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

由于社会经济需求的变化，大河已经发生了巨大的变化。河流管理者和社区正在寻求修复方案，以适应重大的人类影响，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。次级渠道或侧渠道代表了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机会，但由于缺乏对其地貌和水力动力学的了解，次级渠道的恢复受到阻碍。本研究的目的是促进对大型河流次生河道地貌结构和功能的认识，满足对次生河道修复工程设计进行科学探究的迫切需要。这将通过探索马萨诸塞州西南部胡萨托尼克河次级河道中的地形和三维水流结构来完成。本研究将：1)利用声学多普勒流量计量化次级和主河道环境中的三维水流结构和河道形态；2)利用水力和地形指标评估次级河道的河流过程和形态与主河道的不同；3)定量识别次级河道的形态形态和功能过程之间的联系；4)为具有次级河道的河流提供新的概念模型。这项工作将为长期公认的理论研究做出重大贡献，但人们对河流流量的三维性知之甚少。这将是首次在未经修饰的“自然”次生河道中直接测量三维流动结构的研究之一，极大地有助于我们了解河道形态如何影响水力生境变异，并将在横向维度上扩展对河流地貌动力学的理论认识。这项研究的结果将填补我们对次级河道如何运作的理解的重大空白，同时为研究生和本科生，特别是女性提供非凡的学习和培训机会。该项目提高了对大型河流次级河道的科学认识，为评估大型多用途河流侧河道修复项目的效益、成本和效果提供了有力的依据，将影响全国乃至全球的河流管理。更好地了解大型河流次级河道将有助于更有效地将河流恢复和恢复工作和资源集中在大型河流系统的地区，这些地区可以在不损害主要河道和洪泛平原利用的情况下提供最大的利益。

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.