Overview

Project Highlights

 

  • Gain experience in the measurement and simulation of complex natural vegetated river flows.
  • Develop new methods for investigating the impact of plant species and dynamics on river flow.
  • Work with partners at the interface of academia and industry to apply the model to help solve existing management issues.

 

Patches and mosaics of in-stream vegetation are a common feature in many lowland rivers and play a vital role in regulating flow and ecology within river systems. Vegetation can help moderate water temperature extremes, encourage sediment deposition and habitat creation, improve water quality and help maintain flow in drought conditions. However, vegetation can also increase flood risk due to reduced channel conveyance. Therefore, effective management of in-stream vegetation which balances these impacts requires a good understanding of the physical interaction between flow and vegetation patches. Computational fluid dynamics provides a tool for examining such interactions at the millimetre scale.

Traditionally, vegetation has been represented within computational fluid dynamics models using simplified forms such as arrays of rigid cylinders. These are a poor analogue of aquatic macrophytes, which have complex, multi-stemmed structure and are highly flexible, reconfiguring dynamically to the flow. Recently new methods have been proposed for representing vegetation patches within computational fluid dynamics models, using a porosity/permeability approach. The concept shows promise but requires further development to (i) correctly parameterise the model using real data, (i) understand how the impacts vary between species and (iii) account for the motion of vegetation patches within the model.

The aim of this PhD is to use field and numerical methods to better parameterise vegetation patches within a porous media computational fluid dynamics model. In particular, the focus will be quantifying the difference in parameters between different plant species and morphotypes and also incorporating vegetation motion effects.

Specific objectives are likely to include:

  1. Field measurement of the porosity and permeability of different species of aquatic vegetation over a range of field sites and flow conditions
  2. Development of new algorithms and methods for incorporating vegetation dynamics within an existing computational fluid dynamics model framework
  3. Testing and evaluating the performance of the new model using field data

 

Figure 1: Example of an existing numerical model for representing patch-scale flow-vegetation interactions, demonstrating the flow variation in a bare channel (a) as compared to a vegetated channel (b). Green lines indicate vegetation patch locations. Taken from Marjoribanks et al. (2017)

Methodology

The project will involve both field measurement and numerical model development.

Field measurement will be undertaken using the latest at-a-point and whole-field acoustic measurement techniques to capture high resolution flow data for model parameterisation and validation. Manual and automatic surveying techniques, possibly involving UAVs and GPS will be used to measure vegetation patch characteristics.

Computational fluid dynamics modelling will be conducted using PHOENICS and OpenFOAM software using existing models developed by the supervisors as a starting point. Code development will require use of Fortran and C++ and pre-requisite knowledge in programming is advantageous but not a requirement. Data analysis will be carried out in MATLAB and Paraview.

Training and Skills

Project-specific skills will focus predominantly on numerical (computational fluid dynamics) modelling and fluvial-based fieldwork skills, both identified by NERC as ‘most-wanted’ skills within the environmental sector. There will be opportunities throughout the PhD to enhance oral and written communication skills through conference attendance and publication of work in academic journals. The project will also include a placement at Centre for Ecology and Hydrology.

Timeline

Year 1: Comprehensive literature review, familiarisation with CFD software packages, initial field data collection

Year 2: Fieldwork season across 2 or 3 sites, algorithm coding and model development, preliminary data analysis

Year 3: Model testing and validation, application to case-studies, writing up

Partners and collaboration (including CASE)

The project will be undertaken in collaboration with partners at CEH (Dr Ponnambalam Rameshwaran) as well as potentially the National Trust.

Further Details

For more information about this project, please contact Dr Tim Marjoribanks (t.i.marjoribanks@lboro.ac.uk) or Dr Ponnambalam Rameshwaran (ponr@ceh.ac.uk).

For enquiries about the application process, please contact Berkeley Young (b.k.d.young@lboro.ac.uk) , School of Architecture, Building and Civil Engineering, Loughborough University. Please quote CENTA18-LU10 when completing the application form: http://www.lboro.ac.uk/study/apply/research/ .