Definition of Aquifer, Aquiclude, Aquifuge, Aquitard & Perched Aquifer

• Aquifer- An aquifer is an underground layer of water-bearing permeable rock, rock fractures or unconsolidated materials.
• Aquiclude- An aquiclude which is a solid, impermeable area underlying or overlying an aquifer.
• Aquitard- A bed of low permeability adjacent to an aquifer; may serve as a storage unit for groundwater although it does not yield water readily wells.
• Aquifuge- An impermeable body of rock which contains no interconnected openings or interstices and therefore neither absorbs nor transmits water.

TYPES OF AQUIFERS

Aquifers are mainly of two types:

1.Unconfined aquifer

2.Confined aquifer (artesian aquifer)

Unconfined aquifer

Unconfined aquifer or water table aquifer is the one in which a water table serves as the upper surface of the zone of saturation. In such an aquifer, the water table varies in undulating form and in slope. Rises and falls in the water table corresponds to changes in the volume of water in storage within unconfined aquifer.

Confined aquifer

Confined aquifer or artesian aquifer is the one in which ground water is confined under pressure greater than atmospheric by over-lying, relatively impermeable strata. Artesian aquifer usually have relatively small recharge areas as compared with unconfined aquifers. When water is withdrawn from an artesian well, a local depression of the piezometric surface results. This decrease in pressure permits a slight expansion of the water and in some cases a compaction of the aquifer.

Artesian Well

When the water level in a well is below the ground level, but is above the local water table it is known as the artesian well.

Perched Well

It is a special type of unconfined aquifer, and occurs where a ground water body is separated from the main ground water by a relatively impermeable stratum of small aerial extent and by the zone of aeration above the main body of ground water.