Abstract:To better illuminate the relationship of surface sediment in hyporheic zones as a source or sink for surface water and its seasonal conversion rule, this review focuses on research advances in hyporheic zones of rivers and lakes in China and other countries. The main aspects of the review include the water regimes of hyporheic zones and their influence on the transport and transformation of nitrogen, the influence of interior environmental gradients and seasonal variation of the temperature distribution in hyporheic zones on the distributions of aerobic and anaerobic zones and the processes of nitrification and denitrification, and the exchange characteristics and seasonal variation patterns of nitrogen in hyporheic zones with surface water. Some research prospects are proposed based on present research trends and deficiencies in hyporheic zones.

Abstract:Based on the principle of the rainfall station sampling method, the probability distribution of the true value of areal rainfall was deduced, using the estimated areal rainfall, in order to describe the uncertainty of areal rainfall calculation under the conditions of existing rainfall stations. Then, probabilistic flood forecasting was performed in combination with deterministic prediction models. Application of this method to the Huangnizhuang Basin of the Huaihe River shows that it can obtain estimates of the probability distribution of the true value of areal rainfall for any periods of time in the basin and describe the uncertainty of the areal rainfall calculation. Furthermore, using a hydrologic model(e. g. , the Xinanjiang model)and the Monte-Carlo sampling technique, the probability distribution of the predicted flow rate can be estimated, and probabilistic flood forecasting can be carried out.

Abstract:Based on daily water level observations of Taihu Lake during the period from 1954 to 2013, changes of three water level characteristic factors, including the highest annual water level, lowest annual water level, and mean annual water level, were analyzed and compared. In combination with rainfall and water diversion data from the Taihu Lake Basin, the dominant factors driving the three water level characteristic factors are illustrated. Results showed that changes of the highest annual water level were not significant during the period from 1954 to 2013 and its inter-annual variation was mainly controlled by the inter-annual periodic fluctuation of flood season precipitation in the Taihu Lake Basin. However, the lowest annual water level and mean annual water level of Taihu Lake were increasing significantly, with their inter-annual variations mainly controlled by the precipitation fluctuation in the Taihu Lake Basin before 2000. After 2000, their inter-annual variations were mainly controlled by the massive water diversions, such as the water diversion from the Yangtze River to Taihu Lake, maintaining high levels of the lowest annual water level and mean annual water level in spite of less precipitation. In addition, water diversion from the Yangtze River to Taihu Lake causes significant changes of the seasonal distribution characteristics of the occurrence time of the lowest annual water level of Taihu Lake.

Abstract:In this study, the influence of the slope on disturbed yellow-brown soil erosion was investigated through a simulated rainfall experiment. The experimental results show that, when the slope is 20° or less, the infiltration volume decreases with the increase of the slope and the runoff increases with the increase of the slope. The infiltration volume and runoff level off when the slope is between 20° and 26. 5°. The soil erosion amount is basically synchronous with the runoff and increases with the increase of the slope within a certain range of the slope. When the rainfall intensity is 40 mm/h or 60 mm/h, the threshold slope of the tested soil erosion is between 20° and 26. 5°. The threshold slope is greater than 26. 5° when the rainfall intensity increases to 80 mm/h. There are significant linear relationships between the runoff, erosion amount, and rainfall within the range of the test slope.

Abstract:Through a summary of different types and development and utilization modes of available resources in tidal flats, the impacts of development and utilization of tidal flats on hydrodynamic conditions, sediment erosion and deposition, stability of the main channel and flood plain, the ecological environment, biodiversity, and other marine resources in the coastal zone are examined. Models for evaluating the environmental impacts of development and utilization of tidal flats mainly include the ecological-economic model, multi-index analytic hierarchy model, and DPSIR model. According to some significant aspects of the environmental impacts of development and utilization of tidal flats, a few aspects that require attention during the process of planning and implementation of development and utilization of tidal flats are summarized. Finally, protection measures for coastal wetland resources, biological resources, and the ecological environment in reclamation areas are put forward.

Abstract:In order to enhance the underslanding of the occurrence probability of freak waves in coastal areas, using wave data from nine stations in the sea area around Korea in 2009, the occurrence probability of freak waves in Korean coastal areas and the relations between the occurrence probability and three parameters, the effective wave pressure height, season, and water depth, were examined based on the definition of freak waves using wave pressure data. The results show that the occurrence probability of freak waves in Korean coastal areas is close to the predicted value of the Rayleigh distribution and does not vary with the effective wave pressure height and water depth, while the time of frequent occurrence of freak waves changes with the station location. There is no obvious correlation between the occurrence of freak waves in Korean coastal areas and the effective wave pressure height, water depth, and season.

Abstract:In order to study the correlation between the tropical Indian Ocean dipole(IOD)and sea level anomalies, the correlation between the sea surface temperature(SST)and the sea level anomaly(SLA)in the tropical Indian Ocean was analyzed using the empirical orthogonal function(EOF)method and Hilbert-Huang transform method. Based on correlation analysis of the tropical Indian Ocean dipole mode index(DMI)and the Southern Oscillation Index(SOI)and SLA, it is concluded that there may be a certain correlation between the IOD and the El Niñ o-Southern Oscillation(ENSO). In addition, there is a strong correlation between the IOD and sea level changes. Analysis of the DMI and sea level changes in the IOD years proved the seasonal phase locking of the IOD, and the correlation between the season change and sea level change was examined. The results show that there is a strong correlation between the IOD events and sea level changes.

Abstract:In order to solve the problem of velocity profiles in estuarine and coastal areas often deviating from the traditional logarithmic velocity distribution, a momentum exchange coefficient is derived based on log-linear velocity distribution, and an equation describing the vertical distribution of sediment concentration is established based on the diffusion theory. Through validation using measured data regarding vertical stratified sediment concentration in the Yangtze Estuary and Jinshan sea area in Hangzhou Bay, it is found that the new equation describing the vertical distribution of sediment concentration not only overcomes the Rouse equation defect of the surface sediment concentration being zero, but also agrees with the measured sediment concentration along the vertical line, indicating that the equation objectively reflects the vertical distribution rule of sediment concentration in estuary and coastal areas.

Abstract:Based on a physical model experiment, the wavelet transform theory, and the shear instability theory, temporal and spatial variation characteristics of shear waves were investigated under the conditions that the incident waves were regular waves and the topography was a flat slope. By analyzing the wavelet energy spectrum of the shear wave velocity time history under 15 wave conditions, results can be obtained and show that when the incident waves are regular waves and the topography is a flat slope, shear waves can be observed but the temporal and spatial variations are not significant; the variation of shear waves over time is continuous once it has been generated; shear waves are more dominant in the energy spectrum in the direction along the bank than in the spectrum vertical to the shoreline; an increase in the slope will reduce the generated area of shear waves; and the shear wave frequency, caused by the shear instability, changes around 0. 015 Hz with a gradient of 1∶40 or a gradient of 1∶100.

Abstract:Research in China and abroad on the ultimate bearing capacity and long-term stability of an anchorage caisson foundation under a deep overburden layer is reviewed. The basic theories on and research methods applicable to the ultimate bearing capacity, short-term and long-term displacements, and stability of the anchorage caisson foundation are discussed. The research status and existing problems in this field are expounded in detail, and the focus of and trends in future research are also described.

Abstract:Using the restoration project of an abandoned sludge yard as an example, the gas generation process of sludge was investigated through laboratory experiments. A dynamic model of gas generation from sludge was built based on the experiments and correction of the gas generation rate constant based on temperature, which can reflect the actual situation. The gas generation quantity and rate were forecasted using the dynamic model. The results show that the process of gas generation takes as long as 50 years, while the total gas generation quantity and maximum annual gas generation quantity are low. The gas-exhausting system should be included in the design of the cover system, but the concentrated disposal does not need to be considered.

Abstract:In order to investigate the feasibility of using geosynthetic clay liner(GCL)for channel liner systems in cold and salty soil regions, several tests were conducted, including a hydration test, drying-wetting cycle test, freeze-thaw cycle test, and self-healing test. The swelling and permeability characteristics of GCL were studied, and the factors influencing the permeability coefficients of GCL were analyzed. The results show that the hydration solution greatly affects the permeability of the material: the higher the ion concentration is, the greater the permeability coefficient is; and the material cannot be used in construction without hydration. After drying-wetting cycles, the permeability coefficient of the material changes a little, owing to its high self-healing capability. The permeability coefficient gradually decreases with the increase of the number of freeze-thaw cycles, indicating that the material can maintain high impermeability under cold conditions. The bentonites compressibility and permeability coefficient are positively correlated; the degree of deformation decreases with the increasing number of freeze-thaw cycles, meaning that the ability of resistance to deformation of the material increases. GCL can be used in channel liner in cold regions, in the northern China.

Abstract:With regard to a horizontal sand drainage cushion on natural ground, a parameter study using the plane strain finite element method was carried out to investigate the effects of the parameters of the sand cushion and ground on the efficiency of ground consolidation. The influences of the permeability, thickness, and width of the sand cushion on ground consolidation were considered, together with the permeability and thickness of ground soil. Meanwhile, a lumped parameter for the sand cushion and ground soil was adopted, and its relationship with the ground consolidation efficiency was analyzed. It was found that the permeability of the sand cushion on natural ground required by the existing technical specification was unreasonable. The ground consolidation efficiency increases nonlinearly, in a hyperbolic manner, with the lumped parameter. There exists a certain value of the lumped parameter that can meet the requirements of optimum consolidation efficiency. This value can be used as a controlling index for designing a sand cushion on the ground with various soil conditions.

Abstract:In order to obtain accurate parameters for a drive-train model, a method for parameter identification of a three-mass drive-train system with gusty wind excitation is proposed. According to the decoupling of the mechanical dynamics and electrical dynamics of fixed-speed wind turbine generators, the electrical dynamics can be neglected when identifying parameters of a drive-train model. Based on this, a simplified model for fixed-speed wind turbine generators was obtained. The identifiability of the parameters of the drive-train system and the difficulties in parameter identification were analyzed with the trajectory sensitivity analysis method. Finally, the parameters of the drive-train model were identified based on the particle swarm optimization(PSO)algorithm. The identified results are consistent with the trajectory sensitivity analysis results, verifying the feasibility of the proposed parameter identification method.

Abstract:In order to evaluate the reliability of a collector system of an offshore wind farm in the planning stage and to avoid maintenance difficulties caused by the poor accessibility, a method for calculating equivalent availability is proposed combining the probabilistic and deterministic methods. First, according to the characteristics of the largescale offshore collector system, it can be divided into a substation layer, turbine layer, and cable layer, and the availability of each layer of the ring collector system is described using the fault tree algorithm. Second, according to the possible operation state of the ring structure, the availability of a singlestring ring network is calculated. Finally, using a planning offshore wind farm as an example, the reliability and economy of the collector system are compared and analyzed, and different topological schemes of the collector system are also compared, providing quantitative reference indices for topological planning of the collector system of an offshore wind farm.