Hydraulic Head (called “head” in hydro) is the piezometric head measured as a liquid surface elevation, expressed in units of length, at the entrance (or bottom) of a piezometer. It is the height of water that would occur in a piezometer above a given point in the water conveyance of a hydropower system. When water flows from a reservoir into the water conveyance system, some of the head is converted into velocity head and some of the head is lost (see Head Loss).
