No-choke flow in USBR standard horseshoe channel cross-section

Choking problems occur in transitions that have a bed rise higher than a maximum allowable value. Due to the complexity of the United States Bureau of Reclamation (USBR) horseshoe cross-section, a time-consuming trial-and-error procedure is inevitable as a way to determine the maximum allowable bed rise. This paper presents straightforward solutions to calculate a choke-free maximum bed rise for practical changes in bed elevations. The maximum relative errors associated with the proposed equations are less than 1%. A graphical solution is presented to obtain the upstream operating ranges based on non-dimensional specific energy curves. In addition, a direct relationship is developed to determine the critical depth in the transition zone which bears less than 1% relative error. Finally, a choking solution is discussed by considering the energy head loss occurred in the channel transition zone.