Morphodynamic processes in semi-alluvial rivers

冲积河的河床和河岸由水流输送的泥沙组成。因此，通过侵蚀和沉积的形态动力学过程，冲积河可以自由地调整其形态，以达到能够输送水流和来水的平衡尺度。然而，加拿大的大多数河流都是半冲积河流，因为它们流经并切入冰川沉积物（如冰川海洋粘土、冰川坡地），和/或受基岩露头控制。在半冲积河中，人们对水流、泥沙输送和河道形态之间的关系了解甚少，因此无法利用模型来预测河道几何形状（如宽度、深度、坡度）作为水流和泥沙制度的函数。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，以改善水生栖息地，并预测流量或沉积物状态变化（例如，气候变化适应），河流重新调整（例如，高速公路，导航）或溪流基础设施（如水电站大坝，桥梁或管道）的实施的形态和洪水响应。本提案概述了一项研究半冲积河形态动力学的研究计划，最终目标是开发适合半冲积河的河道设计工具，包括粘土河床和受基岩影响的河流。

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.