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，大江大河发生了巨大的变化。河流管理者和社区正在寻求修复替代方案，以适应重大的人类影响，同时建立能够支持健康生态系统的可持续、形态和水力变化的河流系统。次级渠道或边渠道提供了一个机会，可以在不严重影响泛滥平原土地利用的情况下恢复大河流系统的生态系统功能，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。这项研究的目的是加深对大型河流次生河道地貌结构和功能的认识，满足为次生河道修复工程设计提供科学依据的迫切需要。这将通过探索马萨诸塞州西南部Housatonic河上次级河道中存在的地形和三维流动结构来实现。本研究将：1)利用声学多谱勒流量计量化次级河道和主河道环境中的三维水流结构和河道形态；2)利用水力学和地形测量方法评价次级河道的河流演变和形态与主河道河道形态的差异；3)定量识别次级河道形态和功能过程之间的联系；4)形成一个新的概念模型。这项工作将对长期被认识但知之甚少的河流三维流动的理论研究做出重大贡献。这将是首次直接测量未经改造的天然次级河道三维水流结构的研究之一，将大大有助于我们理解河道形态如何影响水生生境的变异性，并将在横向维度上拓展对河流地貌动力学的理论理解。这项研究的结果将填补我们在理解次级河道如何发挥作用方面的重大空白，同时为研究生和本科生，特别是女性提供非同寻常的学习和培训机会。该项目提高了对大型河流次级河道的科学认识，将为评估大型多用途河流旁航道修复项目的效益、成本和绩效提供强有力的基础，从而影响全国乃至其他地区的河流管理。更好地了解大河次要航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能够提供最大效益的大河流系统领域，而不损害主要航道和泛滥平原的利用。

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.