S.A. Ayyoubzadeh - Dept. of Irrig. Hydra. Struc. Eng., TMU, Tehran, Iran
A. Zahiri - PhD Student of TMU, Engineer of KhozestanWater and Power Authority, Iran

Recent advances in two-stage compound channel flowaspects improves our knowledge to take into account many complex features involved in this special type of river flowand hence to increase our ability to cope with more efficiently the flood flows. However, among these only a few studies under unsteady flow conditions are available. Due to the difference of the hydraulic and geometric characteristics between the main river channel and its floodplains, flood waves are differently routed in these two parts of the river cross section. Hence, a modified flood routing of the Saint-Venant equations is needed to deliberate this distinctive pecularity. In this paper, a finite difference method to solve the modified Saint-Venant equations in some homogenous and heterogeneous typical compound channel cross sections are presented. Both explicit and implicit schemes are used in the numerical solution of the basic equations. No difference was observed between the results of these schemes.