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穿过三角洲系统的不同部分对于负责关键沼泽和湿地栖息地可持续未来的资源管理者来说至关重要。 河道分岔（主河道中水流分成两个独立的下游河道的位置）是河流三角洲的常见自然特征。 尽管河流分叉处数量众多，但尚未得到广泛研究，因为传统上认为悬浮沉积物“随流而行”——悬浮沉积物按照流入每个下游分支的水量的比例在下游分支之间分配。这一假设与众所周知的事实相反，即由于二次流以及河道内源汇面积的变化，悬浮沉积物通常在河道上分布不均匀。 该博士论文研究改进项目的目标是通过确定影响悬浮沉积物通过分叉划分的水文和形态参数来解决这些相反的概念。 高分辨率现场数据将在加利福尼亚州中部萨克拉门托-圣华金三角洲受潮汐影响的河流分叉处收集。 仪器将包括一个安装在船上的三维声学多普勒轮廓仪、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，用于测量整个分叉处的水流和悬浮沉积物的分布。水文条件多样。 将计算分岔每个分支的剪切应力、湍流强度、动量通量和悬浮泥沙输送能力，并将其与观测到的泥沙浓度模式相关联。 现场结果将通过使用二维流体动力学模型得到补充，该模型允许外推到更长的时间范围（数月到数年）和替代地点，以便产生关于分叉形态的循环和长期演化的概括。河道中的分叉代表河道网络中的一个“决策点”，其中悬浮沉积物优先流向一个下游支流而不是另一个支流。 尽管这一复杂的“决定”在河流三角洲和河口的发展中发挥着至关重要的作用，但科学家们尚未弄清楚它是如何做出的。 悬浮沉积物为潮汐沼泽栖息地的生长提供了基础，了解为什么一个下游分支比另一个分支接收更多的悬浮沉积物将指导管理者选择成功的沼泽恢复策略。 当水闸、屏障和水坝等流量控制结构改变系统的自然动力学时，这一点尤其重要。 萨克拉门托-圣华金三角洲河口系统承受着巨大的环境压力，这项研究有助于更好地了解塑造这一重要生态系统的过程。 虽然通道分叉处的过程很复杂，但现场技术和计算机建模的最新发展使研究人员首次能够解决基本科学理解中的这一失误。 作为博士论文研究改进奖，该奖项还将为有前途的学生建立强大的独立研究生涯提供支持。