How does the development of particle scale structure control river scale morphology?

沉积物的运输是全球地质循环的一个关键过程，是水生生态系统的基石，对农业、工业和城市、洪水和侵蚀风险危害具有数十亿英镑的影响。了解和预测砾石河床的稳定性非常重要，原因有很多：河床形状的变化会改变河道容量，从而影响洪水风险；河床稳定性影响水流可移动的泥沙量，进而影响下游河道形态和动力；河床是许多物种的栖息地，因此河床的变化将对河流生态系统产生影响；为了有效地管理和恢复河流，河道的设计需要有一个已知的稳定水平。然而，目前预测泥沙夹带和河床稳定性的能力受到我们对影响泥沙运动因素的理解的限制。颗粒大小通常被考虑在内，但其他因素，如沉积物结构（单个沉积物颗粒在3D中堆积在一起的方式）和细沉积物在胶结颗粒中的作用则没有考虑在内。此外，这些因素在河床上的空间变化，产生了或多或少容易被夹带的区域的空间格局，即可蚀性模板。我们假设这种可蚀性的空间格局在控制河床形状以及河床形状在不同流量条件下的变化方面起着重要作用。我们将首次使用高能ct扫描在野外和实验室环境中量化三维沉积物结构的发展，以此来验证这一假设。这些数据将使我们能够确定不同控制和沉积物结构之间的因果关系。将该技术应用于现场和实验室的大量样品，将为了解三维床层沉积物的结构和生产提供重要而独特的数据集。利用现有的理论框架，我们将使用水槽数据和现场数据来产生可用于预测沉积物结构的关系，从而从沉积物输入和流动的控制因素中预测床的可蚀性。这种关系将在一个数值模拟框架内实现，在这个框架中，我们将从现场和水槽中提升到代表额外范围的渠道和流动条件。我们将与最终用户合作，确保将新知识有效地转化为河流管理界政策和业务活动的指导。

The transport of sediments is a key process in the global geological cycle, a cornerstone of aquatic ecosystems and has a multi-billion pound impact on agricultural, industrial and urban, flood- and erosion-risk hazards. Understanding and being able to predict the stability of gravel river beds is important for multiple reasons: changes in river bed shape will change the channel capacity and thus affect flood risk; the bed stability affects the amount of sediment that can be moved by the flow, which will have impacts on the downstream channel morphology and dynamics; the river bed is a habitat for many species, and thus changes in the river bed will have implications for the river ecosystem; and in order to manage and restore rivers effectively, channels need to be designed with a known level of stability.However, current ability to predict sediment entrainment and thus river bed stability is limited by our understanding of the factors that affect sediment movement. Grain size is typically accounted for, but other factors such as sediment structure (the way in which individual sediment grains are packed together in 3D) and the role of fine sediments in cementing grains together are not. Furthermore, these factors vary spatially across the bed of a river, producing a spatial pattern of areas that are more or less easily entrained, i.e. a template of erodibility. We hypothesis that this spatial pattern of erodibility plays an important role in controlling both the shape of the river bed, and how this shape changes under different flow conditions. We will test this hypothesis by quantifying, for the first time, the development of 3D sediment structure in both a field and a laboratory environment using high energy CT-scanning. These data will allow us to identify causal relationships between the different controls and sediment structure. The application of this technique to large numbers of samples from both field and laboratory settings will provide a significant and unique dataset for understanding the structure and production of 3D bed sediments.Using an existing theoretical framework, we will use the data from both the flume and field data to produce relationships that can be used to predict sediment structure, and consequently the erodibility of the bed, from the controlling factors of sediment input and flow. This relationship will be implemented within a numerical modelling framework in which we will upscale from the field and flume to represent additional range of channel and flow conditions. We will work with end-users to ensure that the new knowledge is transferred effectively into guidance for policy and operational activity within the river management community.