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: 2015
• 资助国家: 加拿大
• 起止时间: 2015-01-01 至 2016-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=588401
• 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.

冲积河的河床和河岸由水流输送的沉积物组成。因此，通过侵蚀和沉积的形态动力学过程，冲积河可以自由地将其形态调整到可以输送水流和传入沉积物的平衡尺寸。 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（例如冰川粘土、冰川碛物），和/或受到基岩露头的控制。在半冲积河流中，人们对流量、沉积物输送和河道形态之间的关系知之甚少，因此无法使用模型来预测作为流量和沉积状况函数的河道几何形状（例如宽度、深度、坡度）。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，以改善水生栖息地，并预测对流量或沉积状况变化（例如气候变化适应）、河流重新调整（例如高速公路、导航）或水力发电大坝、桥梁或管道等河内基础设施实施的形态和洪水响应。该提案概述了研究半冲积河形态动力学的研究计划，最终目标是开发适用于半冲积河的河道设计工具，包括粘土床河道和受基岩影响的河流。 通过对一系列涵盖半冲积河流类型的案例研究河段中的形态动力学过程进行系统的现场测量，可以更深入地了解加拿大的半冲积河流。 对于每个案例研究河段，水力几何、河道地形、栖息地特征以及床质、悬浮沉积物、床质运输和三维流的时空分布将在几年内以高分辨率进行调查和绘制。 大多数这些测量将使用申请人开发的方法通过声学多普勒电流轮廓仪（aDcp）进行。观察到的沉积物输送分布将阐明侵蚀和沉积区域之间的沉积物输送路径，这些路径本身是由河道形态和三维时空湍流分布之间的相互作用决定的。 因此，将直接测量决定通道形态的形态动力学过程。 将特别强调评估更多和更少冲积河段之间的差异。 特别是，将评估极端流量、河道形态、可用冲积层和相关栖息地之间的关系。 现场数据将用于开发和验证半冲积河流形态和可用栖息地的数值预测建模工具。 将首次开发专门针对半冲积河道制定的三维形态动力河流建模工具。 这项研究将建立在形态动力学建模的进步基础上，包括自适应网格生成、湍流闭合、自由表面模拟、河岸稳定性和床物质传输程序。 为了模拟半冲积河道，河岸稳定性和沉积物输送程序将考虑从上游接收的母质和冲积沉积物的侵蚀性和输送性，这将是对河流形态动力学建模领域的新贡献。 模型输出将是给定流量的平衡通道形态。 重要的是，每个研究达到的形态动力学模型都将使用观察到的经验现场观察进行校准和验证，这是经常被忽视的关键步骤。