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1.
我国南方强潮海岸红树植物对潮流的调制作用   总被引:2,自引:0,他引:2  
至今,关于红树植物对潮流的调制作用的研究非常有限,尤其是红树植物对垂向流速剖面的影响还不清楚。本研究利用自主研发的自动升降架于大潮期间对浙江南部乐清湾西门岛秋茄种植区的红树林滩进行垂向多点观测。结果表明,在所研究的红树林内,整个垂向剖面的流速普遍较低。树干和冠层引起的拖曳力在垂向上的增加,使得红树林内垂向流速剖面呈现"流速随距底高度增大而减小"的规律。此外,湍流能量密度在垂向上也呈现出与红树植物垂向结构相对应的变化。与光滩(半对数)和盐沼(近"J"形)内流速的垂向结构相比,红树植物以一种不同的方式对垂向流速剖面产生重要影响。  相似文献   

2.
时钟 《海洋科学》2000,24(7):56-56
此项目采用实验(现场、室内)方法研究海岸(河口)高潮滩盐沼泥沙过程 ,即波浪、潮流、海岸盐生植物、细颗粒悬沙和淤泥质底床的相互作用。(1)高潮滩盐沼盐生植物的野外调查 :海岸盐生植物的属种、高度、大小、密度 ;(2)高潮滩盐沼边界层水流结构的现场实验观测 :a.潮流水位、流速、紊动的野外现场观测 ;b.波浪衰减的观测 ;(3)高潮滩盐沼细颗粒悬沙浓度的现场观测 ;(4)高潮滩盐沼地区长期、短期细颗粒泥沙堆积和侵蚀速率的现场观测 ;(5)海岸盐生植物作用下波浪、潮流边界层的室内实验研究 ;(6)海岸盐生植物作用下细…  相似文献   

3.
张卓  宋志尧 《海洋与湖沼》2015,46(5):995-1000
潮流的流速分布和湍流切应力的分布密切相关。为了研究潮流湍流切应力的特征和变化规律,本文从潮流运动方程推导出随潮流呈周期性变化的湍流切应力随深度的分布表达式。从江苏近海现场实测流速剖面中计算得到一个潮周期内的湍流切应力的变化过程。通过将实测值与本文理论解的比较发现,计算值能很好地反映出实测值的变化特征,尤其是能正确地反映潮流在加速和减速过程中,湍流切应力偏离线性分布呈现上凹和下凹的现象,以及只有在加减速转换的时候切应力才呈现线性分布的特点。最后,通过分析湍流切应力振幅及相位沿水深的变化情况,认为反映潮流周期、涡粘性和水深之间关系的参数Ri是决定湍流切应力弯曲程度及分布形态的重要参数。对于近海潮流,水深是影响湍流切应力偏离线性程度的主要因素。  相似文献   

4.
底部切应力作为水动力和泥沙输移模型中的关键参数,对底床泥沙起动、侵蚀淤积速率的研究十分重要。目前基于现场实测流速数据计算底部切应力的理论方法有6种:LP mean法、LP max法、TKE法、TKEW法、RS法和ID法,这些方法都有其特定的适用条件。河口海岸浅水区域水流和波浪作用复杂,遴选合适的方法计算底部切应力非常重要。本文以江苏大丰斗龙港1个观测点(中值粒径为68.56 μm)和上海崇明东滩2个观测点(中值粒径分别为12.89 μm和45.02 μm)为例,利用声学三维高频流速仪ADV (Acoustic Doppler Velocimetry)和波潮仪(RBR wave)进行现场数据采集,分别用6种理论计算方法对底部切应力进行计算,结果表明:(1)LP mean法受到平均流速、仪器探头距离底部床面高度以及波浪强弱的影响,会低估底部切应力;(2)LP max法和TKE法在流速变化幅度较大、波浪作用明显的潮间带浅水环境会高估底部切应力;(3)TKEW法在TKE法的基础上进行了改进,更适用于波浪作用强烈的潮间带浅水环境底部切应力的计算;(4)RS法计算结果受到波浪影响会产生误差,存在较大波浪时,ID法计算结果比RS法计算结果更加可信,但是在水深条件不足时,ID法会高估底部切应力。  相似文献   

5.
互花米草对泉州湾盐沼表层沉积物输运的影响   总被引:1,自引:0,他引:1  
海岸盐沼是海岸湿地系统的重要组成部分,具有很强的环境调节功能.互花米草(Spartina alterniflora)的引种对海岸盐沼的沉积动力产生很大影响.粒度分析结果表明,互花米草盐沼边缘与沉积物平均粒径为6.7φ的等值线分布一致.现场观测表明,互花米草对流速具有明显的阻滞作用,使得光滩流速明显大于互花米草内的流速;在互花米草滩内,随着离盐沼边缘距离、植被高度、植株直径的不同,涨落潮流速也表现出不同的变化趋势.粒径趋势分析结果显示,互花米草盐沼边缘的表层沉积物由光滩向盐沼内输运,潮水沟的存在对沉积物的输运格局具有显著影响.对比分析表明落潮后期的水动力条件控制着研究区内表层沉积物的净输运方向.  相似文献   

6.
江苏王港盐沼潮沟的水动力和悬沙输运过程   总被引:6,自引:2,他引:4  
在江苏王港盐沼湿地的两条潮沟内分别设立观测站位,进行了水位、潮流流速和悬沙浓度的观测。结果表明,潮沟水流的流速与潮位变化率之问存在着显著的线性相关关系,并受到潮沟本身特征(如潮沟级别、坡度、所在部位等)的影响。潮周期中的流速突变现象发生于涨潮初期、潮沟满溢和滩面水归槽阶段。涨潮期间,悬沙浓度和流速有显著的正相关关系,悬沙浓度的变化受再悬浮作用控制;落潮期间,悬沙浓度的变化基本上与流速大小无关,悬沙输运以平流作用为主。大潮期间盐沼潮沟内悬沙净输运方向由陆向海。  相似文献   

7.
粘性泥沙在盐水中冲刷和沉降特性的试验研究   总被引:3,自引:1,他引:2  
本文根据絮凝电化学理论,探讨了淤积物浓度对粘性泥沙起动切应力的影响,获得起动切应力τc与淤积物浓度S的相关式τ_o=KS~(2·33) 该公式得到众多试验资料的证实。冲刷试验表明,具有均匀容重的底床在不同水流切力下,冲刷率随时间基本成直线变化,自养密实底床的冲刷率随时间呈指数曲线变化。试验结果还表明均匀容重底床的冲刷率与水流流速近似成四次方关系,论文运用了窦国仁博士从能量原理获得的床面泥沙动密实系数概念,获得冲刷率的表达式为 E=(K_0)/(C_0~2)-(γsγ)/(γs-γ)(V-V_c)V~3/gdω  相似文献   

8.
基于2018年8月福建三沙湾湾内外共两个定点站位的船基和座底三脚架观测数据,研究了三沙湾底边界动力过程及悬沙输运特征。结果表明,三沙湾湾内湾外两个站位均表现出涨落潮历时相近但涨落潮流速明显不对称的现象,即湾内涨潮流速大于落潮流速,湾外则相反。湾内水体受淡水输入影响较大,表现出落潮期间显著的温盐层化,而涨潮期间水体混合良好;湾外水体受淡水影响不明显,表现为水体温度主导的层化。通过对底边界层动力过程的分析表明,湾内(距底0.75 m)、湾外(距底0.50 m)站位底边界层的平均摩阻流速分别是0.016 m/s、0.013 m/s,且两个站位拖曳系数基本相等(2.03×10-3),表明在相同流速下湾内站位的底部切应力更大,近底沉积物再悬浮和搬运相对湾外站位更为显著。因此观测期间悬沙浓度最大值出现在湾内站位,为109 mg/L,且悬沙在垂向上的分布可达上层水体;湾外站位悬沙浓度更低,并且底部悬浮泥沙仅能影响至距底5 m的水体。悬沙通量机制分解结果表明,三沙湾夏季的潮周期单宽悬沙从湾外向湾内方向净输运,湾内站位向湾内方向净输运74.88 g/(m·s),平流输沙占主导作用,贡献率41.7%;湾外站位向湾内方向净输运10.57 g/(m·s),主要受平流输沙和垂向净环流的控制,贡献率94.9%  相似文献   

9.
联合国环境署(1990)在题为“海相环境的状况”的报告中指出,世界人口约一半集中在海岸地区,因而这些地区人口压力巨大,同时受到污染、风暴潮、地面沉降的威胁,以及高地灌溉水资源枯竭的影响;在低地海岸、河滩和湿地,海平面的上升将会给沿岸城市的工农业生产及人民生活带来极其严重的后果。而盐沼-潮沟体系则是淤泥质海岸缓冲、削减波浪-潮流能量的重要地貌系统,对海岸的保护起着至关重要的作用。潮沟常常贯穿盐沼与泥坪(或沙坪),成为沟通盐沼-泥坪体系物质能量交换的纽带;在淤涨型淤泥质海岸上,细颗粒泥沙被涨潮流沿潮沟输送到盐沼上,结果使盐沼不断向海淤进。而当海平面上升时,盐沼-潮沟系统功能又发生改变,成为削减潮汐能量的“装置”。Pethick(1980,1992)研究了英国Norfolk盐沼潮沟水流的特征,并提出了流速的预报模型;Healey等(1981)在观测中发现了一些与模型不符的情况。本文从地貌和动力方面研究了江苏淤泥质海岸弶港盐沼风车河潮沟的地貌演变与动力演化的关系,以及水动力与地貌因素之间的相互响应机制。  相似文献   

10.
江苏大丰潮滩潮流边界层特征研究   总被引:7,自引:0,他引:7  
2003年7月中小潮期间使用MIDAS-400用户化数据采集系统在江苏大丰潮滩上进行了垂向多层位同步的流速和悬沙浓度观测。根据观测资料研究了潮流作用下的潮滩底部边界层过程,结果表明,观测地点的潮汐不对称现象十分明显,落潮流速、历时和输水输沙量皆明显大于涨潮;在潮周期内的多数时间里流速剖面符合对数分布,但在风力较强、水流快速增加和流速缓慢的情况下,流速剖面常偏离对数分布;悬沙颗粒垂向混合均匀,悬沙浓度剖面符合Rouse公式;落潮时的底部切应力和摩阻流速明显大于涨潮,摩阻流速与各水层流速通常有较好的线性关系;滩面糙度主要与沙纹形态和推移质运动强度有关,它与摩阻流速存在密切关系;悬沙浓度具有明显的减阻效应,受其影响,摩阻流速和底部切应力分别减小了28%~41%和40%~62%。  相似文献   

11.
Velocity profiles in a salt marsh canopy   总被引:7,自引:0,他引:7  
Flow velocity profiles, measured in aSpartina anglica canopy in a laboratory flume, change with the location of measurement and plant stem density. The shear velocity above the canopy is larger than that within the canopy. The reduction ofu * within the canopy will favor the deposition of cohesive sediment. The reducedu * and flow turbulence within the canopy can enhance particle flocculation and settling velocity. The canopy exerts a strong influence on the concentration, settling velocity of the flocs, and deposition rate of the suspended sediment through effects on bed shear stress and turbulence of flow within the canopy.  相似文献   

12.
The interaction of seagrasses with the dynamics of an oscillatory wave induced flow is assessed with a new Lagrangian plant model. The plant model simulates moving plants in canopies and their dissipative effect on the ambient flow. Concomitantly the plant model is interactively coupled to a 3D hydrodynamic numerical model allowing for a bilateral feedback between moving plants and flow. Model results demonstrate that this interaction causes a modification of current profiles within and above a canopy as compared to an undisturbed flow. While the overall effect of submerged plant canopies is a dampening of dynamics, the flow may locally be intensified. The model predicted an intensification of the flow near the top of a canopy in concurrence with field and laboratory observations. Dissipation in the coupled model, due to the applied non-linear friction law, grows exponentially with increasing flow. As a result the permeability of a canopy to the ambient flow decreases with increasing dissipation. Consequently, at high flow velocities, while becoming increasingly impermeable, a canopy acts like an obstacle that deflects the flow above it, which causes the observed intensification. Results for canopies consisting of seagrasses with different leaf structure and plant geometry show remarkable differences in predicted plant motions, current profiles, drag forces, and velocity shear. Predictions for moving plants are compared with those for rigid, less flexible, structures and undisturbed flow.  相似文献   

13.
The combined tidal and wind driven flow and resulting sediment transport in the ocean over a flat bottom at intermediate water depth has been investigated, using a simple one dimensional two-equation turbulence closure model. This model has been verified against field measurements of a tidal flow in the Celtic Sea. The tidal velocity ellipses and the time series of the horizontal velocity components at given elevations above the bottom are well predicted through the water column although there are some deviations between the predicted and measured velocities near the bottom due to the uncertainty of the bottom roughness. For the combined tidal and wind driven flows the velocity profiles, turbulent kinetic energy profiles and surface particle trajectories are predicted for weak and strong winds. Furthermore, the bottom shear stress and the resulting bedload transport have been predicted; the parts of the particle trajectories in the close vicinity of the bottom where the bedload transport exists are displayed. Finally, the direction and magnitude of the surface drift, the depth-averaged mean velocity and the mean bedload transport are given, and the effect of the bottom roughness on the sea surface drift is investigated.  相似文献   

14.
Plant-flow interactions on the surface of tidal wetlands result in flow characteristics that are profoundly different from non-vegetated flows. Reductions in mean flow velocity and turbulence, especially the vertical components, limit vertical mixing and may impact a wide range of processes including geochemical exchanges at the sediment water interface, larval recruitment and dispersion, and sediment deposition and retention. The goal of this paper is to quantify horizontal and vertical components of velocity, turbulence intensity and total turbulent kinetic energy in Spartina alterniflora canopies in southeastern North Carolina and to relate flow characteristics to particulate transport on the marsh surface. Another aim of this paper is to assess the extent to which the distribution of standing biomass affects mean flow and turbulence by comparing S. alterniflora data to other canopy types and through a series of canopy manipulations which altered canopy height and stem densities.The results of this study indicate that flow velocity, turbulence intensity, and total turbulent kinetic energy (TKE) are significantly reduced within the vegetated canopy and that this reduction is inversely related to the amount of biomass present in the water column. Within the canopy, approximately 50% of the initial mean velocity and TKE is reduced within 5 m of the canopy edge. Within the canopy, mean velocity and TKEhoriz usually exceeded vertical velocity or TKEvert and the vertical components of flow were attenuated more strongly than the horizontal. These results suggest that within the vegetation, turbulence contributes more to lateral advection than to vertical mixing. As a result, total suspended solid concentrations were shown to decrease logarithmically with distance from the canopy edge and to decrease at a faster rate in more densely vegetated regions of the canopy (i.e. lower TKEvert) as compared to areas of sparser vegetation (i.e. higher TKEvert).  相似文献   

15.
长江口天然水流中细颗粒泥沙的絮凝作用   总被引:9,自引:0,他引:9  
阮文杰 《海洋科学》1991,15(6):39-43
本文根据1978年水文测验资料,分析了长江口水流对细颗粒泥沙絮凝的影响。从中得出:(1)絮凝使长江口泥沙的竖向运动规律发生改变,出现竖向分层流。(2)存在一絮 凝临界流速,只有当流速小于该值时,絮凝泥沙的竖向运动规律才得以体现。(3)在小于絮凝临界流速的水流中,垂线不同高程处的絮凝条件受水流切应力制约。  相似文献   

16.
Attenuations of solitary wave over a patch of submerged canopy are experimentally investigated. The submerged canopy is modeled by a group of circular cylinder array. The decay coefficients of different wave heights in two water depths along the wave flume are measured for six canopy models, including two canopy heights and three styles of arrangements. The relationships among the decay coefficient, and the dimensionless wave height, submergence ratio, relative height and arrangement of the canopy are experimentally studied. 2D PIV technique is employed to measure the representative flow field inside the canopy. A four-deck flow structure is proposed for wave flow field over shallow submerged canopy. The characteristics of shear flow inside the aligned canopy region are discussed.  相似文献   

17.
Attenuations of solitary wave over a patch of submerged canopy are experimentally investigated. The submerged canopy is modeled by a group of circular cylinder array. The decay coefficients of different wave heights in two water depths along the wave flume are measured for six canopy models, including two canopy heights and three styles of arrangements. The relationships among the decay coefficient, and the dimensionless wave height, submergence ratio, relative height and arrangement of the canopy are experimentally studied. 2D PIV technique is employed to measure the representative flow field inside the canopy. A four-deck flow structure is proposed for wave flow field over shallow submerged canopy. The characteristics of shear flow inside the aligned canopy region are discussed.  相似文献   

18.
生态空心块体是一种兼有调控水流与生态修复功能的工程结构物,在海堤、丁坝等近海工程中被广泛应用。通过室内水槽试验,设计多种来水来沙工况,研究生态空心块体与柔性植被共同影响下的水沙动力特性,重点探究生态空心块体内的水沙动力效应。结果表明:生态空心块体组成的坝体结构缓流效果显著,坝体内外侧水流流速分布差异明显,坝体内部的水流流速远小于外侧水流流速;生态空心块体内紊动强度、雷诺应力在空心块体上方出现拐点,空心块体内紊动强度、雷诺应力均小于外侧;近底层水流在受壁面阻水作用下产生回流,易出现小范围旋涡;由于生态空心块体内水流流速、紊动强度的减小,内部悬沙浓度由表至底逐渐增大;柔性植被的冠层部分对水流减速、促淤效果最为明显,柔性植被会减缓前后相邻侧空心块体的水流流速,增大悬沙浓度。  相似文献   

19.
The vertical structure of the flow variability through the Strait of Gibraltar is studied based on the Gibraltar Experiment and the Word Ocean Circulation Experiment data sets. An analysis of the leading modes of velocity and density variability at the Strait of Gibraltar showed an adjustment of the water masses exchanged through the Strait. Mediterranean mass variations resulting from the water exchanged by barotropic tidal oscillations generate changes of the baroclinic component of the flow that damp these mass variations. This adjustment explains the previously observed fortnightly variation of the shear. Moreover, the adjustment is found to operate for the subinertial time scale flow variability forced by the atmospheric pressure. An analytical model aimed at reproducing variations of the velocity with time and in the vertical is derived. The model includes a depth-varying parameterisation of friction and takes into account density gradient fluctuations across the Strait. The model reproduces the main features of the flow, in particular the shear and the interface depth variations with the tide phase.  相似文献   

20.
Hydraulic roughness over simple subaqueous dunes   总被引:2,自引:1,他引:1  
Detailed studies of flow over subaqueous dunes in laboratory flumes were used to suggest a virtual near-bed layer of twice the dune height in which the mean velocity is accelerated towards the crest by contraction. The mean flow velocity in this layer above the crest, transformed into friction velocity by means of the surface skin roughness, is shown to give values consistent with measured values. The resulting dimensionless shear stress due to skin friction is depth-independent, in contrast to that derived by means of often cited traditional methods. As a result of the relationship between dune height and the thickness of the near-bed layer, an expression for the expansion loss behind dunes was formulated and used to relate form resistance directly to dune height.  相似文献   

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