Abstract:To study the response process of peak water level of the Pearl River Delta on the river-bed deepening due to sandmining, the harmonic analysis is used to remove the influence of nodal modulated fluctuation of tide in water level time series, and a method called the probability density function is adopted to explore the evolution trend of water levels in the delta. The results show that the peak water level decreases significantly after the channel deepening in the upstream regions. In the transition regions, the peak water level rises. In the tide-dominated regions or downstream region, changes of peak water level should be related to the sea level rise or other human activities.

Abstract:In this paper, the construction methods of water recycling system by the reconstruction of pond or wetland for storing rainfall runoff and reusing of irrigation drainage were introduced. The calculation method and design basis for the volume of water recycling reservoir were given. Based on the calculation method, the water recycling system of regulation and storage wetland was constructed. The water quality control techniques in the water recycling wetlands were also introduced, including the efficient purification carrier, screening and attachment of microorganisms, aquatic plant community arrangement, and hydrodynamic microcirculation exchange system. It was found that regional rainfall and rainfall duration are the important factors affecting reservoir volume and water recycling capacity. The design and construction of the cyclic regulation and storage wetland system in Shanghai Chongming paddy field were carried out. After the operation of the cyclic regulation and storage wetland, a total of 6.239.9-9.359.9 m3 of irrigation water was saved.

Abstract:Started from the evolution process of the disaster chain of dammed lake, based on the concept of dammed lake risk assessment, this paper focused on three aspects: the hazard assessment of dammed lake, the breach process and flood routing simulation, and the loss assessment after dammed lake breaching. A comprehensive review has been conducted on the qualitative and quantitative assessment methods around the world, as well as the research status. In addition, the parametric model of beaching, simplified mathematical model, refined mathematical model and flood routing model were compared. The loss calculating method was summarized from two aspects, life loss and economic loss. At last, this paper pointed out the prospect of the future risk assessment of dammed lake in five aspects: uncertainty in the risk assessment, accuracy of outburst flood simulation, quantitative method of outburst loss assessment, quantitative risk assessment system and dynamic risk assessment system.

Abstract:To study the runoff characteristics of small and medium-sized rivers, the Qinhuai River is selected as the research object. According to the topography, water system, production and confluence characteristics, water conservancy projects and downstream tidal level characteristics of Qinhuai River Basin, the hydrological and hydrodynamic model is established to calculate the water level and discharge process of the main sections in the Qinhuai River system. The K-nearest neighbor algorithm (KNN) and the simulating feedback method are selected to correct the simulation results. The results show that the hydrological and hydrodynamic model of the Qinhuai River Basin has a good simulation effect by taking the relative error of flood peak and Nash-Sutcliffe efficiency coefficient as evaluation indexes. The simulation accuracy is further improved after the real-time correction, which enriches the prediction model of medium and small rivers.

Abstract:To deal with problems of low reuse and sharing difficulties of heterogeneous models in the process of hydrological forecasting, this paper proposes a service-based encapsulation and combination method for hydrological models. Through the design of standardized service description, operation, deployment and other encapsulation interfaces, the hydrological model's data-algorithm-module-model multi-granularity splitting and service-oriented encapsulation are realized. Taking the grid Xin’anjiang model (GXM) as an example to verify the proposed method, the experimental result on the Tunxi watershed shows that the method in this paper can effectively improve the reuse ability of model resources and realizes the dynamic configuration technology of the model driven by business requirements, and thus provides basic support for the service encapsulation and sharing application of the hydrological model driven by business needs.

Abstract:The extreme rainstorm process in Beijing from July 15 to 16, 2018 was analyzed by using the data of automatic ground stations, radar and NCEP and the standardized anomaly method. The results show that: the extreme precipitation occurs between the subtropical high and the high trough, with obvious southwest jet in the lower layer and abundant water vapor; when the rainstorm occurs, the standardized anomaly of environmental conditions exceeds 3 σ, which created the favorable dynamic, water vapor and unstable conditions for this extreme precipitation; meso-scale convective system activities can be divided into two stages,the convective system triggering and local heavy rainfall, and the convective system organization strengthening and northward movement of heavy rainfall area, both of which are accompanied by obvious train effect with very high precipitation efficiency; the low-level southwest jet is conducive to the establishment of atmospheric unstable stratification and the continuous transportation of water vapor. Meanwhile, the direction of the ground convergence line is consistent with the direction of the 850 hPa low-level jet and the movement direction of convective system, which is the main reason for the enhancement after the triggering of the convective system.

Abstract:To scientifically control the flood disaster and effectively reduce economic losses in the flood storage area, taking the Mengwa flood storage area in Anhui Province as the research area, the satellite images of Sentinel 1, 2 and Gaofen series were selected as the data sources. The flood submerged area was extracted rapidly by using the region growing algorithm, and the detection maps of water body’s changes during flood periods were plotted. Combined with the land-use type coverage map of Mengwa flood storage area, this study analyzed the spatiotemporal change characteristics of the disaster situation of various land-use types and the total regional disaster situation during July and August 2020 with the GIS technology in the Mengwa flood storage area. The results show that the region growing algorithm combined with multi-source remote sensing data can extract the flood area quickly and accurately, and realize the timeliness and high-frequency monitoring of flood information. In the Mengwa flood storage area, the severe disaster areas were mainly concentrated in the central and northeast regions, while the southwest areas were less affected. Farmland and aquaculture ponds were the most seriously affected, while Baozhuangwei and Zhuangtai were the least affected. There is a strong correlation between the time change of disaster area and flood storage measures, but weak correlation with the local precipitation.

Abstract:Flood forecasting in the near-dam area of reservoir is challenging, and the accuracy of forecasting scheme usually cannot fulfill the requirements of flood prevention and scheduling. To address these problems, the entire near-dam area of Wuqiangxi Reservoir was divided into ten subbasins based on the distribution of historical rainfall centers and the characteristics of runoff generation and concentration. A new forecasting scheme was constructed using the three-source Xin’anjiang model, the model parameters were calibrated and the main causes of simulation errors were investigated based on typical flood events. The results show that the method proposed in this study can achieve the high accuracy of flood forecasting and is well applied in the real-time flood forecasting operation in 2021. The results also indicate that the lack of information on flood releases from water conservancy projects is the main cause of errors in runoff and peak flows.

Abstract:In order to improve the emergency response ability of flood disasters, a three-agent mixed reserve model of emergency materials is put forward in this paper. Based on the analysis of the supply of the three-agent reserves and the demand of materials, a materials reserve distribution model is established, which aims at the minimum government cost and the lowest disaster loss. The allocation model of materials reserves is restricted by the guarantee capacity of each subject, government cost and enterprise profit. Through the simplification of the model, the applicable scope of different reserve modes is determined. Based on the calculation of the examples of flood emergency materials represented by block stone, the optimal allocation structure under different reserve modes is analyzed and compared, and the sensitivity analysis is carried out for the important parameters related to government decision-making. The conclusions are as follows: for the flood emergency materials represented by block stone, it is suggested that the reserve mode should be based on the direct reserve of the government, supplemented by the reserve of enterprises, and supplemented by the reserve of social forces; the purchase cost of materials in the spot market will affect the total amount of material reserves, thus the purchase and reserve cost of government reserve and the price of enterprise option will affect the material reserve structure.

Abstract:Based on the meteorological data, social data and groundwater depth data of Beijing-Tianjin-Hebei, support vector machine (SVM), recurrent neural network (RNN) and long and short-term memory neural network (LSTM) were constructed to simulate the groundwater depth of 13 cities. The adaptability of three models were evaluated in indicators, such as the determination coefficient, root mean square error, mean absolute percentage error, and Nash coefficient. The results showed that LSTM model performed the best, followed by RNN and SVM. Meanwhile, simulation results of different cities demonstrated the least parameter adjustments and the best adaptability of LSTM model for the groundwater depth simulation, and SVM model parameters had the most parameters adjustments. Three models were applied to 6 randomly selected stations for verification and it was shown that in the shallow groundwater depth simulation in North China, LSTM model had good simulation accuracy and reliability, with strong adaptability. Therefore, it is the first choice in the groundwater depth simulation of the studying area.

Abstract:Taking the Meiliang Bay of Lake Taihu as the research object, to investigate the effect of Bellamya aeruginosa degradation on the migration characteristics of tungsten in sediments, the planar optobe technique was used to measure the two-dimensional plane distribution of dissolved oxygen (DO) in sediment-water interface, and the High-resolution Peeper (HR-Peeper) and Diffusive Gradients in Thin Films (DGT) technique were used to analysis the one-dimensional vertical distribution information of dissolved/biological labile tungsten (W) concentration. The results showed that Bellamya aeruginosa decomposition significantly reduced the dissolved oxygen (DO) concentration in the sediment-water interface. Anaerobic conditions formed by degradation caused the concentration increase of dissolved tungsten in the interstitial water and the overlying water. The average concentration of dissolved W in sediments profile increased by 28.92%～114.46% compared with that in the control group and the bioavailability of tungsten at the sediment-water interface was significantly improved according to results measured by the DGT. Similar to tungsten concentration changes, the concentration of iron and manganese also increased significantly during B. aeruginosa decomposition (Day 8), and the change of iron and manganese was significantly positively associated with the concentration change of tungsten (R2≥0.716 and p<0.01), which indicated that the increase of dissolved tungsten concentration was mainly due to the reduction and dissolution of iron-manganese oxides under anaerobic conditions. On days 16 and 36 of degradation, the accumulated tungsten release from B. aeruginosa caused an increase in the tungsten concentration.

Abstract:In order to explore the influence mechanism of different adsorbents (phosphorus-locking agent and oxygen-enhancing agent) on the endogenous pollutant Co in sediments, the Meiliang Bay of Taihu Lake was selected as the study area. Three groups of indoor simulation experiments, including the control group, oxygen-enhancing group and phosphorus-locking group, were designed in this study. Water samples were collected in four stages (the 4th, 30th, 90th and 150th day after the addition of adsorbents) based on the high-resolution pore water sampling device (HR peeper). The vertical distribution characteristics and interaction mechanism of dissolved Co, Fe(Ⅱ) and Mn in sediment profile under the in-situ coverage were explored. The results show that phosphorus-locking agent and oxygen-enhancing agent did not cause drastic changes in Eh and pH in the water body. The dissolved Co concentration in the sediment profile decreased by 1.29%-45.87% while the adsorption effect was the best at 30th day. Comparing with the control group, the release flux of Co at the sediment-water interface of oxygen-enhancing group and phosphorus-locking group decreased by 1.00.μg/(m2·d) and 1.19 μg/(m2·d), respectively. The release of Co in the sediment profile was controlled by the redox of Fe and Mn, and mainly by the redox of Mn. In addition, the adsorption effect of oxygen-enhancing agent on Co was better than that of phosphorus-locking agent, and the reaction time was also longer.

Abstract:Based on the generalized rheological model of viscoelastic materials, a generalized damping model and the dynamic equilibrium equation of structure are derived. The exponential function and Gaussian function are selected as the convolutional kernel functions of the generalized damping model. The seismic response of the Koyna Dam is calculated by the Newmark direct integration method, and the effects of relaxation parameter and time integration step on the seismic response of the dam are also analyzed. Seismic responses of the dam with the generalized damping model and the viscous damping model are compared at last. The results show that the seismic peak response with the generalized damping model is greater than that with the viscous damping model, and the larger the relaxation parameters, the closer the peak response with the generalized damping is to that with the viscous damping. Meanwhile, the exponential model has higher requirements for the time step of numerical integration than the Gaussian model.

Abstract:The large scale pendulum impact test and LS-DYNA numerical model were used to study the effects of different porosity (28%, 42% and 54%) and pore distribution (2.holes, 8 holes, 18 holes, 32 holes and 50 holes) on the cushioning performance of hollow bricks.The results show that the impact force of rolling rock decreases with the increase of the porosity of hollow brick, and the peak value of impact force of rolling rock and the peak value of transfer force of hollow brick buffer layer of 54% porosity hollow brick are reduced by 23% and 46%, respectively, compared to those of 28% porosity hollow brick. The impact force of rolling rock and the transmission force of hollow brick buffer layer decrease with the homogenization of pore distribution. Compared with 2.hole hollow brick, the maximum impact force of 50 hole hollow brick can be reduced by 46% and the transmission force can be reduced by 31%. In addition, the uniform pore structure distribution can effectively increase the transfer force diffusion angle. The transfer force diffusion angle of 50 hole hollow brick is 46% larger than that of 2.hole hollow brick.

Abstract:Based on the three-dimensional upper limit analysis theory with three-dimensional horn-like rotational failure mechanism, the power balance equation was established considering slope angle of the slope crest. The software MATHEMATICA and exhaustive method with constraint optimization were used to solve the minimum of safety factor. Under different parameter c/γH, internal friction angle φ, slope crest angle αand slope inclination angle β, the slope safety factors calculated by the strength reduction method (SRM) and gravity increase method (GIM) were quantitatively compared and analyzed. The results show that when FS is equal to one, the results calculated by GIM and SRM are close to each other and approximately equal to one. When FS is greater than one, GIM is greater than SRM. When FS is less than one, SRM is greater than GIM method. For stable slopes with FS below 1.2, the errors of GIM and SRM methods are within the acceptable range.

Abstract:In order to address the low statistical efficiency and accuracy of the number of armour unit blocks of slope breakwater, a method for the recognition and segmentation of the slope breakwater accropodes based the Mask R-CNN deep learning network was proposed. Firstly, this method used the Mask R-CNN network learning laboratory to collect the feature information of the image. Secondly, the model with the best performance evaluation index was obtained by adjusting the IOU threshold. Finally, the trained Mask R-CNN network was applied in the recognition and segmentation of the armour blocks of the on-site breakwater image. The test results show that when the IOU is 0.5, the average accuracy rate of target segmentation is 91.83% and the average recall rate is 92.94%. Using the trained model to detect the breakwater images taken by drones in actual projects, the identification rate of accropodes is 90.7%, and the shooting angle and height have little effect on the identification accuracy. Therefore, the Mask R-CNN deep learning network can realize the accurate recognition of dense and complex armour layer blocks with good portability and versatility.

Abstract:Based on the maximum contact force crushing criterion of local stress concentration, by considering the global fragmentation and the local fragmentation, the Apollo filling mode and the direction of maximum contact force were combined to establish a discrete element model to simulate the particle crushing of coarsely grained rockfill, and the large relative density test mechanism of large size rockfill was studied. The results show that there are great differences in the meso-mechanical responses under different crushing modes, and the numerical simulation accuracy can be effectively improved by simulating the local crushing mode of large size rockfill. The higher the rockfill strength is, the greater the effect of gradation deviation on the extreme dry density is. When the ratio of density bucket height to diameter is too small, it is not good for the vibration compaction and particle rearrangement of rockfill. In this case, the measured value of maximum dry density of test gradation may be far lower than the theoretical value, and the relative density may be greater than one if the measured value is used as the discriminant standard for on-site compaction detection of rockfill.