Slide 1
Groundwater fills connected pores and fractures
Groundwater is water in saturated pores and fractures beneath the land surface. Most of it does not flow through open underground rivers.
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Caves can carry channel-like flows, but many aquifers store water between sediment grains or within fractured rock. Recognizing the storage geometry helps explain why a well’s behaviour differs from a bucket lowered into a hidden lake.
Slide 2
Porosity measures storage space; permeability describes passage
Porosity measures how much void space a material contains. Permeability describes how readily connected spaces allow fluid to pass through.
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Clay can contain considerable pore space yet transmit water slowly because passages are small and restrictive. A rock with fewer but well-connected fractures can transmit water more readily despite lower overall porosity.
Slide 3
Pressure and height together drive the flow
Groundwater generally flows from higher hydraulic head toward lower head. Head combines pressure and elevation effects into a useful driving measure.
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Flow can therefore have an upward component where pressure is sufficient. Saying groundwater always travels downward overlooks confined aquifers and discharge areas where water rises toward springs or streams.
Slide 4
Recharge and discharge change aquifer storage
Water can enter aquifers by infiltration and leave through springs, streams, wells or other routes. Storage changes when these rates differ.
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Recharge may occur far from a pumping well and may take a long time to arrive. The location where water is extracted is therefore not necessarily the location that controls its replenishment.
Slide 5
Pumping changes nearby head and flow routes
A pumping well lowers nearby hydraulic head and can draw water from surrounding areas. Its influence depends on geology and pumping history.
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Lowered head can reduce discharge to a stream or induce stream water to enter the aquifer. Groundwater and surface water are thus connected parts of a system rather than fully independent supplies.
Sources
- Aquifers and Groundwater
US Geological Survey
- What Is Ground Water?
US Geological Survey