Overview

Vegetation in river channels can have a profound effect on channel conveyance capacity, and the probability of overbank flooding. Aquatic vegetation has two main impacts. First, it introduces additional mass blockage within the channel, reducing the effective cross-sectional area of the channel available to the flow. Second, the vegetation leaf and stem edges represent additional channel boundaries, which will exert friction on the flow, causing momentum loss. Together, these two factors alter the local stage-discharge relationship.

Stage-discharge relationships are essential for flow/flood monitoring and prediction. Therefore, it is important to have a good understanding of any potential sources of error or variability in calculations, caused by factors such as vegetation, especially during periods of high flow. The effect of vegetation on channel capacity is complicated further by the seasonal life-cycle of vegetation growth and decay, as well as the spatial heterogeneity in vegetation distribution at different points in a river network.

While the potential impact of vegetation on rating curves has been acknowledged, there is still a lack of information regarding i) the magnitude of vegetation impacts on channel conveyance capacity, ii) the relative importance of mass/momentum effects, iii) the spatio-temporal variability in in-stream vegetation at the catchment scale; and iv) subsequent effects on overbank flood probabilities.

The aim of this PhD is to apply field and numerical methods to quantify the stage-discharge relationship for vegetated channels and devise a method to account for these impacts in discharge calculations and their effects on flood hazards at the catchment scale.

The specific objectives are likely to include:

O1) Quantifying inter-annual streamflow and vegetation cover characteristics across a range of field sites.

O2) Investigating the relative importance of mass and momentum effects of vegetation in altering discharge characteristics.

O3) Developing seasonally-adjusted stage-discharge calculation methodologies to produce more accurate discharge measurements. This will be applied first for site-specific cases before attempting to upscale the results to the catchment scale.

O4) Quantifying the associated impacts of vegetation on flood hazard at the cross-sectional and catchment scales (e.g. effects on the flood probability and spatial extent).

Macrophytes in the River Tame (Central Midlands, England) ©Slater 06/2015.

Methodology

This project will involve both field monitoring, numerical analysis, and data science methods.

UK-based (Midlands) field monitoring will be conducted using state-of-the-art measurement techniques to capture whole-field and at-a-point hydraulic measurements as well as echo-sounding and aerial photography to capture vegetation area cover and volume blockage data. This monitoring will be undertaken periodically at a number of different sites.

Numerical analysis will include data procesing in MATLAB,  simplified statistical modelling and potentially basic hydraulic modelling.

Data science methods will include data mining and  analysis of large datasets (such as the Environment Agency’s hydrometric archives) in the open-source language R.

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. 

Project-specific training is centered on those skills defined by NERC as ‘most-wanted’ within the environmental sector and will include fieldwork skills, such as flow measurement and characterisation as well as training in numerical modelling (both statistical and hydraulic) and analysis.

There will also be opportunities throughout the PhD to enhance oral and written communication skills through conference attendance and publication of work.

Timeline

Year 1: Comprehensive literature review; Research design for field monitoring campaign; training with field equipment; pilot studies followed by start of field monitoring.

Year 2: Regular periodic pattern of data collection; preliminary data analysis; numerical investigation of mass/momentum effects.

Year 3: Data analysis; development of new stage-discharge methods; analysis of flood impacts; writing up.

Partners and collaboration (including CASE)

This project will be undertaken in collaboration with UK regulatory bodies, who have expertise in flow measurement and flood risk.

Further Details

For more information about this project, please contact Dr Tim Marjoribanks (t.i.marjoribanks@lboro.ac.uk) or Dr Louise Slater (l.slater@lboro.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 CENTA when completing the application form: http://www.lboro.ac.uk/study/apply/research/ .