artesian basin

(hydrology) A geologic structural feature or combination of such features in which water is confined under artesian pressure.

A syncline of permeable rocks with outcrops at the crest of the syncline. Water from rain or streams seeps into this aquifer, moving towards areas of lower hydraulic head. Eventually the rock becomes saturated and the water is under pressure. If a borehole is sunk at depth to tap the water, an artesian well forms from which the water will initially flow upwards without pumping. The term comes from the basin of Artois, in north-west France, and the most famous British example is the London basin where the aquifers are chalk and Lower Eocene sandstones and the aquiclude is London Clay.