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: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=663220
• 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.

冲积性河流由水流输送的泥沙组成河床和堤岸。因此，通过侵蚀和沉积的地貌动力学过程，冲积河流可以自由地将其形态调整到能够输送水流和来沙的平衡尺寸。然而，加拿大的大多数河流是半冲积的，因为它们流过冰川沉积(如冰川粘土、冰川碎屑)，并被切割成冰川沉积，和/或受基岩露头控制。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，因此无法利用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，以改善水生生物栖息地，并预测河流形态和洪水对水流或泥沙状况变化的响应(例如，气候变化适应)、河流重新调整(例如，公路、导航)或实施河流基础设施，如水电大坝、桥梁或管道。该建议概述了研究半冲积河流地貌动力学的研究计划，最终目标是开发适用于半冲积河流的河道设计工具，包括粘土河床河道和受基岩影响的河流。*将通过对涵盖半冲积河流类型范围的一系列案例研究河段的地形动力学过程进行系统的实地测量，加深对加拿大半冲积河流的了解。对于每个案例研究河段，将在几年内以高分辨率调查和绘制河床泥沙、悬浮泥沙、河床泥沙输运和三维水流的水力几何形状、河道地形、生境特征和时空分布。其中大多数测量将使用声学多普勒海流剖面仪(ADCP)进行，使用申请人开发的方法。观测到的泥沙输运分布将阐明侵蚀带和淤积带之间的泥沙输送路径，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，决定河道形态的地貌动力学过程将被直接测量。将特别强调评估多冲积河段和少冲积河段之间的差异。特别是，将评估极端径流、河道形态、可用冲积层和相关生境之间的关系。*现场数据将用于开发和验证半冲积河流地貌和现有栖息地的数值预测建模工具。将首次开发专门用于半冲积河道的三维地貌动力学河流模拟工具。这项研究将建立在地形动力学模拟方面的进展，包括自适应网格生成、湍流闭合、自由面模拟、岸坡稳定性和床料输运程序。为了模拟半冲积河道，岸坡稳定性和泥沙输运程序将考虑来自上游的母质和冲积沉积物的可蚀性和输移，这将是对河流地貌动力学模拟领域的新贡献。模型的输出将是给定水流的平衡流道形态。重要的是，每个研究到达的地貌动力学模型都将使用观测到的经验场观测进行校准和验证，这是经常被忽视的关键步骤。