Dynamics & deposits of braid-bars in the World's largest rivers: processes, morphology & subsurface sedimentology

尽管世界上最大的10条河流几乎消耗了全球陆地面积的五分之一，并向海洋输送了大约三分之一的陆地沉积物，但我们对这些大河的作用知之甚少。考虑到它们直接影响到广泛的环境、社会和经济问题（如洪水、河岸侵蚀、土地流失和基础设施崩溃），并最终形成了世界上一些最有利可图的矿物和化石燃料储备的矿床，这既令人惊讶，又存在问题。目前对大河的了解几乎完全基于对小河道的研究结果。然而，最近的研究让我们有充分的理由认为，将这些知识转移到大河上可能并不容易。因此，迫切需要对世界上最大的河流的河流过程、河道形态和地下沉积学之间的相互作用进行改进的定量理解。解决这一知识差距是一项重大挑战，因为它涉及开发可用于调查跨越广泛时间和空间尺度（从分米/分钟到公里/千年）的过程-产品关系的方法。为了实现这一目标，这项研究将汇集一个由英国和海外研究人员组成的多学科团队。在这个项目中，我们将调查世界上最大的河流之一，阿根廷的Paraná-Paraguay，以了解：(1)是什么控制着水和沉积物的运动以及河道随时间的变化；(2)这对河流沉积物的形成和保存意味着什么。我们将通过实施一项涉及三个关键要素的研究战略来解决这些问题。首先，我们将使用最先进的现场仪器绘制河床形态及其随时间的演变，并测量水和沉积物在河道坝周围和上方的三维运动模式。其次，我们将利用探地雷达技术的最新发展来绘制辫状坝沉积物的三维沉积结构，既包括在当前河流内，也包括在过去几千年来被遗弃的以前活跃地区。第三，我们将开发新的数值模拟方法来研究和量化水与沉积物运输过程、沙洲形成、河道形态演化和沉积物的地下沉积学之间的相互作用。后者将首次结合计算流体动力学模型，该模型提供了控制水和沉积物运动的复杂物理表示，以及能够模拟这些过程如何相互作用以确定数百年至数千年期间河道演化和沉积学的创新降低复杂性模型。这项工作的结果将是世界上第一个关于大河形态如何随时间变化的综合数据库，同时获得驱动这些变化的数据，以及这对沉积物形成的意义。这将使我们能够开发这些河流如何工作的新模型，并使用这些模型来解决有关大河资源及其管理的实际问题。

Despite the fact that the World's 10 largest rivers drain almost one fifth of the global continental land area and deliver about one third of the terrestrial sediment supplied to oceans, we know relatively little about how such large rivers function. This is both surprising and problematic given that they impact directly on a wide range of environmental, social and economic issues (e.g. flooding, bank erosion, loss of land and infrastructure collapse) and ultimately create deposits that host some of the World's most lucrative mineral and fossil fuel reserves. Present understanding of large rivers is based almost entirely upon the findings of studies conducted in small channels. However, recent research gives us good reason to expect that transferring this knowledge to large rivers may not be straight-forward. Consequently, there is an urgent need to develop an improved quantitative understanding of the interactions between river processes, channel morphology and subsurface sedimentology in the World's largest rivers. Addressing this knowledge gap represents a significant challenge because it involves developing methods that can be used to investigate process-product relationships that operate across a wide range of time and space scales (from decimetres/minutes up to kilometres/millennia). This research will bring together a multi-disciplinary team of leading UK and overseas researchers in order to achieve this goal. In this project we will investigate one of the World's largest rivers, the Paraná-Paraguay in Argentina to understand: (1) what controls water and sediment movement and river channel changes over time; and (2) what this means for the formation and preservation of river sedimentary deposits. We will address these issues by implementing a research strategy that involves three key elements. First, we will use state-of-the-art field instrumentation to map river bed morphology and its evolution through time, and measure the three-dimensional patterns of water and sediment movement around and over channel bars. Second, we will take advantage of recent developments in Ground Penetrating Radar technology to map the three-dimensional sedimentary structure of braid-bar deposits, both within the current river and in formerly active areas that have been abandoned over the past few thousand years. Third, we will develop new numerical modelling approaches to investigate and quantify the interactions between water and sediment transport processes, bar formation, evolution of channel morphology and the subsurface sedimentology of deposits. The latter will involve combining, for the first time, Computational Fluid Dynamics models that provide a sophisticated representation of the physics governing water and sediment movement, with innovative Reduced-Complexity models capable of simulating how these processes interact to determine channel evolution and deposit sedimentology over periods of centuries to millennia. The result of this work will be the World's first comprehensive database on how the morphology of a large river changes through time, obtained concurrently with data on what drives those changes and what this means for the formation of sedimentary deposits. This will allow us to develop new models of how these rivers work and to use these models to address practical questions concerning large river resources and their management.