SGER: Fluvial Dynamics of a Large-River Meander Cutoff

曲流是许多天然河流的基本特征，至今尚未得到充分的解释。 河曲的动力学包括河曲弯曲序列随时间的连续演化发展，因为河道横向和向下游迁移。 单个弯曲可以演变成复杂的形式，其特征是多个曲率弧，这些环在它们的入口和出口处演变成弯曲的曲线，形成狭窄的颈部。 洪水期间流经颈部的水流最终导致在该位置形成一条新的河道，这一过程称为曲流断流。 旧的曲流环然后被遗弃的流动的河流作为沉积物堵塞的入口和出口的环路，形成一个牛轭湖。 最近的研究强调了曲流截断在曲流列车动力学或弯曲序列中的重要性。 截止可以有很大的影响弯曲的相互作用，因为这些事件往往会触发新的模式的演变发展的弯曲附近的截止，这反过来又影响其他弯曲整个曲流序列。 这项探索性研究的小额赠款将研究伊利诺斯州-印第安纳州边界上瓦巴什河下游沿着新的曲流截流的发展。 自2008年6月新的截流线形成以来，调查人员一直在监测它，他们将利用这笔资金继续监测它的发展，并研究截流线对下游一条大河汇流动态的影响，瓦巴什在那里流入俄亥俄州河。 调查人员将重点关注截断如何影响河流的三维流动结构，在截断渠道的上游和下游端，截断渠道内和正在截断的曲流环路内的流动结构，以及下游汇合处的动态。 它们将把记录的水流结构模式与河道侵蚀和沉积模式联系起来，以建立不断变化的截止范围内的河流过程和河流形态之间的联系。 这将通过（1）绘制截断河道的现存形态、曲流环路的河床形态，并分析关于截断发生及其对瓦巴什河-俄亥俄河汇合的影响的辅助信息来完成;（2）测量截流口上下游端三维水流结构形态，在不同流动阶段的事件期间，在截断河道内和在曲流环路内;（3）绘制在截断河道的上游端和下游端、在截断河道内和在曲流环路内的侵蚀和沉积模式;（4）测量Wabash-Ohio交汇处的水流结构和沉积模式。该研究项目将为理解曲流断流的动力学做出实质性的贡献，这将为以后开发基于一般过程的曲流数值模型提供信息。 该项目还将加强对截流形成影响下游大型沃巴什-俄亥俄河汇流动态变化的方式的基本理解。 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，并提供宝贵的数据，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截止日期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.