ABSTRACT
The hydraulic grade line is determined by the sum of the pressure and elevation heads measured relative to the centroid of the pipe section. It therefore lies below the energy line by an amount equal to the velocity head in the pipe and represents the height to which liquid will rise in an open stand-pipe connected to the pipeline at any point. The slope of the hydraulic grade line is referred to as the hydraulic gradient. Unlike the energy gradient which must fall continuously in a downstream direction, the hydraulic gradient may rise at enlargements of section. The velocity head is often exceedingly small in comparison with the pressure head and if it is neglected the energy and hydraulic grade lines coincide.
