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

全尺度波浪条件下植被冠层的沉积物输送过程

• 批准号: 1957451
• 金额: --
• 依托单位: University of Aberdeen
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2017
• 资助国家: 英国
• 起止时间: 2017 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-1957451
• 关键词: Sediment; transport; processes; vegetated; canopies

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.

与气候变化相关的海平面上升和风暴增加给沿海地区带来了风险，例如洪水增加以及对娱乐和生态重要（例如动物栖息地）地点的破坏。由于无法适应不断变化的条件和持续维护的费用，传统的“硬”海岸保护解决方案，如海堤、沙坝和堤防等，不能提供有效的长期解决方案。“更软”的基于生态系统的海防解决方案，包括沿海和水生植被，被认为是一个更有希望的替代方案，因为它们能够适应气候变化。以前的研究表明，沿海植被有能力通过消散波浪能和减少沉积物侵蚀来保护近岸地区。尽管大量的研究集中在海岸植被对波浪能的耗散上，但对水动力的研究却少之又少，对泥沙动力学的研究更是少之又少，特别是在全尺寸波浪条件下。一般认为，植被可以通过以下方式影响沉积物的流动性：i)由于植被冠层上方流速降低而“捕获”悬浮沉积物；Ii)由于冠层内流速、近床湍流和床剪切应力的降低，沉积物再悬浮减少；iii)由于植被根结构，海床基底稳定。然而，这些过程的相对重要性尚不清楚，但建立沿海沉积物输运模型至关重要。在本研究中，我将研究在阿伯丁振荡流隧道（AOFT）全尺寸波激振荡流条件下植被对泥沙输运过程的水动力效应。主要目标是量化生物力学植被特征（如几何形状、植被茎密度和灵活性）对近床水动力、床切应力和沉积物输运过程的影响。从这些实验中获得的知识将用于将植被的影响纳入实际的泥沙输送模型。这些泥沙运移模型是海岸工程中用于预测气候变化引起的人为活动和自然过程导致的长期海岸演变的大尺度形态动力学模拟系统的重要组成部分。