Orifice Stage
As the pond stage rises relative the crest elevation, the riser will then act like an orifice, and the flow is defined by the following equation.
| C | = | contraction and energy loss coefficient | |
| A | = | effective orifice area (sq. ft, sq. m) | |
| g | = | acceleration due to gravity | |
| H | = | orifice head (ft, m) |
A Note on Weir to Orifice Transition
The transition between the weir and orifice flow hydraulics is a turbulent transition which is computationally abrupt. To enhance convergence characteristics, Drainage and Utilities supports the formulation of a weir to orifice transition zone. You can specify a hydraulic transition zone height which is (by default) centered about the theoretical transition point. Over this transition range, Drainage and Utilities will linearly interpolate the stand pipe flow between the lower transition elevation at which weir flow governs to the upper transition elevation at which orifice flow governs.