Choke-free flow in trapezoidal channels

is very suitable to design a channel transition from the point of view of a no-choke condition. In this study, the condition of choke-free flow for two types of transitions in trapezoidal channels subject to a rise in bed elevation is considered. Based on the critical flow occurring downstream of the transition zone, the energy equation is solved with the aid of numerical methods to determine explicit equations for the maximum permitted bed rise under a given approaching regime. The presented procedure herein can also be used to determine end sill height in triangular and trapezoidal channel sections to assure hydraulic jump occurrence in stilling basins. Moreover, to determine the limits of upstream-flow depths (the choke-free regions) a suitable dimensionless specific energy equation is presented. This equation can be utilised to choose the operating ranges of upstream flow depths for choke-free flow in subcritical and supercritical upstream flow conditions. Finally energy loss in the transition zone is considered by applying it in the proposed equations.