Collaborative Research: Improved observation and parameterization of bottom boundary layer turbulence and particle properties for sediment fate and transport modeling

泥沙命运和运输模型经常被用来帮助解决与修复工作的环境影响、可靠的自然恢复潜力和极端事件的潜在影响有关的环境问题。为了有效地实现泥沙命运和输运模型，必须精确地参数化河床侵蚀和沉积速率。这些过程取决于物理强迫、沉积物在水柱中的分布以及沉积物的特性，如体积密度、粒度和生物地球化学组成。本研究将采用高分辨率数值模拟以及对物理过程和颗粒特性的原位测量分析来量化影响沉积物再悬浮、沉降和絮凝的湍流强迫和颗粒特性。该项目将学术水平的研究人员直接与积极参与几个美国环保署超级基金站点的从业人员联系起来，并间接与环境研究人员、工程师和政策制定者联系起来。该项目将支持两名研究生的博士研究，他们将由一个多元化的小组指导，并在先进的计算流体动力学、声学和光学场仪器以及环境工程的实际方面进行培训。这项研究的结果将把学术研究的方法和结果与实践联系起来，使量化和预测沉积物和污染物的命运以及向当今污染沉积物地点的运输的新方法得以应用。此外，pi与社区建模工作进行了广泛的合作，并为环境流体动力学规范（EFDC）提供了沉积物运输模块，这是美国环保署使用的最先进的水动力学模型。在本项目中，将部署新型的原位声学和光学仪器平台，并进行实验室实验，以测量湍流、水流和波浪驱动的浅水河口环境中水流和沉积物的物理-生物地球化学特征。声学仪器将测量整个水柱的平均流量和湍流的垂直分布，包括在边界层内，由于水流和波浪。这些仪器将与絮团照相机和光学仪器相结合，用于测量沉降通量、颗粒大小分布和颗粒生物地球化学成分。实验室实验将测量侵蚀速率和原位沉积物岩心的体积密度。对沉积物特征的实地和实验室观测将用于提供高分辨率大涡模拟（LES）模型，该模型可解析湍流、沉积物负载边界层的细节。通过野外观测、实验室实验和LES模型获得的一系列数据将用于了解波浪驱动的河口环境中粒径分布与湍流之间的关系，以及悬浮颗粒的生物地球化学特性如何影响这些动力学。这些动力学将反过来与床的性质有关，以了解湍流和粒度分布如何影响侵蚀速率。最后，LES模型将用于了解絮凝动力学和沉积物诱导分层的影响，这可能会抑制近床湍流并减少随后的侵蚀和沉积物进入水柱的卷带。

Sediment fate and transport models are often utilized to help address environmental questions related to the environmental impacts of remediation efforts, the potential for reliable natural recovery, and the potential impacts of extreme events. In order to effectively implement sediment fate and transport models, bed erosion and deposition rates must be accurately parameterized. These processes are dependent on physical forcing, the distribution of sediment in the water column, and the properties of sediment such as bulk density, particle size, and biogeochemical composition. This research will employ high-resolution numerical simulations along with analysis of in-situ measurements of physical processes and particle characteristics to quantify turbulent forcing and particle properties affecting sediment resuspension, settling, and flocculation. The project links academic-level researchers directly with practitioners actively involved with several USEPA Superfund sites and indirectly with environmental researchers, engineers, and policy makers. The project will support the Ph.D. research of two graduate students who will be advised by a diverse group and trained in advanced computational fluid dynamics, acoustic and optical field instrumentation, as well as practical aspects of environmental engineering. Results from this study will link methods and results from academic research to practice, enabling application of novel methods for quantifying and predicting sediment and contaminant fate and transport to present-day contaminated sediment sites. Additionally, the PIs have worked extensively with community modeling efforts and have contributed sediment transport modules to the Environmental Fluid Dynamics Code (EFDC), a state-of-the-art hydrodynamic model in use by the USEPA. In this project, novel in-situ acoustical and optical instrument platforms will be deployed and laboratory experiments will be conducted to measure the physio-biogeochemical characteristics of flow and sediment in a turbulent, current and wave-driven shallow estuarine setting. Acoustic instrumentation will measure vertical distributions of mean flows and turbulence throughout the water column, including within the boundary layer, due to currents and waves. These will be combined with a floc camera and optical instruments that measure settling flux, particle size distributions and particulate biogeochemical compositions. Laboratory experiments will measure erosion rates and bulk densities of in-situ sediment cores. The field and laboratory observations of the sediment characteristics will be used to inform a high resolution large-eddy simulation (LES) model that resolves the details of the turbulent, sediment-laden boundary layer. The suite of data obtained from the field observations, laboratory experiments, and LES model will be used to understand the relationship between particle size distributions and turbulence in wave-driven estuarine environments and how these dynamics are affected by biogeochemical properties of the suspended particles. These dynamics will in turn be related to properties of the bed to understand how the turbulence and particle size distributions affect erosion rates. Finally, the LES model will be used to understand flocculation dynamics and the effects of sediment-induced stratification that may act to dampen the near-bed turbulence and reduce subsequent erosion and entrainment of sediment into the water column.