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

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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.