LEQ:
How does water move
through underground layers
of soil and rock?
Key Terms: pores, permeable, impermeable, saturated zone,
unsaturated zone, water table, aquifer, artesian well
Where does groundwater come from?
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Begins as precipitation.
Water from precipitation that doesn’t evaporate, or runoff soaks
into the ground.
Affected by the permeability of the land cover.
 Permeability is determined size of the pores in the land cover.
 The smaller the pores the more impermeable the land cover.
 The larger the pores the more permeable the land cover.
Water is pulled into the ground by gravity.
Some of the water is absorbed by roots and used by plants.
The remainder trickles down between particles of soil and
through cracks and spaces in rock layers.
Underground Water Layers
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Water will continue to travel downward between the pores or
cracks in the soil or rock.
When the water reaches an impermeable layer it becomes
trapped.
Water then begins to fill the pores and cracks in the soil or rock
above the impermeable layer.
The soil or rock above the impermeable layer becomes saturated
and is known as the saturated zone.
The top of the saturated zone is called the water table.
Soil and rock layers above the water table still have water flowing
through and are not saturated. This layer above the water table
is called the unsaturated zone.
To help you visualize this concept, see the image on the next
slide.
The Water Table
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Generally follows the shape or contour of the underground
impermeable rock layer.
Depth can vary greatly even over a small area of land.
Heavy rain or lots of melting snow raises the level of the water
table.
Level drops during extended periods of dry weather.
Can meet the ground surface and seep onto the surface as a
spring or into:
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Rivers or streams
Ponds
Wetlands
Aquifers
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An aquifer is any underground layer of rock or soil that
holds water.
The saturated zone between the impermeable layer and
the water table.
Range in size.
Water flows or moves through the aquifer. The
movement and speed of the water in the aquifer
depends on:
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How steep the aquifer slopes.
How permeable the rocks and soil are.
Water can travel hundreds of kilometers and stay in an
aquifer for thousands of years before coming to the
surface again.
Bringing Groundwater to the Surface
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People can remove groundwater from an aquifer by drilling a
well.
For the well to be filled with water, it must be drilled below the
water table and into the aquifer. Can become dry if to much
water is removed to fast.
New water from precipitation that soaks in from the surface can
recharge the aquifer.
Artesian wells.
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A well in which water rises because of pressure within the aquifer
Aquifer is trapped between two layers of impermeable rock or sediment.
Water is under great pressure due to the weight of the water above.
Water will flow out of an artesian well drilled into this aquifer without
pumping.
To help you visualize this concept, see the image on the next
slide.
Investigating Groundwater
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Enter the subterranean world of Groundwater
One More Time !
The
Groundwater
Story