Abstract: In order to adapt to the development conditions of Maozhou Estuary,Lingding Bay,and ensure smooth flood discharge as the primary principle,and to comply with the law of water and sediment movement and river regime development,the regulation line of estuary is selected and optimized. The regulation line scheme is divided into single and double channels. There are two schemes of enclosure filling and enclosure filling and excavation under different broadening rates of the two types of channels. Mathematical simulation and physical model experiment of hydrodynamic sediment are carried out. The results show that the effects of various schemes of estuary regulation line on the rising and falling currents of Lingding Bay are mainly concentrated in Jiaoyi Bay and its adjacent waters,and that after the implementation of the scheme,the erosion and deposition in the surrounding waters have little change and have no adverse impact on the river regime. With the increase of the widening rate,the influence of scheme on the flood discharge in the estuary decreases gradually. According to comprehensive analysis of the impact on hydrodynamics,estuary flood discharge and river regime stability,compared with single-channel and double-channel,the impact on flood level,tidal volume,high and low tide level,flow velocity and riverbed erosion and deposition has good consistency. Under the same broadening rate,the impact of each scheme is of the same magnitude.
Abstract: Keep the seabed stability is of critical importance to estuary regulation and development. Based on the long time-series data such as hydrologic sediment,underwater topography and remote sensing,characteristics and trends of the morphodynamic evolution processes in the Maozhou Estuary of the Lingding Bay is presented by use of the digital elevation model and hydrodynamic mathematical model. In recent decades,the seabed in the Middle Shoal of the Lingding Bay was eroded obviously,which resulted in the separation of the Lanjiang Shoal and Fanshi Shoal,and a new Middle Channel was developed. The outlet channel of the Maozhou Estuary is controlled by the ebb tidal currents,and the channel of the Jiaoyi Bay instead of the flood tidal currents. The Jiaoyi Shoal is of critical importance to maintain the existing pattern of the shoals and the channels in the adjacent sea area. The new trend of the morphodynamic evolution processes of the Lingding Bay is from the effects caused by the large-scale human activities such as tidal flat reclamation and sand mining,which is urgent to monitor.
Abstract: Abundant tidal flat resources exist along the coast zone of the Lingding Bay of the Pearl River Estuary,reclamation of which can ease the contradiction between land resource shortage and demand for social and economic development. The shoreline at the Lingding Bay changed significantly since 1981 due to reclamation of tidal flats. However,there is still a lack of understanding on the cumulative response process of estuarine hydrodynamic environment to reclamation of tidal flats. In this study,eight cases were selected as representative reclamation stages in the Lingding Bay since 1981,a two-dimensional tidal wave mathematical and tidal current mathematical model were developed to analyze the cumulative changing process of tidal volume,constituent tidal amplitude,as well as tidal current velocity. The results show that tidal volume decrease for bay mouth section,Neilingding section,Shenzhen Bay section,as well as Nansha section compared to their conditions in 1981 are about 4.9%-6.0%,9.0%-12.8%,17.8%,and 5%-6.3%,respectively. The M2 constituent tide amplitude in the Lingding Bay in 2018 increases from south to north,and from west to east,which means tidal wave intensifies from south to north in the bay,compared to its condition in 1981. Tidal range change tendency in the Lingding Bay consistent with that of M2 constituent tidal amplitude,while the tidal characteristics in the bay does not changed,the tidal current velocity of the bay decrease generally,with more decrease on the west bank of the bay more than that on the east bank,while the current velocity near the bay top increases slightly,after the aforementioned reclamation stages were performed. The results of this study can inform the protection and utilization of tidal flat resources,protection of coastal engineering,coastal disaster prevention and mitigation on the Lingding Bay of the Pearl River Estuary and similar estuarine bays,as well provide a scientific basis for comprehensive tidal flat utilization and protection.
Abstract: Large-scale and disorderly sand excavation in the Pearl River Delta in recent 30 years has changed the evolution trend of more water and less sediment and the stable river regime,promoting the change of riverbed from slow deposition to large erosion,and the low water level has decreased significantly. This artificial effect has covered and far exceeded the natural evolution of rivers in the same period,and has a crucial impact on water intake and supply,ecological protection,shipping security and so on. On the basis of summarizing the study of water level changes in deltas and estuaries,this paper takes the Pearl River Delta network system as an example,and divides it into perennial tidal current section,seasonal tidal current section and perennial runoff section according to the change of low water level. Among them,the perennial tidal current section is basically not affected by sand excavation;the closer the seasonal tidal current section is to the low-water tidal current boundary,the greater the change of low-water level;and the lower-water level is caused by backward erosion in the perennial runoff section. Combined with the process of water and sediment variation,this paper attempts to explore the response mechanism of hydrodynamics to the rapid evolution of riverbed,in order to provide basis for navigation low water level design.
Abstract: Studies of the high concentration layer (HCL) have great theoretical and practical significance in the protection and utilization of estuarial and coastal areas. In order to better understand the HCL,the physical impacting mechanisms and phase-averaged sediment concentration profile were studied. Combining a 1DV model for the flow-sediment dynamics in the wave-current bottom boundary layer (BBL) and experimental data sets,sensitivity analyses were performed by carrying out computations of several scenarios. Inspired by the 1DV model,the distribution of wave-related sediment diffusivity was proposed,and process-based expressions for the suspended sediment concentration (SSC) profile were derived considering primary impacting factors. Results showed that the HCL is directly related to the wave BBL,which is a combined result of bed forms and flow dynamics. It is not appropriate to establish the relationship of the HCL with a single factor,for instance,the parameters of flow dynamics or bed forms. The effects of stratification and the hindered settling velocity have significant impacts on the HCL. The proposed SSC profile over a flat bed is a distribution of power-Rouse-exponent,while over a vortex rippled bed,it has an exponent-power-Rouse distribution. It is expected that these expressions can be applied in further 2-D and 3-D simulations.
Abstract: The abnormal siltation was present in the E15 foundation trench of the immersed tube tunnel of the Hong Kong-Zhuhai-Macao Bridge,and the installation of the immersed pipe of the submarine tunnel was forced to paused. In order to find out the cause of abnormal silting at the E15 foundation trench,various technical means such as field hydrological and sediment observation,remote sensing image data analysis and numerical simulation have been carried out. In this paper,the water-sand mathematical model is adopted to simulate the diffusion and transport process of the muddy water mass formed by sand mining activities in the upper reaches of Neilingding Island under the action of tidal current,in which the sand source is simulated in the form of surface source. The simulation results show that the muddy water mass formed by sand mining activities can be transported and spread to the foundation trench during the ebb tide of a spring tide,and the daily silt thickness of the E15-E27 foundation trench will be increased by 43.8% under the influence of sand mining activities. The results of numerical simulation provide evidence for finding out the sediment source of abnormal silting in E15 foundation trench. The water and sediment environment in the east of E15 pipe section is complicated. The natural siltation is close to the critical siltation allowable value. The sand mining activity in the upstream water of the foundation trench will bring uncontrollable factors to the siltation at the foundation trench. Therefore,the attention should be paid to the influence of sand mining activities on sediment deposition in surrounding water area.
Abstract: As one kind of innovative marine structure,there still not exist public recognized stability analysis theory and practical method for the deep-buried large diameter steel cylinder yet,which seriously blocked the popularization and application of large diameter steel cylinder structure in practical engineering implementation. In order to further improve the theoretical basis of the new structure,this paper carried out three-dimensional elastic-plastic modeling analysis of deep-buried large diameter steel cylinder which is used as wall structure of artificial island in the project of Hong Kong-Zhuhai-Macao Bridge based on PLAXIS 3-D software. The research results show that the horizontal deformation is relatively enlarged,but the overall stability can be greatly improved when the large diameter steel cylinder structure is deeply buried in soft clay foundation as the artificial island wall,.Combining the numerical simulation results and the theoretical plane strain analysis method provided by OCDI standard,a reliable shear and sliding stability calculation method is finally summarized with one set of quantitative evaluation criteria by verifying the measured data of deep-buried large diameter steel cylinder in the practical engineering of the east-west island of Hong Kong-Zhuhai-Macao Bridge. The research results also provode principle suggestions of the applicability of steel cylinder structure to port engineering,which can provide theoretical basis and Engineering reference for the design and optimization of similar constructions.
Abstract: During the design process of sea-crossing bridges and tunnels,it is necessary to estimate the design flow velocities at different recurrence periods for the project location. However,the lack of on-site long-term flow observation data makes such estimations very difficult. Based on typical storm surge processes with different return periods,a numerical method was proposed for estimating design flow velocities for estuaries and coastal areas,for which the coupling of flood runoff and storm tidal currents was considered for the estuarine areas. According to the measured tide level data from the Macao tide station from 1925 to 2003,the characteristics of historical storm surge processes in the Pearl River estuary were analyzed,and typical storm surge processes of different return periods were obtained based on the results of the analysis of annual extreme frequencies of tidal levels and tidal ranges. Then,a horizontal two-dimensional hydrodynamic numerical model was established to simulate the flow field in the Pearl River estuary under the combined conditions of storm surges with different return periods and general upstream flooding. With such a model,design flow velocities at control points along the Hong Kong-Zhuhai-Macao Bridge were determined.
Abstract: East and west artificial islands are used to realize the transition from bridge to tunnel for Hong Kong-Zhuhai-Macao Cross-sea Tunnel. Immersed tunneling method is applied in sea tunnel and the total length of the sinking section is 5 664 m. The tube sections of E1-E33 are arranged from west artificial island. The standard pipe section is 180 m long,37.95 m wide,11.4 m high and weighs about 80 000 tons. The connection area of the island and tunnel is affected by the deflecting flow and the sudden change of the water depth during the foundation trough excavation,and the flow pattern is complicated. Moreover,the flow pattern will be changed when the sinking joint is subsided. It is necessary to obtain the magnitude of water flow force to guarantee the safe sinking and accurate docking of the immersed tube. By using the undistorted model in a wide flume with the geometric scale of 1:100,the experimental study on the flow distribution and water flow force during the sinking process of the island tunnel is carried out. The results indicate that,when there is no protective measure at the head of the island,the deflecting flow would affect the middle part of tube E1 and the flow velocities on the surface and at the bottom layers are larger than that of the middle layer. When sinking tube E1,the maximum longitudinal flow force can reach 4 601 kN,and the averaged longitudinal flow force of tube E2 is 5 149 kN. After sheltering tube E1,the flow velocity at tube E1 decreases significantly. The middle part of tube E2 is mostly affected by the sheltering body,the maximum increment in the flow velocity reaches to 40%,and the flow velocity of the middle layer is larger than those on the surface and at the bottom layers. The average longitudinal flow force of tube E2 is 5 240 kN. When the sinking tube is completely immersed into the water,the flow velocity in the foundation trench is relatively small,and the water flow force during the sinking process decreases gradually. The vertical distribution of water flow in the connection area of island and tunnel is not exponential one,and the velocity distribution along the length of the pipe section is not uniform due to the influence of deflecting flow on the island head wall. The formula of floating water flow force at the pipe section is not suitable for calculating the magnitude of the water flow force during the sinking process of immersed pipe.
Abstract: Wave and current loads on pile foundation of sea-crossing bridges have always been given priority in the design of sea-crossing bridges. The wave-current force in practical projects is usually obtained by the computing method of wave-current force for single pile foundation recommended in the Code of Hydrology for Harbour and Waterway (JTS145-2015),without reasonable consideration of the influence of local scour shape. In this study,Hong Kong-Zhuhai-Macao Bridge has been taken as an example. Based on physical model test results,a calculation method of wave-current force for pile foundation considering local scour patterns is proposed by modifying the selection of such parameters as velocity,CD and CM in the calculation model. The proposed method,which guarantees the project safety and can be cost-effective as well,has been successfully applied to the design of pile foundation of Hong Kong-Zhuhai-Macao Bridge.
Abstract: The characteristics of local scour around large-diameter submerged cylinders are quite different from the non-submerged ones under combined wave and current conditions. Local scour model tests are carried out in a wave-current flume. A submerged cylinder model was installed in a flat sand bed. The flow velocity around the model was measured,and the development of the scour depth was recorded under various waves,current velocities,current directions and submergence rates. A laser scanner was used to generate the geometry of the equilibrium scour hole. The influence of the submergence rate Sr and the relative cylindrical height hc/D on the equilibrium scour depth is analyzed. The results show that under the same incident wave current conditions,as the relative cylindrical height hc/D decreases,the scour development rate,the scour hole radius and the scour hole depth decrease. When the relative cylindrical height hc/D is larger than 1,the scour depth increases rapidly as the cylinder height increases until a critical value of hc/D is reached. The quasi-equilibrium scour hole is in the shape of a "flipped spoon". The scour hole is symmetrically distributed along the left and right sides of the cylinder. The front of the cylinder is a semi-annular scour hole. A "saddle-shaped" dune is formed due to accumulation of sand scoured away from the cylinder.
Abstract: Based on the generalized vertical coordinate,an unstructured grid numerical method is developed to simulate three-dimensional shallow water flow. The semi-implicated finite difference and finite volume discretization are applied to the momentum equations and conservation equation,such that the model is robust,stable and mass conservation is satisfied both locally and globally. Since unstructured mesh and generalized vertical grid,the proposed numerical model is well suited to fit complicated estuaries and coastal boundaries and yet is sufficiently flexible to set the vertical layers. The test cases of wind-driven currents and lock exchange flow are used to demonstrate the model's capabilities. Comparisons between numerical results and analytical data are presented. The Pearl River Estuaries is modeled and is verified and calibrated with field measurement data. The computed results mimic the field data well.
Abstract: Numerical wave simulation under hypothetical typhoon conditions has a pivotal role in the risk assessment of cross-sea bridges and tunnels. The wind-field generation and the adverse track selection have a large influence on the wave simulation results. This study verified the rationality of wave simulation under a single hypothetical typhoon wind field and analyzed the effects of different typhoon tracks on the waves in different directions of the project area. A numerical wind-wave model in the Pearl River Estuary was constructed according to intensities based on a 300-yr return period and tested via Monte Carlo simulation,which was applied to 104 typhoon tracks selected by the radius method. The results show that the adverse tracks that significantly impact the wave field at the West Artificial Island are within 100 km of the Pearl River Estuary. Seven adverse typhoon tracks reflecting different characteristics were obtained,which provided a basis for further study of the typhoon wave process in the Pearl River Estuary under extreme weather conditions. This study provides methodological support for the wave parameter analysis of large-scale engineering at coasts and estuaries that are susceptible to typhoons.
Abstract: Recently,there are more and more large-scale water engineering construction projects in the Pearl River Estuary,such as waterway regulation,bridge engineering and port construction. The importance of safety of hydraulic structures and sensitivity to typhoon wave damage are one of the key factors of large-scale projects. In this paper,the influence of extreme weather conditions on the design wave parameters of artificial island at the junction of Hong Kong-Zhuhai-Macao Bridge is analyzed and calculated by using typhoon wave numerical model. Firstly,the landing typhoon data affecting the coastal areas of Guangdong Province from 1949 to 2014 are analyzed,and the parameters of typhoon pressure drop and maximum landing wind speed 300-year event in Pearl River Estuary are analyzed by stochastic model. Then,the numerical model of typhoon wave in Pearl River Estuary waters is established. Finally,the unfavorable landing typhoon track is selected,and the wave parameters of east and west artificial islands in the Pearl River Estuary under extreme weather conditions are calculated by using the combination of typhoon parameters 300-year event,and the original design wave elements are reviewed. It can provide new ideas and research methods for the design of other ocean engineering projects.
Abstract: The artificial island of Hong Kong-Zhuhai-Macao Bridge is located in Lingding Sea area,the overtopping could endanger the operation of the artificial island and tunnel in storm period. The overtopping rate is important factors in the design of the artificial island. 2-D physical model tests are carried to study the influence of the different structure factors to wave overtopping,such as armour block type,berm width and elevation,armour width in front of the wall. The test results show that the armour width has significant influence on the overtopping,and the test value is obviously smaller than the calculating value of van der Meer formula when the overtopping rate is relative small. After that,a calculation formula of the average overtopping discharge rate are presented for the artificial island of Hong Kong-Zhuhai-Macao Bridge,in which the armour width factor Kc is involved. The calculating results show good agreement with the experimental data,and can be used in the optimization design and overtopping warning in operation of the artificial island.
Abstract: Lingding Bay has two main hub ports and connected deepwater waterways in South China. Maintaining the stable pattern of "three beaches and two troughs" is the key basis for the Western trough deepwater waterways development in Guangzhou Port. Since 2008,due to artificial sand digging on the middle beach,three huge sand pits with total volume of 7×108 m3 has been formed,which directly affects the evolution of the beach and trough in Lingding Bay. By means of field investigation and numerical simulation,the influence of sand mining on surrounding water body and topography is analyzed. It is pointed out that the sediment concentration in the sediment digging area can increase greatly from 0.2 kg/m3 to 1.5-2.8 kg/m3 (up to 5kg/m3). This will increase the deposition of the nearby seabed and also affect the waters of the Hong Kong-Zhuhai-Macao Bridge. The influence of hydrological factors on the formation of sand pits are calculated. The results show that the main changes of tide level,tidal current and tidal volume are in the sand pit and its adjacent waters. The main changes are the tidal level decreases (less than 1 cm),the tidal current decreases,and sediment deposition is mainly in the sand pit (33 cm/a). The seabed around the pit is scoured,and the scour in the south side is larger. At present,sand pits are mainly silted up,and the time of silting back is expected to take 20 years. When 2#,3# sand pits or 2#,4# sand pits are connected,it is possible to form a new tidal current channel,change the existing pattern of "three beaches and two troughs",and have a negative impact on the existing channel maintenance and port production.