Definitions for "Hydraulic Gradient"
Slope of a water table or potentiometric surface. More specifically, change in head per unit of distance in a given direction, generally the direction of the maximum rate of decrease in head. The difference in hydraulic head divided by the distance along the flowpath.
The difference in potential between two points, divided by the lateral distance between the points.
The difference in hydraulic head between any two points (represented by a difference in water level) defines the 'hydraulic gradient' between those points.