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首页> 外文会议>International Association of Hydraulic Engineering and Research(IAHR) Congress Theme A: Coastal Environment: Processes and Integrated Management; 20030824-20030829; AUTH; GR >COHERENT FLOW STRUCTURES IN GAPS WITHIN MEADOWS OF POSIDONIA OCEANICA
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COHERENT FLOW STRUCTURES IN GAPS WITHIN MEADOWS OF POSIDONIA OCEANICA

机译：海洋波塞冬藻内间隙中的相干流动结构

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摘要

Meadows of the seagrass Posidonia oceanica are found in numerous coastal locations with the Mediterranean Sea. These dense macrophyte stands support highly biodiverse ecological communities that comprise epiphytic micro-flora and -fauna as well as larger organisms which use the meadows as nursery and sanctuary habitats. Often, gaps appear in these meadows as a result of anthropogenic disturbance, storm events or bioturbation. The recovery of these gaps, and their influence on ecological and sedimentary processes are important factors in understanding of the nature of these meadows. The work reported here elucidates the dynamics of the flow within the meadow-with-gap configuration described. This is achieved via laboratory experiments which meadows of Posidonia oceanica are simulated by collections of strips of plastic matched with samples of the seagrass for flexibility, shape, size, density and surface roughness. These are placed in a flume and a flow is passed over them. Three-dimensional velocity measurements are taken at numerous locations within the flow using an Acoustic Doppler Velocimeter. From these, coherent structures in both the mean and turbulent flow components are derived, using analytical techniques taken largely from fluvial geomorphological studies of flow structures over alluvial bedforms. Both the flow discharge rate and the gap extent are varied between experimental runs. The results show that where the gap is wide enough, a large, persistent eddy with cross-flow vorticity develops, above which a turbulent shear zone extends to the water surface. Where the gap is too small for this eddy to form, the flow appears to be dominated by weak upwelling, which orders itself into coherent cells if the gap size is large enough to allow this. Implications for sediment and nutrient dispersion within the meadow and gap are discussed.
机译：在地中海沿岸的许多沿海地区都可以发现海草波西多尼亚大洋洲的草地。这些茂密的大型植物群落支持高度生物多样化的生态群落，其中包括附生的微生物区系和动物区系以及将草甸用作苗圃和避难所栖息地的较大生物。通常，由于人为干扰，风暴事件或生物扰动，这些草甸中会出现空隙。这些间隙的恢复及其对生态和沉积过程的影响是了解这些草地的性质的重要因素。这里报道的工作阐明了所描述的带间隙草地构造中的流动动力学。这是通过实验室实验来实现的，该实验是通过收集与海草样品相匹配的塑料条来模拟波西多尼亚大洋草甸的柔韧性，形状，大小，密度和表面粗糙度。将它们放置在水槽中，并在其上流过。使用声学多普勒测速仪在流中的多个位置进行三维速度测量。利用这些分析技术，可以从这些数据中得出均质和湍流分量的连贯结构，这些分析技术主要取自冲积床形流动结构的河流地貌研究。在实验运行之间，流量排放率和间隙程度均发生变化。结果表明，在间隙足够大的地方，会形成一个大的，持续的，带有横流涡流的涡流，在涡流上方，湍流的剪切带延伸到水面。如果间隙太小而无法形成涡流，则流动似乎被弱上升流所支配，如果间隙大小足够大，则会使自身进入相干单元。讨论了沉积物和养分在草甸和间隙中的扩散。

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