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

尽管世界上10条最大的河流消耗了几乎五分之一的全球大陆面积，并提供了供应给海洋的约三分之一的陆地沉积物，但我们对这些大河的功能知之甚少。这既令人惊讶又有问题，因为它们直接影响到广泛的环境、社会和经济问题(例如洪水、河岸侵蚀、土地流失和基础设施崩溃)，并最终创造出蕴藏着世界上一些最有利可图的矿物和化石燃料储量的矿藏。目前对大河流的认识几乎完全基于在小河道中进行的研究结果。然而，最近的研究给了我们很好的理由，我们有理由预计，将这些知识转移到大河可能不是一帆风顺的。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更好的量化了解。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各种时间和空间尺度(从分米/分钟到千米/千年)的过程-产品关系的方法。这项研究将汇集一个由英国和海外领先研究人员组成的多学科团队，以实现这一目标。在这个项目中，我们将调查世界上最大的河流之一--阿根廷的巴拉那-巴拉圭，以了解：(1)是什么控制着水和泥沙的运动以及河道随时间的变化；以及(2)这对河流沉积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野外仪器绘制河床地貌及其随时间的演变图，并测量河坝周围和上方的水和泥沙运动的三维模式。其次，我们将利用探地雷达技术的最新发展，绘制辫状坝矿床的三维沉积结构图，既包括当前河流中的辫状坝矿床，也包括过去几千年来被遗弃的以前活跃的地区。第三，我们将开发新的数值模拟方法，以研究和量化水和泥沙运移过程、沙洲形成、河道形态演变和沉积物地下沉积学之间的相互作用。后者将首次将计算流体动力学模型与创新的低复杂性模型结合起来，前者提供了控制水和泥沙运动的物理模型的复杂程度，后者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的河道演变和沉积沉积学。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，同时获得的数据还包括驱动这些变化的因素以及这对沉积矿床的形成意味着什么。这将使我们能够开发这些河流如何工作的新模型，并利用这些模型来解决与大型河流资源及其管理有关的实际问题。

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.