Defining the Water Table
The water table is the upper surface of the zone of saturation, where the pores and cracks in the ground are completely filled with water. Below this line, groundwater exists, while above it, the ground contains both air and water, known as the zone of aeration.
Formation and Characteristics
When precipitation falls, a portion of it infiltrates the ground through permeable soil and rock. This water, called groundwater, continues to move downwards until it reaches an impermeable layer, accumulating to fill all available spaces. The water table essentially marks the top boundary of this fully saturated groundwater body, which typically mimics the contours of the land surface above but is flatter.
Practical Examples and Observation
If you dig a hole deep enough, the point at which water begins to fill the bottom of the hole indicates the local water table depth. Similarly, the surface level of a lake, pond, or river is often a direct expression of the water table when it intersects the land surface. Wells are drilled down into the zone of saturation to extract groundwater for various uses.
Importance and Fluctuations
The water table is vital as it represents a primary source of drinking water for much of the world, supplying wells and sustaining streams, rivers, and wetlands during dry periods. Its depth is not constant; it fluctuates with rainfall, snowmelt, and human activities like pumping. Heavy rainfall causes it to rise, while prolonged drought or excessive pumping can cause it to fall significantly.