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|artesian well |
A deep well that passes through impermeable rock or sediment and reaches water that is held under pressure in a confined aquifer. In aquifers of this type, the water in the lower regions is trapped between two layers of impermeable rock and cannot rise to the level of the water table in the upper, unconfined regions. When a well penetrates the confined region, the pressure forces the water to rise within the well until it reaches the elevation of the water table in the unconfined region (a level known as the potentiometric surface). ◇ In a flowing artesian well the water is under enough pressure to rise all the way to the surface without being pumped and must be capped to control the flow.
a man-made spring from which water flows under natural pressure without pumping. It is dug or drilled wherever a gently dipping, permeable rock layer (such as sandstone) receives water along its outcrop at a level higher than the level of the surface of the ground at the well site. At the outcrop the water moves down into the aquifer (water-bearing layer) but is prevented from leaving it by impermeable rock layers (such as shale) above and below it. Pressure from the water's weight (hydrostatic pressure) forces water to the surface of a well drilled down into the aquifer; the pressure for the steady upflow is maintained by the continuing penetration of water into the aquifer at the intake area.