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Modelling the effects of aquatic plant growth and management on the hydraulics of a chalk stream

Sutcliffe, Adam Graeme. 2014 Modelling the effects of aquatic plant growth and management on the hydraulics of a chalk stream. Queen Mary, University of London, PhD Thesis, 363pp.

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Abstract/Summary

One of the major factors affecting flood conveyance in small to medium-sized water courses is the growth of aquatic plants. In-stream vegetation increases the resistance to flow, giving higher flood levels for a given discharge and leading to greater incidence of over-bank flooding. This thesis is focused on vegetation, characteristic of a chalk stream. Here, vegetation management is as much for the provision and maintenance of habitat as for flood risk. In order to balance these two demands, new tools are required which enable sound estimates of both flood conveyance and changes in habitat suitability. To this end, a three-dimensional hydraulic model is developed for a typical chalk stream. A novel methodology for modelling the impact of in-stream vegetation on river flow hydraulics is developed using the double-averaged Navier-Stokes equations. This is implemented within general purpose computational fluid dynamics software and tested using field measurements taken during both summer and autumn, before and after vegetation management. The model performs well when compared to field measurements of flow velocity and turbulent kinetic energy. Results show that the complex three-dimensional morphology of Ranunculus spp is shown to have a key role in energy loss and a marked impact on the distribution of flow velocities and turbulent kinetic energy. Vegetation management is discussed in terms of its effect on flow velocity, turbulent kinetic energy, flow depth, conveyance capacity and in-channel habitat. A sensitivity analysis shows the importance of rigorous data collection and guidance is provided as to which measurements have the greatest influence on calibrated model parameters. Finally, possible implications of the findings of this study for conveyance estimation methodologies and the management of aquatic vegetation are provided.

Item Type: Publication - Thesis (PhD)
CEH Sections: Acreman
Additional Keywords: river hydraulics, aquatic plant, chalk stream
NORA Subject Terms: Ecology and Environment
Hydrology
Date made live: 12 Feb 2015 11:02 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/509700

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