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1.
《Coastal Engineering》2006,53(8):691-704
Water level and current measurements from two virtually enclosed South Pacific atolls, Manihiki and Rakahanga, support a new lagoon flushing mechanism which is driven by waves and modulated by the ocean tide for virtually enclosed atolls. This is evident because the lagoon water level remains above the ocean at all tidal phases (i.e., ruling out tidal flushing) and because the average lagoon water level rises significantly during periods with large waves. Hence, we develop a model by which the lagoons are flushed by waves pumping of ocean water into the lagoon and gravity draining water from the lagoon over the reef rim. That is, the waves on the exposed side push water into the lagoon during most of the tidal cycle while water leaves the lagoon on the protected side for most of the tidal cycle. This wave-driven through flow flushing is shown to be more efficient than alternating tidal flushing with respect to water renewal. Improved water quality should therefore be sought through enhancement of the natural wave pumping rather than by blasting deep channels which would change the system to an alternating tide-driven one. 相似文献
2.
Very small waves and associated sediment resuspension on an estuarine intertidal flat 总被引：2，自引：0，他引：2
Field data from a microtidal estuarine intertidal flat (Tamaki estuary, New Zealand) are used to analyse very small waves (height <10 cm; period 1.0–1.8 s) and associated sediment resuspension under light winds. Mean spectral period at the bed varied over the tidal cycle, driven by changes in surface-wave spectrum and depth-attenuation of orbital motions. Wave-orbital currents exceeded 30 cm/s, disturbing the fine-sand (100–200 μm) matrix of the seabed and resulting in the release of fine silt (particle size <20 μm) at concentrations >120 mg/L. Resuspension was initiated when ∼40% of the maximum zero-downcrossing orbital speeds in a burst exceeded the critical speed for initiation of sediment motion. Sediment concentrations were highest around low tide, when waves were smaller compared to high tide because of a reduced fetch but depth-attenuation of orbital motions was less because the water was shallower. Wave period exerted a control on sediment resuspension through the wave friction factor. There was a hysteresis in the wave Reynolds number such that it was greater on the ebbing tide compared to on the flooding tide: since it did not exceed 3 × 105 the bed was hydraulically smooth, and the wave friction factor therefore is inversely proportional to wave period. Hence, the tidal-cycle hysteresis in wave Reynolds number translated into a smaller wave friction factor on the ebbing tide, and accounting for this caused the ebb and flood sediment concentration data to collapse onto one curve when plotted against wave-induced skin friction. A simple model is presented to evaluate the relative contribution to sediment resuspension of waves associated with weak and strong winds. At the base of the flat (waves competent to resuspend sediment for 5% of the inundation time), waves associated with stronger, infrequent winds dominate resuspension. At the top of the flat (waves competent to resuspend sediment for 30% of the inundation time), waves associated with lighter, frequent winds dominate resuspension. Moderate winds – neither the strongest nor most frequently occurring – dominate resuspension integrated across the profile. The mass of sediment resuspended by waves is greatest towards the top of the flat: shoreward of this, resuspension is smaller because of wave dissipation; seaward of this, resuspension is smaller because of greater depth-attenuation of orbital motions. The location of maximum sediment mass resuspended by waves and the location of maximum duration of resuspension are not necessarily the same. 相似文献
3.
The aim of the present study was to investigate seasonal and spatial patterns of soil oxygen consumption, nitrification, denitrification and fluxes of dissolved inorganic nitrogen (DIN) in a tidal salt marsh of the Lagoon of Venice, Italy. In the salt marsh, intact soil cores including overlying water were collected monthly at high tide from April to October in salt marsh creeks and in areas covered by the dominant vegetation, Limonium serotinum. In May, cores were also collected in areas with vegetation dominated by Juncus maritimus and Halimione portulacoides. In laboratory incubations at in situ temperature in the dark, flux rates of oxygen and DIN were monitored in the overlying water of the intact cores. 15N-nitrate was added to the overlying water and nitrification and denitrification were measured using isotope-dilution and -pairing techniques. The results show that highest soil oxygen consumption coincided with the highest water temperature in June and July. The highest denitrification rates were recorded in spring and autumn coinciding with the highest nitrate concentrations. Soil oxygen consumption and nitrification rates differed between sampling sites, but denitrification rates were similar among the different vegetation types. The highest rates were recorded in areas covered with L. serotinum. Burrowing soil macrofauna enhanced oxygen consumption, nitrification and denitrification in April and May. The data presented in this study indicate high temporal as well as spatial variations in the flux of oxygen and DIN, and nitrogen transformations in the tidal salt marshes of the Venice lagoon during the growth season. The results identify the salt marshes of the Venice lagoon as being metabolically very active ecosystems with a high capacity to process nitrogen. 相似文献
4.
5.
《Oceanologica Acta》1999,22(5):473-485
The hydrological features of Ria de Aveiro, a coastal lagoon on the northwest Atlantic coast of Portugal, were investigated in two sampling surveys carried out between 3/6 and 24/6/97 and between 29/6 and 7/7/97, respectively. There was a significant freshwater inflow into the lagoon during the first survey, especially in the first days, due to the recent rainfalls. Records concerning water level, salinity, temperature and current velocity were performed at several stations located along the four main channels of the lagoon. The type of tide at the mouth was determined and was observed that astronomical tide is the main forcing agent driving water circulation in Ria de Aveiro. The tide at the mouth is semidiurnal and the tidal wave propagation in the lagoon has the characteristics of a damped progressive wave. Typical estuarine longitudinal salinity and temperature gradients connected with the distance to the mouth were identified, whereas vertical and transverse gradients were found unimportant, except in the frontal zone between oceanic and fresh water masses. According to the results, even though Ria de Aveiro should be considered as vertically homogeneous, some channels may reveal characteristics of a partially mixed estuary, depending on the freshwater input. 相似文献
6.
本文以粤西水东湾表层沉积物样品的粒度分布为基本数据,使用对应分析方法并结合地形与波流特征,分析了海湾动力沉积环境。分析结果表明,海湾现代沉积环境可划分为4个动力沉积区。 相似文献
7.
The purpose of this study is to investigate the influence of tidal currents on sea ice in Spitsbergen fjords which may cause rapid decrease of the ice thickness due to erosion and melting of the ice. The effect was studied in-situ near the narrow channel connecting the Van Mijen Fjord and Lake Vallunden. The strong jet-like tidal currents in the strait driven by semidiurnal tide continue into the lake preventing ice freezing along a narrow strip during high tide and relatively warm weather. Understanding the formation of open water regions or regions with thin ice is important for the safe transportation on ice. We estimate conditions and representative time over which strong tidal current influences ice thickness along a narrow strip in solid ice. Changes of tidal phase and decrease in air temperature influence freezing of the strip in one-two days. While the tidal flow leaves the strait it overflows a shallow bar and generates internal lee waves propagating downslope and mixing the water. Tidal forcing of internal waves was measured using pressure gauges and by scanning of the ice surface during flood and ebb phases. Internal waves were measured using three types of CTD instruments and an ADCP current meter. The generation of wave packets occurs every tidal cycle when the current flows into the lake, but no generation occurs during the ebb phase of the tide because the currents over the bar slope are low. Parameters of internal waves are estimated. Model simulations confirm generation of internal wave train by the tidal current descending downslope. 相似文献
8.
King Sound is a 100-km-long embayment located in tropical northwestern Australia with a spring tidal range of 11 m. This is the second largest tide in the world after the Bay of Fundy in Canada. Intertidal areas cover about 800 km2. The upper reaches of the sound are turbid with fine suspended sediment concentration reaching 3 kg m−3. Field studies of the dynamics of water and fine sediment were carried out in the dry seasons of 1997 and 1998. The tide was a propagating wave, shoaling and dissipating by friction as it entered the sound. This mode of propagation generated an asymmetric tidal current with a stronger current at flood than at ebb. An evaporation-driven salinity maximum zone was found in the upper reaches of the sound, and this was also where the turbidity maximum occurred. Tidal pumping by the tidal asymmetry and, possibly, the biological filter formed by muddy marine snow, trapped the fine sediment in the upper regions of King Sound. Wind-driven waves contributed significantly to entrainment of bottom fine sediment, possibly through wave pumping of the sediment and not wave-induced orbital velocities. Field data suggest that erosion of bottom fine sediment was proportional to the sixth power of the tidal current and the third power of the wave height. 相似文献
9.
黄河三角洲飞雁滩沉积物颗粒度分布和粒度参数特征及水动力解释 总被引：2，自引：0，他引：2
黄河三角洲飞雁滩因入海河口改道而缺乏泥沙来源,导致海滩蚀退10余km。近30a来,蚀退后的浅滩在不同潮流和风浪的作用下,浅海滩沉积物颗粒在空间分布上出现明显的差异,表现为浅水区沉积物粗于深水区,来沙少的沉积区粗于来沙多的沉积区。根据2004年实测沉积物颗粒度参数和实测水流及风浪资料分析,该海滩可以分为三个沉积区:I号沉积区,水深较浅,泥沙补给较少,主要受不同风浪的影响,沉积物颗粒组成较粗,以细砂和粉砂为主,分选良好,目前抗冲能力较强;II号沉积区,水深较浅,水流较弱,常受来自高中低潮滩下泄水流携带的细颗粒泥沙影响,沉积物组成粗细混合,以粉砂质粘土为主,分选较差;III号沉积区,水深大,在潮流和风浪作用下,常有来自沿岸尤其I号沉积区的细颗粒泥沙影响,沉积物组成粗细混合,以粘土质粉砂为主,分选较差。黄河三角洲飞雁滩桩106海滩沉积物空间分布较好地反映了泥沙来源和沉积动力条件,该成果可为海岸海滩防护工程规划设计提供科学依据。 相似文献
10.
水动力时空变化对近岸风浪演化的影响——以渤海湾西南岸为例 总被引：1，自引：0，他引：1
采用SWAN模型和ADCIRC模型建立了风浪、潮汐和水流联合作用的耦合数值模式,并通过渤海湾西南岸实测资料对该模式进行了验证。利用该模式分析了近岸区水位和流场时空变化对风浪模拟结果的影响,计算结果表明水位变化对近岸区风浪模拟结果有显著影响,特别是中等大风过程高潮位时波高受水位影响的变化幅值可达0.5m以上,且水深越浅影响越大。但在岸滩平缓的近岸海域由于流速、流向的时空变化不太剧烈,流场作用和波浪辐射应力作用对波浪场的影响都基本可以忽略。在模拟近岸风浪过程时,应选用耦合模式。 相似文献
11.
Vertical accretion in tidal marshes is necessary to prevent submergence due to rising sea levels. Mineral materials may be more important in driving vertical accretion in tidal freshwater marshes, which are found near the heads of estuaries, than has been reported for salt marshes. Accretion rates for tidal freshwater marshes in North America and Europe (n = 76 data points) were compiled from the literature. Simple and multiple linear regression analyses revealed that both organic and mineral accumulations played a role in driving tidal freshwater marsh vertical accretion rates, although a unit mass of organic material contributed ∼4 times more to marsh volume than the same mass input of mineral material. Despite the higher mineral content of tidal freshwater marsh soils, this ability of organic matter to effectively hold water and air in interstitial spaces suggests that organic matter is responsible for 62% of marsh accretion, with the remaining 38% from mineral contributions. The organic material that helps to build marsh elevation is likely a combination of in situ production and organic materials that are deposited in association with mineral sediment particles. Regional differences between tidal freshwater marshes in the importance of organic vs. mineral contributions may reflect differences in sediment availability, climate, tidal range, rates of sea level rise, and local-scale factors such as site elevation and distance to tidal creeks. Differences in the importance of organic and mineral accumulations between tidal freshwater and salt marshes are likely due to a combination of factors, including sediment availability (e.g., proximity to upland sources and estuarine turbidity maxima) and the lability of freshwater vs. salt marsh plant production. 相似文献
12.
On protected mudflats and along sheltered tidal channel margins, wave- and current-generated ripples are frequently observed on surficial and subsurface mud beds, although such bedforms are generally not thought to occur in cohesive sediments. In this paper, examples of such ripple marks in the German Wadden Sea (back-barrier tidal flats of Spiekeroog island) and also along the west coast of Korea (Baeksu tidal flats) are documented and analyzed. The mud ripples are 5–8 cm in spacing and 0.3–0.8 cm in height, and are composed of slightly sandy to virtually pure mud (80–98% mud content). For the Spiekeroog study area, a comparison of in situ particle-size measurements of suspended matter and of dispersed mud collected from the ripples shows that the former consists of low-density flocs which are considerably larger than the constituent grains of the latter. To assess local wave effects, near-bed orbital velocities and orbital diameters were calculated on the basis of standard wave theory using estimated wave parameters at the time of the study (June 2004) as well as wave data recorded nearby within the back-barrier tidal basin. The relationships between grain size, morphometric ripple parameters, and the near-bed orbital diameter show the wave-generated mud ripples to be of the orbital post-vortex type. It is demonstrated that only short-period shoaling (intermediate water depth) waves with periods of 1.5–2.5 s and heights of 0.1–0.5 m are able to generate and maintain such ripples. Corresponding near-bed orbital velocities range from 8–32 cm s–1 and near-bed orbital diameters from 6.25–10 cm. It can be anticipated that increased current shear and turbulence associated with higher and longer waves prevent ripple formation due to the resuspension of settled mud, and the breakdown of suspended flocs and aggregates into smaller particles which then tend to remain in suspension. The most plausible explanation for the formation of the mud ripples is that mud flocs and aggregates deposited from suspension around high-water slack tide under moderate weather conditions initially respond as single (non-cohesive) particles which are hydraulically equivalent to ambient very fine sands. During exposure at low tide, gradual loss of water transforms the rippled mud into increasingly more cohesive mud drapes which are more resistant to erosion. Unless destroyed during high-energy events, the mud ripples may remain intact long enough to become buried and thereby preserved. Indeed, occasional but persistent observations of ripples in sub-Recent to ancient mudrocks document their preservation potential. 相似文献
13.
Anna Badosa Dani Boix Sandra Brucet Rocío Lpez-Flores Xavier D. Quintana 《Estuarine, Coastal and Shelf Science》2006,66(3-4):513-522
The role of the hydrological regime in the nutrients and zooplankton composition and dynamics has been analysed in five lagoons of La Pletera salt marshes (NE Iberian Peninsula) during a complete hydrological cycle (2002–2003). Two of the lagoons have their origin in the old river mouths while the other three were recently created in the framework of a Life Restoration project. This fact has also allowed us to study the effect of the lagoon age on nutrient and zooplankton composition and dynamics. The salt marsh hydrology is determined by a prolonged period of confinement without water inputs, irregularly interrupted by sudden water inputs due to flooding events (sea storms or intense rainfalls). While the dynamics of oxidized nitrogen compounds in the lagoons depends on the water inputs variability within each hydrological cycle, the internal load of phosphorus, total nitrogen and organic matter is related more to the cumulative mechanisms during the confinement periods. Accumulation processes may be easily related to lagoon age, since old lagoons have higher content of nutrients and organic matter, suggesting that these lagoons progressively accumulate nutrients during the successive confinement events. This is the usual case for most Mediterranean salt marshes without an artificially manipulated water regime. The zooplankton community in La Pletera integrates the effects of both the hydrological regime and the lagoon age since the former determines the temporal pattern of the main zooplankton species and the latter explains differences in composition and structure between old and new lagoons. 相似文献
14.
Mingzheng Wen Hongxian Shan Shaotong Zhang Xiaolei Liu 《Marine Georesources & Geotechnology》2019,37(1):96-102
The objective of this study was to investigate that the effects of different hydrodynamic conditions on sediment resuspension on a tidal mudflat in the Yellow River Estuary. A field experiment was conducted on an intertidal flat of the Yellow River Delta, China. The sediment resuspension concentrations and hydrodynamic conditions were obtained in the field from September 2–7, 2013. The resuspended sediment concentrations induced by wave loading were compared with those induced by coupled wave–current actions in Yellow River Delta. The results were as follows: (1) when the wave height was higher than 10?cm and the shear stress induced by the waves was greater than the critical stress of the seabed sediments, the surface seabed was eroded and sediment was resuspended. In addition, 60% of the significant wave heights were larger than 10?cm on the intertidal flat of the Yellow River Delta. (2) The contribution of waves to sediment resuspension was greater than 30% when the significant wave height is higher than 10?cm, and the average contribution of waves to sediment resuspension was 51%. The mechanism of wave-induced sediment resuspension and processes of sediment resuspension were described in this paper. 相似文献
15.
为准确把握新鹤海湾的演变特征和水动力条件,采用现场观测和GIS技术对其地形变化、冲淤分布和冲淤量进行探讨,并利用数值模拟分析波浪、潮流和泥沙共同作用对海湾演变的影响。结果表明:海湾演变对连续台风的响应不同,表现为先冲后淤,其中苏拉作用下的冲刷量为台风过境后全年的2倍左右;受东南季风的影响,春夏冲淤幅度较大,海湾冲淤分布为南冲北淤,波高分布不均与涨潮流入湾时的向北偏转是其主要原因;波流共同作用下的底床切应力约为潮流单独作用时的10倍,波浪是导致海湾冲刷的主要因素,常浪下底床切应力小于临界冲刷应力,泥沙不易起动,因此海湾冲刷主要是由极端天气时的大浪所导致的。 相似文献
16.
Aymeric Jouon Jean Pierre Lefebvre Pascal Douillet Sylvain Ouillon Loys Schmied 《Coastal Engineering》2009,56(5-6):599-608
The south-west reef lagoon of New Caledonia is a semi-enclosed basin where, on first approximation, dominating sea state component corresponds to locally generated wind waves. This study aims to evaluate the ability of the wave model WAVEWATCH III to simulate wind wave distribution in this particular fetch-limited context, with a given parameterisation. In order to evaluate the consistency of the simulation results, wave parameters were measured in situ by a wave and tide recorder (WTR9 Aanderaa) and by an acoustic Doppler velocimeter (ADV Sontek). This study underlines specific constrains for the deployment of instruments to assess the characteristic parameters of low amplitude and high frequency wind-waves. Special care was taken in the comparison step as, on one hand the wave model did not simulate the propagation of low-frequency oceanic waves inside the lagoon, and on the other hand the measured spectra bear an intrinsic limitation for high frequencies. The approximation of a sea state dominated by wind waves is verified on the study site. The accuracy of the simulation results is discussed with regards to the wind forcing applied to the model. 相似文献
17.
台风作用下水体的挟沙能力研究对深入认识台风暴潮作用下泥沙运动规律、滩槽演变特征以及提升数学模型和物理模型技术等方面具有重要意义。文中从台风波能对泥沙的悬浮作用入手,建立了台风浪作用下的挟沙能力公式;依据能量叠加原理,完善了传统的河口海岸挟沙能力公式（窦国仁挟沙能力公式）,使公式能够同时概括潮流、波浪和台风浪作用下的泥沙运动特征,并应用近年来长江口北槽实测的台风期近底水沙资料对公式进行了率定验证,在此基础上分析了台风期北槽近底含沙量变化特征。 相似文献
18.
Tidal measurements and a depth-averaged 2D model are used to examine wave progression and circulation in a long, shallow, micro-tidal lagoon in Sri Lanka. Ranges and phase lags for different tidal constituents are used to calibrate the model. A single drag coefficient, Cd = 0.0032, gives almost perfect agreement with data. Current measurements are used for validation of the model. The lagoon tide consists of a combination of progressive and standing waves, where progressive waves dominate in the outer part and standing waves in the inner. A Lagrangian based particle-tracking method is developed to study tidally and wind induced residence times. If tides were the only factor affecting the residual circulation, the residence time inside the narrowest section would be approximately 100 days. Steady winds (of typical monsoon average) decrease the residence times to 60–90 days. Estuarine forcing due to net freshwater supply is not modelled (due to lack of reliable runoff data), but independent, long-term salinity observations and calculations based on volume and salt conservation during periods of negligible freshwater supply (the lagoon is seasonally hypersaline) indicate residence times ranging from 40 to 80 days. Model derived residence times based on tides alone represent a minimum exchange. Even weak forcing, through winds, excess evaporation or freshwater supply efficiently reduces residence times. 相似文献
19.
基于海南新村潟湖2020年12月水文和水质多要素实测数据,研究了该海域的潮汐、潮流变化特征,并探讨了潮位变化对潟湖营养盐的影响。结果表明,新村潟湖的潮汐为不规则全日潮,潟湖口门处的潮流为往复流,涨潮历时15 h,落潮历时10 h。大、小潮期间3个观测站点溶解性无机氮(DIN)浓度变化范围为0.91~20.87 μmol/L,磷酸盐(PO3-4)浓度变化范围为0.11~5.92 μmol/L,硅酸盐(SiO2-3)浓度变化范围为2.36~134.75 μmol/L。大、小潮期间,潟湖内3个观测站点DIN、PO3-4、SiO2-3浓度随着涨、落潮过程发生变化。潟湖口门处流速对观测站点潮位变化有着重要的影响,潮通量基本决定了潮位的变化。潟湖口门处和渔排密集区域的营养盐浓度与潮位呈现显著的负相关关系,潮流流速对口门处和渔排密集区域的营养盐变化有着重要影响。该研究结果将为新村潟湖的污染治理及生态修复提供科学依据。 相似文献
20.
Suspended matter regime in the Yellow Sea 总被引：3，自引：0，他引：3
John D. Milliman Li Fan Zhao Yiyang Zheng Tiemin Richard Limeburner 《Progress in Oceanography》1986,17(3-4)
Winter and summer oceanographic conditions in the Yellow Sea produce distinctly different distributions and compositions of suspended particles within the water column. During the winter, strong northwest winds cool and mix the local water column and generate surface waves which resuspend bottom sediment in the north Yellow Sea and in the shoal regions of the western Yellow Sea near Jiangsu Province, and transport it southwards. Wintertime suspended particle concentrations in nearbottom waters can exceed 500 mg/l in nearshore areas and 20 mg/l in offshore waters.During the summer, light southerly winds and a strongly stratified water column localize the distribution of resuspended sediments. Nearbottom concentrations of suspended particulates are generally less than 10 mg/l. Nearsurface concentrations generally are not dissimilar from those seen during the winter, but the particles are primarily biogenic rather than resuspended mineral grains. 相似文献