Groundwater is water that is found below the ground surface. About 30% of the world’s fresh water is stored as groundwater while less than 1% is stored in streams, rivers, lakes and other surface water bodies. It is stored in and flows through aquifers and, to a lesser degree, aquitards.
What are aquifers and aquitards?
An aquifer is a layer of fractured rock, gravel, sand or limestone below the ground surface with enough space between the particles to hold groundwater and allow it to flow through. An aquitard is a layer of rock or clay below the ground surface that is tightly compacted and so water cannot easily be held within it or flow through it.
What are unconfined, confined and semi-confined aquifers?
Where the aquifer material between the ground surface and the water table is porous it is known as an unconfined aquifer. Where an aquifer is overlain by an aquitard it is known as a confined aquifer. Semi-confined aquifers occur near the edge of the confining layer (or aquitard) or where the aquitard is very thin or more permeable allowing more water to move through it. Unconfined and confined aquifers react differently to change.
Aquifers and the water cycle
This diagram shows a cross section of aquifers and aquitards and a basic water cycle. Diagram: ©Spatial Vision Innovations Pty Ltd (2015)