artésien

Artésien (artesian) refers to groundwater and wells that are supplied by a confined aquifer under natural pressure. The term is derived from the French artésien, from Artois, a region in northern France, where such wells were first described. In English, the adjective and the noun are used to describe both the water and the wells themselves.

In artesian conditions, groundwater is confined between impermeable layers and recharged at a higher elevation than the discharge point. The natural pressure causes water in a borehole to rise above the top of the aquifer. If the hydraulic head is sufficient, water may flow at the surface without pumping; such wells are called flowing artesian wells, while non-flowing wells still tap pressurized water. The level to which water rises in a well is known as the piezometric surface, a practical measure of hydraulic head.

Artésien occurrences are widespread wherever confined aquifers exist, across Europe, the Americas, Africa, and Oceania. One of the largest and most well-known artesian systems is the Great Artesian Basin in Australia, which spans about 1.7 million square kilometers and supports numerous springs and wells.

In contemporary usage, "artesian" mainly describes the type of well or its water and appears in hydrogeological literature, civil engineering, and environmental contexts. See also: artesian well; confined aquifer; piezometer; groundwater hydraulics.