Doctoral Dissertation Research: Spatial and Temporal Patterns of Suspended Sediment Transport at a Tidal River Bifurcation

博士论文研究：潮汐河分叉处悬浮泥沙输送的时空模式

• 批准号: 0402104
• 负责人: John Wilson
• 金额: $ 1.2万
• 依托单位: University of Southern California
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-03-15 至 2006-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0402104&HistoricalAwards=false
• 关键词: Doctoral; Dissertation; Research; Spatial; Temporal

Understanding how water and sediment move through different parts of a deltaic system is of fundamental importance to resource managers who are charged with sustainable futures of critical marsh and wetland habitat. Channel bifurcations (locations in a primary channel where the flow divides into two separate downstream channels) are common natural features of fluvial deltas. Despite their abundance, river bifurcations have not been studied extensively because it is conventionally assumed that suspended sediment "goes with the flow" -- that suspended sediment is partitioned between the downstream branches in proportion to water discharge into each downstream branch. This assumption is contrary to the well-known fact that suspended sediment is typically distributed unevenly across channels because of secondary flows and because of varying source-sink areas within a channel. The goal of this Doctoral Dissertation Research Improvement project is to address these contrary notions by identifying the hydrologic and morphologic parameters that influence the division of suspended sediments through a bifurcation. High-resolution field data will be collected in a tidally influenced river bifurcation on the Sacramento-San Joaquin Delta located in central California. Instrumentation will include a boat-mounted, three-dimensional Acoustic Doppler Profiler, several Optical Backscatterance Sensors, a Global Positioning System, and a range of other electronic sensors and manual devices to measure water flow and the distribution of suspended sediment throughout the bifurcation over a variety of hydrologic conditions. Shear stress, turbulence intensity, momentum flux, and the suspended sediment transport capacity of each branch of the bifurcation will be calculated and related to the observed pattern of sediment concentrations. The field results will be complemented by the use of a two-dimensional hydrodynamic model, which allows extrapolation to longer time frames (months to years) and to alternative sites in order to produce generalizations about cyclic and long-term evolution of bifurcation morphology.A bifurcation in a river channel represents a "decision point" in a channel network where suspended sediment is preferentially directed towards one downstream branch over another. Scientists have yet to decipher how this complex "decision" is made despite its critical role in the development of river deltas and estuaries. Suspended sediment provides the base on which tidal marsh habitat grows, and knowing why one downstream branch receives more suspended sediment over another will guide managers in selecting successful marsh restoration strategies. This is particularly important when flow control structures such as floodgates, barriers, and dams modify the natural dynamics of the system. The Sacramento-San Joaquin Delta-Estuary system is under immense environmental stress and this study contributes to a larger understanding of the processes that shape this vital ecosystem. While the processes at a channel bifurcation are complex, recent developments in field techniques and computer modeling allow researchers to address this lapse in basic scientific understanding for the first time. 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.

了解水和沉积物如何在三角洲系统的不同部分中移动，这对于负责具有关键沼泽和湿地栖息地的可持续期货的资源经理而言至关重要。 通道分叉（在主要通道中的位置，该流量分为两个单独的下游通道）是河流三角洲的常见自然特征。 尽管河流分叉尚未得到广泛的研究，因为通常认为悬浮的沉积物“与流动” - 悬浮的沉积物是在下游分支之间划分的，以与排放到每个下游分支的水分成比例。这个假设与众所周知的事实背道而驰：悬浮的沉积物通常由于次要流而跨通道不均匀地分布，并且由于通道内的源链接区域变化。 该博士学位论文研究改进项目的目标是通过确定通过分叉影响悬浮沉积物分裂的水文和形态学参数来解决这些相反的观念。 高分辨率的现场数据将收集在位于加利福尼亚州中部的萨克拉曼多 - 山华金三角洲的潮汐影响的河分叉中。 仪器将包括船安装的三维声学多普勒探测器，几个光学反向散射传感器，一个全球定位系统以及一系列其他电子传感器和手动设备，以测量水流的水流和悬浮沉积物的分布，整个Bifurcient the Bifurcation the Bifurcation the Mydologic Cresentation the Bifurcation。 将计算剪切应力，湍流强度，动量通量以及分叉每个分支的悬浮沉积物运输能力，并与观察到的沉积物浓度模式有关。 使用二维流体动力学模型将补充该田间结果，该模型允许外推到更长的时间范围（几个月到几年）和替代位点，以产生有关循环和长期长期演化的概括性的概括，对河道中的分支中的Bifurciation在河道中的bifuntermations在频道中的一个型号却是一个暂停的，而不是一个暂停的台阶，而不是一个暂停的态度。 尽管科学家在河流和河口的发展中起着至关重要的作用，但尚未破译这种复杂的“决定”。 悬浮的沉积物提供了潮汐沼泽栖息地的基础，并且知道为什么一个下游分支在另一个分支上获得更多悬浮的沉积物，这将指导经理选择成功的沼泽修复策略。 当流动控制结构（例如闸门，障碍物和大坝）修改系统的自然动态时，这一点尤其重要。 萨克拉曼多山华金三角洲座系统处于巨大的环境压力下，这项研究有助于对塑造这一重要生态系统的过程有更大的了解。 虽然渠道分叉的过程很复杂，但现场技术和计算机建模方面的最新发展使研究人员可以首次解决基本科学理解的这种失误。 作为博士学位论文研究改进奖，该奖项还将提供支持，使有前途的学生能够建立强大的独立研究职业。