In order to reduce the flow energy of weirs to preserve downstream dams, raise the water surface in channels, increase the underflow gates discharge, diminish the uplift pressure under the hydraulic structures and create a control section for discharge measurement, the flow must be transmitted from supercritical to subcritical. Quick transition of the flow regime accompanies by expansion, turbulence, water circulation and local head loss together with a hydraulic jump. Hydraulic jump is a type of rapidly varied flows and must be controlled and restrained. By employing a proper transition structure the total water head would be reduced gradually, and flow regime would be changed uniformly along the transition. Afterward, the hydraulic jump could be eliminated and consequently, the supercritical flow would be transmitted to a subcritical flow regime. In the present study, in order to change the flow regime from supercritical to subcritical and to reach an uniform gradually varied flow, a special transition is introduced based on the energy principle and Chow’s (1959) suggested method. Linear water surface profile and energy gradient line was assumed to estimate the transition surface profile. Different flow discharge with upstream Froude numbers between 1.5 and 6.5 were tested. The proposed transition is suitable for irrigation and drainage systems. For obtaining all unknown transition geometrical parameters, three programs were written using Matlab software (ver. 7.1). Regarding to a comprehensive theoretical analysis, the transition profile equations were obtained based on complete omission of hydraulic jump. Results of the theoretical models show that for high values of the transition length, the downstream depth is not depended on the transition length and is almost higher than the downstream depth of the equivalent dir=ltr Key words: Supercritical flow, Subcritical flow, Omission of hydraulic jump, Partial hydraulic jump, Transition
