ground water (1)

Perched Water Table:-

* Upper surface of Ground water which is held in an isolated area & much above main water table.

   * It is due to local geological conditions like occurrence of isolated impervious rock body within an impervious rock body within an  porous permeable  area .This isolated patch of impervious layer may cause local accumulation of water, thus creating a secondary water table of limited extent much above the main water table.

  It does not supply water on large-scale, such water bodies prove highly deceptive, misleading, in ground water exploration works.  But  yield is very short. In such cases drilling is to be extended further so that the ambiguity is cleared out.

 * Artesian Wells:-

  *Artesian water is confined water which is under hydrostatic head. Under favorable geological condition water may rise in a well under it’s ownhead at least upto the surface or may even rise out of surface upto reasonable height, such wells are called Artesian wells. If hydrostatic head is not enough to rise the water up to the surface without overflowing such type are called sub-artesian wells.  Name of water as artesian is derived from abundance of such wells are in the  Artois region of middle Europe

* Geological Structure:-  1)Essential condition for the artesian pressure is that the aquifer must extend to and outcrop a level higher than the level of point where well is dug.  2)A basin shaped topography is most favorable for producing artesian condition .3) Aquifer sandwiched between two impervious beds.

 1)The existence of suitable type of aquifer which should be slightly inclined or broadly synclinal in nature and should always be enclosed on both sides by impervious strata.

2) Due to faulting:-Artesian condition produced

3) Due to dyke:- Artesian condition produced

e.g.            1. Florida, Dakota basin U. S. A.

                 2. Great Australia basin.

                3. Gujarat Alluvial basin.

 4)Exposure of the aquifer in the catchment at higher level to provide sufficient hydraulic head.

5)Adequate rain fall in the catchment area to provide sufficient supply of water.

6)No other way for the escape of water except through the well.