On the Possibilities of Application of Exchange Discharge Model in Estimation of a Rating Curve at a River Gauging Station

The exchange discharge model (EDM) is the model that was developed for the estimation of a stage-discharge curve and flood routing in compound channels. It was thoroughly tested against experimental data in different compound channel layouts. However, there is a little evidence on its application in rivers. This paper studies EDM performance in estimating stage-discharge curve at two gauging stations on the same river with different hydraulic conditions and compares its results with the traditional, divided channel method (DCM). The contribution of momentum fluxes due to turbulence diffusion and mass exchange to the total energy loss are analysed. It is found that EDM parameter values (psi(t) and psi(g)) depend on the hydraulic conditions at a gauging station. In the case of M1-type water surface profile, the psi(t)-value increases and the effect of mass transfer is negligible. In the case of M2-type profile, the psi(t)-value decreases and the momentum flux due to mass transfer becomes dominant. Nonetheless, the lower psi(t)-value does not result in smaller additional loss due to turbulence diffusion, since the velocity difference between the main channel and the floodplain increases. Although the EDM and DCM provide approximately the same total discharge, EDM gives more realistic discharge distribution (main channel discharge is reduced and that on the floodplain is increased by 30-40% due to mass transfer caused by non-prismaticity of the channel).