A novel measure of vegetation roughness in river channel hydraulics

Supervisor: Dr Andrew Folkard

Deadline for Applications: Applications accepted all year round
Funding Type: Self-Funded Students Only
Type of Study: PhD


The presence of aquatic vegetation in rivers, streams and man-made watercourses makes a big difference to how much water they can carry, and is a major factor in determining their ecological health and water quality. It can also affect the extent to which rivers flood or dry out, because of its control on the rate of flow. Thus understanding the flow resistance of aquatic vegetation is a crucial aspect of river management. Recent work by the supervisory team suggests that a fundamental reappraisal is required of the way in which this flow resistance is quantified, and in particular that the spatial scale at which this is done is much more carefully considered.

The project will tackle this problem by hypothesising that the traditional approach - based on assigning Manning's roughness coefficients based on visual observations and look-up tables - should be replaced with an alternative approach, based on comparing rating curves for gauged river sites, with and without vegetation. The project would investigate whether this new approach can characterise the effect of aquatic plants on flow discharge and depth, and thus their equivalent roughness at the reach scale, and conversely whether it can provide a surrogate measure of plant standing crop. It would also investigate whether these curves can be used to investigate the changing resistance of vegetation under flood conditions, and the importance of the spatial arrangement of vegetation at the reach scale.

Funding Notes

This project is offered on a self-funding basis, although we are actively seeking funds to support it from a variety of sources. Fees for EU and non-EU students are available from Andy Harrod on request.


1. Folkard AM (2010) Vegetated flows in their environmental context: a review. Proceedings of the Institution of Civil Engineers - Engineering & Computational Mechanics, in press (available on request from Dr. Folkard at the email address above).

2. Knight, D.W. et al. (2010). Practical channel hydraulics: roughness, conveyance and afflux. CRC Press

3. O'Hare, M.T. et al. (2010) Variability in roughness measurements for vegetated rivers near base flow, in England & Scotland. Journal of Hydrology, in press (available online: DOI: 10.1016/j.jhydrol.2010.02.036