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1.
Numerical modeling of tidal currents, sediment transport and morphological evolution in Hangzhou Bay, China 总被引：4，自引：0，他引：4
A 2D depth-averaged numerical model is set up to simulate the macro-scale hydrodynamic characteristics, sediment transport patterns and morphological evolution in Hangzhou Bay, a large macro-tidal estuary on the eastern coast of China. By incorporating the shallow water equations, the suspended sediment transport equation and the mass-balance equation for sediment; short-term hydrodynamics, sediment transport and long-term morphological evolution for Hangzhou Bay are simulated and the underlying physical mechanisms are analyzed. The model reproduces the spatial distribution patterns of suspended sediment concentration (SSC) in Hangzhou Bay, characterized by three high SSC zones and two low SSC zones. It also correctly simulates the residual flow, the residual sediment transport and the sediment accumulation patterns in Hangzhou Bay. The model results are in agreement with previous studies based on field measurements. The residual flow and the residual sediment transport are landwards directed in the northern part of the bay and seawards directed in the southern part. Sediment accumulation takes place in most areas of the bay. Harmonic analysis revealed that the tide is flood-dominant in the northern part of the bay and ebb-dominant in the southern part of the bay. The strength of the flood-dominance increases landwards along the northern Hangzhou Bay. In turn sediment transport in Hangzhou Bay is controlled by this tidal asymmetry pattern. In addition, the direction of tidal propagation in the East China Sea, the presence of the archipelago in the southeast and the funnel-shaped geometry of the bay, play important roles for the patterns of sediment transport and sediment accumulation respectively. 相似文献
2.
Cohesive sediments exhibit complex rheological behaviors that are non-Newtonian and time-dependent when subjected to external loading. This paper presents the results of an investigation on the theological properties of three types of dense cohesive sediments, collected from the mouth of the Yangtze River, the shoal of the ttangzhou Bay, and the Yangcheng Lake in China. A set of rheological parameters （including viscosity, yield stress, etc.） was studied based on experiments that were conducted with a RheolabQC rheometer. Measurements of the flow curves, shear stress-time responses, and yield stresses were made. The solid-liquid transition of the dense cohesive sediments occurred both in the shear rate ramp tests and the shear stress ramp tests. This transition was not direct, but it was mediated by a transitional deformation regime or stress plateau. Both the Herschel-Bulkley model and Carreau model were able to describe the theological behavior of dense cohesive sediments, and the empirical expressions for calculating the parameters in these models were obtained by a dimensional and regression analysis. The yield stresses determined by the shear stress ramp test and by the vane method were compared and discussed. The influence of the water content on the rheological properties of dense cohesive sediments was considered. 相似文献
3.
LIN Chengkun 《国际泥沙研究》1992,(2)
In the light of the regional physiography and its effect on clay mineral composition of cohesive sediment (d < 0.005 mm) the source area of cohesive sediment in the Yangtze Estuary can be identified as three supplying regions: the main stem of the Yangtze River, the deltaic region of the abandoned Yellow River including the northwest Huanghai Sea and the Hangzhou Bay. Based on the evaluation of clay mineral composition in the supplying regions and the converging region, a computational model is established. More than 89.6% of cohesive sediment comes from the Yangtze River, a considerable amount is replenished from the deltaic region of the abandoned Yellow River while some part of the cohesive sediment load is transported from the Yangtze Estuary to the Hangzhou Bay. Computation results reveal that the annual deposit of cohesive sediment in the Yangtze Estuary amounts to 45.54 x 106 t. The annual cohesive sediment load replenished from the deltaic region of the abandoned Yellow River is 27.30 x 106t, while the annual cohesive sediment load transported to the Hangzhou Bay is 22.47 x 106 t. The amount of deposit in the Yangtze Estuary has been checked against the value obtained by comparing bathemetry of the Yangtze Estuary in 1915 and 1963. 相似文献
4.
Modeling the tidal channel morphodynamics in a macro-tidal embayment,Hangzhou Bay,China 总被引：2，自引：0，他引：2
The Hangzhou Bay is a macro-tidal bay located to the south of the Changjiang estuary in China. Along its northern shore, a large-scale tidal channel system has developed, which includes a main northern tidal channel, with a length of more than 50 km and a width up to 10 km, and a secondary southern tidal channel. A process-based morphodynamic model, incorporating the cohesive sediment transport module of Delft3D, is used to analyze the physical processes and mechanisms underlying the formation and evolution of this tidal channel system. The results show that spatial gradients of flood dominance, caused by boundary enhancement via current convergences, is responsible for the formation of the channel system, due to a combination of the various factors such as funnel-shaped geometry hindering associated with the presence of islands, and flow deviation by the southern tidal flat and so on. The model results agree well with the real morphological features. This study also indicates that the reclamation of the southern tidal flat imposes a profound influence on the morphological evolution of the tidal channel system in the Hangzhou Bay. It is feasible to use the model to simulate long-term estuarine morphological changes with cohesive sediment settings. 相似文献
5.
Cheng LIU Yun HE Joseph Hun-Wei LEE Zhao-Yin WANG Dr. Asso. Prof. International Research Training Center on Erosion Sedimentation Beijing China & Anhui Institu 《国际泥沙研究》2002,17(2)
1 INTRODUCTION Shanghai, Chinas largest metropolitan area with a population of about 14 million, is situated at the mouth of the Yangtze River, and bordered with the East China Sea to the east, Hangzhou Bay to the south, and the provinces of Zhejiang and Jiangsu to the west. It is a region with intensive distribution of rivers and lakes. The good geographic location and natural conditions have provided the city with superiority in its social and economic center and port city of the co… 相似文献
6.
The distributions of particulate heavy metals and its indication to the transfer of sediments in the Changjiang Estuary and Hangzhou Bay,China 总被引：7，自引：0，他引：7
Particulate heavy metals (Cu, Pb, Cd) were measured following intensive sampling in June and October 1994 at 70 stations in the Changjiang Estuary and Hangzhou Bay, China. In the study area, particulate Cu and Pb have a similar level that is higher than the concentration of particulate Cd. Cu, Pb and Cd concentrations in suspended sediments are higher than those in bed load. In the middle of Hangzhou Bay, heavy metal concentrations in suspended sediments and bed load are similar. This may be the result of the frequent exchange between them, which is due to the strong dynamic condition. A negative relationship was observed between concentrations of heavy metals in bed load and bulk density. Fine-grained sediments were the main carriers of heavy metals. Sedimentary dynamics dominate the fate of heavy metals in these sites. The distributions of metals (especially Cu) in suspended sediments can indicate the transfer of sediments in this area. 相似文献
7.
Grain size characteristics of surface sediment and its response to the dynamic sedimentary environment in Qiantang Estuary,China 总被引：2，自引：0，他引：2
The composition and grain size characteristics of sediment in estuarine and coastal environments provide important information on the material source, hydrodynamic environment, environmental events,etc. However, few studies have focused on the sediment characteristics of the entire Qiantang Estuary,particularly, on the correlation between hydrodynamics and sediment properties. Through systematic sampling of the surface sediment in a large area of the Qiantang Estuary, the spatial distribution ch... 相似文献
8.
为了检验体潮与海潮的理论模型,分析了中国东西重力潮汐剖面（1981年9月-1985年1月）。同时,为研究LaCoste ET-20和ET-21重力仪的格值系统,建立了一条由17台LaCoste G型和2台LaCoste D型重力仪观测的重力垂直基线。在基线上标定的结果表明,ET-21重力仪的格值大了1％。由标定得到的格值计算剖面上各测站的潮汐因子,经海潮改正后,接近Wahr模型值,振幅因子的残差:O1波小于0.3μGal,M2波小于0.4μGal。但是上海和拉萨的观测经海潮改正后,相位迟后有很大的改善,振幅因子却更偏离于模型值,其潮汐异常主要是近海的海潮模型不完善,以及在海潮计算中,所采用的地球模型未考虑地壳与上地幔的横向不均匀性所引起。 相似文献
9.
Yang Bin Yang Yifan Yang Zhongliang Feng Xi Ye Qing Yu Liangliang Ou Jian 《Ocean Dynamics》2021,71(10):1011-1031
Ocean Dynamics - Waves characteristics of the developing windfarm in the semi-enclosed Hangzhou Bay are distinctive due to the East Asian monsoon and frequent typhoons. In this paper, statistical... 相似文献
10.
Data are presented on long-term salinity behaviour in San Francisco Bay, California. A two-level, width averaged model of the tidally averaged salinity and circulation has been written in order to interpret the long-term (days to decades) salinity variability. The model has been used to simulate daily averaged salinity in the upper and lower levels of a 51 segment discretization of the Bay over the 22-yr period 1967–1988. Monthly averaged surface salinity from observations and monthly-averaged simulated salinity are in reasonable agreement. Good agreement is obtained from comparison with daily averaged salinity measured in the upper reaches of North Bay.The salinity variability is driven primarily by freshwater inflow with relatively minor oceanic influence. All stations exhibit a marked seasonal cycle in accordance with the Mediterranean climate, as well as a rich spectrum of variability due to extreme inflow events and extended periods of drought. Monthly averaged salinity intrusion positions have a pronounced seasonal variability and show an approximately linear response to the logarithm of monthly averaged Delta inflow. Although few observed data are available for studies of long-term salinity stratification, modelled stratification is found to be strongly dependent on freshwater inflow; the nature of that dependence varies throughout the Bay. Near the Golden Gate, stratification tends to increase up to very high inflows. In the central reaches of North Bay, modelled stratification maximizes as a function of inflow and further inflow reduces stratification. Near the head of North Bay, lowest summer inflows are associated with the greatest modelled stratification. Observations from the central reaches of North Bay show marked spring-neap variations in stratification and gravitational circulation, both being stronger at neap tides. This spring-neap variation is simulated by the model. A feature of the modelled stratification is a hysteresis in which, for a given spring-neap tidal range and fairly steady inflows, the stratification is higher progressing from neaps to springs than from springs to neaps.The simulated responses of the Bay to perturbations in coastal sea salinity and Delta inflow have been used to further delineate the time-scales of salinity variability. Simulations have been performed about low inflow, steady-state conditions for both salinity and Delta inflow perturbations. For salinity perturbations a small, sinusoidal salinity signal with a period of 1 yr has been applied at the coastal boundary as well as a pulse of salinity with a duration of one day. For Delta inflow perturbations a small, sinusoidally varying inflow signal with a period of 1 yr has been superimposed on an otherwise constant Delta inflow, as well as a pulse of inflow with a duration of one day. Perturbations in coastal salinity dissipate as they move through the Bay. Seasonal perturbations require about 40–45 days to propagate from the coastal ocean to the Delta and to the head of South Bay. The response times of the model to perturbations in freshwater inflow are faster than this in North Bay and comparable in South Bay. In North Bay, time-scales are consistent with advection due to lower level, up-estuary transport of coastal salinity perturbations; for inflow perturbations, faster response times arise from both upper level, down-estuary advection and much faster, down-estuary migration of isohalines in response to inflow volume continuity. In South Bay, the dominant time-scales are governed by tidal dispersion. 相似文献
11.
The baroclinic response of a stratified coastal embayment (Lunenburg Bay of Nova Scotia) to the observed wind forcing is examined using two numerical models. A linear baroclinic model based on the normal mode approach shows skill at reproducing the observed isotherm movements and sub-surface currents during a time of strong stratification in the bay. The linear model also shows that the isotherm movement in Lunenburg Bay is influenced by the wind forcing and propagation of baroclinic Kelvin waves from neighbouring Mahone Bay. The effects of nonlinearity and topography are investigated using a three-dimensional nonlinear coastal circulation model. The nonlinear model results demonstrate that the nonlinear advection terms generate a gyre circulation at the entrance of Lunenburg Bay, and the slope bottom topography at the mouth of the bay strengthens the sub-surface time-mean inflow on the southern side of the bay. A comparison of model-calculated currents in different numerical experiments clearly shows that baroclinicity plays a dominant role in the dynamics of wind-driven circulation in Lunenburg Bay. 相似文献
12.
自20世纪60年代以来,大陆岩石圈流变学取得了较大的进展,理论和应用研究不断深入.理论上,人们不仅认识到在构造运动中岩石圈介质是流变体而非简单的刚体性和弹性体;并利用矿物和岩石的实验结果提出了岩石圈流变分层的概念,建立了一维流变模型;进而用流变的观点解释了一些具体构造现象,而且开始了三维流变结构的研究,提出了岩石圈流变结构的横向分块纵向分层的观点.应用上,人们已从把流变强度曲线简单地运用于运动学或动力学模型的阶段,进入了在三维空间中定量研究地球动力学问题的阶段.随着岩石圈流变学研究的深入及大陆岩石圈的复杂性,新的问题也不断涌现. 相似文献
13.
The objective of this paper is to investigate the rheological behavior of kaolinite and Hendijan mud, located at the northwest part of the Persian Gulf, and the dissipative role of this muddy bed on surface water waves. A series of laboratory rheological tests was conducted to investigate the rheological response of mud to rotary and cyclic shear rates. While a viscoplastic Bingham model can successfully be applied for continuous controlled shear-stress tests, the rheology of fluid mud displays complex viscoelastic behavior in time-periodic motion. The comparisons of the behavior of natural Hendijan mud with commercial kaolinite show rheological similarities. A large number of laboratory wave-flume experiments were carried out with a focus on the dissipative role of the fluid mud. Assuming four rheological models of viscous, Kelvin-Voigt viscoelastic, Bingham viscoplastic, and viscoelastic-plastic for fluid mud layer, a numerical multi-layered model was applied to analyze the effects of different parameters of surface wave and muddy bed on wave attenuation. The predicted results based on different rheological models generally agree with the obtained wave-flume data implying that the adopted rheological model does not play an important role in the accuracy of prediction. 相似文献
14.
Coastal plain of Hangzhou Bay, to the south of the present Yangtze Estuary, is closely linked to the evolution of the Yangtze River delta. However, absolute age of Pre-Holocene sediments is limited, which hinders the understanding of this area's environmental evolution. In this study, using optically stimulated luminescence (OSL), single aliquots and single grains of quartz and K-feldspar were used to date the late Quaternary sediments in coastal plain on the southern Hangzhou Bay. The vertical difference in particle size composition render either silt- or sand-sized quartz for dating. Cross-checking of multiple OSL dating methods indicated that the upper ∼65 m recorded the Holocene part of the succession; sediment from a depth of 136.6 m was dated to ∼180 ka. It was found that the single-grain method was more reliable in comparison to single-aliquot age, the former minimized the effect of signal components. Single-grain quartz and K-feldspar luminescence yielded consistent ages at sample depth of 136.6 m (∼160–180 ka), while the latter gave robust age at depth of 115.5 m (∼150 ka). This chronology is in general in accordance with neighbouring cores and can constrain paleomagnetic dating results in those cores. Taking together, the study site has thickest Holocene deposits in comparison to the highland centered around Taihu Lake on the southern Yangtze delta. Moreover, the luminescence characteristics of quartz from different sample depths, behaved differently with respect to luminescence sensitivity, signal components and saturation level, perhaps reflecting varied provenance and weathering characteristics caused by climate change. 相似文献
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17.
David W. Ostendorf Paula L. S. Rees Shawn P. Kelley Alan J. Lutenegger 《Journal of Hydrology》2004,290(3-4):259-274
We consider the response of a deep unconfined horizontal aquifer to steady, annual, and monthly recharge. A groundwater divide and a zero head reservoir constrain the aquifer, so that sinusoidal monthly and aperiodic annual recharge fluctuations create transient specific discharge near the reservoir and an unsteady water table elevation inland. One existing and two new long-term data sets from the Plymouth-Carver Aquifer in southeastern Massachusetts calibrate and confirm hydraulic properties in a set of analytical models. [Geohydrology and simulated groundwater flow, 1992] data and a new power law for tritiugenic helium to tritium ratios calibrate the steady recharge that drives the classical parabolic model of steady hydraulics [Applied Hydrogeology, 2001]. Observed water table and gradient fluctuations calibrate the transient recharge models. In the latter regard, monitoring wells within 1 km of Buttermilk Bay exhibit appreciable specific discharge and reduced water table fluctuations. We apply [Trans Am Geophys Union 32(1951)238] periodic model to the monthly hydraulics and a recharge convolution integral [J Hydrol 126(1991)315] to annual flow. An infiltration fraction of 0.79 and a consumptive use coefficient of 1.08×10−8 m/s °C relate recharge to precipitation and daylight weighted temperature across all three time scales. Errors associated with this recharge relation decrease with increasing time scale. 相似文献
18.
B. I. Birger 《Izvestiya Physics of the Solid Earth》2018,54(6):849-858
The laboratory experiments with rock samples show that creep under small strains is transient and can be described by the linear hereditary rheological Andrade model. The flows that recover isostasy (including the postglacial rebound flows) cause the strains in the crust and mantle, which are as low as at most 10–3 and, hence, demonstrate transient creep. The effective viscosity characterizing the transient creep is lower than that at the steady creep and depends on the characteristic time of the considered process. The characteristic time of restoration of isostatic equilibrium (isostatic rebound) after the initial perturbation of the Earth’s surface topography is at most 10 kyr and, therefore, the distribution of the rheological properties along the depth of the mantle and the crust differs from the distribution that corresponds to the slow geological processes. When considering the process of isostatic rebound, the upper crust can be modeled by a thin elastic plate, whereas the underlying crust and the mantle can be modeled by the halfspace with transient creep in which the rheological parameter is inhomogeneous with depth. For this system, the continuum mechanics equations are solved by means of the Fourier and Laplace transforms. The vertical displacements that violate the isostasy propagate from the area of the initial perturbation along the Earth’s surface and can be considered as the mechanism of the present-day vertical movements of the crust. Comparing the obtained results with the observation data allows estimating the Andrade parameter. The use of the Andrade rheological model makes it possible to quantify the relationship between the effective viscosity of the asthenosphere corresponding to the postglacial flows and the seismic Q-factor of this layer. 相似文献
19.
利用含气非饱和Biot-Stoll模型研究了声波在海底表层沉积物介质中的传播,讨论了骨架耗散、含气饱和度对快纵波、慢纵波和横波速度和衰减的影响,并与Biot模型的结果进行了对比.研究结果表明:孔隙流体黏滞耗散与骨架耗散共同影响声波传播速度和衰减,低频情况下骨架耗散引起的衰减占主要地位,高频情况下骨架耗散引起的衰减较小;少量气体(<1%)的引入显著改变了快纵波速度,气体含量的变化对快纵波衰减影响很大,低频情况下气体对慢纵波速度的影响不大,而对横波速度的影响较大,气体含量的变化对慢纵波和横波衰减影响较小.利用超声波测量系统测量了一例杭州湾海底沉积物样品的纵波速度和衰减,当含气量趋近0%时,Biot-Stoll模型预测的纵波速度和实验测量结果较为一致. 相似文献
20.
We show that geodetic data from the Bay Area Regional Deformation (BARD) network indicate asymmetric motion across the San Andreas fault in the San Francisco Bay Area (SFBA), resulting from a strong contrast in rigidity across the fault, as determined previously from seismological data. Assuming asymmetric motion across the fault, we determine the location and size of the maximum strain rate in the region. We find that, compared to the determination using a symmetric model of deformation, it is shifted eastward and its value increases from ～0.4 μstrain/yr to ～0.65 μstrain/yr. Such strain rate amplitudes are consistent with previous geodetic slip rate estimates. We confirm that the geological units located east of SAF are entrained by the motion of the Pacific Plate and that the San Andreas fault (SAF) is the real rheological limit between the Pacific and North-American Plates. The asymmetry of rheology constrained in this study implies the strain rate maximum in SFBA is likely located between SAF and the Hayward fault system. This also has implications for hazards in the northern SFBA, in particular on the Rodgers creek fault. 相似文献