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31.
Morphodynamics of ebb-tidal deltas: a model approach 总被引：1，自引：0，他引：1
S. M. van Leeuwen M. van der Vegt H. E. de Swart 《Estuarine, Coastal and Shelf Science》2003,57(5-6):899-907
The results of 2DH numerical models of the Frisian Inlet (located in the Dutch Wadden Sea) are discussed to gain further knowledge about the physical mechanisms causing the presence of both ebb-tidal deltas and of channels and shoals in tide-dominated inlet systems. A hydrodynamic model, extended with sediment transport formulations, was used to verify earlier conceptual models that deal with ebb-tidal delta characteristics. The model does not confirm their hypothesis concerning the observed spatial asymmetry of ebb-tidal deltas and suggests that long-term morphological simulations are needed to understand this aspect. Furthermore, the model indicates that the initial formation of the ebb-tidal delta is mainly due to convergence of the tidally averaged sediment flux related to residual currents, whilst the net sediment transport in the basin is mainly caused by tidal asymmetry. A second model (accounting for feedbacks between tidal motion and the erodible bottom) was used to simulate the long-term bathymetric evolution of the Frisian Inlet under fair weather conditions. This model reproduces the gross characteristics of the observed morphology: the presence of a double-inlet system with two distinct ebb-tidal deltas having different sizes and the presence of channels and shoals. The role of the ‘Engelsmanplaat’, a consolidated shoal in the middle of the Frisian Inlet, was not found to be crucial for the morphodynamic stability of this inlet system. 相似文献
32.
The paper gives relationships for predicting reservoir circulation generated by radial and tangential jets. These relationships show the importance of the reservoir's aspect-ratio, and the Reynolds number of the jet.Details are also given of concentration-experiments using the conductivity and fluorimetric methods, and incorporating various inlet and outlet arrangements. Peripheral and radial dispersion-coefficients were obtained, and found to be of the same order of magnitude. These coefficients were dependent on the size of the model and on the local Reynolds numbers. The values of dispersion coefficients for reservoirs are similar to those for one-dimensional open channel flow. 相似文献
33.
The Relationships between Chemical Measures and Potential Predictors of the Eutrophication Status of Inlets 总被引：1，自引：0，他引：1
Measurements of nutrients, dissolved oxygen and trace metals in bottom waters, taken just before the fall turnover, have been evaluated as indicators of eutrophication in inlets. Samples for these analyses were collected in 34 inlets in eastern Canada. The dominant factor (31% of the variance of the dataset) from a principal component analysis of the resulting data was clearly related to eutrophication. This factor included phosphate, ammonia, silicate, dissolved oxygen, iron and manganese, but not cadmium and zinc. It was used to rank inlets according to eutrophication. Comparisons of these rankings with measures of inlet shape revealed that several measures of the significance of sills were good predictors of the eutrophication status. Tidal prism flushing times, and other geometric measures, were poor predictors of eutrophication. Measures of anthropogenic inputs to the inlets were also poor predictors of the eutrophication status: apparently natural processes dominate anthropogenic inputs in these inlets. 相似文献
34.
Alphonse Nahon Déborah Idier Nadia Sénéchal Hugues Féniès Cyril Mallet Julie Mugica 《地球表面变化过程与地形》2019,44(11):2112-2125
In coastal areas, sea level rise (SLR) and changing wave climates are expected to be the main oceanic drivers of shoreline adjustments. These drivers have been shown to vary on a wide spectrum of spatial and temporal scales. Nonetheless, a general rule about how this variability impacts global shorelines remains to be articulated. Here, we discuss the impacts of wave climate changes and SLR on the evolution of a barrier spit–inlet system over the last 250 years. The distal end of the Cap Ferret barrier spit, SW France, has undergone large-scale oscillations that were well correlated with variations of the decadal average of the winter North Atlantic Oscillation (NAO) index. The local wave climate hindcast supports that increased alongshore wave energy fluxes associated with the positive phase of the NAO were responsible for the updrift retreat of the spit. By opposition, the spit has elongated downdrift when waves were less energetic and more shore normal, as during the negative phase of the NAO. In addition, lower rates of SLR appeared to be necessary for the spit to develop, as higher rates of SLR very likely forced the adjacent inlet to enlarge, at the expense of the spit. These results should help to predict and detect coastal adjustments driven by climate change and by climate variability. © 2019 John Wiley & Sons, Ltd. 相似文献
35.
The morphological changes of spits and inlets of the Chilika lagoon, the largest brackish water tropical coastal lagoon in Asia, are investigated using real-time kinematic GPS observation and numerical models during 2009–2013. The seasonal/interannual variations of the spit and inlet cross-sectional areas with varying widths and depths are recorded in association with different physical processes. The results show significant changes in spit morphology: particularly, the south spit accreted continuously, while the middle and north spits eroded. The cross-sectional depth of inlets becomes narrower and deeper during summer and winter seasons, while they are wider and shallower during the monsoon. The model results show that sediment transport rate is larger during monsoon and summer, while it is relatively less during the winter. Alongshore, sediment transport is predominantly northward throughout the study period. The result shows that gain/loss of the spits and closure/opening of inlets are significantly controlled by the high wave power, longshore drifts, and river discharge. The study demonstrates that the combined use of observational and numerical models is very effective to understand the changes of spit and inlet morphology and their impact on ecological conditions of the lagoon environment. 相似文献
36.
Estuarine processes in the arctic lagoons are among the least studied but important subjects, especially considering the rapid warming of arctic water which may change the length of ice-free period in the summer. In this paper, wind-driven exchange flows in the micro-tidal Elson Lagoon of northern Alaska with multiple inlets of contrasting widths and depths are studied with in situ observations, statistical analysis, numerical experiments, a regression model on the basis of dynamics, and remote sensing data. Water velocity profiles were obtained from a bottom deployed acoustic Doppler current profiler(ADCP) in the northwestern Eluitkak Pass connecting the Beaufort Sea to the Elson Lagoon during a 4.9 day ice-free period in the summer of 2013. The subtidal flow is found correlated with wind(R~2 value ～96%). Frequently occurring east, northeast and north winds from the arctic atmospheric high-and low-pressure systems push water from the Beaufort Sea into the lagoon through the wide inlets on the eastern side of the lagoon, resulting in an outward flow against the wind at the narrow northwestern inlet. The counter-wind flow is a result of an uneven wind forcing acting through the asymmetric inlets and depth,an effect of "torque" or vorticity. Under northwest wind, the exchange flow at the northwestern inlet reverses its direction, with inward flows through the upwind northwestern inlet and outward flows through the downwind eastern inlets. A regression model is established based on the momentum equations and Taylor series expansions. The model is used to predict flows in July and August of 2015 and July of 2017, supported by available Landsat satellite images. About 73%–80% of the time the flows at Eluitkak Pass are out of Elson Lagoon for the summer of 2015 and 2017. Numerical experiments are conducted to corroborate the findings and illustrate the effects under various wind conditions. A quasi-steady state balance between wind force and surface pressure gradient is confirmed. 相似文献
37.
INTRODUCTIONTidalchannelsareimportantgeomorphologicunitsalongsiltcoasts.Theyhaveanevidentfunc tionfortidalflatbecausetheyareassociatedwithitsrapidbayheadwarderosionandlateralswing ing.Thetidalchannelsdevelopalongthecoastandplayanimportantroleinseaandlandinterac tion .Manyscientistsresearchedthetidalchannels (Bayliss Smith ,1 978;Shao ,1 988;Zhang ,1 995) .TheScientificandTechnicalCommitteeofShandongProvince (1 991 )investigatedthecoastoftheHuanghe (Yellow)RiverDeltaandresearchedtheti… 相似文献
38.
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
39.
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
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
40.
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