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

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和控制海岸沙丘发展的一系列相互作用中的关键联系。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，就不可能确定一个给定的风事件是否会产生输送。这种情况阻碍了风沙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吹运输阈值条件模型。这项工作与以前的方法不同，它包含了一个新的术语，该术语解释了沉积物层中存在的粒度范围。基于对先前公布的数据的检查，新模型提供了显著改进的预测能力。此外，该模型还包含了表面湿度对阈值条件的影响，这是许多海滩的一个关键复杂因素。现场实验将在两个地点（得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。在运输事件开始前，风速和地面水分含量将被监测。移动观测站将分别由一个三维声速风速计和一组以麦克风为基础的跳跃探测器组成，它们将被安装在海滩上不同湿度的位置。风速计和跃变探测器将实时记录，表面湿度测量将使用为此目的设计的手持光学设备进行。在实地研究期间记录的数据将允许验证和校准模型。这项研究代表了对当前用于解释和模拟风沙运输的理论框架的重大偏离。研究结果将进一步深入了解沙滩上沙子的运移，如果所提出的模型得到成功验证，这项研究将显著提高预测能力。这将为研究人员和海岸管理者提供更准确的估计，了解有多少沙子从海滩运输到沙丘，以及这些事件何时和在什么条件下发生，从而改进大规模沉积物预算的计算。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，本研究将解决一个最棘手的因素，使风沙在海滩上的运输复杂化：频繁出现的表面水分可以抑制甚至完全阻止风吹沙的运动。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。

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.