An improved method of calculation for steady uniform flow in prismatic main channel/flood plain sections

Abstract

Some experimental results are presented from the SERC Flood Channel Facility at Hydraulics Research, Wallingford, for discharge and boundary shear stress distribution in symmetrical compound channel/flood plain sections of varying flood plain width and roughness. These are used to assess the performance of several standard discharge calculation methods, which assume different locations of the interface between main channel and flood plain sub-areas. It is shown that these methods can produce large errors in total and, more particularly, component discharges, which increase significantly with flood plain width and roughness. A modified form of the above methods is discussed, which makes a more realistic allowance for interaction at the main channel/flood plain interface. It achieves this by incorporating the 0-indices, first suggested by Radojkovic to characterise momentum transfer between adjacent sub-areas, into the calculation. This modified method is shown to be considerably more accurate than the standard methods in calculating total and component discharges. A tentative regression equation is presented for calculating 0-indices from easily identifiable cross-section characteristics.