Author(s): Peter R. Wormleaton; Mile End Road; Martin J. Marriott; Unversity Way
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Keywords: Compound channels; Meandering channels; Flood flows; Turbulent flow modelling
Abstract: This paper contains the results of an experimental and numerical investigation of flow patterns in two different meandering channel geometries with the same sinuosity (centre-line planform geometry), main channel meander width/floodplain width ratio and main channel aspect ratio, but with different main channel widths. Both bankfull and overbank flows were considered. The bend radius/main channel width ratio (r/bc) of the wider main channel was 1. 0 and for the narrow channel it was 1. 8. Thus the wider case was well below the Bagnold (1960) criterion of r/bc < 2 for the formation of flow separation and a re-circulation zone upstream of the bend apex. This was indeed observed in the wider case at bankfull flow, but not in the narrower case, which was nearer the Bagnold criterion. At overbank flow it was observed that the separation zone disappeared. This led to a significant increase in the main channel component of the flow for the wider main channel, which was not observed for the narrower case, where the separation zone was absent throughout. The flows were computed using a 3-D simple k-ε turbulence model. It somewhat underestimated the full extent of the recirculation zone in the wider channel case, which is a feature of methods relying on the Boussinesq eddy viscosity relationship. Nevertheless it did successfully capture the salient features of the flows throughout and provided good estimates of bulk discharge.
Year: 2007