CENTA NERC - The dynamics and sedimentology of large river confluences

River confluences are important nodal points in alluvial networks, representing often abrupt downstream changes in discharge, grain size and channel geometry that in turn may exert a significant control on channel morphology, migration and avulsion. While confluences are thus important across a range of disciplines, the focus of this project is in linking the morphology with the likely sedimentology to gain a longer term perspective on these key nodes in the river.
Most importantly, dynamic river confluences have the potential to create some of the points of deepest incision into underlying sediments and hence their subsequent fill has been argued to possess the highest preservation potential of fluvial channels. Since the depth of junction scour and mobility of the confluence are determined by flow processes in the confluence hydrodynamic zone, it can be surmised that differing junction dynamics may produce a range of characteristic confluence zone sedimentology. Furthermore, understanding the planform mobility of confluences, and thus the potential spatial extent of basal scour surfaces, particularly in large rivers, is key to interpreting alluvial stratigraphy, discriminating between autocyclic and allocyclic processes and reconstructing palaeohydraulics.
Our current understanding of confluence morphodynamics has been dominated by examples of largely static, small and experimental fluvial systems. There is therefore a need to critically examine, describe and quantify the morphodynamics and associated sedimentology of dynamic large river confluences which this project will address.

The successful student will undertake field and desk based research on a range of large river confluences. Desk-based methods will be used first with the student using remote sense imagery and GIS to build up a picture of how the chosen field sites have evolved over recent time periods. This will then inform the field data collection which will will require a range of geophysical surveys from boat-based platforms i.e. echo sounding as well as ground penetrating radar surveys over sites of former confluences to extend the timescale of investigation. The choice of which specific sites to focus on will be determined after completion of the desk based work but might include, for example, active sites such as the junctions of the Arkansas and Mississippi rivers in America and the Bermejo and Paraguay rives in Argentina.