Collaborative Research: Grain to Channel Scale Experimental and Numerical Investigation of Cohesive Sediment Transport

每年，美国因水土流失而损失数十亿美元的财产和大片的栖息地。为了减轻与侵蚀有关的损害和生境丧失，恢复项目向侵蚀地区输入沉积物。这些恢复工作的成功取决于它们保留沉积物的能力，因此恢复设计需要对沉积物输运有很好的了解。目前，有既定的方法来预测非粘性沉积物的运输，如砂和砾石，相对于流动条件和沉积物颗粒大小。然而，仍然很难预测粘性沉积物的迁移，例如粘土或泥浆，它们在水生生态系统中普遍存在，由非常细的颗粒组成。预测粘性泥沙输运是具有挑战性的，因为这些细颗粒有很强的趋势粘在一起，形成聚集体。这些聚集体极大地改变了泥沙颗粒的有效粒径及其与水流的相互作用。该项目将联合收割机实验和数值模拟相结合，在一系列尺度，以了解如何细粘性颗粒形成聚集体和聚集如何控制沉积物在水中的运输。将建立粘性泥沙输运的预测方程。这项研究的结果将有助于改善恢复项目的设计，以减轻侵蚀驱动的财产和栖息地的损失。下一代环境科学家和工程师将接受研究生、博士后和本科生水平的培训。将制作有关侵蚀的科学录像并向公众传播。示范实验将用于提高K-12学生对环境科学的兴趣和公众对侵蚀的理解。本研究将结合联合收割机多尺度实验与数值模拟，以了解控制黏性泥沙输运的基本物理因素。该研究将直接解决与粘性泥沙输运动力学的多尺度和多物理性质有关的关键挑战，这些挑战目前阻碍了对这些过程的理解。这包括以下事实：在河道和生态系统尺度上发生的迁移受纳米级粘土颗粒之间的微观至中尺度相互作用的控制，而纳米级粘土颗粒是沉积物凝聚力的主要贡献者，并受颗粒力学和流体流动之间的多物理场耦合的控制。计划中的研究将结合联合收割机纳米到微米共焦成像和粗粒度分子动力学（CGMD）模拟，微观到中尺度毫流体实验和计算流体动力学（CFD）模拟，和渠道规模的水槽和室外流实验和CFD模拟，从根本上了解粘土聚集和凝胶化对渠道的关键影响，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Each year, the United States loses billions of dollars in property and large areas of habitat to erosion. To mitigate erosion-related damages and habitat losses, restoration projects import sediment to eroded areas. The success of these restoration efforts depends on their ability to retain sediment, so that restoration design requires a good understanding of sediment transport. Currently, there are established methods for predicting the transport of non-cohesive sediment, such as sand and gravel, relative to flow conditions and sediment particle size. However, it remains difficult to predict the transport of cohesive sediment, such as clay or mud, which is ubiquitous in aquatic ecosystems and consists of very fine particles. Predicting cohesive sediment transport is challenging because these fine particles have a strong tendency to stick together and form aggregates. These aggregates greatly change the effective size of the sediment particles and their interaction with the flow. This project will combine experiments and numerical simulations at a range of scales to understand how fine cohesive particles form aggregates and how aggregation controls the transport of sediment in water. Predictive equations for cohesive sediment transport will be developed. The results of this study will help improve designs of restoration projects to mitigate erosion-driven property and habitat losses. Next-generation environmental scientists and engineers will be trained at the graduate, postdoctoral, and undergraduate levels. Science videos about erosion will be created and disseminated to the public. Demonstration experiments will be used to raise K-12 students’ interest in environmental science and public understanding of erosion. This study will combine multiscale experiments and numerical simulations to understand the fundamental physical factors governing cohesive sediment transport. The study will directly address key challenges related to the multiscale and multiphysics nature of cohesive sediment transport dynamics that currently inhibit understanding of these processes. This includes the fact that transport that occurs at channel and ecosystem scales is controlled by the micro- to mesoscale interactions between nanometer-size clay particles, which are the main contributors to sediment cohesiveness, and by the multiphysics couplings between particle mechanics and fluid flow. The planned research will combine nano- to microscale confocal imaging and coarse-grained molecular dynamics (CGMD) simulations, micro- to mesoscale millifluidic experiments and computational fluid dynamics (CFD) simulations, and channel scale flume and outdoor stream experiments and CFD simulations to fundamentally understand the critical impacts of clay aggregation and gelation on channel-scale cohesive sediment transport.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.