A basin is separated from other basins by higher areas that limit the basin. These areas are called watersheds. From these areas of greater elevation, or watersheds, the terrain slopes until it reaches the river basin. We say that there is an incline down to the river basin. This incline is called the slope .
Subterranean waters can remain stored for long periods or they can be moving.
The rocks found under the ground surface can be permeable or impermeable . They are permeable if they quickly absorb the water that penetrates the ground. They are impermeable if they impede the passage of water, that is, they stop the filtration. Permeable rocks absorb the rainwater, and little by little they get filled up. Once they are completely filled, we say that they are saturated.