Abstract:Since flood is formed by storm, flood forecasting is the continuity of precipitation prediction. In recent 30 years, numerical weather prediction has made great advance, but the attempt to apply watershed hydrological model in flood forecasting is slow. The reasons for the different accuracies between numerical weather prediction and flood forecasting are investigated. Successful experience of numerical weather prediction and the problems of watershed hydrological model in the application of flood forecasting are discussed by means of comparison of the weather model and the watershed hydrological model. Problems discussed are the prediction methods and the forecasting time, the initial fields and the boundary value fields, data assimilation and data fusion. It is expected that great inspirations to flood forecasting can be obtained from the successful experience of numerical weather prediction. In the near future, seamless connection can be realized between weather prediction and flood forecasting, and as a result, the accuracy of flood forecasting can thus be improved and the forecasting time can be extended.

Abstract:The goal of water governance is specified from five dimensions, including resources, economy, sociality, ecology and environment. The evaluation index system of the water governance in China is systematically designed. The current situation of water governance is comprehensively evaluated and the variation trend of China's water governance in 2020-2050 is forecasted using the hierarchical equal weight method and the target consistency method. The results show that the index of water governance has been increased quickly from below 0. 235 to near 0. 70 since the reform and opening-up. The acceleration period of water governance is from 2010 to 2015, in which the water governance index has increased about 50%. It is expected that the water governance index will exceed 0. 85 by 2020, and the harmonization between economic development and water resources utilization will be realized. The index of water governance will reach 0. 95 by 2030, and the harmonization between economic development and water pollution will be realized. The capacity of water safety support can be significantly improved and the water governance targets can be realized basically. The index of water governance will reach the optimum value of 1 by 2050, and the water resources utilization, water pollution discharge, water disaster loss and water ecology degradation area will be zero growth, fully achieving the harmony between human and water.

Abstract:Genetic programming and correlation coefficient methods were used to identify the key hydrologic indicators of fish resources. The results show that the fish biomass downstream of the dam is positively correlated with the annual maximum flow, high pulse duration and the average monthly flow in October and December. The biomass of the four major Chinese carps is positively correlated with the rise rate of water level, 7-day maximum flow and the average monthly flow in May and June. The biomass of the Chinese sturgeon is positively correlated with the base flow index and the rise rate of water level, but it is negatively correlated with the annual minimum flow, and the number of daily hydrologic reversals. These pertinent hydrologic indicators reflect the influences of the magnitude, change rate and duration of water discharge on fish. Nonlinear functions are established between pertinent hydrologic indicators and fish resources. By comparing the simulated values with the observed ones, it can be concluded that the genetic programming method is more suitable than the correlation coefficient method for identifying the key hydrologic indicators affecting fish resources.

Abstract:In order to study the hydrodynamic process of a neck cutoff, on the basis of the field observational data of a meandering river at the Zoige Basin in the Yellow River source region, a numerical model is set up based on the incompressible Reynolds averaged Navier-Stokes equation, k-ε turbulent model, and finite volume method. Free surface is taken into consideration by σ coordinate transformation. Change of the flow diversion ratio, variation of the three dimensional velocity field, and the flow structures in the upstream and downstream were analyzed during the neck cutoff process. It shows that the flow diversion ratio and width-depth ratio gradually increases with the development of the neck cutoff and the widening of the new channel, revealing a positive linear correlation. Velocity field of the old bend channel is not affected at the initial stage of the neck cutoff. As the flow diversion ratio increases gradually in the new channel, the discharge, average water depth, and the mean velocity in the old channel decreases gradually, while the discharge in the new channel increases. Average water depth and mean velocity in the new channel shows a characteristic of first increase and then decrease. Neck cutoff does not change the velocity distribution in the upstream but has strong influence on the flow structure at the apex of the downstream bend.

Abstract:To investigate the impacts of the total dissolved gas(TDG)supersaturated water with sediments on fish due to flood discharge from high dams, rock carp(Procypris rabaudi Tchang)and chub(Hypophthalmictuthys molitrix)were chosen as test objects and acute exposure experiments were performed to investigate the effects of TDG supersaturated water on different species. Tolerance and difference were analyzed based on the indexes of abnormal behavior, death rate, and median lethal time of the fish. The experimental results show that abnormal behaviors and symptoms of bubble disease are obvious on the test fish during the initial stage of the experiment and the abnormity was found firstly on rock carp. Under the same TDG supersaturated water condition, increase of sediment concentration can lead to a decreased median lethal time for both rock carp and chub, but the latter has longer median lethal time, revealing that chub has much stronger adaptability and endurance capacity. Moreover, when TDG supersaturation level remains a high value, even low sediment concentration can cause a high mortality of fish. TDG supersaturation level is the major reason for fish death, but the acceleration effects from sediment cannot be ignored.

Abstract:The influence of E-B model parameters in high modulus zone on the finite element calculation results of ultra-high inlaid concrete faced rockfill dam is investigated in the present study. Based on the orthogonal test, the model parameters of the high modulus zone of the ultra-high inlaid concrete faced rockfill dam are taken as the main reference variables and their sensitivity on the dam settlement u₃、panel deflection w and slope stress σ has been analyzed. The results show that the bulk modulus radix K_b, internal friction angle φ and the bulk modulus index m have higher sensitivity, indicating a higher impact on the calculation result. However, the elasticity modulus K and the elasticity modulus index n have lower sensitivity relatively and the calculation result is less influenced. Thus, parameters of E-B model with high sensitivity should be taken as the main target in the inversion analysis to save the computational cost, and other parameters can be determined via engineering analogy. As a result, the purpose of improving the calculation efficiency under the premise of accuracy can be achieved.

Abstract:Due to the discontinuity of soilbag materials, experiments of a soilbag under biaxial compression were modeled using discrete element method, and the mechanical characteristics of the soilbag were analyzed on a mesoscopic level. Monte-Carlo algorithm is introduced to randomly generate an assembly of soil particles with a certain grain composition. The contact between soil particles is simulated by a combination of a spring-dashpot-slider model, while the contact between bag particles is simulated by a rubber band-dashpot model. The results show that the bearing capacity of the soilbag is much higher than that of soil without a bag. When failure occurs, the overall deformation of the soilbag is also far higher than that of soil without a bag, and the tension between particles has a non-uniform distribution. The stress-strain relationship obtained from simulations agrees well with the theoretical formula. Under vertical loads, the intergranular force chains develop from the uniform circular distribution to the direction of the large principal stress, while the soil particles move to the both sides. Bag breakage is the direct reason for the soilbag to reach the ultimate strength.

Abstract:Based on the properties of high membrane faced rock-fill dams(MFRD), deformation principles of the seepage-proofing face membrane and the deformation characteristics of the main materials are analyzed. The design and selection of face membranes and their spread out and periphery anchorage are expounded. The safety check method of the anti-seepage membrane deformation is analyzed and a systematic safety check method for face membrane deformation is proposed. After pointing out the defects about safety check method for liquid expansion of face membranes on gravel cushion in early research, a more feasible safety check method in engineering design and application is proposed.

Abstract:Aiming at the lack of geological and hydrological data, a stability analysis method for the reservoir slopes is proposed. First, the overall geotechnical properties of the slopes are extracted using the remote sensing technology, and then the detailed geological data for the slopes is derived through an inversion model based on the monitoring data of a certain slope with deformation and failure. Finally, the deformation of each individual slope can be traced and predicted by the coupling analysis model. This method has been applied to the stability analysis of typical slopes in the Three Gorges Reservoir Region, and the results show that the predicted displacement and direction of the landslide mass basically agrees with field observation. The predicted trajectory direction of the main landslide tendency also agrees well with observation.

Abstract:In a simulated seawater environment, urea-hydrolyzate strain ATCC11859(Bacillus pasteurii)was used to conduct microbial-induced calcium carbonate precipitation(MICP)aqueous solution tests and immersion method to reinforce sand column. The reinforcement effect of seawater environment on the microbial-induced calcium carbonate precipitation was investigated. The results of the aqueous solution experiments show that the seawater environment inhibits the final production of calcium carbonate during the MICP process. The immersion tests further show that the unconfined compressive strength of the strengthened specimens in seawater environment is lower than that in freshwater environment when specimens are reinforced for the same time. With the growth of time, the unconfined compressive strength of sand column samples in seawater environment is increasing.

Abstract:To study the influence of different relative distances of guide vanes on the pressure pulsation characteristics of a S-shaped extension tubular pumping system, three-dimensional steady calculation and unsteady calculation were applied under 4 different relative positions of guide vanes by using ANSYS CFX software and the reliability of the numerical simulation was verified by a model test. The results show that the pump head and efficiency increase first and then decrease with the increasing of the guide vanes’ relative distance, and the pump head can be affected much more obviously. The relative distance of the guide vanes has no influence on the dominant frequency of the monitoring points, but it has greater impact on the amplitude. With an increase of the relative distance at the guide vanes’ inlet position, the amplitudes of dominant frequency and cross section area of high pressure pulsation strength can decrease. The pressure pulsation strength variation near the flange side is more obvious than that near the hub side. The amplitude of the dominant frequency decreases first and then increases at the guide vanes’ outlet and the cross-section area of high pressure fluctuation strength decreases first and then increases. The performance of the pump is optimum when the relative position of the guide vanes is set to be 16 mm.

Abstract:To analyze the potential safety problems in the long-term operation of concrete dams, the degree of safety for concrete dams was quantified based on the long-term monitoring data. A safety evaluation index system was established by analyzing the essential safety factors affecting concrete dams. Then, the subjective weight based on analytic hierarchy process (AHP) and the objective weight based on data independence and data fluctuation (DIDF) theory were used to calculate the combination weight of each index. Finally, a comprehensive evaluation model for the long-term safety of concrete dams was constructed based on the ideal point method. The validated result of an engineering example shows that the weight of each index and the safety degree of the concrete dam calculated by the model are in accordance with the actual operation of the project.

Abstract:Finite volume method with first order and second order Godunov schemes is presented to simulate and analyze the water hammer problem. Firstly, the Riemann solver is used to solve the discrete flux and the convection term is considered. MUSCL-Hancock method is used to reconstruct the second order precision Godunov scheme, while the MINMOD slope limiter is introduced to avoid spurious oscillations. The virtual boundary method is proposed to deal with the boundary calculations, which can realize a unified calculation scheme for all the nodes inside the computational domain and at the boundaries. Analysis shows that the virtual boundary method can ensure the accuracy of the calculation results, and it can also avoid the complexity of the boundary computation. The results predicted by the first-order Godunov scheme are identical with those from the Method of Characteristics(MOC). When the Courant number is less than one, the transient pressure calculated from the first-order Godunov scheme and the MOC scheme may appear serious numerical dissipation. However, the second-order Godunov scheme can effectively suppress numerical attenuation and obtain more accurate and stable results. In the cases with a low Maher number, the convection term can be neglected in simulations.

Abstract:Considering that the systematic monitoring data for existing roller compacted asphalt concrete core wall dams is insufficient and some problems have been exposed for several projects during operating, such as the impacts of deformation of dam body and foundation on the safety of asphalt core wall, seepage and leakage, construction defects and so on, it is very necessary to summarize the experience of the engineering construction and design techniques for roller compacted asphalt concrete dams in time. According to the characteristics and development of roller compacted asphalt concrete core wall dams among earth and rockfill dams in Xinjiang for nearly 30 years, combined with the special environment and hydrogeological conditions of “severe freezing, high altitude, high earthquake intensity, deep overburden, and excessive sediment”, the construction technologies and applications of asphalt concrete core wall dams are summarized. Structural partitioning of the dam body, mechanical properties and durability of the core wall, application of the gravel aggregate, techniques of construction during cold weather and interlayer bonding, and techniques of seepage prevention treatment of deep overburden are reviewed. The achievements of dam construction are summarized and the technical development in the future as well as the problems for further study are proposed. Practice shows that asphalt concrete core wall dams of 100 m are safe in the severe natural environmental conditions in Xinjiang and it is absolutely possible to break through 150 m in the future with carefully summarized experience, elaborate design and meticulous construction.

Abstract:In order to provide useful information for the sea levee protection under the background of global climate change, this paper gives a comprehensive review on the research of combined wave and surge overtopping. The latest research findings on overtopping discharge, flow characteristics on the inner slope, and turbulence features induced by combined wave and surge overtopping are summarized. It shows that the basic parameters of combined wave and surge overtopping can be estimated reasonably, based on which the flow equivalency among wave overtopping, surge overflow and combined wave and surge overtopping is discussed. It is pointed out that the different characteristic flow patterns between combined wave and surge overtopping and wave overtopping, as well as their impacts on levees need to be investigated so as to provide better references for the design, assessment and reinforcement of levees.