An aquifer is an subterranean layer of water in fractured rock,
or unconsolidated material such as gravel or sand. Large aquifers,
such as the limestone aquifer in the South East and the Tertiary
aquifer in Adelaide, can be good sources of water.
There are two types of aquifer: unconfined and confined. A unconfined
aquifer is the most common. It forms where the soil or rock layer
is partly filled with water or has no impermeable or semi-permeable
layer stopping the water level from rising. It contains groundwater
that is not subjected to any pressure other than its own weight.
A confined aquifer is a saturated aquifer that is over- and underlaid
by a confining bed. The groundwater is contained under sufficient
pressure to allow it to rise above the aquifer if the overlying
confining bed is penetrated.
Groundwater does not flow in underground streams as is commonly
believed, unless it is in cavernous limestone. Instead it flows
through the pores and fractures of the aquifer. The more permeable
an aquifer, the faster the flow. Rates of flow can vary from less
than 1 metre a year in clay to more than 200 meters in permeable
limestone. Groundwater usually flows from areas of recharge to
discharge; usually from high elevation to low elevation. Discharge
areas are rivers, lakes, springs and the coast.
The most reliable way of collecting information about groundwater
is by drilling a well into the aquifer. Information that can be
obtained from a groundwater bore include porosity and permeability,
and water quality data.
