Sediment transport processes in vegetated canopies under full-scale wave conditions

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Sea level rise and increased storminess associated with climate change presents risks for coastal areas such as increased flooding and damage to recreational and ecologically important (e.g. animal habitats) sites. Conventional "hard" coastal protection solutions such as seawalls, groynes, and dykes etc. do not offer effective long term solutions due to an inability to adapt to changing conditions and the expense of continued maintenance. "Softer" eco-system based coastal defence solutions, involving coastal and aquatic vegetation, are considered to be a more promising alternative because of their ability to adapt to climate change . Previous studies have shown the ability of coastal vegetation to protect nearshore sites by dissipating wave energy and reducing sediment erosion. Although a considerable amount of research has focussed on the dissipation of wave energy by coastal vegetation, far less studies have focused on the hydrodynamics and even fewer on the sediment dynamics, particularly under full-scale wave conditions. It is generally argued that vegetation can affect sediment mobility by: i) the "trapping" of suspended sediments due to reduced flow velocities above the vegetation canopy; ii) reduced sediment resuspension due to in-canopy reductions in flow velocities, near-bed turbulence, and bed shear stress and iii) the stabilisation of the seabed substrate due to the vegetation root structure. However, the relative importance these processes remains unknown, yet it is crucially important to develop coastal sediment transport models. In this study I will investigate the hydrodynamic effects of vegetation on sediment transport processes under full-scale wave-induced oscillatory flow conditions in the Aberdeen Oscillatory Flow Tunnel (AOFT). The main objectives are to quantify the effect of bio-mechanical vegetation characteristics such as geometry, vegetation stem density, and flexibility on the near-bed hydrodynamics, bed shear stress and the sediment transport processes. Knowledge gained from these experiments will be used to incorporate the effects of vegetation into practical sediment transport models. These sediment transport models are a crucial part of large-scale morphodynamic modelling systems used in coastal engineering to predict long-term coastal evolution as a result of anthropogenic activities and natural processes resulting from climate change.