Overview

Project Highlights:

  • Chance to work on some of the World’s most iconic rivers
  • Mix of geomorphological, sedimentological, field and image analysis methodologies
  • Link to ongoing broader international research projects to provide additional experience and opportunities

 

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.

Multibeam echosounder data showing the structure of a 50 m deep scour at Chandpur where the Meghna and Padma rivers meet in Bangladesh. Data from a current NERC project led by Sambrook Smith with Best.

Methodology

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.

Training and Skills

CENTA students are required to complete 45 days training throughout their PhD including a 10 day placement. In the first year, students will be trained as a single cohort on environmental science, research methods and core skills. Throughout the PhD, training will progress from core skills sets to master classes specific to the student's projects and themes. 

The research student will benefit from designing a field programme and working in a multidisciplinary team and from participating in a large and active graduate research school within Birmingham’s School of Geography, Earth and Environmental Sciences. The research programme will provide the student with training in geomorphology; sedimentology; geophysics; geomatics; and analysis of environmental data.

Timeline

Year 1: Undertake essential research training, develop key research questions that the project will tackle based on literature review and develop the field based methods required to get the data needed to meet project objectives. Undertake desk-based research of imagery using GIS to quantify rates and patterns of recent change at the chosen field sites.

Year 2: Based on work from year 1, design and conduct a field program to quantify the rates and controls of confluence dynamics for the range of field sites chosen.

Year 3: Data synthesis and analysis of field data to derive key controls on confluence mobility. Use this data to validate and test a numerical model of confluence dynamics that can be applied widely to other sites and contexts. Poster presentation at a UK conference and an oral presentation at an international conference, paper production, thesis writing and submission.

Partners and collaboration (including CASE)

The successful student will benefit from the co-supervision of Prof. Jim Best at the University of Illinois at Urbana-Champaign. Prof. Best is a world leader in the science of river confluences and a secondment at UIUC would be possible if desired to extend the range of training opportunities available to the student. The student will also have the opportunity to gain additional skills via involvement in a number of large ongoing NERC projects led by Sambrook Smith on related topics.

Further Details

Greg Sambrook Smith, UoB, g.smith.4@bham.ac.uk