Groundwater Flow
You know that things move downward as a result of gravity. Groundwater, for the most part, is no exception. But take a look at this diagram and notice that the groundwater follows a curved upward path from point A to point B. What causes this upward flow that seems to violate the law of gravity? What is going on is similar to what happens when you stick a dry sponge into a shallow bowl of water. Even if the water does not completely cover the sponge, water flows upward from the bottom of the bowl, wets the bottom part of the sponge, and then continues moving laterally and upward through the sponge to eventually wet the entire sponge. The water does this because fluids in porous materials (like water in a sponge or groundwater in an aquifer) like to move from areas of high pressure to areas of low pressure.
Point A on the diagram is under greater pressure than point B. Here is what happens to groundwater flow in the area shown:
- Water enters the zone of aeration (soil above the water table) and flows downward as a result of gravity.
- When the water hits the water table, it continues to move downward due to the pull of gravity, but is also pulled toward areas of lower pressure. Thus, it may begin a curved path upward toward point B, because point B is under less pressure.
- All groundwater is in constant motion due to this principle.
- As you can see in the picture, groundwater near a shallow well may only be underground for a few days or years. But deeper groundwater flows very slowly and may stay in one place for hundreds or thousands of years.
