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

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.