Collaborative Research: Flocculation Dynamics in the Fluvial to Marine Transition

合作研究：河流向海洋转变中的絮凝动力学

• 批准号: 2204852
• 负责人: Jeffrey Nittrouer
• 金额: $ 29.07万
• 依托单位: Texas Tech University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-10-01 至 2022-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2204852&HistoricalAwards=false
• 关键词: Collaborative; Research; Flocculation; Dynamics; Fluvial

Rivers deliver fine muddy sediment eroded from upstream landscapes to coastal regions. Upon arrival, mud can deposit in or move through the rivers, bays, estuaries, marshes, and deltas of the region. Forecasting where the mud goes when it arrives is important for society. For example, accurately forecasting the movement and deposition of mud in these regions is important for predicting and evaluating the effectiveness of river diversion projects aimed at using sediment deposits to build deltaic landscape, fostering healthy water quality, and/or evaluating how mud deposits shoal waterways and therefore impede vessel navigation. Yet, the prediction of mud movement through coastal waters is difficult. The difficulty is due in large part to the limited ability to measure and model how mud particles change when suspended in water. Small mud particles tend to clump together and form aggregates known as flocs, which grow or shrink depending on turbulence levels in the flow and the salinity, biological content, and amount and type of sediment in the water. The settling speed of muddy sediment is directly related to the size and density these flocs. This research will evaluate the nature of mud particle movement in river and coastal waterways by collecting detailed measurements that will inform and validate physically-based models of floc dynamics. The research pairs laboratory experiments and comprehensive field surveys from one of the largest coastal deltas in the world, the lower Mississippi River in Louisiana. The team will engage high school women interested in STEM careers through summer camp programs at Virginia Tech, and train graduate and undergraduate students from underrepresented minority groups about physical processes of sediment transport. By combining engineering and earth science studies, students will be exposed to cross-disciplinary objectives and therefore equipped to handle basic and industry science, and/or policy-related fields.The research team will quantify mud floc sizes as a function of the changing turbulent shear, salinity, and water-column sediment concentration conditions that exists across the fluvial to marine transition (FtMT) of the Mississippi River. The three primary zones of this transition are the freshwater fluvial section, the saline-stratified and laterally confined estuarine reach, and the laterally unconfined near-shore river plume. Four central hypotheses will be tested: (1) in the freshwater riverine reach, flocs produce vertical stratification of mud; (2) mixing in the estuarine reach at the interface of the near-bottom salt wedge produces rigorous floc growth; (3) modifications to turbulent shear through the laterally unconfined river plume is a central driver of floc growth and thus increased mud settling velocity; and (4) minimal correlation between floc size and local turbulence and salinity is due in part to disequilibrium between floc size and local conditions. These hypotheses will be tested by integrating field and laboratory studies that measure the vertical, longitudinal, and temporal distributions of floc size, sediment concentration, salinity, and turbulent shear over the FtMT. The team will use this knowledge to inform and validate flocculation models that can be integrated into larger hydrodynamic models used by coastal scientists and engineers to enhance predictions of the transport and fate of fine sediment. Measurements developed as part of the study will also initiate a global community database housing key information needed to develop and calibrate computer models predicting the movement and deposition of mud.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

河流将上游景观侵蚀的细泥质沉积物输送到沿海地区。到达后，泥浆可能沉积或移动穿过该地区的河流、海湾、河口、沼泽和三角洲。预测泥浆到达时的去向对于社会很重要。例如，准确预测这些地区泥浆的运动和沉积对于预测和评估旨在利用泥沙沉积物构建三角洲景观、促进健康水质和/或评估泥浆沉积物如何影响水道的河流改道项目的有效性非常重要从而妨碍船舶航行。然而，预测沿海水域的泥浆运动很困难。困难在很大程度上是由于测量和模拟泥浆颗粒悬浮在水中时如何变化的能力有限。小泥浆颗粒往往会聚集在一起并形成称为絮凝体的聚集体，絮凝体的生长或收缩取决于水流​​中的湍流水平以及水中的盐度、生物含量以及沉积物的数量和类型。泥质沉积物的沉降速度与这些絮凝物的尺寸和密度直接相关。这项研究将通过收集详细的测量数据来评估河流和沿海水道中泥浆颗粒运动的性质，这些测量数据将为基于物理的絮凝体动力学模型提供信息和验证。该研究结合了实验室实验和对世界上最大的沿海三角洲之一——路易斯安那州密西西比河下游的综合实地调查。该团队将通过弗吉尼亚理工大学的夏令营项目吸引对 STEM 职业感兴趣的高中女性，并对来自代表性不足的少数群体的研究生和本科生进行有关沉积物运输物理过程的培训。通过将工程学和地球科学研究相结合，学生将接触到跨学科的目标，从而有能力处理基础科学和工业科学和/或政策相关领域。研究团队将量化泥絮体尺寸作为不断变化的湍流的函数密西西比河河流到海洋过渡区 (FtMT) 存在的剪切力、盐度和水柱沉积物浓度条件。这种过渡的三个主要区域是淡水河流段、盐层分层和横向限制的河口河段以及横向不受限制的近岸河流羽流。将测试四个中心假设：（1）在淡水河段，絮凝物产生泥浆垂直分层； (2)在河口河段近底部盐楔交界面处的混合产生了剧烈的絮体生长； (3) 通过横向无约束的河流羽流对湍流剪切的修改是絮凝体生长的主要驱动力，从而增加了泥浆沉降速度； (4) 絮凝体大小与局部湍流和盐度之间的最小相关性部分是由于絮凝体大小与局部条件之间的不平衡。这些假设将通过整合现场和实验室研究来测试，这些研究测量 FtMT 上絮体尺寸、沉积物浓度、盐度和湍流剪切的垂直、纵向和时间分布。该团队将利用这些知识来告知和验证絮凝模型，​​这些模型可以集成到沿海科学家和工程师使用的更大的水动力模型中，以增强对细小沉积物的运输和命运的预测。作为研究的一部分开发的测量还将启动一个全球社区数据库，其中包含开发和校准预测泥浆运动和沉积的计算机模型所需的关键信息。该奖项反映了 NSF 的法定使命，并通过使用基金会的评估进行评估，被认为值得支持。智力价值和更广泛的影响审查标准。

项目成果

FlocARAZI: An In‐Situ, Image‐Based Profiling Instrument for Sizing Solid and Flocculated Suspended Sediment

FlocARAZI：一种基于图像的原位分析仪器，用于确定固体和絮凝悬浮沉积物的尺寸

• DOI: 10.1029/2021jf006210
• 发表时间: 2021-10-12
• 期刊: Journal of Geophysical Research: Earth Surface
• 作者: R. Osborn;Br;on Dillon;on;D. Tran;E. Abolfazli;K. Dunne;J. Nittrouer;K. Strom
• 通讯作者: K. Strom

Examining the impact of emissions scenario on lower Mississippi River flood hazard projections

检查排放情景对密西西比河下游洪水灾害预测的影响

• DOI: 10.1088/2515-7620/ac8d53
• 发表时间: 2022-09
• 期刊: Environmental Research Communications
• 影响因子: 2.9
• 作者: Dunne, K. B. J.;Dee, S. G.;Reinders, J.;Muñoz, S. E.;Nittrouer, J. A.
• 通讯作者: Nittrouer, J. A.