SGER: Fluvial Dynamics of a Large-River Meander Cutoff

蜿蜒曲折是许多天然河流的基本特征，但尚未得到充分解释。曲流河的动力学涉及随着航道的横向和向下迁移，曲流河弯曲序列随时间的不断演变发展。单个弯曲可以演化成复杂的形式，其特征是多个弧形的曲率，这些环在其入口和出口处演变为向后弯曲，形成一个狭窄的颈部。洪水期间流经颈部的水流最终导致在这个位置开发一条新的河道，这一过程被称为曲流河切断。老的曲流环随后被流淌的河流抛弃，因为沉积物堵塞了环的出入口，形成了一个牛弓湖。最近的研究强调了曲折截止线在曲折列车或弯道序列动力学中的重要性。截止点可能会对弯道相互作用产生重大影响，因为这些事件通常会触发与截止点相邻的弯道的新的进化发展模式，进而影响整个曲折序列中的其他弯道。这一小笔探索性研究拨款将研究沿伊利诺伊州-印第安纳州边界的瓦巴什河下游河段新的曲流线的发展。调查人员自2008年6月新的分水岭形成以来一直在监测，他们将使用这一奖项的资金继续监测其发展，并检查分界线对沃巴什河流入俄亥俄河下游一条大河汇流动态的影响。研究人员将重点研究截流如何影响截流航道上下游两端的河流三维水流结构，截流航道内和被截流的曲流环内的发展水流结构，以及紧邻下游汇合处的动力学。他们将把记录在案的水流结构模式与河道冲刷和沉积模式联系起来，以在不断演变的分界线内建立河流过程和河流形态之间的联系。这将通过(1)绘制现有的截流河道地貌、曲流环的河床形态图，并分析有关截流发生及其对瓦巴什河-俄亥俄河交汇处影响的辅助信息；(2)测量不同水流阶段截流上游和下游端、截流河道内和曲流环内的三维水流结构；(3)绘制截流上游和下游端、截流河道内和曲流环内的冲刷和淤积模式；以及(4)测量瓦巴什-俄亥俄州交汇处的水流结构和沉积模式。这项研究项目将在野外对曲流河截流动力学的理解做出重大贡献，这将为以后基于过程的一般曲流河数值模型的发展提供信息。该项目还将加强对切断线的形成如何影响紧邻下游的大型沃巴什-俄亥俄河汇合处不断变化的动态的基本理解。该项目将产生更广泛的积极影响，为研究生和本科生提供研究和培训机会，并提供有价值的数据，使地方政府机构和其他利益攸关方能够确定如何处理新的分界线和相关变化对土地管理的影响。

Meandering is a fundamental characteristic of many natural rivers that has yet to be adequately explained. The dynamics of meanders involves the continuous evolutionary development of sequences of meander bends through time as the channel migrates laterally and downstream. Individual bends can evolve into complex forms characterized by multiple arcs of curvature, with these loops evolving to curve back upon themselves at their entrance and exit to form a narrow neck. Flow across the neck during floods eventually leads to the development of a new channel at this location, a process known as a meander cutoff. The old meander loop is then abandoned by the flowing river as sediment plugs the entrance and exit of the loop to form an oxbow lake. Recent research has emphasized the importance of meander cutoffs in the dynamics of meander trains, or sequences of bends. Cutoffs can have a substantial influence on bend interactions, because these events often trigger new patterns of evolutionary development of bends adjacent to the cutoff, which in turn affect other bends throughout a meander sequence. This Small Grant for Exploratory Research will examine the development of a new meander cutoff along the lower reach of the Wabash River on the Illinois-Indiana border. The investigators have been monitoring the new cutoff since the days after it formed in June 2008, and they will use funds from this award to continue to monitor its development and to examine the influence of the cutoff on the dynamics of a large-river confluence immediately downstream where the Wabash flows into the Ohio River. The investigators will focus on how the cutoff affects the three-dimensional flow structure of the river at the upstream and downstream ends of the cutoff channel, the developing flow structure within the cutoff channel and within the meander loop that is being cutoff, and the dynamics at the confluence immediately downstream. They will relate documented patterns of flow structure to patterns of channel erosion and deposition to establish linkages between fluvial processes and fluvial forms within the evolving cutoff. This will be done by (1) mapping the extant morphology of the cutoff channel, the bed morphology of the meander loop, and analyzing ancillary information on the occurrence of the cutoff and its influence on the Wabash River-Ohio River confluence; (2) measuring patterns of three-dimensional flow structure at the upstream and downstream ends of the cutoff, within the cutoff channel and within the meander loop during events of different flow stages; (3) mapping patterns of erosion and deposition at the upstream and downstream ends of the cutoff, within the cutoff channel, and within the meander loop; and (4) measuring the flow structure and mapping patterns of sedimentation at the Wabash-Ohio confluence.This research project will make a substantial field-based contribution to the understanding of the dynamics of meander cutoffs, which can later inform development of general process-based numerical models of meandering. The project also will enhance basic understanding of the ways that the formation of the cutoff affects the changing dynamics of the large Wabash-Ohio river confluence immediately downstream. The project will have positive broader impacts by providing research and training opportunities for graduate and undergraduate students and for providing valuable data to enable local government agencies and other stakeholders to determine how to deal with the land-management implications of the new cutoff and related changes.