lower river and the deteriorated river regime of some lower channels. Two-bank regulation can generate a narrow deep channel through spur dikes or other regulation projects, cause most of the sediment to be transported by floods due to the large sediment transport capacity of the narrow deep channel and the operation of the Xiaolangdi Reservoir, and eliminate adverse river regimes, such as transverse rivers and inclined rivers. It is pointed out that the main problems regarding two-bank regulation are as follows: large floods are still likely to occur in the lower Yellow River, the regulation project leads to rises in the water lever, the increasing sediment-carrying capacity causes the discharged sediment to influence the narrow channels in Shandong Province and the Yellow River Estuary, and the implementation of regulation projects leads to land ownership problems, diversion of water from the Yellow River, and environmental impacts.

Abstract:Based on a few studies concerning permafrost distribution and mechanisms of the freezing-thawing cycle of active layers influencing groundwater system in terms of groundwater flow and its interaction with surface water in permafrost region, this paper reviews the knowledge of groundwater flow and its interaction with surface water by analyzing studies of the contribution of groundwater flow to channel runoff, groundwater flow paths, and coupled flow and heat transport models. The results indicate that the contribution of groundwater flow to channel runoff varies greatly in different permafrost regions due to the spatial heterogeneity of permafrost. Although identification of groundwater flow paths based on chemical and isotopic tracers will help establish conceptual model of groundwater flow system in permafrost region, however, the analysis results are qualitative or semi-quantitative. Moreover, coupled flow and heat transport models of multi-phase groundwater, which link the vibration of permafrost and the hydrological response process, have already made it possible to quantify groundwater flow processes and groundwater’s interaction with surface water. Future research should devote more attention to improving the practicability of the models in actual catchments.