Artesian Condition If a well is drilled into a confined aquifer, the water can rise above its level in the aquifer because of extra hydrostatic (fluid) pressure, and it is called an artesian condition. Alternatively, when an aquifer is wedged between layers of relatively impermeable materials and consequently under pressure, it is said to be under artesian condition. The water in an artesian system may or may not rise all the way to the surface and some pumping may be necessary to bring it to the surface for use. In such a condition, rather than describing the height of the groundwater table, geologists refer to the height of the potentiometric surface, which represents the height to which the water's pressure would raise the water if the water were unconfined. This level will be somewhat higher than the top of the confined aquifer where its rocks are saturated, and it may be above the ground surface.
Artesian conditions depend upon certain requirements: a) an inclined aquifer whose lower end is buried and upper end is exposed, b) impervious layers above and below the aquifer that prevent leakage and allow hydrostatic pressure to develop, c) precipitation that infiltrates the aquifer at its exposed end, d) a spring or well that allows the water of the aquifer to discharge.
An extensive aquifer under artesian conditions is found in the ganges floodplain and in the atrai basin. In Rajshahi graben, Rajshahi-Charghat-Joypurhat horst and Rangpur-Lalmonirhat layered aquifers also show that they are under artesian condition. The piedmont deposits of chittagong, the Meghna estuarine floodplains of noakhali and the northern districts are not considered favourable for extensive groundwater development. Aquifers in the area are under artesian condition. At places semi-confined conditions exist but leakage from the overlying water-bearing formations is negligible. [Md Sazzad Hossain]