It is extremely difficult to carry out fine management and control of the full life cycle of water conservancy objects due to their large quantites, a wide range of types, a wide spatial distribution, complex operation environments, and many interrelated factors. To solve this problem, a fundamental approach is to combine a certain water conservancy big data technology characterized by association analysis with a professional mechanism model characterized by causality, integration and fusion, and efficient process; to analyze the massive and multi-source data intelligently; and to proactivily present useful highly-visualized results to management decision-makers. This paper provides a review on the concept of water conservancy big data and its technology system, along with an overview on the research status quo of natural law analysis, situation research and judgment, trend prediction, and decision optimization for water conservancy. We find that the future trend in big data technology development is toward scenario-based demands, management integration, analysis intelligence, service platforms, and guarantee systems. In water conservancy big data application, data are fundamental, analysis is the core, and the ultimate goal is to improve the efficiency of water treatment by using big data technology. Thus, we should deeply tap the real demands of water conservancy business management; integrate the panoramic data in the fields of water disasters, water resources, water environment, water ecology, and water engineering; comprehensively lay out the research on basic theories and core technologies, so as to accelerate the deep integration of big data technology with water conservancy and support the complete transformation and upgrade of water governance in China.

The Bohai Bay is encircled by the Bohai Sea economic zone and faces high pressure of environmental protection due to its high pollution load. Water exchange capacity is a key factor of environmental capacity, and in the bay it is dominated by tides and winds. This study develops a water age model using an Eulerian approach, and simulates the role of winds in water exchange in this bay, focusing on comparison of the water age and its temporal and spatial distribution characteristics between two cases ? under the combined effects of tides and winds, and under the effect of tides only. The results show wind action is a crucial factor of water exchange that greatly accelerates the exchange between the bay and the Yellow Sea. Seasonal variations in water age reveal that the exchange between the bay and the central Bohai Sea is strong in winter and weak in summer.

The performance of hydraulic turbines, as the core mechanical equipment for developing hydropower, determines the development and utilization rate of hydropower. Driven by the progress of modern science and technology, hydraulic turbine technology has made a great progress in China, it has experienced the developing stages of introduction, absorption, digestion and recreation, and now has reached an internationally advanced level after a rapid development over recent two decades. This paper focuses on the key research advances made in the field of turbine technology in the past two decades, based on a comprehensive synthesis of research achievements in this field in China and abroad. The progress is summarized in three parts: hydrodynamic foundation of hydraulic turbines, optimal design theory of hydraulic turbine flow components, and development of new hydraulic turbines. This paper also discuss the problems in some of the research fields and present a prospect for the development trends in hydraulic turbine technology.

Spatial heterogeneity is an essential property of precipitation and water resources. Based on the results of the second integrated assessment to water resources in China, the Lorenz curve is used to calculate Gini coefficients and Lorenz asymmetric coefficients, which represent the degree and source of spatial heterogeneity respectively. Results indicate that different types of water resources in China show considerable or strong spatial heterogeneity. And the heterogeneity across different water resources divisions increases from east and south coasts to northwest, depending on the area, average precipitation, and other natural conditions. For each division, the heterogeneity in precipitation is the smallest, followed by groundwater resource, total water resources, and surface water resource; and water resources heterogeneity is featured with asymmetry dominated by those sub-divisions with less amount of water resources, or relative symmetry.

Driven by the carbon peaking and carbon neutrality goals, new forms of energy generation such as wind power and solar power have developed rapidly. To solve the problems of intermittency and volatility in the power system, it is necessary to build matched energy storage facilities. In this paper, the gravity energy storage type of taking water as the medium is defined as Water Energy Storage. A comprehensive comparison is made between different forms of energy storage available at present and in the future, from the aspects of technical principle, economy, environmental impact, and operation safety. The results show Water Energy Storage is the best form of energy storage for supporting new energy development and New Power Systems in the next period of time. This paper also explores the planning idea, regulation calculation, evaluation method, development modes, and other key technologies and relevant policies for pumped storage, hydropower expansion and cascade reservoir energy storage, and takes an outlook for their development in the future. The study would help to plan and design new energy development and New Power Systems.

When the Mann-Kendall (MK) method is used to detect the trend in serially correlated hydrological series, it is often difficult to obtain an accurate result, due to the influences by significant higher-order autocorrelation components or the trend damage in removing the lag-1 autocorrelation in the series. Aiming at this difficulty, this paper presents a hybrid MK test model combining a modified over-whitening (MOW) process and assembling the change point tests in regression and variance and the detrended methods to segment the original series and provide a set of suitable sub-series to over-whitening. In this model, the over-whitening is calculated in sections to remove the high-order autocorrelation while destroying the original trend component as little as possible. The test results of the runoff series at Linjiacun, Shenmu, Zhaoshiyao and Hengshan hydrologic stations indicate that the segmental over-whitening process can retain the trend change in the original series when eliminating its significant lag-high autocorrelation and ensure more accurate results in the MK trend test on over-whitened series.

When the general segmentation model is applied to the apparent cracks in the dam face concrete, the network suffers the problem of depth increasing that leads to excessive model parameters and certain loss of effective crack features. To reduce network memory occupation and feature loss, this paper develops a lightweight crack segmentation method based on a convolutional neural network. The network adopts an encoding-decoding structure, and uses a depth-separable convolution module and a lightweight feature extraction module to construct a cascade encoder; it is equipped with a decoder to fuse cross-scale information in the second stage of the encoder and to reconstruct the pixel-level geometric information lost in feature extraction to improve the accuracy of network segmentation. The experimental results show the model size of the network trained on the crack dataset of dam face concrete is 10.8 MB or a size reduction of 90.8% from U-Net, with its PA of 73.3% and IoU of 85.4%. The results verify the network is feasible in dam face crack segmentation and useful for improving the efficiency of dam face detection and maintenance.

To better understand the effect of disturbance in overlying water on nitrogen and phosphorus release from aquaculture pond sediments, we collected sediment samples from aquaculture ponds, designed laboratory experiments of nitrogen and phosphorus release in the condition of overlying water stirred mechanically for seven consecutive days at different stirring speeds, and measured concentrations of ammonia nitrogen, nitrate nitrogen and SRP in the overlying water and sediment pore water. The results showed that faster mechanical stirring increased the concentration of ammonia nitrogen at the early stage but in hydrodynamic conditions it was a short-term effect and a dynamic equilibrium between release and adsorption was gradually reached. A higher stirring speed promoted the release rate of nitrate nitrogen with a higher peak concentration, indicating the release rate of nitrate nitrogen from the pore water in dynamic ponds to be significantly different from that in the static pond case. The release rate of SRP was also increased to a certain degree by increasing the stirring speed. Fitting of pseudo-first-order kinetic equations to the process of SRP release reveals multiple correlation coefficients R2 greater than 0.92 and an extremely significant level (P < 0.01) of the equations fitted, showing a satisfactory representation of the process.

This paper first reviews the advancements in dam construction and development in hydraulic engineering, and summarizes the conceptualization of digital dam and its related research achievements. Then, we present an interpretation of the difference between the two concepts of digital dam and smart dam, based on a brief discussion on several disadvantages of digital dam, including insufficient depth in intelligent analysis of massive data and relatively low fusing level of site monitoring, simulation analysis and intelligent control. Smart dam is a new concept that is based on the digital dam conceptualization but emphasizes a specific form of dam development, i.e. adoption of new-generation information technologies as a basic means, such as Internet of things, intellectual technology, cloud computing, and big data. This concept also means a specific intelligent system of dam management and operation that is dynamic, refined, and perceivable in analysis and control. Besides, a smart dam often has distinctive features such as integrity, interoperability, fusion-expansibility, autonomy, and robustness. Third, we describe a basic framework of smart dams in detail, including a real-time information perception module, an interconnected real-time transmission module, an intelligent real-time analysis module, and an intelligent real-time management decision system, focusing on analysis of the progress and superiority of smart dams over digital dams in independent information collection, smart reconstruction analysis, intelligent decision, and integrated visualization. Finally, we explore key directions of smart dam research in fundamental theory, key technology, and management and operation system.

With popularization and application of the project general contracting model in the water conservancy and hydropower industry, the integrated design and construction model led by design has become an effective means of reducing costs and increasing efficiency, unified management, and scientific decision-making. This paper reviews the recent advances in the research of general contracting models, design models, construction models, and design and construction collaboration models for the water conservancy and hydropower industry in China and overseas; and clarifies the current pain points of this industry and its major bottlenecks in developing and implementing such integrated models. We investigate the key roles and concept of applying the informatization technology forefront, deepening technological innovation and practice, and adopting the top-down design and lean construction models in solving the existing problems of low design optimization efficiency in design and construction integration, cumbersome mutual feedback of design and construction information, and low level of intelligent construction. To further develop this concept, taking the digital twin technology as a basic application framework for the future, we expound key research directions for further research, and suggest how to promote the integrated design and construction in hydropower development and overcome the shortcomings in water conservancy informatization.

The SWMM model has been widely used in urban rainfall-runoff simulation and design of sponge cities. A quantitative analysis on the parameters of this model is crucial to parameter identification and uncertainty reduction. In this study, a variance-based Sobol method and different accuracy assessment standards are used to quantitatively analyze the sensitivity of the SWMM model parameters in a case study of the Huangtaiqiao catchment under floods of different levels. Results show that (1) the parameters are different in sensitivity when accuracy assessment standard or flood level is varied, indicating a great uncertainty in model parameters. (2) The Nash coefficient depends much on Dstore-Imperv, MinRate, Roughness (rivers), and Roughness (conduits). (3) Interaction between the parameters is frequent in small flood cases, while it diminishes with a trend toward concentration as flood level is raised. (4) The Sobol method, suitable for the sensitivity analysis of urban hydrological models, can provide the sensitivity of each parameter and the interaction between different parameters.

Owing to their great height and large volume, high-fill embankments are subject to differential settlement that often reduces their safety and stability, and therefore the post-construction settlement of such embankments should be examined carefully. This paper develops a practical creep calculation method based on the finite element method for calculation of post-construction settlement by a time-dependent UH model and the simplified one-dimensional creep deformation computation method that could be combined with the layer-wise summation method. Field observation data collected at the Chengde airport are used to verify this method. Comparison of the calculations and field data shows that new method is able to achieve reliable predictions of post-construction settlement and hence to provide useful guidance for the following construction of the airport.

Along with rapid change in global climate and fast development in urbanization, the frequency of urban waterlogging events becomes increasingly higher. Dongguan is located in the Pearl River Delta, a region of high-level economic development that is vulnerable to attacks by storm surges and high level floods in its outer rivers. Hence, waterlogging threat to this city is becoming increasingly higher and its waterlog control requires a storm water model for evaluation of its existing drainage capacity and risks of waterlogging. This study coupled LISFLOOD-FP (a 2D hydrodynamic model) with SWMM (a 1D model for a drainage system) in simulations of rainstorms and waterlogging over a study area covering typical regions of Dongguan and obtained following conclusions. By constructing a SWMM model and coupling SWMM and LISFLOOD-FP for the city, we simulated the inundated area of waterlogging and its water depth. Verification with the measured rainfall data of 13-6-2008 rainstorm shows that this coupling model was effective and satisfactory. Then, the model was used to simulate the design rainfalls with return periods of 0.5, 1, 2, 5, and 20 years. Results indicates that as the return period increases from 0.5 to 20 years, the discharges are increased at outfalls, overflow discharges, and the number of flooding nodes in the study area, and the floods have earlier peak flows and longer durations. And the inundated area increases from 0.92 to 1.93 km2, with a portion of 0.02 to 0.25 km2 subject to flooding deeper than 2m. In the study area, high risk waterlogging covers Dongzong road, Dongchengxi road, Yinshan street, and Donghui road.

The Wudongde and Baihetan hydropower stations on the Jinsha River are the largest hydropower projects under construction with application of the most challenging technologies under complicated environmental conditions. Construction of the 300-meter super high concrete arch dams is faced with multiple key technological obstacles and management challenges in safety and high quality. Based on the principle of intelligent closed-loop control of comprehensive perception, real analysis and real-time control, this paper deeply integrates the modern information technologies with hydropower engineering construction and formulates an intelligent dam construction technology route focusing on the core construction processes and main business processes. To meet the demands of building these two dams in safety and high quality, key technologies ? such as whole-process real-time monitoring of concrete construction, real-time control of concrete temperature, whole life cycle safety and work performance evaluation, performance review of low-heat cement concrete dam, and in-depth research of an intelligent construction platform iDam ? have been explored and applied, and related intelligent control equipment and management systems have been developed. Engineering practice shows that the key technologies and management platforms achieved in the intelligent construction have greatly improved the technology performance and management efficiency of project construction, enhanced the core competitiveness of Chinese hydropower industry, and provided better technical support for the development of hydropower project and infrastructure construction along the Belt and Road.

Studies of rill flow hydraulic characteristics are essential to understand the mechanism of rill erosion and develop soil erosion prediction models. This paper presents an analysis on hydraulic characteristics of the rill flows on slope land based on a series of runoff scouring laboratory experiments for the conditions of different soil bulk densities (1.2, 1.35 and 1.5 g/cm3), flow discharges (2, 4, 8 and 16 L /min), and land slopes (5°, 10°, 15°, 20° and 25°). The results show that both flow discharge and land slope are important factors influencing flow velocity. And flow velocity can be expressed in a power function of land slope and flow discharge with the former as the major factor; soil bulk density has a certain influence on flow velocity and its effect varies with land slope. The Reynolds number, varying in the range of 248 to 1932, is independent from soil bulk density or land slope, and has a linear relationship with flow discharge. All the rill flows tested are supercritical of Froude number greater than one. The influence of soil bulk density on the Froude number also varies with land slope, similar to that of flow velocity. The resistance coefficient in the range of 0.04-0.955 increases first and then decreases with the increasing slope or flow discharge, and its dependency on soil bulk density is significant, manifesting a decreasing trend in the case of mild or steep land slope.

To mitigate adverse effects caused by impoundment of the Three Gorges reservoir (TGR), a reservoir optimization model for improving the satisfaction of minimum ecological water demands (SMEWD) by the Dongting Lake and increasing the TGR power output has been developed in this work. This optimization model couples a water level prediction method using support vector regression (SVR) and is solved with a chaos-genetic algorithm (CGA). The results show that both the SMEWD and the power output were significantly improved via optimization of the TGR operation. In an average year, the satisfaction was increased from 85.40% to 89.44%, and the power output increased by 3.09%; In a wet year, conventional operation was able to meet the minimum ecological demands with an increase of 5.85% in the output; In a dry year, the satisfaction was increased from 65.58% to 66.42% with the output increased by 3.42%. This study demonstrates that improvement on the ecological environment of river-connected lakes can be achieved by optimizing reservoir operation.

Trend-free pre-whitening (TFPW) is a key method for removing the effect of autocorrelation when a non-parametric Mann-Kendall (MK) trend test is used in analysis of river runoff series. However, its rationality and applicability are questioned in the cases that some hydrological changes occur in a changing environment, thus catching researchers’ increasingly attention. In this study, we adopted a hybrid TFPW for data-preprocessing prior to applying the MK trend test to evaluate its performance in analysis of the runoff series featured with hydrological changes, focusing on six detrending measures, i.e. the slope method (SM), EMD method, first order differential method (FD), log-linear detrending method (LLD), 5-point linear moving average method (LMA), and linear regression moving average method (LRMA). This approach is coupled with two pre-whitening methods, one for removing autocorrelation AR(1) only, and the other for removing all the AR(n)s where n stands for all the lag orders of significance. A case study was taken testing the runoff series gauged at the three gauge stations of Dingjiagou, Shenmu and Suide in northern Shaanxi that represent three types of trend changes in the series respectively. These calculations, as results of different hybrid TFPW-MK testing, were compared with those by conventional and modified MK methods. The comparison shows that different hybrid TFPWs give different MK test results of the runoff series. All the detrending methods are good and similar when only AR(1) is removed, while when all the AR(n)s are removed, only LMA and LRMA work satisfactorily and even the SM, if coupled with the conventional TFPW, works poorly deviating far away from the real case. This indicates that among all the TFPW methods, LRMA with AR(n) being retained is the best owing to less autocorrelation information lost in its detrending process and more autocorrelation removed in its pre-whitening. In addition, the conventional TFPW-MK, or SM coupled with the AR(1) removal, can still achieve acceptable results, and the original TFPW procedure is effective only when AR(1) is removed.

To alleviate energy crisis and environmental degradation and enhance the development and use of renewable energy, this study develops a numerical model of a semi-submersible multi-floating body wave power plant through combining wave energy conversion technologies of point absorption and raft type. The device is mainly composed of a central floating platform, an array of oscillating floats, a hydraulic system, and structure connecting floats to the platform, and collects wave energy from the oscillating floats on the sea surface. To improve its collecting efficiency, we numerically simulate and examine its energy conversion using AQWA hydrodynamic simulations, and analyze the frequency domain responses of a single float with different values of parameters such as the mass, size, and structure of the floats. And a detailed analysis is made on the time domain responses of a single float and the whole device under sea conditions of wave height of 1 m and wave periods of 5 s and 3 s. The results show that the geometry of the underwater part of the float has a great influence on its added mass and wave excitation force, and that a cylindrical float of 2 m in diameter features larger amplitude of vertical oscillations. This suggests that in the condition of low wave frequencies, the floats with such a design can capture wave energy closer to the maximum extent, thereby improving overall efficiency. For the floats working at high wave frequencies, they should have a conical shape, the diameter increased appropriately, and the weight reduced so as to capture more wave energy. By optimizing float structure, the energy collection efficiency of the device is raised by about 95%, indicating the importance of float structure in efficiency improvement.

This article reviews the historical development of dam construction, summarizes the developing trend and key technologies of intelligent construction of dams, sorts out the relationship between the key issues in intelligent construction and intelligent control, and presents a basic control theory for intelligent construction of dams. The concept and definition of intelligent control and its characteristics, theoretical structure and elements are elaborated in detail, and "intelligent decision-making plus automatic control" is clearly defined as its two core elements. On this basis, an intelligent control system for dam construction－featured with the functions of autonomous perception and cognitive information, intelligent organization planning and decision-making tasks, and automatic control of executive agencies to accomplish goals－is constructed; its design concept, component elements, module characteristics, and application levels are explained. This intelligent control theory lays a theoretical basis for solving a variety of dam construction problems: structural service state control, full life cycle safety performance evaluation, construction risk prediction, early warning during dam construction, and cost control. It is also essential to realize the intelligent construction goal of high quality, high efficiency, safety, economy and greenness.

Three- and two-dimensional models are used in combination to simulate and analyze the influence of tidal turbines on the hydrodynamic conditions in the near-field and far-field, and applied in a case study of the Putuo-Hulu islands tidal energy test field. We present a method for generalization of tidal turbines that, based on the energy equation, calculates resistance loss in the flow passage to determine the equivalent roughness of the turbines, construct a three-dimensional model of the turbines’ near-field flow in the frame of Computational Fluid Dynamics (CFD), and simulate and analyze the velocity distributions in seven conditions of different combinations of turbine rotating speed and inflow velocity. A two-dimensional tidal model is developed on the finite element method (FEM) solving the shallow water equations, and the influence of turbine operation is simulated using larger roughness at the grid nodes occupied by the turbines. Results show that the size of affected zone depends on the tidal flow velocity and the terrain near the berth, and that the further away from the turbines, the less incidence from the turbines into the flow field. In the far-field, the influence is not significant and the flow velocity varies in the range of 2% - 8% relative to the velocity before the turbines.