Headwall

Headwall

This is a structure that forms an entrance to an underground pipe or culvert. Usually, it is a wall built around the upper end of the conduit with side walls or wingwalls that guide flows into the conduit.

In DRAINS, headwalls are used  where an open channel enters a pipe or set of pipes, and overflows may occur over the top of the headwall. 

If water rises above the nominated overflow level for the headwall, the headwater level will be set by weir characteristics or an elevation-discharge relationship defined in the property sheet for the overflow route leading out of the headwall.

The DRAINS headwall should only be located at the entrance to a pipe.  In engineering practice, the term 'headwall' is sometimes applied to the outlet of a pipe where flow discharges into an open channel or waterbody, or 'tails out' flows, spreading them over an area of land.  In DRAINS an outlet of this kind must be modelled as a node, as shown below: