Incipient Jump Conditions for Flows over a Vertical Sill

The incipient jump condition is defined as the critical condition for the formation of a surface roller immediately upstream of a sill. The incipient jump conditions can be classified in two categories. In one case, the incipient jump occurs by increasing the sill height from the state of the splashing flow. In the other case, raising the tailwater level from the splashing flow condition yields the incipient jump. The mechanisms for both cases of the incipient jump conditions are explained. Also, the effect of the channel width on the incipient jump condition is discussed. The application of the momentum equation yields a prediction for each incipient jump condition. For wide channels, in which two-dimensional breaking occurs, the agreement between the predicted and experimental results is satisfactory. The formation of a forced jump is required for the design of a stilling basin.