Abstract:To cope with the new challenges of environmental flow research under hydrology, climate and ecosystem changes, research results from both China and abroad have been summarized. Five aspects of shortcomings in the current environmental flow research are pointed out, which also belong to frontier problems and challenges, including(1)Global environmental change and instability; (2)Dynamic simulation of eco-hydrological process in which the transition of hydrological regime from static evaluation to dynamic characteristic evaluation is the key; (3)Characteristics of eco-hydrological relationship in which the coupling research of ecosystem state, process variables and species characteristics, and the research of ecological characteristics, spatial and temporal scales of environmental flows are the key points; (4)Key indicators in environmental flow evaluation; (5)Ecology extension of environmental flow forecasting. To solve these problems, research directions of environmental flows in the background of the Anthropocene are proposed. Dynamic adaptive management of ecological objectives and basic research of ecology from local to reginal areas should be strengthened. Mechanisms of eco-hydrological response based on process should be completed and phased implementation of non-hydrological indicator coupling should be intensified. Evaluation and application of environmental flows under adaptive management should be strengthened to guarantee ecological integrity.

Abstract:Determination of pollution source in sudden pollution accidents can be solved through convection-diffusion equation by reverse time integral. However, such method may result in divergence of numerical calculations. In this study, an objective function is established to solve the adjoint equation and the original equation by using the method of adjoint. Then, the extremums of the objective function are obtained by the successive iteration calculation method. In the end, the pollution source inversion can be realized. In order to verify the effectiveness of the method, pollution source was inverted by using the spatial and temporal distribution of the pollutant concentration, in which both single and double pollution source were included. The results show that the average relative errors between calculated values and analytical solutions are less than 15%, which can be accepted in engineering applications.

Abstract:To objectively and veritably reflect the impacts of water supply benefits in an ecological water supply system and to remedy the drawbacks of traditional indirect calculation methods which are incapable of considering all the benefits, emergy analysis is applied to quantify the benefits of ecological water supply by converting the input and output of the ecological producing system into a unified dimension. The emergy chart of the ecological producing system has been drawn and the energy analysis table has been set up. The benefit sharing coefficient of ecological water supply was calculated based on which the total benefit of ecological water supply and the benefits of pre-stere water were obtained. Beijing-Tianjin-Hebei region, an emergency water supply area in the Eastern Route of the South-to-North Water Diversion Project, was taken as an example to calculate the benefit sharing coefficient of the ecological water supply and the benefits of pre-stere water using the data in 2015. The results are 4. 08%, and 5. 48 yuan/m³, respectively.

Abstract:Dualistic water cycle theory is used to analyze the structure of urban water utilization, based on which the model for urban water allocation is constructed considering the balanced quality and quantity, and the method of multi-objective programming is used to obtain the alternative allocations. System entropy, which is derived from revised information entropy, is used to evaluate the alternatives. This approach is applied in urban water allocation of Kunming, and the conclusion is that, the system entropy will be lower when giving higher weight to the ecological benefit, or giving equal weights to the production, living, environmental and ecological benefits, which will benefit the healthy and sustainable development of water resources system. The case study also shows that this method can not only provide a concise and effective evaluation for urban water system but also give suggestions for the structural adjustment and system development.

Abstract:Based on the statistics, analysis and comparison of the salinity, hydrology and terrain data in the Qibao Reach of Qiantang Estuary in more than 10 years, the results show that due to the influence of runoff and tidal currents, the most intensive mixing of salt-water and fresh water occurs in the reach from Zhakou to Cangqian. Strong runoff corresponds to lower chlorinity while higher chlorinity is accompanied by strong tides. The vertical and lateral distribution of chlorinity is relatively uniform, but the concentration in the main channel is greater than that in the marginal bank. Saltwater intrusion is weak in continuous wet years and continuous dry years, but it is strong in the first year of the runoff transition from abundant to dry. In spring tide, influenced by tidal wave deformation and tidal bores, flood tidal force is greater than ebb tidal force and saltwater intrusion is tend to occur. Tidal range is an important indicator of tidal power, which determines the strength of saltwater intrusion. Tidal range has indicative impacts on salt-water intrusion in estuaries.

Abstract:Factors including the upstream dam breaking time T₁, water depths in front of the upstream dam H₁ and downstream dam H₂, upstream reservoir area S₁ and downstream reservoir area S₂ that can influence the dam-break flood evolution in the downstream reservoir, the initial flood wave height and the initial runup height in front of the downstream dam, are discussed based on physical model tests. The results show that, the evolution process of a dam break flood in the downstream reservoir can be divided into four stages: flood wave forming, flood surging, reflection superposition and oscillation attenuation. The initial runup height of the flood wave in front of the downstream dam decreases with the increase of T₁, H₂, and S₂, while increases with H₁, but it has no obvious correlation with the upstream reservoir area S₁. In addition, the empirical formula of the initial wave height in front of the downstream dam is proposed, and the influence degree of each factor on the initial wave runup height from high to low is obtained in the following order: T₁, S₂, H₁, and H₂.

Abstract:To investigate the mitigation of tsunami waves by coastal rigid vegetation, the interaction between a solitary wave and unsubmerged rigid vegetation on different beach slopes was studied by both laboratory experiments and numerical simulations. The laboratory experiments were conducted in a wave flume, and the effects of different incident wave heights, vegetation densities and beach slopes on the wave run-up were examined. Boussinesq equations were improved and validated by the experimental data, based on which the drag force coefficient of vegetation was obtained. The results show that the drag coefficient increases with the increase of vegetation density but decreases with the increase of beach slope. The dimensionless transmitted wave height behind the vegetation and the subsequent dimensionless run-up height on the slope decrease with both the increase of the dimensionless incident wave height and the vegetation density. When the beach slope is increased, the dimensionless transmitted wave height increases but the variation of the dimensionless run-up height is insignificant. Finally, an empirical power-law relation is obtained to predict the dimensionless wave run-up height through the dimensionless wave height, the vegetation density and the beach slope by regression analysis.

Abstract:To further improve the calculation accuracy of farmland evapotranspiration and irrigation, and to optimize agricultural irrigation water resources allocation, the spatial and temporal distribution characteristics of the crop coefficients of winter wheat, summer maize and cotton in Hebei Province are analyzed using the segment single value averaged crop coefficient method based on the daily meteorological data from 1955 to 2014 in Hebei Province. The results show that from 1955 to 2014, the coefficients of winter wheat, summer maize and cotton crop has a non-significant downward trend, and the average crop coefficients during the whole growth period are 0. 86, 0. 85 and 0. 83, respectively. In different periods of birth, the coefficient for winter wheat, summer maize and cotton crop are in the variation interval of ［0. 40, 1. 29］, ［0. 49, 1. 24］ and ［0. 30, 1. 29］, respectively. In the whole growth period, the crop coefficients of both winter wheat and summer maize show an increasing trend at Xingtai as the center. The cotton crop coefficient increases gradually from west to east with unobvious spatial differences. In different growth periods, the crop coefficient in most reproductive periods of wheat and cotton gradually increase from west to east, but the crop coefficient of summer maize gradually increases from Xingtai to all round. The decrease of wind speed and sunshine duration are the main reasons for the decrease of crop coefficient.

Abstract:For massive concrete structures such as concrete gravity dams, the materials have random spatial distribution properties due to the influences of raw materials and their mixing, as well as the pouring construction. Using the discretization theory of the local average method for a stationary random field, a computational formula of the structural random response for gravity dams is derived based on Neumann expansion stochastic finite element. Corresponding calculation method for the reliability of gravity dams is proposed together with a programmed Matlab code. A cantilever beam is given for the validation of the method and the influence of element size and fluctuation scale of the random field on structural reliability is discussed. The tensile strength reliability of the dam heel is also calculated. The results show that the reliability of a dam can be influenced significantly by the fluctuation scale. Reliability increases with a decreasing fluctuation scale, and it is undervalued if the elastic modulus is considered as a single random variable. In addition, the discretized element size of the random field should be determined by the fluctuation scale and it should not be too large. The suggested element size is less than 1/10~1/8 of the fluctuation scale.

Abstract:Based on the similarity criteria of incipient velocity, an experimental study is performed on a 1∶60 overall physical model to study the sediment flushing effects and sand funnel patterns of two desilting galleries and one bottom tunnel under designed operating conditions to provide a basis for the design and arrangement of the desilting facilities in front of the Dagu Hydropower Station Dam. The results show that the ultimate desilting effect is less affected by the operating order of the desilting tunnels. The patterns of sand funnels are mainly determined by the sediment property, and the slope of the sand funnels is close to the underwater repose angle of non-cohesive sediments under deep reservoir water level. The design scheme for the desilting facilities in Dagu Hydropower Station guarantees the condition of clear in front of the hydropower intake.

Abstract:In order to overcome the shortcomings such as insufficient information mining capability of conventional water level prediction methods and unclear mechanism of heuristic algorithms, an water level prediction method based on long short-term memory(LSTM)neural network is proposed. Direct monitoring data such as water level and unit output are used in this method and the middle errors caused by the indirect calculation of the outflow and inflow can be avoided, which improves the accuracy of water level prediction. A hybrid method based on the gradient descent algorithm and Broyden-Fletcher-Goldfarb-Shanno(BFGS)algorithm is used to train the model, and the step length is determined by the Wolfe-Powell line search method to accelerate convergence. The proposed method is used to predict the water level at the upstream and downstream of the Gezhouba Hydropower Station. The results show that this method can continuously predict the downstream water level for 6 hours and the upstream water level for 3 hours with high accuracy, providing technical support for the real-time scheduling of the Gezhouba Reservoir.

Abstract:In order to study the scale effect of aeration in a scaled model of flood discharge and energy dissipation, as well as to get more accurate test data, the shape of the air jet and the aeration quantity(volume fraction)in a plunge pool with hydraulic models of scale 1∶100 and 1∶50 are studied and compared. The experimental results show that the air jet diffusion in different scaled models is very different from each other, although with the similar orifice shape. The air jet scatters into the plunge pool in an arc shape for the 1∶100 model while it scatters in an ellipse shape for the 1∶50 model. Differences of the air jet patterns further lead to different air entrainment quantity in the plunge pool. The air entrainment quantity in the jet impact area for the 1∶100 model is higher than that of 1∶50 model, and the peak air entrainment quantity is about 50% for the former while it is about 40% for the latter. Comparison of the spatial distribution of the air entrainment quantity in the plunge pool shows that aeration of 1∶100 model has a relatively smaller lateral distribution and a relatively larger vertical distribution.

Abstract:To study the water-permeable characteristics and hydrodynamic characteristics of permeable structures, a specific physical flume model test with a PIV flow field measurement system combined with a Flow3D numerical simulation was used to study the water surface profile and permeable rate variation law of an open trapezoidal permeable submerged dam. The results show that the height of backwater and hydraulic drop near the submerged dam decreases with the increase of permeability, and a reverse slope phenomenon appears in the water surface behind the submerged dam with different permeability. Under the same cross-section average flow rate conditions, larger water depth corresponds to lower relative backwater height. When the water depth is greater than 2 times of the dam height, backwater gradually disappears. Under the condition of the same water depth in the far field in front of the dam, hydraulic drop height increases with the increase of cross-section average flow velocity. Finally, a comprehensive calculation formula of permeability is obtained by regression analysis of the numerical calculation results. It is proved that the maximum deviation between the empirical formula calculation results and the measured values is within 5%, showing a certain reliability.

Abstract:Smooth particle hydrodynamics(SPH)method is used to study the characteristics of hydraulic jumps in a stilling basin with two kinds of sinusoidal corrugated beds under five conditions. Numerical results were compared with existing experimental values to verify the feasibility and applicability of the proposed numerical model and method. Characteristics of the water surface profile, the velocity distribution, the length of hydraulic jump, the conjugate depth ratio and the energy dissipation rate were analyzed. The present research shows that the results of SPH method is in a good agreement with experiments. The velocity distribution in the hydraulic jump section is non-uniform with relatively intensive free surface fluctuation. Eddies are formed due to the relative motion between the flow layers. With the increase of Fr number under the same conditions, the aeration and the free surface breakage phenomenon are more severe, and the influence range of the eddies gradually becomes wider. The energy dissipation rates on corrugated beds in all cases are above 47%, about 10% higher compared with those on smooth beds.

Abstract:The research progresses on river patterns of the tail reach for inflow rivers at home and abroad are reviewed and summarized. Various methods for determining the scope of the tail reach for inflow rivers are stated and the plane shape characteristics and evolution characteristics of the tail reach are analyzed. The similarities and differences of river patterns between inflow and fluvial rivers are then compared and the formation of river patterns and the key factors that control the transformation of river patterns of the tail reach are further discussed. Aiming at the shortcomings of the current research, it is pointed out that future research can be strengthened in the aspects of river pattern characteristics, mechanisms of river pattern formation and quantification of the influencing factors of river pattern transformation.

Abstract:In order to optimize the shape of aeration devices and study their hydraulic characteristics, based on previous research achievements and engineering application experience, the mechanisms of flow aeration on mitigating cavitation erosion, dynamic characteristics of aeration flow, and shape and arrangement of aeration devices are reviewed in this study. Aiming at the shortcomings of the current research, it is suggested that research on the microcosmic mechanism of multi-bubble interaction such as cavitation bubble-air bubble-boundary interaction, the evolution law of aeration concentration and bubble characteristics in near-wall(floor, side wall)water body, and the optimization of aeration facility shape under complex conditions should be further strengthened.