Final answer:
The hydraulic gradient represents the slope or steepness of the hydraulic head, which is the potential energy per unit weight of water. The potentiometric surface is the level to which water will rise in a confined aquifer under the pressure of its own weight. These concepts are important in understanding the flow and distribution of water in porous media.
Step-by-step explanation:
The hydraulic gradient refers to the change in water pressure per unit distance along a flow path in a fluid, usually water, through a porous medium such as soil or rock. It is a measure of the slope or steepness of the hydraulic head, which is the potential energy per unit weight of water.
The potentiometric surface, on the other hand, is the imaginary surface to which water will rise in a confined aquifer under the pressure of its own weight. It represents the level to which water will rise in boreholes or wells that penetrate the aquifer.
For example, in a sloping aquifer, such as a hill, the hydraulic gradient will be steeper on the downhill side, indicating a greater pressure drop per unit distance. This can cause water to flow from areas of high hydraulic head to areas of low hydraulic head. The potentiometric surface in this case would be higher on the uphill side, reflecting the higher water level due to the greater pressure.