The concept of hydraulic gradient line and total energy line is very useful in the study of flow of fluids through pipes.

• Hydraulic Gradient Line (H.G.L)

It is defined as the line which gives the sum of pressure head (p/w) and datum head (z) of flowing fluid in a pipe w.r.t some reference line.

OR

It is the line which is obtained by connecting the top of all vertical ordinates, showing the pressure head (p/w) of a flowing fluid in a pipe from the center of the pipe.

• Total Energy LIne (T.E.L)

It is defined as the line which gives the sum of pressure head, datum head and kinetic head of a flowing fluid in a pipe w.r.t some reference line.

OR

It is the line which is obtained by connecting the tops of all vertical ordinates showing the sum of the pressure head and kinetic head from the center of the pipe.