Braided rivers are very dynamic systems which have complex controls over their planform and flow dynamics. Vegetation is one variable which influences channel geometry and pattern, through its effect on local flow hydraulics and the process continuum of sediment erosion-transport-deposition.
The aim of this PhD is to develop an advanced understanding of the interaction between vegetation characteristics e.g. density, and river channel morphology, with a focus on the hydraulic and geomorphological processes that explain this relationship. Previous research in this field has been contradictory; with Gran and Paola (2001) finding that increasing vegetation density decreased the number of active channels. In contrast, Coulthard (2005] observed that as vegetation become denser there was an increase in the number of channels. Preliminary experiments by the supervisory team (Pattison and Roucou, 2016) have found that the relationship between vegetation density and the braiding index is more complex than previous thought.
Understanding the effect of vegetation in these highly dynamic systems has multiple consequences for human activity and management. For example, increasing/decreasing channel stability for economic growth/infrastructure on floodplain, flood hazards, and ecological/habitat impacts. This project aims to link small scale vegetation-hydraulics-geomorphology process understanding gained through controlled flume experiments to large scale global braided river systems through using remote sensing methods.
The specific objectives of the research are likely to include:
- Conduct laboratory experiments to assess the impact of vegetation characteristics e.g. density, size, flexibility on river channel pattern and morphology, using Structure from Motion photogrammetry to produce high resolution DEM’s.
- Develop and apply automated algorithms to determine vegetation characteristics e.g. density and river channel morphology e.g. braiding index, from remotely sensed images of global river systems.
- Assess the relationship between vegetation characteristics and channel morphology from global database developed in Objective 2, and compare this to small scale experimental relationships.
A combination of laboratory flume experiments combined with Structure for Motion Digital Photogrammetry and Remote Sensing will be utilised.
Laboratory experiments will be carried out in a 13m*2.4m flume. Variables of vegetation density, size and flexibility will be studied. The availability of high resolution low-cost digital cameras is creating new opportunities to reconstruct digital elevation models with high resolution and the dynamic sediment erosional/depositional processes using Structure from Motion (SfM) Photogrammetry. Acoustic Doppler Velocimetry will be used to measure flow velocity in 3D along with a novel force measuring devise to directly measure the drag force exerted on vegetation and sediment. Furthermore, coloured coded particle sizes will be used to understand the transport of different particle sizes.
High resolution, multi-temporal satellite imagery of large river systems will be used to classify river channel water distribution and depth, vegetation characteristics, and exposed sediment bars, for different reaches of braided river systems. It is possible some fieldwork may be required to ground truth this classification on one braided river system.
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 CENTA research themes.
Individual support will be given by the team of supervisors with frequent meetings to discuss ideas, plans and progress. Furthermore, project specific training will be provided on software (such as Matlab, PhotoModeller Photogrammetry software). Presenting work at national and international conferences will build confidence and communication skills throughout the PhD.
Year 1: Conduct a comprehensive literature review, identify research gaps and specific project aims and objectives. There will be general and subject specific training. You will gain familiarity with the software that will be used throughout the project (mainly PhotoModeller), and the logistics of using the hydraulic flume. Experiments will be designed and preliminary data collected.
Year 2: Laboratory experiments will continue. An automated classification system for the remotely sensed satellite images will be developed and applied.
Year 3: Any neccessary fieldwork for ground truthing will be undertaken. Data analysis of laboratory results and thesis writing. Dissemination at international conferences.
Partners and collaboration (including CASE)
We will engage with Dr Walter Bertoldi from the Environmental Hydraulics and Morphodynamics group at the University of Trento, Italy. His research interests are in the linkages between water, sediment and vegetation, focussing on braided river geomorphology. It is possible he could provide some fieldwork data to ground-truth the satellite imagery classification.
Dr Melanie Kirchhoefer works at the Forest Research Institute of Baden-Württemberg. The Forest Research Institute is specialised in using remote sensing data to analyse vegetation biomass which will be an important part of this PhD project.
For enquiries about the application process, please contact Berkeley Young firstname.lastname@example.org, School of Civil and Building Engineering, Loughborough University.