Water table is a free water surface in an unconfined aquifer.
A well driven into an unconfined aquifer will indicate a static water level. This water level is corresponding to the water table level at that location. It is constantly in motion adjusting its surface to achieve a balance between the recharge and outflow.
Fluctuations in water table level
Fluctuations in water level occurs due to:
- lowering of ground water due to heavy pumping of the wells.
- rise in the water of an irrigated area with poor drainage.
- during various seasons of the year.
In general, it follows the topographical features of the surface.
If it intersects the land surface, then ground water comes out to the surface in the form of springs or seepage.
Perched water table
Sometimes a lens or localised patch of impervious stratum occur inside an unconfined aquifer. It retains a water table above the general water table. Such type which is retained around the impervious material is known as perched water table.
Usually it is of limited extent and the yield from such a situation is very small. In ground water exploration, it is always confused with the general one.
Reference : Engineering hydrology by K. Subramanya