Long-term ferry-ADCP observations of tidal currents in the Marsdiep inlet   总被引：3，自引：1，他引：3  

Maarten Cornelis Buijsman  Herman Ridderinkhof 《Journal of Sea Research》2007,57(4):237-256

A unique, five-year long data set of ferry-mounted ADCP measurements in the Marsdiep inlet, the Netherlands, obtained between 1998 and 2003, is presented. A least-squares harmonic analysis was applied to the water transport, (depth-averaged) currents, and water level to study the contribution of the tides. With 144 tidal constituents, maximally 98% of the variance in the water transport and streamwise currents is explained by the tides, whereas for the stream-normal currents this is maximally 50%. The most important constituent is the semi-diurnal M₂ constituent, which is modulated by the second-largest S₂ constituent (about 27% of M₂). Compound and overtides, such as 2MS₂, 2MN₂, M₄, and M₆, are important in the inlet. Due to interaction of M₂ with its quarter-diurnal overtide M₄, the tidal asymmetry in the southern two thirds of the inlet is flood dominant. The amplitudes of all non-astronomic constituents are largest during spring tides, strongly distorting the water level and velocity curves. The M₂ water transport is 40° ahead in phase compared to the M₂ water level, reflecting the progressive character of the tidal wave in the inlet. The currents are strongly rectilinear and they are sheared vertically and horizontally, with the highest currents at the surface above the deepest part of the inlet. During spring tides, near-surface currents can be as large as 1.8 m s^− 1. Due to the relative importance of inertia compared to friction, the M₂ currents near the centre (surface) lag maximal 20° (3°) in phase with the currents near the sides (bottom). The tidal-mean currents are directed into the basin in the shallower channel to the south and out of the basin in the deeper channel to the north.  相似文献   

The measurement of sand transport in two inlets of Venice lagoon,Italy     

C.L. Amos  M. Villatoro  R. Helsby  C.E.L. Thompson  L. Zaggia  G. Umgiesser  V. Venturini  D. Are  T.F. Sutherland  A. Mazzoldi  F. Rizzetto 《Estuarine, Coastal and Shelf Science》2010

Sand transport in Lido and Chioggia inlets was measured using modified Helley–Smith sand traps equipped with 60-micron nets. The traps had an efficiency of about 4% only but provided enough material for analysis. Very fine sand (0.07 < d < 0.11 mm) only was collected in the traps. Transport of sand was greatest in the bottom 10% of the water column and followed a Rouse profile. Sand extended to a height of about 4 m above the bed during peak flows corresponding to the estimated thickness of the boundary layer; and observed in synoptic ADCP profiles. The sand in the benthic boundary layer was largely inorganic (>95%); above this layer, organic content varied widely and was greatest near the surface. The movability number Ws/U_∗$W_s/U_{\ast }$ showed a linear relationship to dimensionless grain diameter (D_*): (Ws/U_∗)=(D_∗/10)$\left(W_s/U_{\ast }\right)=\left(D_{\ast }/10\right)$; D_* < 10. Sand concentration in suspension was simulated by a mean Rouse parameter of −2.01 ± 0.66 (Lido inlet) and −0.82 ± 0.27 (Chioggia inlet). The β parameter ( Hill et al., 1988) was correlated with D_* and movability number in the form: β=2.07−2.03D_∗+59(Ws/U_∗)²$\beta =2.07-2.03D_{\ast }+59{\left(W_s/U_{\ast }\right)}^2$ (r² = 0.42). Von Karman's constant was back-calculated from a Law of the Wall relationship as a test on the accuracy of U_* estimates; a mean value of 0.37 ± 0.1 (compared to the accepted value of 0.41) suggest U_* was accurate to within 10%. The constant of proportionality (γ = 3.54 × 10⁻⁴) between reference concentration (C_a) and normalized excess bed shear stress was in line with the published literature.  相似文献   

Forcing of large-scale cycles of coastal change at the entrance to Willapa Bay, Washington     

Robert A. Morton  H. Edward Clifton  Russell L. Peterson 《Marine Geology》2007,246(1):24-41

Anomalous morphological features within large estuaries may be: (1) recorders of external forces that periodically overwhelm the normal morphodynamic responses to estuarine energy fluxes, and (2) possible predictors of cycles of future coastal change. At the entrance to Willapa Bay, Washington, chronic beach erosion and frequent coastal flooding are related to the historical northward channel migration that destroyed the protective sand spits of Cape Shoalwater. Northward channel migration since the late 1800s conforms to the long-term net sediment transport direction. What requires explanation is periodic southward relocation of the trunk channel by as much as 5 km, and attendant construction of moderately large sand spits on the north side of the bay such as Kindred Island, Tokeland Peninsula, and Cape Shoalwater.Both autocyclic and allocyclic processes may have been responsible for trunk channel realignment and associated spit deposition. Channel recycling may occur when the main channel becomes overextended to the north and the tidal flow is inefficient because of its decreased gradient and increased susceptibility to shoaling by the growth and migration of tidal sand ridges. Under those conditions trunk channel relocation would be facilitated by increased wave heights and water levels of El Niño winter storms. However, co-seismic subsidence is the most likely mechanism for abruptly increasing sand supply and longshore transport that would favor discrete periods of channel relocation and spit deposition. Unless external forcing changes sand supply and predominant sediment transport directions in the future, the relative rise in sea level, frequent winter storms, and local deficit in the sand budget assure that beach erosion will continue at the mouth of this large estuary.  相似文献   

Along channel flow and sediment dynamics at North Inlet, South Carolina     

Christopher A. Wargo  Richard Styles   《Estuarine, Coastal and Shelf Science》2007,71(3-4):669-682

In May of 2005, an observational program was carried out to investigate the along channel hydrodynamics and suspended sediment transport patterns at North Inlet, South Carolina. Along channel variability, which is important in establishing sediment transport pathways, has not been characterized for this system. Measurements of water column currents, salinity, bed sediment, suspended sediment concentration, and particle size distribution were obtained over a complete tidal cycle along the thalweg of the inlet entrance. Along channel currents, shear stress and bed sediment distributions vary significantly in space and time along a 3 km section bracketing the inlet throat. Most of the variability is consistent with geomorphic controls such as bed elevation variability and channel width. The highest velocities, shear stresses, suspended sediment concentration and bed sediment grain size are observed in the narrowest section of the inlet throat. Magnitudes systematically decrease along the channel toward the marsh as changes in channel geometry and branching reduces flow energy. Due to tidal asymmetry, the ebb phase contains significantly higher currents and associated sediment transport. Over the complete tidal cycle, depth integrated transport is directed towards the marsh landward of the intersection of Town and Debidue Creek. In contrast, net transport is out of the inlet seaward of this intersection. Sediment grain size distributions show 35% more material less than 63 μm on flood, suggesting net landward transport of fines.  相似文献   

山东荣成月湖潮汐汊道的时间-流速不对称特征   总被引：3，自引：3，他引：3  

贾建军  高抒  薛允传 《海洋学报》2003,25(3):68-76

月湖是山东半岛东端的一个小型潮汐汊道.在月湖进行了潮位、潮汐观测及地形测量,运用两种方法从潮位记录推算出口门落潮主干道垂线平均流速和断面平均流速.发现除涨潮优势型和落潮优势型外,月湖还表现出另外两种时间-流速不对称,即涨潮历时大于落潮历时且涨潮流速大于落潮流速、涨潮历时小于落潮历时且涨潮流速小于落潮流速.月湖的时间-流速不对称特征与不规则潮汐、涨(落)潮的流速跟潮位的匹配关系、汊道口门的断面形态、口门特殊的水流结构及循环过程等因素有关.时间-流速不对称类型的研究,对于理解潮汐汊道系统的沉积动力行为及进行人工整治有一定意义.  相似文献   

潮汐汊道A-P关系中参数C和n的控制因素   总被引：7，自引：0，他引：7  

高抒  张红霞 《海洋科学》1997,21(4):23-27

与沿岸漂砂相联系的潮汐汊道系统达到均衡态时的Ａ－Ｐ关系可表示为Ａ－ＣＰ＾ｎ。根据对Ａ－Ｐ关系的模拟，本文提出在均衡条件下ｎ值必然大于１，潮汐汊道Ａ－Ｐ关系表现出弱分形现象。其原因是对应于一定强度的沿岸漂砂较小汊道以口门宽度减小，流速增大来维持均衡关系。模拟实验还表明，参数Ｃ的大小与沿岸输砂率、淡水径流量和潮汐类型有关，这些因素对参数ｎ稍有影响。前人研究有时遇到ｎ〈１的情况，这可能是由于统计分计的某  相似文献   

Long‐term morphological impacts of the opening of a new inlet on a multiple inlet system     

A. Pacheco  Ó. Ferreira  J. J. Williams 《地球表面变化过程与地形》2011,36(13):1726-1735

In this study, the artificial opening of a new tidal inlet in an existing multiple inlet system is shown to significantly modify the adjacent nearshore and backbarrier morphology, as well as both updrift and downdrift shorelines. The study focuses on the dominant Faro‐Olhão and Armona inlets in the Ria Formosa barrier island system of southern Portugal. The equilibrium state and future evolution of the system are inferred using a range of morphological and hydrodynamic indicators, including the evolution of the inlet cross‐section, changes in tidal prism, and changes in the dimensions (length and area) of barrier islands. The results reveal how the morphology of an interconnected two‐inlet bay system and the adjacent coastlines has evolved following the artificial opening and stabilization of Faro‐Olhão inlet since 1929. A clear relationship between barrier island size, inlet cross‐section/width, and tidal prism is demonstrated. Decadal time‐scale changes in the tidal prism of the two interconnected inlets are shown to be the main mechanism responsible for morphological change, and have resulted in the remobilization of ebb‐tidal delta sediments deposited during previous hydraulic configurations. These changes, in turn, have contributed to a narrowing of Armona inlet and an increase in the size of Culatra Island. The work highlights the importance of ebb‐tidal deltas both as sand reservoirs and as conduits through which sand exchange between estuaries or lagoons and the open coast is regulated. It also shows the pivotal role of ebb‐tidal deltas in trapping longshore‐transported sediment and releasing it again during periods of increased wave activity. The findings have implications regarding the accurate assessment of the stability of multiple inlet systems. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

湛江港潮汐汊道落潮三角洲沉积动力过程   总被引：6，自引：1，他引：6  

张乔民  郑德延 《地理学报》1995,50(5):421-429

湛江港是华南海岩规模最大的中潮溺谷湾型潮汊道港湾，口外发育规模巨大、形态典型的落潮三角洲。依据据现场调查资料分析，落潮三角洲具有马蹄形浅滩包围中央深槽的地貌结构，由中心至周边为粗砂至极细砂同心半圆带状分布的表层沉积分布，中央深槽落潮流动力为主，周边浅滩波潮流动力为主的动力场结构。  相似文献