Morphodynamic processes in semi-alluvial rivers

半冲积河流的形态动力过程

• 批准号: RGPIN-2014-05411
• 负责人: Rennie, Colin
• 金额: $ 1.75万
• 依托单位: University of Ottawa
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=611628
• 关键词: Morphodynamic; processes; semi; alluvial; rivers

An alluvial river has bed and banks composed of sediment transported by the flow. Consequently, through the morphodynamic processes of erosion and deposition, an alluvial river is free to adjust its morphology to equilibrium dimensions that can convey the flow and incoming sediment. The majority of rivers in Canada, however, are semi-alluvial because they flow over, and cut into, glacial deposits (e.g. glaciomarine clays, glacial tills), and/or are controlled by bedrock outcrops. Relations between flow, sediment transport, and channel form are poorly understood in semi-alluvial rivers, thus models are not available to predict channel geometry (e.g., width, depth, slope) as a function of the flow and sediment regimes. Canadian river engineers and scientists require these models as design tools for river restoration to improve aquatic habitat, and to predict morphological and flood response to changes in flow or sediment regime (e.g., climate change adaptation), river realignment (e.g., highways, navigation), or implementation of instream infrastructure such as hydroelectric dams, bridges, or pipelines. This proposal outlines a research plan to study semi-alluvial river morphodynamics, with the ultimate objective of developing river channel design tools suitable for semi-alluvial rivers, including clay-bed channels and rivers influenced by bedrock. Deeper understanding of semi-alluvial rivers in Canada will be gained by means of systematic field measurement of morphodynamic processes in a set of case study reaches that encompass the range of semi-alluvial river types. For each case study reach, hydraulic geometry, channel topography, habitat features, and spatiotemporal distributions of bed material, suspended sediment, bed material transport, and three-dimensional flow will be surveyed and mapped at high resolution over several years. Most of these measurements will be conducted with an acoustic Doppler current profiler (aDcp) using methodologies developed by the applicant. Observed sediment transport distributions will elucidate sediment transport pathways between zones of erosion and deposition, which are themselves dictated by interactions between the channel morphology and three-dimensional spatiotemporal turbulent flow distribution. Thus, the morphodynamic processes that determine channel morphology will be measured directly. Special emphasis will be placed on assessing differences between more and less alluvial reaches. In particular, relations between extreme flows, channel morphology, available alluvium, and associated habitat will be assessed. The field data will be used to develop and validate numerical predictive modelling tools for semi-alluvial river morphology and available habitat. A three-dimensional morphodynamic river modelling tool specifically formulated for semi-alluvial channels will be developed for the first time. This research will build upon advances in morphodynamic modelling including adaptive grid generation, turbulence closure, free-surface simulation, bank stability, and bed material transport routines. In order to model semi-alluvial channels, the bank stability and sediment transport routines will consider the erodibility and transport of both the parent material and alluvial sediments received from upstream, which will be a novel contribution to the field of morphodynamic river modelling. The model output will be the equilibrium channel morphology for a given flow. Importantly, each study-reach morphodynamic model will be calibrated and validated using the observed empirical field observations, which is a crucial step too often ignored.

冲积河流的河床和河岸由水流搬运的沉积物组成。因此，通过侵蚀和沉积的形态动力学过程，冲积河流可以自由地调整其形态，以达到平衡尺寸，从而可以输送水流和泥沙。然而，加拿大的大多数河流都是半冲积河流，因为它们流过并切入冰川沉积物（如冰川粘土，冰川冰碛），和/或受基岩露头的控制。在半冲积河流中，水流、泥沙输移和河道形态之间的关系知之甚少，因此没有模型来预测河道几何形状（例如，宽度、深度、坡度）作为水流和泥沙状况的函数。加拿大河流工程师和科学家需要这些模型作为河流恢复的设计工具，以改善水生生境，并预测水流或沉积物状况变化对形态和洪水的反应（例如，气候变化适应），河流重新调整（例如，高速公路、导航），或诸如水电大坝、桥梁或管道的即时基础设施的实施。该提案概述了研究半冲积河流形态动力学的研究计划，最终目标是开发适用于半冲积河流的河道设计工具，包括粘土床河道和受基岩影响的河流。 在加拿大的半冲积河流将获得更深入的了解，通过系统的实地测量的形态动力学过程中的一组案例研究达到，包括半冲积河流类型的范围。对于每个案例研究达到，水力几何形状，通道地形，栖息地的特点，和时空分布的河床物质，悬浮泥沙，河床物质运输，和三维流将调查和高分辨率绘制了几年。其中大部分测量将使用申请者开发的方法，用声学多普勒海流剖面仪进行。所观察到的泥沙输运分布将阐明侵蚀和沉积区之间的泥沙输运路径，这本身是由通道形态和三维时空湍流分布之间的相互作用决定的。因此，将直接测量确定通道形态的形态动力学过程。将特别强调评估冲积程度不同的河段之间的差异。特别是，极端流量之间的关系，通道形态，可用冲积层，相关的栖息地将进行评估。 实地数据将用于开发和验证半冲积河流形态和现有生境的数值预测建模工具。将首次开发专门为半冲积河道制定的三维形态动力学河流建模工具。这项研究将建立在形态动力学建模的进步，包括自适应网格生成，湍流闭合，自由表面模拟，银行的稳定性，和床料运输例程。为了模拟半冲积河道，河岸稳定性和泥沙输运程序将考虑上游母质和冲积泥沙的可蚀性和输运，这将是对地貌动力学河流建模领域的一个新贡献。模型输出将是给定流量的平衡通道形态。重要的是，每个研究达到形态动力学模型将使用观察到的经验实地观察，这是一个关键的步骤往往被忽视校准和验证。