Influence of boundary roughness on velocity and discharge in compound river channels

Results are presented of an experimental compound channel research programme carried out at the UK Flood Channel Facility including fixed and mobile main channel boundaries together with two flood plain roughnesses. For comparison data from a natural compound river channel are also presented. Velocity and discharge relationships are explored illustrating the complex behaviour of compound river channels and calling attention in particular to the errors incurred in applying conventional methodologies to discharge assessment in overbank flows. Relationships are presented for velocity and discharge ratios which could form the basis of mathematical modelling of overbank flow estimation methods. The research also represents a step towards prototype conformity by the introduction of mobile boundaries.