Three-dimensional k–∊ numerical modelling of overbank flow in a mobile bed meandering channel with floodplains of different depth, roughness and planform

Abstract

In this paper, data from a series of experiments on overbank flow in mobile bed meandering channels, carried out on the UK Flood Channel Facility (FCF) atHRWallingford, are compared with computational results using a standard three dimensional k–e turbulence model (SSIIM). The experimental data covered several different floodplain depths, roughnesses and planforms. The roughness on the floodplains was modelled in SSIIM using notional rods, which penetrated the water depth as did the elements used to roughen the floodplain on the FCF. Experimental results for bankfull flow were used to optimize the main channel bed roughness. This was then applied to all of the overbank cases with no further adjustments or optimization. The results show that the numerical model gave good agreement for the variation of main channel discharge through a meander wavelength. It also captured all salient features of the secondary flows and circulation, although in some cases it tended to underestimate their magnitude. Distribution of depth-averaged flow across the main channel was very well modelled at the cross-over sections, but less satisfactorily at the apices. The model also captured the existence of re-circulation zones on the floodplain, which were observed in the FCF experiments