Flow regulating structures, also known as control structures, are very common in storm water drainage systems and in combined sewer systems. The most common control structures are weirs and orifices.

In Bentley StormCAD , you can attach a weir or orifice at either the upstream end or the downstream end of a conduit, or at both ends of the conduit. A control can also have a flap gate which allows flow to travel in only one direction. Hydraulically these controls are treated as internal boundaries, i.e., the empirical weir or orifice equations are used to replace the momentum equations in the Saint Venant equations and the continuity equation is simply that the flow is the same between the upstream face and the downstream face of the internal boundary (control structure).

For more information on flow control structures, see: