Hydraulic and Geomorphic Controls on the Evolution of Cluster Bedforms in Gravel-Bed Streams

砾石床流中簇状河床演化的水力和地貌控制

• 批准号: 0331485
• 负责人: Thanos Papanicolaou
• 金额: $ 14万
• 依托单位: University of Iowa
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-06-30 至 2006-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0331485&HistoricalAwards=false
• 关键词: Hydraulic; Geomorphic; Controls; Evolution; Cluster

0208358PapanicolaouSmall-scale cluster bedforms are prevalent in gravel-bed rivers. An understanding of their mechanics is needed for better understanding of river processes, as well as the development of accurate predictions of bed roughness characteristics, stage-discharge relations, bedload transport, and implementation of restoration plans. Cluster microforms are one component of the nonlinear system of gravel-bed rivers. Flow structure and entrainable sediment produce clusters; once developed, they in turn influence sediment transport and the surrounding flow field.Clusters add to bed stability and delay of sediment motion. Self-organized clusters have been called a "product of stochastic encounters among individual grains." In natural streams, cluster bedforms are thought to form during recession of flow events great enough to create selective mobilization of bed sediment. Some think that clusters form in quasi-stable equilibrium so as to maximize flow resistance, producing a wavelength to particle diameter ratio of 20. Still others suggest that clusters are a "kinematic wave" or migratory, rather than stable structure.The project entails extensive laboratory flume experiments to understand the evolution of cluster microforms. A major- goal is to define the near bed turbulence structure to improve the understanding of the coupling between near-bed turbulence and sediment transport when clusters are present. A series of experiments will be conducted for non-unisized spheres to examine the cluster geometry, the flow ranges under which clusters form, remain stable, and disintegrate, and the interaction between near-bed hydraulic parameters and clusters bedforms. The reduced number of variables in the laboratory experiments will allow specific relations between the hydraulic parameters, sediment supply, and resulting particle clusters to be isolated and quantified. Recent advances in high-resolution cameras and acoustic sensors for measuring turbulence around clusters, combined with the development of hardware for image analysis and bed scanning will allow simultaneous measurements of local sediment transport and adjacent near-bed flow at turbulence-resolving frequencies without disturbing the flow.

0208358Papanicolaou 小规模簇状河床普遍存在于砾石河床河流中。 为了更好地理解河流过程，以及准确预测河床粗糙度特征、阶段流量关系、河床输送和恢复计划的实施，需要了解它们的力学。 簇状微形态是砾石河床非线性系统的组成部分之一。 流动结构和夹带泥沙产生团簇；一旦形成，它们就会影响沉积物的输送和周围的流场。簇会增加床层的稳定性并延迟沉积物的运动。 自组织簇被称为“单个颗粒之间随机相遇的产物”。在天然溪流中，簇状河床被认为是在水流衰退期间形成的，其强度足以产生河床沉积物的选择性流动。 一些人认为团簇在准稳定平衡状态下形成，从而使流动阻力最大化，从而产生 20 的波长与颗粒直径之比。还有一些人认为团簇是一种“运动波”或迁移性结构，而不是稳定的结构。该项目需要进行大量的实验室水槽实验，以了解团簇微形态的演变。 主要目标是定义近床湍流结构，以提高对存在团簇时近床湍流与沉积物输运之间耦合的理解。 将对非统一尺寸的球体进行一系列实验，以检查团簇的几何形状、团簇形成、保持稳定和分解的流动范围，以及近床水力参数和团簇床形之间的相互作用。 实验室实验中变量数量的减少将允许分离和量化水力参数、沉积物供应和产生的颗粒簇之间的特定关系。 用于测量团簇周围湍流的高分辨率相机和声学传感器的最新进展，再加上图像分析和床扫描硬件的开发，将允许在湍流解析频率下同时测量局部沉积物输送和相邻的近床流，而不会干扰流动。