Submerged Orifice Hydraulics

When the orifice is submerged, the flow is defined by the following equation for both orifice types:

C	=	contraction and energy loss coefficient
A	=	effective orifice area (sq. ft, sq. m)
g	=	acceleration due to gravity
H	=	orifice head (ft, m)

The orifice head, H, is measured as the difference between the water surface elevation and the greater of the center elevation of the circular orifice or the controlling tailwater elevation.

By inspection it can be seen that the equation is mathematically invalid whenever H is less than zero (i.e., the water surface is below the centroid during unsubmerged conditions).

Also, for the equation to be applied correctly, assume that the flow area must be fully submerged.