Note: Weir and Orifice Flow Equations for a Weir in SWMM 5
If you use a weir in SWMM 5 then two flow equations are used
1. The weir uses the weir flow equation when the head at the weir is between the invert elevation of the weir and the crown of the weir and
2. An orifice equation when the head is above the weir crown or the weir is submerged.