Modeling the impact of wind and waves on suspended particulate matter fluxes in the East Frisian Wadden Sea (southern North Sea)   总被引：3，自引：1，他引：2  

Karsten A. Lettmann  Jörg-Olaf Wolff  Thomas H. Badewien 《Ocean Dynamics》2009,59(2):239-262

Suspended particulate matter (SPM) fluxes and dynamics are investigated in the East Frisian Wadden Sea using a coupled modeling system based on a hydrodynamical model [the General Estuarine Transport Model (GETM)], a third-generation wave model [Simulating Waves Nearshore (SWAN)], and a SPM module attached to GETM. Sedimentological observations document that, over longer time periods, finer sediment fractions disappear from the Wadden Sea Region. In order to understand this phenomenon, a series of numerical scenarios were formulated to discriminate possible influences such as tidal currents, wind-enhanced currents, and wind-generated surface waves. Starting with a simple tidal forcing, the considered scenarios are designed to increase the realism step by step to include moderate and strong winds and waves and, finally, to encompass the full effects of one of the strongest storm surges affecting the region in the last hundred years (Storm Britta in November 2006). The results presented here indicate that moderate weather conditions with wind speeds up to 7.5 m/s and small waves lead to a net import of SPM into the East Frisian Wadden Sea. Waves play only a negligible role during these conditions. However, for stronger wind conditions with speeds above 13 m/s, wind-generated surface waves have a significant impact on SPM dynamics. Under storm conditions, the numerical results demonstrate that sediments are eroded in front of the barrier islands by enhanced wave action and are transported into the back-barrier basins by the currents. Furthermore, sediment erosion due to waves is significantly enhanced on the tidal flats. Finally, fine sediments are flushed out of the tidal basins due to the combined effect of strong erosion by wind-generated waves and a longer residence time in the water column because of their smaller settling velocities compared to coarser sediments.

Karsten A. LettmannEmail:

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On the sensitivity of tidal residuals off the west coast of Britain to mesh resolution     

J. Eric Jones  Alan M. Davies 《Continental Shelf Research》2007

An irregular mesh model of the west coast of Britain is used to examine the sensitivity of tidal residuals to mesh resolution in the region. Computed residuals are compared with earlier published results determined with a high resolution (1 km grid) finite difference model of the eastern Irish Sea. Initial calculations show that tidal residuals are largest in nearshore regions particularly in the vicinity of headlands. Local refinement of the mesh in these regions leads to a more detailed picture of the flow field, particularly adjacent to the coast. Although large scale offshore features of the flow can be resolved using the high resolution finite difference model, such an approach leads to a “stair case” representation of the coastal boundary with an adjacent near coastal region of spurious tidal residuals. By using an irregular mesh that follows the coast, this effect is removed. In the Mersey river region the tidal residual is resolved with a mesh resolution of 120 m, although calculations show that its distribution is particularly sensitive to small scale features of the topography. A variable mesh that can accurately represent the lateral variations in river width and details of topography in both the nearshore and estuarine environment appears essential in modelling the coastal spread of freshwater plumes from rivers and pollutants discharged into the near coastal environment.  相似文献   

Benthic ecosystem development in an artificial tidal flat constructed from dredged spoil     

Ishii R  Nakano Y  Nakai S  Nishijima W  Okada M 《Marine pollution bulletin》2008,56(12):2059-2066

Dredged spoil (DS) was used as a silt and clay additive in the construction of artificial tidal flats from mountain sand (MS). As the ratio of DS in the sediment media increased, the number of emerging macrobenthos increased. The composition of the macrobenthic community was also affected by the addition of DS, and the changes might be dependent on the ratio of DS to MS. In addition, the macrobenthos in the artificial tidal flats was more abundant than that in the control tidal flat, which was constructed with natural tidal flat sediment. With a silt and clay content of 25%, polychaetes Ceratonereis erythraeensis and Capitella sp. and the gastropod Batillaria cumingii were dominant, whereas no bivalves were present. With less silt and clay (5% and 10%), the bivalves Ruditapes philippinarum and Musculista senhousia were observed in the artificial flats, while their numbers in the control tidal flat were lower.  相似文献   

Temporal and spatial variations in density and velocity fields of the waters of Gareloch,Scotland     

P. Lindsay 《Environmental Geology》1996,28(4):201-212

 Spatial variations in the density and velocity fields have been observed in the Gareloch (Scotland) during surveys in 1987–1988 and 1993–1994. The variation of the density field has been analyzed on a variety of time scales from semidiurnal to seasonal in order to quantify effects caused by the forcing factors of tidal mixing, freshwater input, and wind. Initial results indicate that water density in the loch is controlled (to a major degree) by the freshwater input from runoff from the local catchment area and from freshwater entering on the flood tide from the Clyde Estuary. It is estimated that during winter periods the high freshwater flows from the rivers Leven and Clyde into the Clyde Estuary account for up to 75% of the freshwater creating the density structure in the loch. Analysis of long-term dissolved oxygen data reveals that major bottom water renewals occurred between July and January in the years 1987–1994. Major bottom water dissolved oxygen renewals have a general trend but during the year sporadic renewals can take place due to abnormal dry spells increasing the density of the water entering from the Clyde, or consistently strong winds from the north reducing stratification in the loch and producing better mixed conditions. Velocities vary spatially, with the highest velocities of up to 0.6 m s^–1 being associated with the velocity jet effect at the constriction at the sill of the loch. Observed near-surface mid-loch velocities increased as the vertical density gradients in the upper layers increased. This indicates for the observed conditions that increased stratification in the upper layers inhibits the entrainment rate and hence rate of gain of thickness of the wind-driven surface layer, resulting in increased surface velocities for a given wind speed and direction. The main flow is concentrated in the upper 10 m and velocities below 10 m are low. Observed mean spring tide surface velocities are on average 30% greater than mean neap tide surface velocities. Received: 22 May 1995 · Accepted: 23 August 1995  相似文献   

长江口与杭州湾的泥沙与河床演变对上海港及其通海航道建设的影响   总被引：5，自引：0，他引：5  

林承坤 《地理学报》1990,45(1):78-89

在长江口与杭州湾泥沙和河床演变研究的基础上,对上海港的选址与建设及上海港通海航道的治理与利用,提出了新的设想。  相似文献   

CHARACTER OF SIMPLIFIED NAVIER-STOKES EQUATIONS FOR NEAR THE LEADING EDGE PART OF TWO-DIMENSIONAL LAMINAR FLOW PAST A FLAT PLATE     

田纪伟  王新生 《中国海洋湖沼学报》1994,12(4):351-360

Starting from the Simplified Navier-Stokes(SNS)equations presented at first by Godovachev-Kuzmin-Tsopov,and Gao Zhi,Davis,the authors analyze the character of the SNS equations for the laminarflow near the leading edge of a flat plate and far away from the plate by using the Weiner—Hopf meth-od and Fourier transform.It is proved that the solution of the SNS equations agree with the solution of the Navier-Stokes equations for flow near the leading edge of the plate and far away from the plate.How to match the solution of the SNS equations to the Blasius solution of the boundary layer equationsis also discussed.  相似文献   

Intercomparison between finite element and finite volume approaches to model North Sea tides     

Silvia Maßmann  Alexey Androsov  Sergey Danilov 《Continental Shelf Research》2010

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放射性同位素定年技术在崇明岛潮滩沉积速率上的应用研究   总被引：1，自引：0，他引：1  

汤奇峰  黄园英  刘久臣  徐清  王晓春  谭科艳  刘晓端 《岩矿测试》2010,29(6):667-673

选取崇明岛北侧由东至西4个潮滩沉积柱,分析137Cs、226Ra和210Pb放射性比活度,应用210Pb和137Cs放射性同位素定年方法计算崇明岛潮滩沉积物沉积速率。对于东西两端,210Pb方法测得速率分别为3.08cm/a和2.34 cm/a,而137Cs测得速率分别为6.19 cm/a和2.06 cm/a。结果表明,137Cs定年方法计算出的潮滩沉积速率普遍大于210Pb方法结果;但两者反映了相同的速率规律。崇明岛主力生长方向为东和东北,西侧沉积作用相对较弱,表现出"东快西慢"的特点。沉积纵向上,1954年以来,自下而上沉积速率逐渐减缓。  相似文献   

Modelling impact of northerly wind-generated waves on sediments resuspensions in the Dover Strait and adjacent waters     

Nicolas Guillou  Georges Chapalain 《Continental Shelf Research》2011,31(18):1894-1903

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Ammonium adsorption by tidal flat surface sediments from the Yangtze Estuary   总被引：12，自引：0，他引：12  

L.?J.?Hou  M.?LiuEmail author  H.?Y.?Jiang  S.?Y.?Xu  D.?N.?Ou  Q.?M.?Liu  B.?L.?Zhang 《Environmental Geology》2003,45(1):72-78

Ammonium adsorption by sediments plays an important role in the cycle of nitrogen in the estuarine tidal flat ecosystem. Ammonium adsorption on tidal flat sediments from the Yangtze estuary was studied using the simulation experiment. The findings indicated that there was linear adsorption by the tidal flat sediments for the lower ammonium concentration (<10 mM) in the overlying waters. The adsorption coefficient of ammonium in the study area ranged from 3.81 to 9.00, and had a significant positive correlation with total organic carbon (r = 0.779, = 0.02284 , n=8), reflecting that organic matter might be one of the main factors controlling the behavior of ammonium adsorption. It also showed that salinity had a pronounced effect on ammonium adsorption, and that salinity affected the distribution of ammonium between the sediments and waters. The amount of ammonium adsorption on sediments gradually decreased with the increasing salinity. Especially within the range of lower salinity, just a little change of salinity had a dramatic influence on ammonium adsorption by sediments.  相似文献