Sharp crested weirs can be placed as control structures in conduits. Other control structures include orifices, functional structures and depth discharge curves.

To insert weirs into the start or stop ends of a conduit:

1. Set Has Start Control Structure? or Has Stop Control Structure? to True in the Physical:Has Control Structure section of the Property Editor for the conduit.
2. Click the Ellipse (...) button that appears next to the Start Control Structure or Stop Control Structure field. This opens the Conduit Control Structure dialog box.
3. Select New > Weir.

Weirs can be placed in any shape of conduit but the weir structure itself is treated as being in a rectangular section. The weir length is the distance across this section measured perpendicular to the flow (for all except side weirs).