Glossary - A - aquifer

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An aquifer is an underground layer of water-bearing permeable rock, or unconsolidated materials (gravel, sand, silt, or clay) from which groundwater can be usefully extracted using a well (bore). A common misconception is that groundwater exists in underground rivers (e.g. caves where water flows freely underground), while the truth is that the pore spaces of rocks in the subsurface are simply saturated with water, which can be pumped out and used for agricultural, industrial or municipal uses. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology.


In non-mountainous areas (or near rivers in mountainous areas), the main aquifers are typically unconsolidated alluvium. They are typically composed of mostly horizontal layers of materials deposited by water processes (rivers and streams), which in cross-section (looking at a two-dimensional slice of the aquifer) appear to be layers of alternating coarse and fine materials.


Globally, the three main categories of geological (aquifer) materials - in order of importance are:

  • unconsolidated sediments - loose, not lithified, not cemented - e.g. sands, gravels
  • sedimentary rocks - layered, variable grain size and type in a sequence or formation. Water is confined to pore spaces, bedding fractures, other fractures
  • ingeous rocks - rocks cooled from molten state. As such almost inpermeable. Water in fractures

In groundwater studies some very important aquifer parameters are: porosity, permeability, hydraulic conductivity and storativity.

For more detailed information - see Wikipedia