Doctoral Dissertation Research: Field Investigation of the Influence of Surface Moisture on the Initiation of Motion in Wind-Blown Sand Transport on Beaches

博士论文研究：表面湿度对海滩风沙输送运动启动影响的现场调查

• 批准号: 0928014
• 负责人: Steven Namikas
• 金额: $ 1.16万
• 依托单位: Louisiana State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-08-01 至 2011-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0928014&HistoricalAwards=false
• 关键词: Doctoral; Dissertation; Research; Field; Investigation

The movement of sand by wind is the primary mechanism responsible for delivering sand from beach to dune. As such, it represents a critical linkage in the suite of interactions that connect these places and that control coastal dune development. A key uncertainty lies in the identification of the threshold condition, that is, the wind energy level at which transport begins. Without accurate representation of this threshold, it is not possible to determine whether a given wind event will generate transport. This situation hampers intermediate-scale modeling of aeolian sediment budgets, as it is not currently possible to reliably predict the occurrence of transport events. The goal of this doctoral dissertation research project is to validate and calibrate a new model of the threshold condition for windblown transport on beaches. This effort differs from previous approaches in the inclusion of a new term that accounts for the range of grain sizes present in the sediment bed. The new model provides significantly improved predictive capabilities, based on examination of previously published data. Further, the model also encapsulates the effect of surface moisture on the threshold condition, a key complicating factor on many beaches. Field experiments will be conducted at two locations (Padre Island, TX, and Cape San Blas, FL) to verify the model. Wind velocity and surface moisture contents will be monitored leading up to the start of transport events. Mobile stations, each comprised of a 3-D sonic anemometer and an array of microphone-based saltation detectors, will be installed on the beach at locations of various moisture contents. The anemometers and saltation detectors will be logged in real time, and surface moisture measurements will be conducted using a handheld optical device designed for this purpose. The data recorded during the field study will allow validation and calibration of the model.This study represents a significant departure from the current theoretical framework that is used to explain and model windblown sand transport. The results will provide improved insight into the transport of sand on beaches, and if the proposed model is successfully validated this study will significantly advance predictive capabilities. This will in turn improve calculations of larger-scale sediment budgets by providing researchers and coastal managers with more accurate estimates regarding how much sand is transported from beach to dune, and when and under what conditions such events can occur. This will contribute to modeling of post-storm dune recovery, for example, and for predicting the time required for dune re-establishment and reconstruction programs. Finally, this study will address one of the most problematic factors complicating wind blown sand transport on beaches: the frequent presence of surface moisture which can inhibit or even completely prevent the movement of sand by wind. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.

风沙运动是将沙子从海滩输送到沙丘的主要机制。因此，它代表了连接这些地方并控制沿海沙丘开发的一系列互动中的关键联系。一个关键的不确定性在于阈值条件的确定，即运输开始时的风能水平。如果没有这个阈值的准确表示，就不可能确定给定的风事件是否会产生输送。这种情况阻碍了对风沙沉积收支的中等尺度模拟，因为目前还不可能可靠地预测运输事件的发生。本博士论文研究项目的目标是验证和校准一个新的海滩风速输送门槛条件模型。这一努力与以前的方法不同之处在于加入了一个新的术语，该术语解释了沉积物床中存在的粒度范围。根据对以前发布的数据的检查，新模型提供了显著改进的预测能力。此外，该模型还包含了地表湿度对阈值条件的影响，这是许多海滩上一个关键的复杂因素。现场实验将在两个地点(德克萨斯州帕德雷岛和佛罗里达州圣布拉斯角)进行，以验证该模型。在交通活动开始之前，将监测风速和地表水分含量。移动站将安装在海滩上不同含水率的位置，每个移动站由一个三维声波风速计和一个基于麦克风的跳跃探测器阵列组成。风速计和跃变探测器将被实时记录，并将使用为此目的设计的手持光学设备进行地表湿度测量。实地研究期间记录的数据将允许对该模型进行验证和校准。这项研究与目前用于解释和模拟风沙输送的理论框架有很大不同。研究结果将有助于更好地洞察海滩上的沙粒运移，如果建议的模型成功验证，这项研究将显著提高预测能力。这反过来将改善对更大规模泥沙预算的计算，为研究人员和海岸管理人员提供更准确的估计，以确定有多少沙子从海滩输送到沙丘，以及此类事件发生的时间和条件。例如，这将有助于建立风暴后沙丘恢复的模型，并预测沙丘重建和重建计划所需的时间。最后，这项研究将解决使海滩上的风沙运输变得复杂的最有问题的因素之一：经常存在的表面湿度可以抑制甚至完全阻止风吹沙的移动。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立研究生涯。