The Hydraulic Gradient Line is the differene of the total head available to the device and the velocity head.
Hydraulic Gradient Line = Total Head - Velocity Head
What is the Energy Gradient line
The Energy Gradient Line refers to the total head available to a fluid. Consider a horizontal pipe carrying a fluid. If a pitot tube is connected in the line as shown in the figure, the fluid will rise to a particular height in the pitot tube.
This height is called the Energy Gradient line.