Modelling hydraulic and physical features of riverine fish habitats

在英国，43%的河流栖息地被归类为严重改变，并且继续存在进一步开发的压力（抽象，防洪等）。通常情况下，河流的水动力环境因水深、水深和河床护面材料的纵向和横向变化而更加丰富，这促进了二次流、湍流的产生以及局部流速和水深的变化。这些三维水力特征构成了淡水无脊椎动物和鱼类多样性所必需的各种生境条件。然而，水力和水文生态模型（如PHABSIM，MesoHABSIM），定义的目标鱼类的物理栖息地的可用性的变化，在河流流动通道的几何形状的变化通常使用一维的水力方法，并产生复杂的水深测量的河流中的原油速度和水位预测。在调整现有的河流环境以满足水框架指令时，必须保持自然特征，稳定性和排放能力，同时加强生态化过程，但在实践中，鱼类的最佳条件分类很差。现有的协议，用于评估鱼的游泳性能的基础上的区域平均水速度，并进行在游泳室与光滑的床和壁边界。没有考虑到鱼在水柱内的位置和湍流的大小（例如，速度的时间变化），因此鱼类的游泳性能和耐力目前可能被大大高估了底层（底栖）鱼类，而低估了中上层（水柱）鱼类。此外，在天然河流（水深可变;粗糙的河床和河岸、床型、植被、岛屿和人造结构）中产生的湍流特征（湍流的大小与时间平均速度的关系）与理想化的游泳室中产生的湍流特征明显不同。在卡迪夫，学生将收集详细的经验数据水槽的水力条件下不同的流动条件与各种栖息地的修改，以评估这如何影响底层和底栖鱼类的游泳性能。学生将开发一种栖息地建模方法，其中通用开源三维计算流体动态代码（例如FLUENT，Pheonics，OpenFOAM，TELEMAC）与编程和后处理软件环境（如MATLAB）相关联，其中新的栖息地适宜性规则基于新数据和现有生态模型实施。

In the UK, 43% of river habitats are classified as severely modified and there is continued pressure for further development (abstractions, flood protection etc). Typically, the hydrodynamic environment of a river is enriched by longitudinal and lateral variations in bathymetry, water depth and bed armour material, which promotes the generation of secondary currents, turbulence, and variation in local flow velocity and flow depth. These three-dimensional hydraulic features constitute a variety of habitat conditions essential for freshwater invertebrate and fish diversity. However, hydraulic and hydro-ecological models (e.g. PHABSIM, MesoHABSIM) that define changes in physical habitat availability for target fish species given a change in river flow channel geometry typically use a one-dimensional hydraulic approach and generate only crude velocity and water level predictions in rivers of complex bathymetry. In adapting existing riverine environments to meet the Water Framework Directive, it is essential to maintain the natural character, stability and discharge capacity whilst enhancing recolonisation processes, but in practice the optimal conditions for fish are poorly classified. Existing protocols for evaluating fish swimming performance are based on the area mean water velocity and are conducted in swimming chambers with smooth bed and wall boundaries. No consideration is given to the position of the fish within the water column and magnitude of the turbulence (e.g. the temporal variation of the velocity) so fish swimming performance and stamina could be currently drastically over-estimated for demersal (bottom dwelling) fish and under-estimated for pelagic (water column) fish. Furthermore, the turbulence signature (magnitude of turbulence in relation to the time-averaged velocity) produced in a natural river (with variable bathymetry; rough bed and banks, bedforms, vegetation, islands and man-made structures) will be distinctly different to that produced in an idealised swimming chamber. At Cardiff, the student will collect detailed empirical data on the hydraulic conditions of a flume under different flow conditions with various habitat modifications to assess how this affects the swimming performance of demersal and benthic fish. The student will develop a habitat modelling approach whereby a generic open source 3-D Computational Fluids Dynamic code (e.g. FLUENT, Pheonics, OpenFOAM, TELEMAC) is linked to a programming and post-processing software environment, such as MATLAB, in which new habitat suitability rules are implemented based on the new data and existing ecological models.