Secondary airflow patterns under offshore winds over coastal foredunes: implications for aeolian sediment transport

沿海前缘近海风下的二次气流模式：对风沙输运的影响

• 批准号: NE/F019483/1
• 负责人: Derek Jackson
• 金额: $ 50.74万
• 依托单位: University of Ulster
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FF019483%2F1
• 关键词: Secondary; airflow; patterns; under; offshore

One of the cited criteria for development of coastal sand dunes is onshore wind. The presence of large sand dune systems on coasts where the predominant wind blows offshore is therefore difficult to explain and usually they are attributed to the past occurrence of onshore winds and, by implication, subsequent changes in climate. Recent studies have shown that offshore winds can be deflected or 'steered' by existing dunes so that their direction changes. This can occur to such an extent that a process known as 'flow reversal' can arise, whereby the initially offshore wind actually flows onshore at the beach. This process is important because it can cause sand to be blown from the beach and into the dunes, causing them to grow. This may be central in explaining the presence of extensive dunes on coasts where the dominant wind is offshore, but is also important in how dunes recover after periods of wave erosion during storms. Offshore winds have traditionally been excluded from sediment budget calculations for coastal dunes, but if they do transport sand onshore, this may have been an important oversight leading to underestimates of the volume of sand being transported by wind. Recent work by the applicants has for the first time been able to measure (rather than simply infer) landward aeolian (wind-blown) sediment transport associated with local topographic steering of offshore directed airflow. In this proposal we intend to investigate the controls on this process (for example, the dune shape and wind velocities under which flow reversal occurs) and the mechanisms involved in deformation of the flow and resulting sediment transport. An ultimate goal is to quantify the role of offshore winds on foredune development and behaviour. We will use a combination of field measurement of wind and sediment transport coupled with state-of-the-art aerodynamic modelling. Our working hypothesis is that offshore winds contribute substantially to foredune behaviour on leeside coasts. We propose to test this hypothesis on an ideal field site, Magilligan Strand, Northern Ireland which is a coast dominated by offshore winds and with a variety of foredune topography, well-sorted, uniform sand and the benefit of being in a secure military zone. It has the added benefit of having an established meteorological station and being easily accessible to facilitate rapid equipment deployment in response to the occurrence of suitable wind conditions. In keeping with the NERC strategy, this proposal brings together a unique combination of novel approaches from the engineering and environmental sciences (the modelling approach was developed for snow drift) to address the important question of the origin and morphodynamics of aeolian dunefields on leeside coasts. Our research methodology involves the application, for the first time, of 3-D computational fluid dynamics (CFD) modelling to natural coastal dunes, coupled with an array of high frequency sediment transport and airflow measurements using equipment developed by the researchers. A particularly novel component of the study is that the model will be used to steer the deployment of the field instruments for optimal data gathering and this field data will then be used to modify and improve the model simulations. The research team combines the necessary expertise in modelling, high-resolution field measurement, and the physics of aeolian sediment transport to enable an integrated approach to the research. The investigation is necessarily equipment-intensive due to the complexity of the natural environment being studied. However, the high temporal resolution and close spatial deployment of the equipment array will allow us to collect an unprecedented field dataset that is of sufficiently high resolution to enable analysis of turbulence zones and characterisation of the internal boundary layer dynamics that are essential to understanding sediment transport under offshore winds.

海岸带沙丘形成的标准之一是陆上风力。因此，在主要风向离岸吹的海岸上出现大型沙丘系统是很难解释的，它们通常归因于过去发生的陆上风，并由此暗示随后的气候变化。最近的研究表明，海上风可以被现有的沙丘偏转或“操纵”，从而改变方向。这种情况可能会出现一种被称为“回流”的过程，即最初的离岸风实际上在海滩上向岸上流动。这个过程很重要，因为它会导致沙子从海滩吹到沙丘上，导致沙丘生长。这可能是解释主要风向为离岸的海岸上大量沙丘存在的核心，但在风暴期间波浪侵蚀后沙丘如何恢复也很重要。传统上，离岸风被排除在沿海沙丘的沉积物预算计算之外，但如果它们确实将沙子输送到岸上，这可能是一个重要的疏忽，导致被风输送的沙子体积被低估。申请人最近的工作首次能够测量（而不是简单地推断）与近海定向气流的当地地形转向有关的向陆风沙（风吹）沉积物运输。在本提案中，我们打算研究这一过程的控制因素（例如，发生水流逆转的沙丘形状和风速）以及水流变形和由此产生的泥沙运输的机制。最终目标是量化海上风对前丘发展和行为的作用。我们将结合现场测量的风和沉积物输运加上最先进的空气动力学模型。我们的工作假设是，离岸风在很大程度上促进了背风海岸的前丘行为。我们建议在一个理想的场地上测试这一假设，北爱尔兰的Magilligan Strand，这是一个由离岸风主导的海岸，拥有各种前沙丘地形，分类良好，均匀的沙子，以及处于安全军事区的好处。它还有一个额外的好处，即拥有一个已建立的气象站，并且易于到达，以便在适当的风况发生时迅速部署设备。为了与NERC战略保持一致，该提案将工程和环境科学的新方法（建模方法是为雪漂而开发的）结合在一起，以解决背风海岸风成沙丘的起源和形态动力学的重要问题。我们的研究方法首次将三维计算流体动力学（CFD）模型应用于天然海岸沙丘，并使用研究人员开发的设备进行一系列高频沉积物输送和气流测量。该研究的一个特别新颖的组成部分是，该模型将用于指导现场仪器的部署，以获得最佳的数据收集，然后这些现场数据将用于修改和改进模型模拟。研究小组结合了建模、高分辨率现场测量和风成沉积物运输物理方面的必要专业知识，使研究能够采用综合方法。由于所研究的自然环境的复杂性，调查必然需要大量的设备。然而，设备阵列的高时间分辨率和近距离空间部署将使我们能够收集前所未有的现场数据集，该数据集具有足够高的分辨率，可以分析湍流区和内部边界层动力学特征，这对于理解海上风下的沉积物运输至关重要。

项目成果

Seasonal Variations in Airflow Over the Namib Dune, Gale Crater, Mars: Implications for Dune Dynamics

• DOI: 10.1029/2018gl079598
• 发表时间: 2018-09-28
• 期刊: GEOPHYSICAL RESEARCH LETTERS
• 影响因子: 5.2
• 作者: Cornwall, Carin;Jackson, Derek W. T.;Cooper, J. Andrew G.
• 通讯作者: Cooper, J. Andrew G.

Monitoring Cross-shore Intertidal Beach Dynamics using Oblique Time-lapse Photography

使用倾斜延时摄影监测跨岸潮间带海滩动态

• DOI: 10.2112/si95-215.1
• 发表时间: 2020
• 期刊: Journal of Coastal Research
• 作者: Guisado-Pintado E

Dune gardening? A critical view of the contemporary coastal dune management paradigm

沙丘园艺？

• DOI: 10.1111/area.12692
• 发表时间: 2021
• 期刊: Area
• 影响因子: 2.2
• 作者: Cooper A

Structure-from-Motion-Derived Digital Surface Models from Historical Aerial Photographs: A New 3D Application for Coastal Dune Monitoring

• DOI: 10.3390/rs13010095
• 发表时间: 2021-01-01
• 期刊: REMOTE SENSING
• 影响因子: 5
• 作者: Grottoli, Edoardo;Biausque, Melanie;Cooper, J. Andrew G.
• 通讯作者: Cooper, J. Andrew G.

Using wind run to predict sand drift

利用风跑预测流沙

• DOI: 10.1002/esp.4848
• 发表时间: 2020
• 期刊: Earth Surface Processes and Landforms
• 影响因子: 3.3
• 作者: Baas A