Author(s): M. Jesson; M. Sterling; J. Bridgeman
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Keywords: No Keywords
Abstract: Within natural rivers, sediment and vegetation can vary significantly from reach to reach and within a cross section. As a result, lateral bed heterogeneity is a feature of almost all in-bank river flow. Despite this common occurrence, there is a lack understanding of how such changes in roughness can alter the overall resistance of a particular reach of river and how this in turn affects its conveyance capacity. This paper presents the preliminary results of a research programme aimed at characterising flow in a heterogeneous channel. Rather than focusing simply on adjustments to empirical flow parameters such as Manning’s n and roughness coefficients, the research aims to identify turbulent structures and secondary flows within the channel, enabling a physical understanding of the effects of the heterogeneous bed to be evaluated. In order to achieve this, an idealised heterogeneous channel bed was constructed in a 22m experimental channel at the University of Birmingham. Detailed3-D velocity and boundary shear stress measurements were recorded at more than 500 grid points over a cross-section of the channel at a fixed flow rate. From these measurements, the mean parameters and turbulent velocity fluctuations were determined. Quadrant-Hole analysis was used to highlight the propagation of turbulence from the channel bed.
Year: 2010