Fluvial Dynamics of Large River Secondary Channels: Hydraulic Habitat, Channel Morphology, and Potential for Restoration

由于社会经济需求的驱动，大型河流发生了巨大的变化。河流管理者和社区正在寻求恢复替代方案，以适应人类的重大影响，同时建立可持续的、形态和水力变化的河流系统，能够支持健康的生态系统。二级河道或侧道是在不严重影响洪泛区土地利用的情况下恢复大型河流系统生态系统功能的一个机会，但二级河道的恢复因缺乏对其地貌和水力动力学的了解而受到阻碍。本研究的目的是促进对大型河流二级河道的地貌结构和功能的了解，满足科学调查的关键需求，为二级河道修复工程的设计提供信息。这将通过探索马萨诸塞州西南部胡萨托尼克河二级河道中的地形和三维水流结构来实现。这项研究将：1）使用声学多普勒流量计量化次级和主河道环境中的三维流动结构和河道形态，2）使用水力和地形度量评估次级河道中的河流过程和形式与主河道中的河流过程和形式如何不同，3）定量识别次级河道中的形态形式和功能过程之间的联系，以及4）为具有次级河道的河流提供新的概念模型。 这项工作将大大有助于理论研究的长期认识，但了解甚少，三维流动的河流。 这将是第一个研究直接测量三维流动结构在未经修改的“自然”二级渠道，大大有助于我们了解如何渠道形态影响水力栖息地的变化，并将扩大河流地貌动力学的理论认识在横向尺寸。 这项研究的结果将填补显着的差距，我们了解二级河道的功能，同时提供非凡的学习和培训机会，为研究生和本科生，特别是妇女。 该项目对大型河流二级河道的科学认识得到加强，将为评估大型多用途河流侧河道恢复项目的效益、成本和绩效提供坚实的基础，从而影响全国及其他地区的河流管理。 更好地了解大型河流的次级河道将有助于更有效地将河流恢复和重建工作和资源集中在大型河流系统的地区，这些地区可以提供最大的利益，而不影响主要河道和洪泛区的利用。

Large rivers have been dramatically altered by modifications driven by socio-economic needs. River managers and communities are seeking restoration alternatives that accommodate significant human impacts while also establishing sustainable, morphologically and hydraulically varied river systems that are capable of supporting healthy ecosystems. Secondary channels, or side channels, represent an opportunity to restore ecosystem functionality to large river systems without seriously affecting floodplain land uses, but restoration of secondary channels is hampered by a lack of knowledge about their geomorphic and hydraulic dynamics. The goal of this research is to advance the understanding of the geomorphic structure and function of large river secondary channels, satisfying the critical need for scientific inquiry to inform the design of secondary channel restoration projects. This will be accomplished by exploring topographic and three-dimensional flow structures present in secondary channels on the Housatonic River in southwestern Massachusetts. This research will: 1) quantify three-dimensional flow structure and channel morphology in secondary and main channel environments using Acoustic Doppler flow meters, 2) evaluate how fluvial processes and forms in secondary channels differ from those in the main channel using hydraulic and topographic metrics, 3) quantitatively identify linkages between morphologic form and functional processes in secondary channels, and 4) inform a new conceptual model for rivers with secondary channels. This work will contribute significantly to theoretical research on the long-recognized, but poorly understood, three-dimensionality of flow in rivers. It will be one of the first studies to directly measure three-dimensional flow structure in unmodified "natural" secondary channels, greatly contribute to our understanding of how channel morphology influence hydraulic habitat variability, and will expand the theoretical understanding of river geomorphological dynamics in the lateral dimension. The results of this study will fill significant gaps in our understanding of how secondary river channels function while at the same time providing extraordinary learning and training opportunities for both graduate and undergraduate students, particularly women. The enhanced scientific understanding of large river secondary channels produced by this project will impact river management throughout the country and beyond by providing a strong basis for evaluating the benefits, costs, and performance of side-channel restoration projects on large, multi-purpose rivers. A better understanding of large-river secondary channels will serve to more efficiently focus river restoration and rehabilitation efforts and resources in the areas of large river systems that can provide the greatest benefits without compromising main channel and floodplain utilization.