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，世界上最大的10条河流都是沙床河道，它们消耗了全球近20%的陆地面积，并向海洋输送了33%的陆地沉积物。许多有沙床河道的河流集水区受到人为活动的影响，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经历突然和灾难性的环境问题，例如导致建筑物倒塌的主要河岸退缩，河床退化和洪水，以及导致栖息地退化的河道转移。尽管这些河流在环境、社会和经济方面具有重要意义，但我们一直在努力建立可靠的模型，以说明砂床河是如何工作的，它们是如何运输沉积物的，河流在几十年和几个世纪里是如何变化的，它们是如何产生我们在世界上看到的各种渠道模式的，以及河流是如何应对气候、侵蚀率和人类干扰等环境驱动因素的变化的。最近的研究表明，砂床河流的形态、功能和模式在很大程度上取决于它们携带的沙子是悬浮运输（即在水柱中携带）还是作为床载（与床接触移动）。此外，理论表明，在泥沙大小和典型砂床河流流动条件的范围内，存在着从河床输沙到悬浮输沙的巨大转变。然而，控制沙子运输方式与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定量理解泥沙悬浮作为控制砂床河流形态的作用。为此，我们将实施一项涉及三个关键要素的研究策略：首先，我们将应用一种创新的图像采集技术来获取数据集，这些数据集可以在非常高的空间分辨率（厘米）下，在大面积（公里）和多个时间尺度（天到年）上量化河床形态。其次，我们将使用最先进的现场仪器来同时测量流量和沉积物运输过程及其与一系列流量的河流形态的关系。第三，我们将开发并应用二维和三维数值模型，在河床、沙洲和整个河流尺度上量化河流过程与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沙床河流中测试我们的模型，并对比水流状况和河床沉积物质地。一旦得到验证，我们的模型将提供强大的新工具，我们将作为开源代码发布给科学界，用于预测和理解沙床河流如何响应环境变化。我们将与项目合作伙伴HR Wallingford密切合作，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，并通过致力于教育推广的国家组织发布，从而实现这项研究对最终用户和教育的重大好处。

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.