The interaction of waves with seaweed farms: wave attenuation and intra-farm hydrodynamics

在苏格兰，海藻养殖被公认为是一个具有巨大增长潜力的产业。苏格兰的大多数农场都靠近海岸，在一个典型的4公顷或更小的网格系统中种植海带物种，如Saccharina latissima；该行业的发展将需要扩大农场规模，并进一步向海外转移。海藻养殖的成功增长需要对影响养殖场生产力和养殖场所在海洋环境的物理和生物过程有充分的了解。这些过程包括波浪和农场之间的水动力相互作用。海浪在水柱内产生水运动，与海藻相互作用并从波浪中吸收能量，导致波浪在农场传播时衰减。根据入射波的情况、水深、养殖场的大小、海藻的覆盖范围及其特性，波浪能量的减少可能是显著的；因此，海藻养殖场可以通过显著减少到达邻近海岸线的海浪能量，潜在地提供重要的海岸保护服务。近年来，利用植被进行所谓的基于自然的海岸保护受到了很多研究的关注，尽管这些研究主要集中在底栖植被上——海草草甸、盐沼和红树林。对底栖海藻的波浪衰减的关注要少得多，对悬浮的近水面海藻的关注就更少了，就像在海藻养殖场中配置的那样。海洋环境干预的规划和设计需要应用水动力模型，旨在预测干预对包含干预区域的波浪和当前气候的影响。常用的模型有用于海流预报的FVCOM （Finite Volume Community Ocean Model）和用于海浪预报的频谱波模型SWAN （simulation Waves Nearshore）。这些模型不能在精细尺度上解决流体动力学问题；相反，为了应用于海藻养殖场，需要使用基于物理论证和实验数据的半经验模型来结合植被对流/波的影响。对于底栖植被，SWAN中已经实施了拟议的公式，但对于近地表悬浮海藻，尚未提出相应的公式。拟议研究的目标是：(i)进行实验室实验，调查波浪与海藻养殖场的相互作用，重点是养殖场内的流体动力学和波浪衰减。（ii）根据实验所得的见解和数据，开发新的农业效应对波浪衰减的半经验公式，可在沿海波浪水动力模型中实施。（iii）在SWAN中实施新公式，并应用于多个海藻养殖场方案，以研究养殖场参数对波浪衰减的潜在影响。

Seaweed cultivation is well recognised as an industry with substantial potential for growth in Scotland. Most farms in Scotland are close to shore, growing kelp species such as Saccharina latissima on a grid system that is typically 4 hectares or smaller; development of the industry will require increasing farm size and moving further offshore. Successful growth in seaweed farming requires sound understanding of the physical and biological processes affecting farm productivity and the marine environment in which farms are located. These processes include the hydrodynamic interactions between waves and farms.Sea waves generate water motions within the water column, which interact with the seaweed and take energy from the waves, resulting in wave attenuation as the waves propagate across the farm. Depending on the incident wave conditions, the water depth, the farm size, the seaweed coverage and its properties, the reduction in wave energy can be significant; a seaweed farm can therefore potentially provide an important coastal protection service by significantly reducing the wave energy that reaches the adjacent coastline. The use of vegetation for so-called nature-based coastal protection has received a lot of research attention in recent years, though that research has focused mainly on benthic vegetation - sea grass meadows, salt marshes and mangroves. Much less attention has been paid to wave attenuation over benthic seaweeds , and even less to suspended, near-surface seaweeds, as configured in seaweed farms.Planning and design of interventions in the marine environment require application of hydrodynamic models that aim to predict the impact of the intervention on the wave and current climate in the area containing the intervention. Commonly used models include FVCOM (Finite Volume Community Ocean Model) for current prediction and the spectral wave model SWAN (Simulating Waves Nearshore) for waves. Such models do not resolve the fluid dynamics at fine scale; instead, for application to seaweed farms, the vegetation effects on the flow/waves need to be incorporated using semi-empirical models based on physical argument and data from experiments. Proposed formulae have already been implemented in SWAN for benthic vegetation, but corresponding formulae for near-surface, suspended seaweed have yet to be proposed.The objectives of the proposed research are:(i) Conduct laboratory experiments to investigate wave interaction with seaweed farms, with focus on intra-farm hydrodynamics and wave attenuation.(ii) Based on insights and data from the experiments, develop new semi-empirical formulae for farm effects on wave attenuation, which can be implemented within coastal wave hydrodynamic models.(iii) Implement the new formulae in SWAN and apply to several seaweed farm scenarios to investigate the potential impact of farm parameters on wave attenuation.