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

这一快速反应研究项目将通过分析路易斯安那州和密西西比州密西西比河冲积谷最下游与2011年洪水相关的漫滩沉积物，研究极端事件对大河洪泛区地貌的影响。 调查人员将借鉴并寻求促进自然地理学，河流地貌学和沉积学的两个知识体系：（1）极端事件对沉积过程和大型低地，筑堤，蜿蜒河流的洪泛区建设的作用和（2）下密西西比河的现代地貌调整，以应对洪水控制。 他们将收集材料和数据，以研究以下研究问题的可能答案：如何将2011年洪水产生的漫滩沉积物的沉积物厚度和纹理特征与研究区域以前的大规模洪水（1973年）进行直接比较？ 不同筑堤宽度的洪泛区断面的漫滩沉积厚度是否不同？ 顺流（纵向）或扩散（横向）沉积机制控制沿着筑堤洪泛区的漫滩沉积吗？ 他们将从事实地工作，对漫滩沉积物进行实验室分析，基于地理信息系统对激光雷达得出的洪泛区高程进行评估，并进行定量分析。 他们将确定与记录1973年洪水的已发表研究相同的位置处的漫滩沉积物厚度。 他们将从保存的沉积结构中推断漫滩水流方向，量化沉积物结构，将沉积特征与河漫滩高程和与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个河段，该河段是唯一一个接收所有支流排水的地方，并且在密西西比河流域内具有最高的流量，从而对与北美有记录的最大流量事件之一的创纪录洪水阶段相关的洪水沉积物进行采样。 现场研究设计将允许直接检查防洪堤对沉积物的影响。 与河流西侧相反，东部洪泛平原河段没有筑堤，这使得从河流到谷壁的漫滩沉积物运输畅通无阻。 研究区是上游最重要的防洪结构在北美，旧河控制结构，其功能部分取决于水位流量关系，调整与洪泛区高程。 此外，自20世纪80年代以来，研究河段已被证明具有越来越高的水位，虽然有机会从大型河流的大洪水中取样漫滩沉积物是罕见的，但有机会在同一河段内从两次大洪水中取样漫滩沉积物是前所未有的，该项目将从洪水沉积文献中引用最多的研究之一（Kobel等人，1974）的精确位置重新取样。 因此，该项目的结果预计将有更广泛的环境科学家，包括水文和水力工程师，自然地理学家，河岸生物学家，地质学家和河道内流专家的相关性。 该项目将为研究生和本科生提供现场，实验室和基于计算的教育和培训经验，并将为洪泛区管理人员和政策制定者提供有价值的信息和见解。

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.