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

沙床河流主宰着地球表面的排水。例如，世界上10条最大的河流都是沙床河道，它们消耗了全球近20%的大陆土地，提供了33%的陆地沉积物供应给海洋。许多河流集水区，其中存在沙床渠道，受到诸如大坝建设、取水、河流工程或砍伐森林等人为活动的影响。因此，这些集水区的河流可能会经历突如其来的灾难性环境问题，例如导致建筑物倒塌的重大河岸后退、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强有力的模型，研究沙床河流是如何工作的，它们如何输送泥沙，河流在几十年和几个世纪里如何变化，它们如何产生我们在世界上看到的各种河道形态，以及河流如何对环境驱动因素的变化做出反应，例如气候、侵蚀率和人类干扰。最近的所有研究表明，沙床河流的形态、功能和模式强烈依赖于它们携带的沙子是悬浮运输(即在水柱中携带)还是作为推移质(与河床接触移动)。此外，理论表明，在沙床河流典型的泥沙大小和水流条件范围内，有一个戏剧性的转变，从推移质到悬沙为主的输沙。然而，控制沙子输送方式和由此产生的河流形态之间联系的物理机制在很大程度上仍未得到解释。该项目将开发新的模型和对泥沙悬浮物作为控制砂床河流形态的作用的定量理解。我们将通过实施一项涉及三个关键要素的研究战略来实现这一点：第一，我们将应用创新的图像获取技术来获得数据集，这些数据集在大范围(KM)和多时间尺度(天到年)上以非常高的空间分辨率(Cm)量化河床形态。其次，我们将使用最先进的现场仪器来同时测量水流和泥沙的输送过程，以及它们与不同排放范围内河流形态的关系。第三，我们将开发和应用二维和三维数值模型，以量化河床、沙洲和整个河流尺度上的河流过程和河道形态之间的相互作用。我们将使用现场数据集在不同大小的砂床河流中测试我们的模型，这些河流具有不同的水流状况和河床泥沙质地。一旦得到验证，我们的模型将提供强大的新工具，我们将以开放源代码的形式向科学界发布这些工具，用于预测和了解沙床河流如何响应环境变化。这项研究还将带来显著的最终用户和教育收益，我们将通过与项目合作伙伴HR Wallingford密切合作实现这一点，并通过制作一系列针对地理A-Level课程的高质量学习材料和教学资源，并通过坚定致力于教育推广的国家组织发布。

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.