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The University of Southampton
Geography and Environmental Science

British Hydrological Society prize recognises outstanding student achievement

Published: 6 September 2012

Geography and environment graduate Thomas Greenwood has been named runner-up in the British Hydrological Society's annual student prize. It was awarded for his 'outstanding' undergraduate dissertation on the Impact of Large Woody Debris Dams upon Flow Resistance in the Highland Water.

The dissertation was supervised by Professor Paul Carling and was nominated by Geography and Environment to be considered for this annual prize.

Dissertation abstract: The presence of large woody debris (LWD) in fluvial systems can have major influences on hydraulic, geomorphological, hydrological and ecological processes. The effect of accumulations of LWD on flow hydraulics is now a key issue in fluvial engineering on the basis that wood is a substantial creator of form drag, and thus, it is a major contributor to total flow resistance. This effect is considered herein, with the study focussing on an empirical investigation of the Highland Water: a low order, gravel-bed stream in the New Forest, Hampshire. Total flow resistance is quantified by using both the Darcy-Weisbach friction factor and the Manning equation.

Roughness components are then partitioned using a technique designed to measure the hydraulic importance of LWD. Debris in the Highland Water is found to have an overwhelming influence on the flow, which is shown by high resistance coefficients. Relationships between flow resistance and channel properties (discharge, slope and debris) show patterns which agree with the established theory in the literature.

However, it is shown that the partitioning technique is unsuitable for the channel and so a critique of the approach is presented. It is concluded that further work should focus on advancing a technique to more accurately partition roughness elements in debris-choked streams such as the Highland Water.

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