Headworks is a civil engineering term for any structure at the head or diversion point of a waterway. It is smaller than a barrage

Barrage (dam)

A barrage is a type of dam which consists of a line of large gates that can be opened or closed to control the amount of water passing the dam. The gates are set between flanking piers which are responsible for supporting the water load...

and is used to divert water from a river into a canal or from a large canal into a smaller canal.

Historically the phrase "headworks" derives from the traditional approach of diverting water at the start of an irrigation network and the location of these processes at the "head of the works".

The term is most commonly used in irrigation and canal engineering projects in South Asia.