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

这项建议的目的是通过研究不列颠哥伦比亚省弗雷泽河沿岸的鳗草草甸，促进我们对植被在海岸地貌变化中作用的理解。世界海岸线是极具活力的系统，构成了各种社会经济和生态利益攸关方的战场，由于持续的人为改变和海平面加速上升，海岸线面临着越来越大的压力。传统上，地貌学家将海岸地貌演变作为水流、泥沙输送和海底形态调整的函数。最近，人们认识到，这种传统的方法未能将鳗草草甸等水生植被的影响纳入海岸地貌动力学。然而，众所周知，植被的存在会通过提供流动阻力和引起湍流产生来改变流体动力学。植被通常被称为“地貌工程师”，因为它倾向于造成泥沙淤积。然而，对植被周围的沉积物动力学仍缺乏基于过程的了解。基于我以前在沙床环境中的水流和泥沙输运方面的工作，因此，这项拟议计划的具体目标是研究从单个鳗草斑块到沿海海湾的大尺度动力学，鳗草的存在如何影响湍流结构、床面剪应力和泥沙动力学的时空变化。这项工作采取端到端的方法，从第1-3年的首次直接实地观测开始，第3年进行系统的实验室实验，直到第3-5年使用业界领先的模拟套件进行区域规模的数值模拟。现场活动包括使用我们自己的仪器对不列颠哥伦比亚省最大的连续鳗草系统弗雷泽河三角洲的鳗草系统进行基于船舶和着陆器的水声调查。现场实验将为系统的实验室实验提供信息，使用模拟的鳗草叶片和沙质沉积物来获得床面剪应力和折合沉降速度的参数化，以便在数值模式中实施。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。然后，这些模型将被用来研究植被变化对滩涂排水和滩涂输沙环境的影响。我们的最终目标是在这些模型套件中充分表示海岸植被，这将使我们能够更准确地预测随着发展或气候变化而发生的海岸变化。因此，拟议的工作是及时的，对包括开发商、顾问、工程师、环保主义者和沿海社区在内的一些沿海利益攸关方来说是直接的利益攸关方。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做出宝贵的贡献和产生持久的影响。

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.