The effect of eelgrass meadows on the morphodynamics of coastal sedimentary systems

本提案的目标是通过研究不列颠哥伦比亚省弗雷泽河沿岸的鳗草草甸，促进我们对植被在沿海地貌变化中的作用的理解。世界海岸线是一个高度动态的系统，形成了各种社会经济和生态利益相关者的战场，并且由于持续的人为改变和海平面加速上升而承受着越来越大的压力。传统上，地貌学家研究了沿海景观的演变，将其作为水流、沉积物运输和海底形态调整的功能。最近，人们认识到，这种传统方法未能将水生植被（如大叶藻草甸）对海岸形态动力学的影响整合起来。然而，已知植被的存在通过提供对流动的阻力和引起湍流的产生来改变流体动力学。植被通常被称为“地貌工程师”，因为它们有引起沉积物沉积的倾向。然而，基于过程的对植被周围沉积物动力学的理解仍然缺乏。基于我之前对砂层环境中水流和沉积物运输的研究，本项目的具体目标是研究大鳗草的存在如何影响湍流结构、河床剪应力和沉积物动力学的时空变化，从单个大鳗草斑块到沿海海湾的大规模动态。这项工作采用端到端的方法，从1-3年级的初始直接实地观测开始，在3年级进行系统的实验室实验，直到3-5年级使用行业领先的建模套件进行区域尺度的数值模拟。现场活动包括使用我们自己的仪器在弗雷泽河三角洲的大叶藻系统上进行船舶和着陆器水声调查，这是不列颠哥伦比亚省最大的连续大叶藻系统。现场实验将为系统的实验室实验提供信息，使用模拟的大叶藻叶片和沙质沉积物来获得床层剪切应力和降低沉降速度的参数化，以便在数值模型中实现。我们的建模工作将从对当前植被配方的关键测试开始，并将系统地测试和实施我们的新参数化。这些模型将用于研究植被变化对潮滩排水和潮滩输沙环境的影响。我们的最终目标是在这些模型套件中充分代表沿海植被，这将允许更准确地预测开发或气候变化后的沿海变化。因此，拟议的工作是及时的，对许多沿海利益相关者，包括开发商、顾问、工程师、环保主义者和沿海社区都有直接的兴趣。我们使用业界领先的开源建模软件，将确保为潜在的最终用户提供有价值的贡献和持久的影响。

The goal of this proposal is to advance our understanding of the role of vegetation in coastal geomorphological change, by studying eelgrass meadows along the Fraser River, BC. The world's coastlines are highly dynamic systems that form the battleground of various socio-economic and ecological stakeholders and are experiencing increased pressure through ongoing anthropogenic alteration and accelerated sea-level rise. Conventionally, geomorphologists have examined coastal landscape evolution as a function of adjustments of flow, sediment transport and seabed morphology. More recently, it has been acknowledged that this conventional approach fails to integrate the influence of aquatic vegetation such as eelgrass meadows in coastal morphodynamics. Yet, the presence of vegetation is known to alter fluid dynamics by providing resistance to the flow and causing turbulence production. Vegetation is often referred to as a `geomorphic engineer', due to propensity to cause sediment deposition. However, a process-based understanding of the sediment dynamics around vegetation is still lacking. Building on my previous work on flow and sediment transport in sand-bedded environments, the specific objective of this proposed program is therefore to examine how the presence of eelgrass influences spatio-temporal variations in turbulent flow structure, bed shear stress, and sediment dynamics from an individual eelgrass patch to the large-scale dynamics of coastal bays. The work takes on an end-to-end approach starting with initial direct field observations in Years 1-3, systematic laboratory experiments in Year 3, through to regional-scale numerical simulations using industry-leading modelling suites in Years 3-5. Field campaigns comprise ship- and lander-based hydro-acoustic surveys using our own instrumentation over the eelgrass system of the Fraser River Delta, the largest continuous eelgrass system in BC. The field experiments will inform systematic laboratory experiments using simulated eelgrass blades and sandy sediment to arrive at parameterizations of bed shear stress and reduced settling velocities for implementation in numerical models. Our modelling effort will begin with a critical test of current formulations for vegetation and will systematically test and implement our new parametrization. The models will then be used to examine the effect of changes in vegetation on tidal flat drainage and sediment transport environment of tidal flats. Our ultimate aim is to adequately represent coastal vegetation in these model suites, which will allow a more accurate prediction of coastal change following development or climatic changes. The proposed work is therefore timely and of immediate interest to a number of coastal stakeholders, including developers, consultants, engineers, environmentalists, and coastal communities. Our usage of industry-leading, open-soure modelling software will ensure valuable contribution and lasting impact for potential end-users.