Modelling how sediment suspension controls the morphology and evolution of sand-bed rivers

沙床河流支配着地球表面的排水系统。例如，世界上10条最大的河流，几乎占全球大陆陆地的20%，并将33%的陆地沉积物输送到海洋，都是砂床通道。许多河流集水区，其中存在砂床通道，受到人为活动，如水坝建设，取水，河流工程，或森林砍伐。因此，这些集水区的河流可能会遇到突发性和灾难性的环境问题，如导致建筑物倒塌的主要河岸退缩，河床淤积和洪水，以及导致栖息地退化的河道转移。尽管这些河流具有环境、社会和经济意义，但我们一直在努力建立健全的模型，以了解砂床河流如何运作，它们如何运输沉积物，河流如何在几十年和几个世纪内发生变化，它们如何产生我们在世界上看到的各种河道模式，以及河流如何应对气候等环境驱动因素的变化，侵蚀率和人为干扰。最近的研究表明，沙床河流的功能和形态很大程度上取决于其携带的泥沙是否以悬浮状态输送（即，在水柱中携带）或作为床负荷（与床接触移动）。此外，理论表明，在沙床河流典型的泥沙粒径和水流条件的范围内，推移质向悬浮为主的输沙发生了戏剧性的转变。然而，物理机制，控制之间的联系，如何输沙和由此产生的河流形态仍然在很大程度上无法解释。该项目将开发新的模型，并从数量上了解沉积物悬浮对砂床河流形态的控制作用。我们将通过实施涉及三个关键要素的研究策略来实现这一目标：首先，我们将应用创新的图像采集技术来获得数据集，这些数据集可以在大面积（公里）和多个时间尺度（天到年）上以非常高的空间分辨率（cm）量化河床形态。其次，我们将使用国家的最先进的现场仪器，以获得并发测量流量和泥沙输运过程及其关系的河流形态在一定范围内的排放。第三，我们将开发和应用二维和三维数值模型，以量化河床，酒吧和整个河流尺度的河流过程和通道形态之间的相互作用。我们将使用现场数据集来测试我们的模型在不同大小的砂床河流，并与对比流态和床沉积物纹理。一旦得到验证，我们的模型将提供强大的新工具，我们将以开源代码的形式向科学界发布，用于预测和了解砂床河流如何应对环境变化。这项研究也将有显着的最终用户和教育效益，我们将通过与项目合作伙伴HR Wallingford密切合作，并通过制作一系列针对地理A级课程的高质量学习材料和教学资源来实现，并通过国家组织发布，坚定地致力于教育推广。

Sand-bed rivers dominate the drainage of the Earth's surface. For example, the world's 10 largest rivers, that drain almost 20% of global continental land & deliver 33% of the terrestrial sediment supplied to the oceans, are all sand-bed channels. Many river catchments, in which sand-bed channels are present, are subject to anthropogenic activities such as dam construction, water abstraction, river engineering, or deforestation. As a result, the rivers in these catchments can experience sudden and catastrophic environmental problems such as major bank retreat that promotes building collapse, river bed aggradation and flooding, and channel shifting that leads to habitat degradation. Despite the environmental, social and economic significance of these rivers, we have struggled to produce robust models of how sand-bed rivers work, how they transport their sediment, how rivers change over decades and centuries, how they produce the variety of channel patterns we see in the world, and how rivers respond to a change in environmental drivers such as climate, erosion rates and human interference.Very recent research indicates that the morphology, functioning and pattern of sand-bed rivers is strongly dependent upon whether the sand that they carry is transported in suspension (i.e. carried in the water column) or as bedload (moving in contact with the bed). In addition, theory suggests that, over the range of sediment sizes and flow conditions that are typical of sand-bed rivers, there is a dramatic shift from bedload to suspension-dominated sand transport. However, the physical mechanisms that control the link between how sand is transported and the resulting river morphology remain largely unexplained. This project will develop new models and quantitative understanding of the role of sediment suspension as a control on the morphology of sand-bed rivers. We will do this by implementing a research strategy that involves three key elements: First, we will apply an innovative image acquisition technique to obtain datasets that quantify river bed morphology at very high spatial resolutions (cm) over large areas (km) and multiple timescales (days to years). Second, we will use state-of-the-art field instrumentation to obtain concurrent measurements of flow and sediment transport processes and their relationship to river morphology over a range of discharges. Third, we will develop and apply two- and three-dimensional numerical models to quantify the interactions between riverine processes and channel morphology at bedform, bar and whole river scales. We will use field datasets to test our models in sand-bed rivers of different sizes and with contrasting flow regimes and bed sediment texture. Once validated, our models will provide robust new tools, which we will release as open-source code to the scientific community, for predicting and understanding how sand-bed rivers respond to environmental change. This research will also have significant end-user and educational benefits, which we will realise by working closely with project partner HR Wallingford, and by producing a collection of high-quality learning materials and teaching resources aimed at the Geography A-level curriculum, and released via national organisations with a strong commitment to educational outreach.