RAPID: Collaborative Research: Floodplain Sedimentation from an Extreme Event: The 2011 Lower Mississippi River Flood

RAPID：合作研究：极端事件造成的洪泛区沉积：2011 年密西西比河下游洪水

• 批准号: 1149405
• 负责人: Richard Kesel
• 金额: $ 0.55万
• 依托单位: Louisiana State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-01 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1149405&HistoricalAwards=false
• 关键词: RAPID; Collaborative; Research; Floodplain; Sedimentation

This rapid-response research project will examine the impact of extreme events on the geomorphology of large river floodplains by analyzing overbank deposits associated with the 2011 flood in the lowermost reaches of the Mississippi River alluvial valley in Louisiana and Mississippi. The investigators will draw on and seek to contribute to two bodies of knowledge in physical geography, fluvial geomorphology, and sedimentology: (1) the role of extreme events on sedimentation processes and floodplain construction of large lowland, embanked, meandering rivers and (2) the modern geomorphic adjustment of the Lower Mississippi River in response to flood control. They will gather materials and date to examine possible answers to the following research questions: How do sediment thicknesses and textural characteristics of overbank deposits derived from the 2011 flood directly compare with a previous, large-scale flood (1973) in the study area? Do overbank sedimentation thicknesses differ for floodplain transects of various embanked (leveed) widths? Do advective (longitudinal) or diffusive (lateral) sedimentation mechanisms control overbank deposition along embanked floodplains? They will engage in field work, laboratory analyses of overbank sediments, geographic information system-based evaluations of LiDAR-derived floodplain elevations, and quantitative analyses. They will determine overbank sediment thickness at locations identical to a published study documenting the 1973 flood. They will infer overbank flow direction from preserved sedimentary structures, quantify sediment texture, associate sedimentary characteristics with floodplain elevation and distance from the channel, and compare the 2011 data with data from the 1973 flood. Their work will focus on a reach of the Lower Mississippi that is the only location to receive drainage from all tributaries and has the highest discharge within the Mississippi River basin, thereby sampling flood deposits associated with record flood stages from one of the largest recorded discharge events in North America. The field study design will permit a direct examination of the impact of flood-control levees on sedimentation. In contrast to the western side of the river, the eastern floodplain reach is not embanked, which permits unimpeded overbank sediment transport from the river to the valley wall. The study area is upstream from the most important flood-control structure in North America, the Old River Control Structure, whose function is partially dependent on stage-discharge relations that adjust with floodplain elevation. Furthermore, the study reach has been shown to have increasingly high stages for a given flood discharge since the 1980s.While it is rare to have an opportunity to sample overbank deposits from large floods on large rivers, it is unprecedented to have the opportunity to sample overbank deposits from two large floods within the same reach, this project will resample the exact locations from one of the most cited studies in the flood sedimentation literature (Kesel et al, 1974). The results of this project therefore are expected to have broader relevance for environmental scientists, including hydrologic and hydraulic engineers, physical geographers, riparian biologists, geologists, and instream-flow specialists. The project will provide field-, lab-, and computationally based education and training experiences for graduate and undergraduate students, and it will provide valuable information and insights to floodplain managers and policy makers.

这一快速反应研究项目将通过分析2011年路易斯安那州和密西西比州密西西比河冲积河谷最下游的洪水相关的岸上沉积，来研究极端事件对大型河流泛滥平原地貌的影响。研究人员将利用并寻求对自然地理学、河流地貌学和沉积学的两个方面的知识做出贡献：(1)极端事件对沉积过程和大片低地、内滩、曲折河流的泛滥平原建设的作用；(2)密西西比河下游为应对洪水控制而进行的现代地貌调整。他们将收集材料和数据，以研究下列研究问题的可能答案：2011年洪水产生的岸上沉积的沉积物厚度和结构特征如何与研究地区先前的大洪水(1973年)直接比较？漫滩沉积厚度对于不同堤岸宽度的滩涂横断面是否有所不同？平流(纵向)或扩散(横向)沉积机制是否控制了堤岸泛滥平原的岸上沉积？他们将从事实地工作、对岸上沉积物的实验室分析、基于地理信息系统的激光雷达洪水平原高程评估，以及定量分析。他们将在与记录1973年洪水的出版研究相同的地点确定岸上沉积物厚度。他们将从保存下来的沉积结构中推断漫滩水流方向，量化沉积物结构，将沉积特征与泛滥平原海拔和距离河道的距离联系起来，并将2011年的数据与1973年洪水的数据进行比较。他们的工作将集中在密西西比河下游的一段河段，那里是唯一从所有支流接收排水的地方，也是密西西比河流域流量最高的地方，从而从北美有记录以来最大的泄洪事件之一中取样与创纪录的洪水阶段相关的洪水沉积。实地研究设计将允许直接检查防洪堤坝对沉积的影响。与河的西侧不同，东部的泛滥平原河段没有围堤，这使得河岸泥沙可以畅通无阻地从河流向河谷壁输送。研究区域位于北美最重要的防洪结构--老河控制结构的上游，其功能部分依赖于随滩地高程调整的水位-流量关系。此外，研究表明，自20世纪80年代以来，对于一次特定的洪水，研究河段的水位越来越高。虽然有机会从大河上的大洪水中取样岸上沉积物的机会很少，但有机会从同一河段内的两次大洪水中取样岸上沉积物的机会是史无前例的，该项目将从洪水沉积文献中被引用最多的研究之一中重新取样确切的位置(Kseel等人，1974)。因此，该项目的成果预计将对环境科学家具有更广泛的意义，包括水文和水利工程师、自然地理学家、河岸生物学家、地质学家和河流水流专家。该项目将为研究生和本科生提供基于现场、实验室和计算机的教育和培训经验，并将为泛滥平原管理人员和政策制定者提供有价值的信息和见解。