Flow and Benthic Ecology 4D (FLOWBEC)

海底附近的水流强度对生物和群落，即底栖生物，有重大影响。例如，洋流可能影响提供给生物体的食物数量，或者它们可能控制孢子和幼虫在海底定居和生长的能力。潮汐能装置本身就会干扰海床附近的水流，其干扰程度取决于装置的设计。特别地，尾迹将在装置体的下游以及叶片或转子下游增加湍流的确定区域产生。这些对环境水流的干扰可能会对海床上的底栖生物群落产生影响。四年来，在SeaGen潮汐涡轮机下游三个固定地点对底栖动物的观察显示，该装置对底栖动物没有影响；然而，这些观测在空间上是非常有限的。最终，需要能够预测潮汐装置或装置对底栖生物的可能影响，而不是依赖于昂贵的安装后调查。能够做出预测的主要困难之一是无法预测由潮汐能装置引起的环境电流的变化。然而，最近数值模拟的发展有可能在1米或更好的尺度上描述潮汐能装置下游的流场，早期结果表明，与典型装置相关的局部半永久性区域可能存在流量增加或减少。鉴于这些进展，该提案打算在斯特兰奇福德海峡的SeaGen潮汐能装置下游进行详细的底栖生物调查，并将底栖生物群落分布与高分辨率数值模型预测的当前场进行比较。这一对比对于理解底栖生物潮汐能装置引起的流量变化的后果将迈出重要的一步，同时也可以对未来装置的部署做出预测。贝尔法斯特女王大学将监督所需的底物取样计划，该计划将由NUI Galway的人员执行，并将与爱丁堡大学（UoE）密切联系，后者正在FLOWBEC的单独组件投标中开发必要的数值模型。该模型将允许在1米或更高的空间尺度上进行当前预测。底栖生物的分布将通过连续两年春季在SeaGen下游200米处拍摄的一系列主要下拉视频图像来表征。使用精确的水下DGPS系统，每张图像的位置将被记录到1m以上。高威大学将对视频图像进行分析，以量化每个采样点的底栖生物和海底性质。统计分析将与UoE小组密切联系，以确定平均速度和湍流速度分量与底栖生物分布之间的关系。将密切注意评估一个适当的参数来描述适合于生物学的速度的湍流成分。分析还将考虑底栖生物与海底物理性质之间的相互作用。这项研究将发展正在进行的工作，在更大的空间尺度上建立洋流和底栖生物群落之间的关系，得到了SeaGen开发公司MCT的支持。通过预测底栖生物群落与安装潮汐能装置引起的环境电流场变化之间的关系，研究结果将对整个海洋能源工业具有重要价值。

The strength of currents near the seabed has a major effect on the organisms and communities, that is the benthos, that occur there. The currents may, for example, affect the amount of food supplied to the organisms or they may control the ability of spores and larvae to settle and grow on the seabed. By their very nature, tidal energy devices will disturb the current flow near the seabed with the degree of disurbance depending on the design of the device. In particular a wake will be produced downstream of the body of the device as well as a defined zone of increased turbulence downstream of the blades or rotor. These disturbances to the ambient flow may be expected to have an influence on the benthic communities present on the seabed. Observations of the benthos at three fixed sites downstream of the SeaGen tidal turbine over four years have shown no influence of the device on the benthos; however these observations are very limited spatially. Ultimately there is a need to be able to predict the possible influence of a tidal device or devices on the benthos rather than relying on costly post-installation surveys. One of the main difficulties in being able to make predictions has been the inabiltiy to predict changes in the ambient current flow resulting from tidal energy devices. However recent developments in numerical modelling have the potential to describe at a scale of 1m or better the flowfield downstream from tidal energy devices with early results indicating that there may be localised semi-permanent zones of increased or decreased flow associated with a typical device. Arising from these developments, the proposal intends to carry out detailed benthic surveys downstream of the SeaGen tidal energy device in Strangford Narrows and compare the benthic community distributions with the current field predicted from the high resolution numerical models. The comparison will make a major step in understanding the consequences of flow changes resulting from tidal energy devices on the benthos and also allow predictions to be made for future device deployments. Queen's University Belfast will oversee the required benthic sampling programme, which will be carried out by personnel from NUI Galway, and will liaise closely with the University of Edinburgh (UoE) who are developing the necessary numerical model within a separate component bid of FLOWBEC. The model will allow current predictions at a spatial scale of 1m or better. Benthic distributions will be characterised by a major series of drop-down video images taken up to 200m downstream of SeaGen during the spring in two consecutive years. The position of each image will be recorded to better than 1m using a precision underwater DGPS system. The video images will be analysed by the University of Galway to quantify the benthos and the nature of the seabed at each sampling point. Statistical analyses will be carried out in close liaison with the UoE team to establish the relationship between the mean velocity and the turbulent velocity component and the distribution of the benthos. Close attention will be paid to assessing an appropriate parameter to describe the turbulent component of the velocity that is appropriate to the biology. The analysis will also consider the interaction between the benthos and the physical nature of the seabed. The study, which will develop ongoing work establishing the relationship between currents and benthic communities on a coarser spatial scale, is supported by MCT, the developers of SeaGen. The results will be of major value to the marine energy industry as a whole by allowing the prediction of relationships between benthic communities and changes in the ambient current field resulting from the installation of tidal energy devices.