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

沉积物去向和迁移模型经常被用来帮助解决与补救努力的环境影响、可靠的自然恢复的潜力以及极端事件的潜在影响有关的环境问题。为了有效地实施泥沙去向和输运模型，必须准确地将河床冲刷和淤积速率参数化。这些过程取决于物理作用力、沉积物在水柱中的分布以及沉积物的性质，如堆积密度、颗粒大小和生物地球化学组成。这项研究将使用高分辨率数值模拟以及对物理过程和颗粒特性的现场测量分析，以量化影响泥沙再悬浮、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USEPA超级基金网站的从业者联系起来，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，他们将得到不同群体的建议，并接受高级计算流体力学、声学和光学现场仪器以及环境工程实践方面的培训。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去向的新方法得以应用，并将其转移到当今受污染的沉积物地点。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)贡献了泥沙输送模块，EFDC是美国环保局使用的最先进的水动力学模型。在这个项目中，将部署新型的现场声学和光学仪器平台，并将进行实验室实验，以测量在湍流、水流和波浪驱动的浅水河口环境中水流和泥沙的物理-生物地球化学特征。声学仪器将测量由于水流和波浪引起的平均水流和湍流在整个水柱中的垂直分布，包括在边界层内。这些仪器将与测量沉降通量、颗粒粒度分布和颗粒生物地球化学组成的絮凝剂相机和光学仪器结合在一起。实验室实验将测量原位沉积物岩心的侵蚀速率和体积密度。现场和实验室对沉积物特征的观测将被用来提供一个高分辨率的大涡模拟(LES)模式，该模式解决了湍流、含沙边界层的细节问题。从现场观测、实验室实验和大涡模拟获得的一套数据将被用来理解波浪驱动的河口环境中颗粒尺寸分布和湍流之间的关系，以及悬浮颗粒的生物地球化学性质如何影响这些动力学。这些动力学将反过来与床层的性质相关，以了解湍流和颗粒尺寸分布如何影响侵蚀速率。最后，LES模型将被用来理解絮凝动力学和泥沙诱导层化的影响，这可能起到抑制近床层湍流的作用，并减少随后泥沙进入水柱的侵蚀和卷吸。

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.