Transitional Flow Between Orifice and Non-Orifice Regimes at a Rectangular Canal Gate

The main objective of this research was to analyze the hydraulic transition between nonorifice and orifice flow regimes at a rectangular sluice gate, and to determine the value of a coefficient (Co) used to define the transition between orifice and non-orifice flow conditions. Several dozen data sets were collected in a hydraulic laboratory, each including the measurement of upstream and downstream water depth for five different gate openings, and 17 different steady-state discharges from 0.02 to 0.166 m3/s. Various approaches were tested to define the limits of the non-orifice-to-orifice regime transition; one of these uses the specific-energy equation for open-channel flow. Once the transition limits were defined, an estimation of the non-orifice-to-orifice transition coefficient, Co, was made. The transition coefficient was defined as the ratio of gate opening to upstream water depth. The experimental results indicate that orifice flow always exists when Co is less than 0.83, and non-orifice flow always exists when Co is greater than 1.00. To determine the flow regime (orifice or non-orifice) within the range 0.83 \u3c Co \u3c 1.00, it is necessary to consider the submergence, S, which is the ratio of downstream to upstream water depth