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1.
An artificial sand wave on the Dutch shoreface of the North Sea has been studied in conditions with relatively strong tidal currents in the range of 0.5 to 1 m/s and sediments in the medium sand size range of 0.2 to 0.5 mm. The sand wave is perpendicular to the tidal current and has a maximum height and length of the order of 5 m and 1 km, respectively. The sand wave is dynamically active and shows migration rates of the order of a few metres per year. A numerical morphodynamic model (DELFT3D model) has been used to simulate the morphological behaviour of the sand wave in the North Sea. This model approach is based on the numerical solution of the three-dimensional shallow water equations in combination with a surface wave propagation model (wind waves) and the advection–diffusion equation for the sediment particles with online bed updating after each time step. The model results show that the sand wave grows in the case of dominant bed-load transport (weak tidal currents; relatively coarse sediment; small roughness height; low waves) and that the sand wave decays in the case of dominant suspended transport (strong currents, relatively fine sediment, large roughness height; storm waves). 相似文献
2.
In this study, the combined actions of waves and tidal currents in estuarine and coastal areas are considered and a 2D mathematical model for sediment transport by waves and tidal currents has been established in orthogonal curvilinear coordinates. Non-equilibrium transport equations of suspended load and bed load are used in the model. The concept of background concentration is introduced, and the formula of sediment transport capacity of tidal currents for the Oujiang River estuary is obtained. The Dou Guoren formula is employed for the sediment transport capacity of waves. Sediment transport capacity in the form of mud and the intensity of back silting are calculated by use of Luo Zaosen＇ s formula. The calculated tidal stages are in good agreement with the field data, and the calculated velocities and flow directions of 46 vertical lines for 8 cross sections are also in good agreement with the measured data. On such a basis, simulations of back silting after excavation of the waterway with a sand bar under complicated boundary conditions in the navigation channel induced by suspended load, bed load and mud by waves and tidal currents are discussed. 相似文献
3.
Alan William Niedoroda Donald J.P. Swift Thomas Sawyer Hopkins Chen-Mean Ma 《Marine Geology》1984,60(1-4):331-354
An open ocean shoreface typical of long, wave-dominated sandy coasts has been examined through a combination of extensive field measurements of wave and current patterns with computations of marine bedload transport and sedimentation. Sand transport on the upper shoreface is dominantly controlled by waves with only secondary transport by currents. Sand on the middle and lower shoreface, as well as the inner continental shelf is entrained by storm waves and transported by a complex pattern of bottom boundary layer currents.
Storm events have been studied and modeled for the shoreface off Tiana Beach, Long Island. The dominant effect of coastal frontal storms is to cause significant shore-parallel bedload transport with important shore-normal secondary components. These storms tend to result in net offshore transport of sand removed from the beach and surf zone systems. The bedload transport during a storm is convergent on the shoreface leading to accretion. Most accretion occurs on the upper shoreface with lesser deposits covering the middle and lower shoreface as well as the inner continental shelf. Longer-term equilibrium can be maintained by slow return of sand up the shoreface during non-storm conditions.
Annual and geologic time-scale budgets of shoreface sand transport and sedimentation yield equilibrium, net accretion or net deposition. The annual balance results from an integration of the event-scale bedload transport patterns and morphologic responses. These processes and responses have feedback mechanisms which stabilize the system over longer, but not geologic, time scales. Geologic time scale balances are controlled by relative sea level changes and relative availability of sediment supply with the event-scale shoreface and transporting processes providing the mechanism to produce the changes in long-term morphology and sedimentation patterns. In the area of study, the long-term pattern is one of net shoreface erosion, and the permanent loss of sand to the shelf floor. 相似文献
4.
Field measurements were conducted in Mont-Saint-Michel Bay, a megatidal embayment (spring tidal range of 15 m), in order to monitor, over the course of a tidal cycle, sediment transport variability due to waves and tides on the upper part of a tidal flat characterised by shallow water depths. Sensors used to measure currents, water depth and turbidity were installed just above the bed (0.04 m). Two experiments were conducted under contrasting hydrodynamic conditions. The results highlight wave activity over the tidal flat even though observed wind waves were largely dissipated due to the very shallow water depths. Very high suspended sediment concentrations (up to 6 kg/m3) were recorded in the presence of wave activity at the beginning of the local flood, when significant sediment transport occurred, up to 7 times as much as under conditions of no wave activity. This influence may be attributed to the direct action of waves on bed sediments, to wave-induced liquefaction, and to the erosive action of waves on tidal channel banks. The sediment composition, comprising a clay fraction of 2-5%, may also enhance sediment transport by reducing critical shear stress through the sand lubrication effect. The results also show that antecedent meteorological conditions play an important role in suspended sediment transport on the tidal flat. Total sediment flux directions show a net transport towards the inner part of the bay that contributes to deposition over the adjacent salt marshes, and this tendency also prevails during strong wave conditions. Such sediment transport is characterised by significant variability over the course of the tidal cycle. During fair and moderate weather conditions, 83% and 71% of the total flux was observed, respectively, over only 11% and 28% of the duration of the local tidal cycle and with water depths between 0.04 and 0.3 m. These results suggest that in order to improve our understanding of sediment budgets in this type of coastal environment, it is essential to record data just at the beginning and at the end of tidal submergence close to the bed. 相似文献
5.
在沙纹床面输沙过程中，假设水流从涡中取出并搬运的悬移质数量与推移质运动的沙星成比例，由12组细沙实验结果得到了沙纹床面净输沙的方向和输沙强度公式，并与他人的实验结果进行对比。 相似文献
6.
Empirical formulas have been developed to calculate the fractional bed-load and suspended-load transport rates and near-bed suspended-load concentration under non-breaking waves and currents for coastal applications. The formulas relate the bed-load transport rate to the grain shear stress, the suspended-load transport rate to the energy of the flow system, and the near-bed suspended-load concentration to the bed-load transport rate, velocity and layer thickness. Adequate methods are adopted to determine the bed shear stress due to coexisted waves and currents. The hiding and exposure mechanism in nonuniform bed material is considered through a correction factor that is related to the hiding and exposure probabilities and in turn the size composition of bed material. The developed formulas have been tested using a large database of single-sized sediment transport and several sets of multiple-sized sediment transport data collected from literature, and compared with several existing formulas. The developed formulas can provide reasonably good predictions for the test cases. 相似文献
7.
Alan M. Davies Jiuxing Xing John M. Huthnance Philip Hall Laurenz Thomsen 《Progress in Oceanography》2002,52(2-4)
A three dimensional time-dependent baroclinic hydrodynamic model, including sediment transport and incorporating a turbulence energy sub-model, is used in cross sectional form to examine sediment movement at the shelf edge off North West Iberia at 42°40.5’N where measurements were made as part of the OMEX-II programme. These calculations are complemented by a simpler, in essence time-independent model, which is used to examine the sensitivity of the sediment distribution over the slope (from a shelf-break source) to changes in the specified values of horizontal and vertical diffusion coefficients. The philosophy of the paper is to use idealized tidal, wind and wind wave forcing to examine changes in sediment distribution resulting from these processes. Calculations with the time-dependent and steady state models give insight into both the role of events and long-term effects. The steady state model focuses on the off-shelf region, whilst the time-dependent model considers on-shelf events.Tidal calculations showed that for the stratification used here the internal tide in the OMEX region was primarily confined to the shelf edge and ocean. A mean on-shelf sediment transport in the surface layer and off-shelf transport at the bed was found. Across-shelf circulations produced by up-welling/down-welling favourable winds gave rise to on-shelf/off-shelf currents in the bottom boundary layer with an opposite flow in the surface layer. In the case of an up-welling favourable wind, sediment suspension was at a maximum in the near coastal region, with sediment being advected off shore in the surface layer. With a down-welling favourable wind, surface sediment was advected towards the shore, but there was offshore transport at the bed. Near the shelf edge any upwelling flow had the tendency to return this sediment to the surface layer from whence it was transported on-shore. So in essence the sediment was trapped within an on-shelf circulation cell. Wind waves effects increased the total bed stress and hence the sediment concentration and its transport, although its pattern was determined by tidal and wind forcing.The time independent model with increased/decreased lateral diffusivity gave an enhanced/reduced horizontal sediment distribution for a given settling velocity. As the settling velocity increases, the down-slope movement of sediment is increased, with a reduction in the thickness of the near-bed sediment layer, but with little change in its horizontal extent. 相似文献
8.
DOU Xiping LI Tilai DOU Guoren
Senior Engineer River Harbour Engineering Department Nanjing Hydraulic Research Institute Nanjing P. R. China Senior Engineer Nanjing Institute of Hydrology Water Resourses Nanjing P. R. China
Academician Nanjing Hydraulic Research Institute Nanjing P. R. China 《中国海洋工程》1999,(3)
Based on the non-equilibrium suspended load transport equation,bed load transport equationand sediment transport capacity formulas derived by Dou et al.,a 2-D numerical model of total sedimenttransport in the Yangtze Estuary is presented.In the model,the actions of tidal currents and wind waves andthe effect of salinity on sediment transport are considered.An automatically generated boundary-fitted grid isused to fit the boundaries of the estuary and the boundaries of engineering projects.The verification of calcu-lations shows that the sediment concentration,the deformation of riverbed and siltation in the channels causedby typhoons can be successfully simulated. 相似文献
9.
Onshore sandbar migration at Tairua Beach (New Zealand): Numerical simulations and field measurements 总被引：1，自引：0，他引：1
B. van Maanen P.J. de Ruiter Giovanni Coco K.R. Bryan B.G. Ruessink 《Marine Geology》2008,253(3-4):99-106
We observed the onshore migration (3.5 m/day) of a nearshore sandbar at Tairua Beach, New Zealand during 4 days of low-energy wave conditions. The morphological observations, together with concurrent measurements of waves and suspended sediment concentrations, were used to test a coupled, wave-averaged, cross-shore model. Because of the coarse bed material and the relatively low-energy conditions, the contribution of the suspended transport to the total transport was predicted and observed to be negligible. The model predicted the bar to move onshore because of the feedback between near-bed wave skewness, bedload, and the sandbar under weakly to non-breaking conditions at high tide. The predicted bathymetric evolution contrasts, however, with the observations that the bar migrated onshore predominantly at low tide. Also, the model flattened the bar, while in the observations the sandbar retained its steep landward-facing flank. A comparison between available observations and numerical simulations suggests that onshore propagating surf zone bores in very shallow water (< 0.25 m) may have been responsible for most of the observed bar behaviour. These processes are missing from the applied model and, given that the observed conditions can be considered typical of very shallow sandbars, highlight a priority for further field study and model development. The possibility that the excess water transported by the bores across the bar was channelled alongshore to near-by rip-channels further implies that traditional cross-shore measures to judge the applicability of a cross-shore morphodynamic model may be misleading. 相似文献
10.
J.S.M. van Thiel de Vries M.R.A. van Gent D.J.R. Walstra A.J.H.M. Reniers 《Coastal Engineering》2008,55(12):1028-1040
Large-scale physical model tests were conducted with different wave periods to examine the physical processes driving dune erosion. The model tests have been carried out in a flume (2DV) with a sandy dune exposed to extreme surge and wave conditions [Van Gent, M.R.A., Van Thiel de Vries, J.S.M., Coeveld, E.M., De Vroeg, J.H. and Van de Graaff, J., 2008. Large-scale dune erosion tests to study the effect of wave periods. Coastal Engineering. doi:10.1016/j.coastaleng.2008.04.003.]. Detailed measurements in time and space of water pressure, flow velocities and sediment concentrations were performed in the near shore area. The data revealed that both short- and long waves are important to inner surf hydrodynamics. Depth averaged flows are directed offshore and increase towards the shore line. The corresponding mean sediment concentrations rise sharply towards the dune face (up to 50 g/l near the bed). The strong increase in the mean sediment concentration towards the dune face correlates well with the maximum wave surface slope which in turn is coupled to both the pressure gradient and the near-bed wave-breaking induced turbulence. Analysis shows that the pressure gradient is only partially coupled to the flow acceleration suggesting that the latter cannot always be used as a proxy for the first. Weak correlation is obtained with the near-bed flows related to the bed shear stress. Tests with a larger wave period resulted in a larger dune erosion volume. During these tests more wave energy (combined incident and infragravity waves) reached the dune face, but more importantly, this wave energy is dissipated by fewer waves resulting in more intense wave breakers and steeper wave fronts. It is therefore expected that the wave-breaking induced near-bed turbulence increases resulting in significantly higher (O(100%)) mean sediment concentrations. In addition the mean flow velocities are comparable, yielding a substantially larger offshore directed sediment transport capacity. This increase in offshore directed transport is only partially compensated by a concurrent increase in the wave related onshore transport capacity associated with intrawave processes, resulting in a net increase in the dune erosion rate. 相似文献
11.
Estimates have been made of the suspended sand transport at two sites on the Middelkerke Bank, in the southern North Sea, from suspended sand profiles and current meter measurements over a period of approximately 40 days. Sand resuspension was mainly due to waves while transport was dominated by a few hours when large waves coincided with peak flood currents. Soulsby's relationships for the stress under combined currents and waves were found to be poor predictors for the observed near-bed concentrations; the mean stress,
, predicting 45% of the variance while the maximum stress,
, predicted just 15%, and overestimate the effects of the waves. When the influence of the stress due to the waves is reduced, the variance explained increases to 67%. The sand transport rate on the steep slope of the bank was 10 times that of the southern end, and was up-slope at 25° to the bank axis, in the direction of the major axis of the tidal ellipse. The transport on the steep slope was mainly in the size range 100–140 μm which did not occur in any significant proportion in samples of the sea bed at that site but was advected from deeper water to the southeast. Excluding this finer component the transport rates of coarser sand (>200 μm) at the two sites were similar over the 40-day period. The up-slope transport during storms suggests that waves play an important part in the bank maintenance and are not simply the mechanism which prevents the continual growth of the sand bank due to asymmetrical transport by the tidal currents alone. The transport rates are consistent with a time-scale of 102–103 years for the formation of the Middelkerke Bank. 相似文献
12.
量测了在水深0.5m的情况下波浪、水流通过水平沙床所产生的床沙输移。实验波高为0.15m，周期分别为1.4和2.0s。首先量测纯波浪下的床沙输移，然后量测波流共同作用下，水流与波浪行进方向一致其稳定速度分别为0.02,0.04,0.06m/s时的床沙输移，结果表明，2个沙槽所得的总输沙率在波周期2.0s时最大，净输沙率在波周期1.4s时最大，将波叠加在速度为0.02m/s的水流上时，2种波型的净输沙率都增加约1倍，水流为0.04m/s和0.06m/s时2种波型的净输沙率分别都减少。 相似文献
13.
Owing to lack of observational data and accurate definition,it is difficult to distinguish the Kuroshio intrusion water from the Pacific Ocean into the South China Sea(SCS).By using a passive tracer to identify the Kuroshio water based on an observation-validated three-dimensional numerical model MITgcm,the spatio-temporal variation of the Kuroshio intrusion water into the SCS has been investigated.Our result shows the Kuroshio intrusion is of distinct seasonal variation in both horizontal and vertical directions.In winter,the intruding Kuroshio water reaches the farthest,almost occupying the area from 18°N to 23°N and 114°E to 121°E,with a small branch flowing towards the Taiwan Strait.The intrusion region of the Kuroshio water decreases with depth gradually.However,in summer,the Kuroshio water is confined to the east of 118°E without any branch reaching the Taiwan Strait;meanwhile the intrusion region of the Kuroshio water increases from the surface to the depth about 205 m,then it decreases with depth.The estimated annual mean of Kuroshio Intrusion Transport(KIT) via the Luzon Strait is westward to the SCS in an amount of –3.86×106 m3/s,which is larger than the annual mean of Luzon Strait Transport(LST) of –3.15×106 m3/s.The KIT above 250 m accounts for 60%–80% of the LST throughout the entire water column.By analyzing interannual variation of the Kuroshio intrusion from the year 2003 to 2012,we find that the Kuroshio branch flowing into the Taiwan Strait is the weaker in winter of La Ni?a years than those in El Ni?o and normal years,which may be attributed to the wind stress curl off the southeast China then.Furthermore,the KIT correlates the Ni?o 3.4 index from 2003 to 2012 with a correlation coefficient of 0.41,which is lower than that of the LST with the Ni?o 3.4 index,i.e.,0.78. 相似文献
14.
潮流场对渤、黄、东海陆架底质分布的控制作用 总被引：10，自引：0，他引：10
朱玉荣 《海洋地质与第四纪地质》2001,21(2):7-13
运用二维潮流数学模型，模拟了渤、黄、东海陆架的M2潮汐、潮流。结果表明，渤、黄、东海陆架的潮流有强弱之分以及往复流和旋转汉之别。在此基础上，计算了8种粒径沙的湖平均悬移输沙率、潮平均推移输沙以及相应的输沙率散度。根据输沙率散度的正负，划分了海底冲刷区与淤积区。根据不同粒径泥沙输沙率散度的相对大小，确定出海底的主要底质类型为砂质沉积、粉砂质泥沉积和以粉砂为主的混合沉积。计算结果表明，海底3种主要底负类型的分布格局与海底的冲淤格局以及与输沙率矢量的发散和聚合状况基本一致。在渤、黄、东海陆架，沙脊主要在强往复流区形成，沙席主要在强或较强的旋转流区形成，泥质沉积主要在弱潮流区形成。砂质沉积、泥质沉积以及混合沉积这3种主要底质类型并非孤立存在，而是受渤、黄、东海陆架潮流场控制而形成的一个完整的潮流沉积体系。渤、黄、东海陆架的砂质沉积与泥质沉积并非残留沉积，而是潮流沉积。在没有冷涡的情况下，黄、东海陆架的典型泥质沉积在弱潮流环境中同样可以形成，因此，认为冷涡并非黄、东海陆架典型泥质沉积形成的必要条件。 相似文献
15.
Barotropic tide in the northeast South China Sea 总被引：2，自引：0，他引：2
Beardsley R.C. Duda T.F. Lynch J.F. Irish J.D. Ramp S.R. Ching-Sang Chiu Tswen Yung Tang Yang Y.-J. Guohong Fang 《Oceanic Engineering, IEEE Journal of》2004,29(4):1075-1086
A moored array deployed across the shelf break in the northeast South China Sea during April-May 2001 collected sufficient current and pressure data to allow estimation of the barotropic tidal currents and energy fluxes at five sites ranging in depth from 350 to 71 m. The tidal currents in this area were mixed, with the diurnal O1 and K1 currents dominant over the upper slope and the semidiurnal M2 current dominant over the shelf. The semidiurnal S2 current also increased onshelf (northward), but was always weaker than O1 and K1. The tidal currents were elliptical at all sites, with clockwise turning with time. The O1 and K1 transports decreased monotonically northward by a factor of 2 onto the shelf, with energy fluxes directed roughly westward over the slope and eastward over the shelf. The M2 and S2 current ellipses turned clockwise and increased in amplitude northward onto the shelf. The M2 and S2 transport ellipses also exhibited clockwise veering but little change in amplitude, suggesting roughly nondivergent flow in the direction of major axis orientation. The M2 energy flux was generally aligned with the transport major axis with little phase lag between high water and maximum transport. These barotropic energy fluxes are compared with the locally generated diurnal internal tide and high-frequency internal solitary-type waves generated by the M2 flow through the Luzon Strait. 相似文献
16.
苏北中部滨海平原成陆机制研究 总被引：8，自引：0，他引：8
苏北中部滨海平原位于废黄河三角洲和长江三角洲之间，其形成与全新世最大海侵之后长江、古黄河的供沙历史和供沙状况密切相关，并且现今海域南黄海辐射沙洲的辐聚点也位于这段海岸，故探讨其成陆机制具有重要意义。本文数值模拟了公元８世纪时该区的Ｍ２潮汐、潮流，在此基础上，计算了７种粒径泥沙在当时潮流场中的净输运状况，划分了海底冲淤区。计算结果表明，公元８世纪时苏北岸外存在大致以东台为顶点的辐射状古潮流场，其分布格局与现今苏北岸外大致以京港为顶点的辐射关潮流场基本一致，该辐射状潮流场的存在是由当时台东岸外的独特驻潮波波腹所决定的。进入苏北岸外古辐射状潮流场中的泥沙，在辐聚、辐散的潮流作用下，每一个潮周期均自ＮＥ、ＳＥ方向向东台附近海域净输运泥沙，在东台附近海域发生淤积。由此认为，苏北中部滨海平原是大致以东台为顶点的辐聚、辐散潮 相似文献
17.
风暴过程中潮滩悬沙浓度和悬沙输运的变化及其动力机制——以长江三角洲南汇潮滩为例 总被引：1，自引：1，他引：0
悬沙浓度是淤泥质海岸重要的环境指标。为探讨潮滩悬沙浓度和悬沙输运对风暴事件的响应过程及其动力机制,于2014年9月"凤凰"台风过境前、中、后在长江三角洲南汇潮滩进行了现场观测,获得同步高分辨率的水深、波高、近底流速和浊度剖面时间序列(9个潮周期)。结果表明,风暴中平均和最大波高、波-流联合底床剪切应力、悬沙浓度和悬沙输运率可比平静天气高数倍;风暴期间高潮位低流速阶段悬沙沉降导致近底发育数十厘米厚的浮泥层(悬沙浓度大于10 g/L)。研究认为风暴事件中淤泥质海岸悬沙浓度和悬沙输运的剧烈变化其根本动力机制是风暴把巨大能量传递给近岸水体,进而显著增大波-流联合底床剪切应力,导致细颗粒泥沙再悬浮。 相似文献
18.
A previously published wave-averaged version of Bailard's sediment transport formulation, intended for use in a numerical model of shelf sand transport, is compared against available field observations from literature. The objective was to test the performance of the transport relation over the wide range of hydrodynamical conditions that can occur at sea. A modified data analysis method was used to assess the reliability of the field observations. The modification consists of a method to cluster the data into classes to enable statistical analysis. The sediment transport formulation is part of the classification method. The method is in principle also suitable to reduce the size of data sets of non-cohesive sediment transport obtained with modern electronic equipment. The results show that the quality of the published field observations is fair, and that the wave-averaged Bailard formulation performs well for low and medium transport regimes in both currents and waves. For those conditions, it yields a slight overprediction of the transports, and a nearly uniform behaviour as a function of the conditions. The formulation underestimates transport rates for very high flow velocities in absence of waves, which is in agreement with earlier findings. The present version of Bailard's wave averaged sediment transport formulation is suitable for computing the local transport rates of fine to coarse sand on continental shelves in conditions ranging from small currents to moderate currents combined with non-breaking waves. 相似文献
19.
粤西水东湾现代沉积环境特征与泥沙搬运路径 总被引：1，自引：0，他引：1
对粤西水东湾沉积地貌单元的现代沉积物分布特征分析与泥沙净搬运矢量计算表明，滨面斜坡沉积物主要由砂粒级物质组成，粒级参数Ｍｄ，ＱＤ和ＳＫ具有从海向岸、自东向西变化的总趋势，泥沙净搬运趋势以向岸和西北为主。落潮三角洲沉积物较其邻近滨面斜坡有所粗化，分选从中部向两侧变好，泥沙在落潮流与波浪驱动下沿落潮三角洲边缘向西运动。口门内潮汐通道深槽泥沙净搬运趋势指向湖。湖区的沉积物以泥质为主，分选中等至差，并形成绕涨潮三角洲的泥沙环流元。 相似文献
20.
L. D. Wright 《Geo-Marine Letters》1981,1(3-4):173-179
Benthic nearshore currents were measured continuously for a week over the subtidal zone fronting an open coast, macrotidal
beach (spring tide range 9.5 meters) in Northwestern Australia. The shore-parallel currents were dominated by the semidiurnal
tide; however pronounced asymmetries expressed the contributions of higher harmonics. Northerly flows at high tide were considerably
stronger and of longer duration than southerly flows at low tide. Considering the combined effects of sediment agitation by
waves and net transport by the tidal currents, it is shown that a mechanism may exist which could produce net northerly transport
of “bed load” and southerly transport of suspended load. 相似文献