The effect of sloping floodplain on flow resistance and discharge in straight compound channels with single floodplain

Abstract

This research work describes the study of two types of floodplains (i.e., flat and sloped) to investigate the influences of sloped single floodplains on a compound channel in terms of conveyance capacity, velocity distribution, and resistance to flow. To this end, were made four single floodplain compound channel models, including one flat floodplain and two models with a sloping floodplain in positive (4 % and 9 % transverse slope bed) and one negative transverse slope (−4%) and each of the models was investigated under different flow discharges. The results show that the main channel is more efficient for conveying water when the floodplain is positively sloped compared to the flat floodplains. The water conveying capacity of the main channel increases by 10.9 % in the positive transverse slope compared to the flat floodplain and decreases by 3.4 % in the negative transverse slope. For both low and high flow discharges, the average velocities in the main channel and the floodplain with a highest positive transverse sloped bed were 15.7 % and 11.23 % higher, respectively, compared to the flat floodplain. On the negative transverse slope, the Manning roughness coefficient, n, is frequently higher than that of other cases. In a case with negative transverse sloped bed (i.e., θ = −4%), the Manning's n in the main channel and flat floodplain was 8.33 % and 14.05 % higher than that of the flat floodplain. The Darcy-Weisbach friction factor, f, in a compound channel with a positive transverse sloped bed on a floodplain was 5.7 % higher than in a flat floodplain.