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How do different aquifers respond to change?

How do different aquifers respond to change?

Aquifers respond differently to changes in rainfall, pumping depending on whether they are unconfined, semi-confined or confined.

Unconfined aquifers

These aquifers are very responsive to rainfall and pumping. They exhibit a seasonal pattern that mimics rainfall and pumping – groundwater levels fall during drier months when pumping demand is high and recover during the wetter months when demand is low.

Semi-confined and confined aquifers

These aquifers are less susceptible to changes in rainfall and pumping as they are protected by overlying aquitard.  Groundwater levels in semi-confined aquifers mimic rainfall patterns but the response is delayed as the water has to seep further down to reach the aquifer. These aquifers show an immediate response to pumping.  This is because pumping generally occurs during the dry season (summer) when rainfall (recharge) is low.

Very deep confined aquifers

These aquifers show no relationship at all to rainfall patterns as they are buried under many layers of aquifers and aquitards. They do respond to pumping, however the effects may not be seen immediately as there is generally vast volumes of groundwater held in storage which balance out any extraction.

Groundwater flow systems and response to change

How groundwater responds to change is also influenced by flow systems as discussed on our How does groundwater move page.  Groundwater that flows through local flow systems reacts quickly to changes in pumping or climate and the impact is greater.  In regional flow systems the impact may not be seen for many, many years and the impact will be more subdued.

Response to change

Line graph showing that over 100 years, local flow systems respond quickly to change compared to intermediate and regional flow systems.

This graph show how groundwater responds to change in different flow systems over time. Diagram: ©Spatial Vision Innovations Pty Ltd (2015)

Page last updated27th May 2015
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