Abstract:When there is reservoir control in the upstream of the watershed, the storage coefficient K and weighting coefficient X of the Muskingum method are difficult to calibrate through measured data. To estimating K and X , a relationship between the K and X and physical characteristics of the river channel is established. Then, the Muskingum method is used to derive the inter-basin flood by routing the upstream inflow to the downstream, and subtracting the upstream routed flood from the downstream flood to obtain the inter-basin flood. The example of inter-basin flood calculation from Qingfengling Reservoir, Xiaoshiyang Reservoir to Juxian in the Shuhe River Basin shows that the difference between the inter-basin flood calculation method based on the Muskingum method and the Xin’anjiang model is minor, but the former method can consider the differences in hydraulic characteristics of different river sections for parameter estimation.

Abstract:To investigate the impact of spatial autocorrelation on the accuracy of spatial interpolation for the precipitation of rainstorm events, based on the daily precipitation data from 102 rainfall stations in the Wujiang River Basin from 2009 to 2018, 88 rainstorm events were screened out. These events were interpolated using the inverse distance weighting(IDW), radial basis function(RBF), ordinary Kriging(OK), and co-Kriging(CoK) methods. Moran’s I was employed to quantitatively analyze the spatial autocorrelation of each rainstorm event precipitation at the 102 rainfall stations, and this study compared the interpolation accuracy of different methods for rainstorm event precipitation with varying spatial autocorrelation. The results show that with the increase of spatial autocorrelation of rainstorm event precipitation, indicated by the Moran’s I index, the accuracy of all four interpolation methods improves to varying degrees, and the accuracy improvement of OK method and CoK method is more obvious. For the average basin, when the Moran’s I is less than 0.28, the RBF method is recommended, whereas when the Moran’s I is greater than or equal to 0.28, OK is recommended. For the rainstorm center, when the Moran’s I is less than 0.4, RBF is recommended, when it is greater than or equal to 0.4, OK or CoK is recommended.

Abstract:To analyze the characteristics of extreme precipitation changes in Lijiang River Basin under the background of global climate change, based on the daily precipitation data of various meteorological gauges from 1963 to 2019, the modified ETCCDI indices are used to analyze the trend of extreme precipitation in Lijiang River Basin at gauge scale and the whole basin scale using two non-parametric testing methods, innovative trend analysis(ITA) method and Mann-Kendall method. In addition, the annual precipitation, flood season precipitation and the occurrence time of extreme precipitation events are also included in the analysis. Results show that the annual precipitation and flood season precipitation are increasing from 1963 to 2019. The extreme precipitation indices show spatial distribution pattern of decreasing from northwest to southeast in the basin and the indices at all gauges show an upward trend in general. Besides, the occurrence time of the earliest extreme precipitation event within a year is generally delayed in the north of the basin and advanced in the southern part. At the same time, there is an obvious difference in the trend significance test results of extreme precipitation indices between ITA and Mann-Kendall methods, and the sensitivity of ITA is stronger.

Abstract:To better protect fresh groundwater resources, it is urgent to explore the hydrodynamic mechanism of seawater intrusion in coastal aquifers under complex hydrogeological conditions. In this study, a rigorous combination of laboratory experiments and numerical simulations was used to explore the mechanism of seawater intrusion under the combined influence of aquifer heterogeneity and tides. The results showed that spatial distribution of saltwater-freshwater in coastal heterogeneous aquifers was significantly different under the static and tidal sea boundaries. Tidal action reduced the intrusion distance of the saltwater wedge by 30.8%, resulting in a threefold increase in the width of the mixing zone around the saltwater wedge. Tidal action generated an upper saline plume (USP) in the intertidal zone, and fresh groundwater discharge was the key resistance to the accumulation of saltwater in the USP. When the flux of fresh groundwater discharge increased, the USP area would decrease. Under the same hydraulic gradient, the distance of seawater intrusion increased with the increasing permeability, regardless of static/tidal and homogeneous/heterogeneous conditions.

Abstract:To maximize the comprehensive benefits of multifunctional reservoirs, a multi-objective optimization operation model for power generation, water supply, flood control, ice prevention, and ecology of cascade reservoirs in the upper reaches of the Yellow River was constructed. Multiple linear regression model, random forest model, and LightGBM machine learning model were combined to extract multi-objective operation rules for cascade reservoirs, and the extraction effect was evaluated by combining improved Taylor plots and typical operation schemes. The results show that the two machine learning models have overall better performance in extracting operation rules than traditional multiple linear regression model. The newly introduced LightGBM model training results have more practical guidance significance, and can effectively guide the optimization of reservoir discharge under power generation, water supply, and balanced operation needs.

Abstract:This paper utilized the method of dynamic system response curve (DSRC) to retrieve the real precipitation of the “23·7” extreme rainstorm in Beijing based on the observed discharge data in 5 typical watersheds with severely damaged rain stations and poor reliability of measured rainfall of Yongding River and Daqing River Basins. Several indices including the Root Mean Square Error (RMSE), PEARSON correlation coefficient ( R ), and Nash-Sutcliffe efficiency coefficient (NSE) were employed to validate the effectiveness of the DSRC method. The characteristics within different duration of the observed rainfall (before inversion) and the retrieved rainfall (after inversion) were both summarized and compared to the actual rainfall (approximated by the multi-source precipitation fusion), to demonstrate the accuracy of the inversion series. Results shows that the DSRC method can effectively retrieve the average areal precipitation process, while the average RMSE between the observed and actual series and between the retrieved and actual rainfall are 5.97, 3.86 mm, respectively. The average R are 0.67 and 0.82, and the average NSE are 0.27 and 0.67. The retrieval performance of the DSRC method is closely related to the XAJ model simulation performance and whether the rain-gauge station can accurately capture the peak rainfall. Even in the case of rain-gauge station damages and the data transmission interruption, the DSRC method is still able to retrieve the actual precipitation which exhibits significant continuity characteristics.

Abstract:A three-dimensional hydrodynamic and sediment numerical model was used to simulate and analyze the local three-dimensional hydrodynamic characteristics and erosion-deposition characteristics of permeable double spur dikes with different opening rates and arrangement spacings, as well as their effects on aquatic habitats. The results show that the flow field structure around the permeable double spur dike is rich, forming the inner circulation of the upper spur dike, the main and auxiliary circulation between the dams and the slow flow area behind the lower spur dike, which is conducive to the enrichment of organic matter. When the opening rate is 15 %, the main circulation area and inter-dam vorticity of the pemeable double spur dike are the largest. The vorticity and turbulent kinetic energy near the dam increase with the increase of the arrangement spacing. Controlling the opening rate and appropriately increasing the arrangement spacing are beneficial to the migration of benthic organisms. The ratio of the maximum shear stress to the upstream shear stress gradually decreases with the increase of the opening rate and the arrangement spacing. Appropriately increasing the arrangement spacing and selecting a larger opening rate can reduce the scour of the discharged water on the riverbed behind the dam. The range and height of siltation in the dam and behind the dam decrease with the increase of the opening rate, and increase with the increase of the arrangement spacing. In the actual project, properly increasing the opening rate and the arrangement spacing can better achieve the effect of deceleration and siltation of the permeable spur dike, and provide abundant bait for benthic organisms.

Abstract:To study the flow characteristics of the vortex-type grit chamber and improve the sand removal efficiency, the flow characteristics and sand removal efficiency of the vortex-type grit chamber initially set up in a sewage pumping station were analyzed by RSM model and DPM model based on the numerical simulation method. In view of the shortcomings of the vortex-type grit chamber, the optimization scheme of adding deflector plate were proposed, and the flow characteristics and sand removal efficiency of deflectors in different schemes with different lengths were compared. The results show that the water flow in the vortex-type grit chamber presents a spiral shape due to the horizontal circulation and elevation circulation caused by wall barrier and impeller blade rotation. When the water flow enters the pool along the inlet channel, it has an impact on the rotating water flow in the pool body, and the inlet flow with high velocity shifts to the center of the pool under the action of pressure difference, which easily rolls away the sand particles near the center of the pool, affecting the sand removal effect of the vortex-type grit chamber. Adding a baffle at the end of the inlet channel can effectively reduce the impact of the inlet flow on the rotating water flow in the sand settling basin and make the water flow that hits the baffle turn down to the bottom of the pool, thus improving the sand removal efficiency. Comparing the three baffle schemes, the sand removal effect is better when the length of the baffle is 2 000 mm. The sand removal efficiency of 0.10, 0.15, 0.20 mm sand particles increased by 7%, 11% and 2%, respectively.

Abstract:Aiming at the prominent and serious leakage problem of retaining structures of deep foundation pits in water-rich sand layers, a dynamic risk analysis method for deep foundation pit leakage based on the Bayesian network is proposed to adapt to the change of leakage risk over time during excavation and improve the objectivity of evaluation. Taking the leakage disease of deep foundation pits in water-rich sand layers in Hangzhou as the background, a risk analysis index system covering stratigraphy, supply, structure, and deformation was established. The static Bayesian network model was constructed using the Bayesian network and the Leaky-Max hypothesis to analyze the sensitivity of leakage risk probability and the risk factors as well as indices of loss. The results of engineering case analysis show that the dynamic loss, probability and risk level of leakage during the excavation of deep foundation pits in water-rich sand layers obtained by this method are consistent with the actual engineering situation, which verifies the rationality of the method that can be used to predict the leakage risk of retaining structures of deep foundation pits in water-rich sand layers.

Abstract:In order to reveal the macroscopic and microscopic damage law of sandy loam on the embankment of the Yellow River under freeze-thaw cycles, the changes in the shear strength, the deformation damage characteristics, the development trend of force chain, and the evolution of fabric tensor of sandy loam on the embankment were analyzed by the triaxial shear test and the numerical simulation of the discrete element under different numbers of freeze-thaw cycles. The results showed that freeze-thaw cycles significantly reduced the shear strength of sandy loam and induced the sandy loam to freeze and thaw, with the average loss of shear strength by 24.06% after 15 freeze-thaw cycles. The maximum diameter of the bulging damage zone of sandy loam became smaller after freeze-thaw cycles, and the average decrease of maximum contact force was 26.89%. The normal contact number of fabric tensor increased slightly after the freeze-thaw cycle, the normal contact force group tensor decreased significantly, and the degree of anisotropy was weakened. The strong-contact and full-contact equivalent anisotropies of sandy loam before and after the freeze-thaw cycle were lower than that before the freeze-thaw cycle, and the strong-contact equivalent anisotropy coefficients showed the same as the trend of bias stress change. Based on the discrete element simulation results, a prediction model for the shear strength of embankment sandy loam with the number of freeze-thaw cycles as the control parameter was established, with a better prediction effect.

Abstract:In order to solve the problem of drag reduction and vibration suppression of the cylinder flow, a numerical study has been conducted to investigate several key factors affecting the performance of a wavy cylinder. The study with the 3 000 Reynolds number explores the influence of suction and blowing, azimuth (defined as the angle between the suction and blowing device and the opposite direction of incoming flow), and momentum coefficient on various aspects, including the lift and drag characteristics of the cylinder, the distribution of time-averaged pressure and velocity, and the development of flow structures in the near wake. To accomplish this, on the shape of the wave surface, the study uses the steady suction and blowing active control means with the use of the numerical method of large-eddy simulation (LES). The results show that steady suction control proves to be more effective than blowing control in terms of drag reduction and vibration suppression in the wavy cylinder. The lift and drag coefficient of the wavy cylinder decreases with the increase of momentum coefficient when the steady suction azimuth is located on the windward side. Conversely, when the steady suction azimuth is on the leeward side, a pattern emerges: the coefficients initially decrease, then increase, and finally decrease again. This observed behavior can be primarily attributed to the delaying effect of steady suction on flow separation, achieved by absorbing low-velocity fluids. Consequently, this process weakens the downstream and transverse Reynolds stresses in the wake, thereby reducing the pressure difference between the cylinder’s front and back surfaces. Moreover, it notably narrows the width of the near wake of the wavy cylinder in the transverse direction. Under the appropriate suction momentum coefficient and azimuth working condition, the recirculation zone of Saddle section near wake is basically eliminated, and the downstream appears “band vortex”, where the lift and drag fluctuation is significantly controlled and the mean drag coefficient is reduced by 83.84% compared to uncontrolled wave cylinders.

Abstract:In view of the frost-heaving damage problems such as uplift, dislocation, and collapse that are common in earth-rock dam slope protection in cold areas, using the gravel cushion and dam fill earth-rock mixture of an earth-rock dam slope protection project in cold areas as the research objects, this study conducted triaxial tests on the soil-rock mixture of earth-rock dam slope protection with different temperature and rock content under low confining pressure, and analyzed effects of different confining pressure, temperature and rock content on the mechanical properties of the soil-rock mixture. The results show that the stress-strain curves of the samples with low stone content are strain softening type under lower confining pressure, and gradually change to strain hardening type with the increase of confining pressure. Under normal temperature conditions, when the confining pressure is low, the volume deformation of the sample with different stone content shows the phenomenon of contraction followed by the dilatancy, but when the confining pressure is high, the volume deformation of the sample shows the phenomenon of contraction, and the greater the confining pressure, the greater contraction. At different freezing temperatures, the volume deformation of soil-rock mixture shows the phenomenon of contraction followed by the dilatancy, and the lower the test temperature, the greater the dilatancy deformation. With the increase of rock content, the chimerism between gravels is strengthened, and the internal friction angle of the soil-rock mixture increases but the cohesion decreases. With the decrease in temperature, the water inside soil-rock mixtures gradually turns into ice. Under the action of ice cementation, the internal friction angle and cohesion of soil-rock mixtures increase.

Abstract:To ensure the secure and prolonged operation of offshore wind turbines with rock-socketed monopile foundation, an experiment investigation is carried out to study the mechanical distinctions between such foundations and soil-based alternatives. The study involves an indoor 1 g model test to analyze the impact of stratigraphic property and loading condition on both the bearing capacity and mechanical properties of the rock-socketed pile. The research reveals that: The horizontal stiffness and bearing capacity of a rock-socketed monopile is significantly higher than that of a pure sand one with relatively a small length to diameter ratio. Under the horizontal monotonic cyclic loading, the cumulative displacement of the pile top develops rapidly in tens of cycles at the beginning, and tends to be stable in the later cycles; an equilibrium state exists for the cumulative pile-top displacement of rock-socketed monopiles. At the early stage of the cyclic loading, the stiffness of the pile foundation increases with the number of cyclic loads, mainly due to the vibrational density effect of sand, and the structural stiffness is basically stable after the sand is compacted. When the cyclic load amplitude is relatively large, the pile-rock interface is damaged and detached in the heavily weathered rock at the late loading stage, and the stiffness of the structure decreases. In the horizontal loading tests, the position of maximum bending moment of a rock-socketed monopile is always higher than that of a pure sand one, and the position of maximum bending moment of a pile decreases with the increase of cyclic loads whether the monopile is rock-socketed or not. A destructive static loading test is conducted subsequent to the cyclic loading tests, and the ultimate failure mode of the foundation obviously varies for the monopiles socketed in weathering rocks of different degrees.

Abstract:To clarify the wave properties at different locations in the Beaufort-Mackenzie Sea area when sea ice varied significantly under violent storm condition, based on the observed winds, waves and daily sea ice data of one of northwest arctic storm (Oct. 5-8, 2008) during open water season in the Beaufort-Mackenzie Sea area, changes of sea ice concentration, developing stage and sea ice size are studied. Waves are simulated with SWAN model under dramatic variations of wind velocity, wind direction and sea ice during the storm, and comparison study is also carried out between model simulations with sea ice mode covering realistic sea ice information(sea ice concentration, development stage and size information) and different sea ice concentrations as model boundary. The results show that reasonable simulation results are obtained in areas off sea ice cover region by using the two sea ice modes; sea ice mode covering realistic sea ice information gives more precise waves simulation results during storm. Simulation with sea ice mode covering realistic sea ice information indicates that dramatic changes of wind velocity, wind direction and sea ice induce severe variations of wave strength and distribution in Beaufort-Mackenzie region, the most violent waves occur at the biggest wind time.