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Groundwater
AIM: Where does all the water go?
Water Cycle (hydrologic cycle)
Water enters the
atmosphere…
►
Evaporation – Water
changes from a liquid to a
gas. Most water
evaporates from the
oceans. Latent heat is
stored. Wind and high
temps speed up
evaporation.
►
Transpiration – water in
plants evaporates
►
Evapotranspiration – all
evaporation from earth
and plants.
Water leaves the atmosphere…
► Condensation
–
Water changes from a
gas to liquid to form
clouds. Latent heat is
released.
► Precipitation
– any
form of water that falls
from clouds (rain,
snow, sleet, hail)
Where does it go?
► Runoff
–water that
flows over the ground,
eventually leads back
to a larger body of
water
► Accumulation
–
when water collects
into large bodies, or
falls directly into it
Where does it go?
►
Infiltration – when
water seeps (sinks)
into the ground to be
stored as groundwater
in the water table.
►
Groundwater flow –
when water moves
while underground
Factors that affect infiltration
► 1.
Porosity: the size of
the spaces between
sediments in the
ground or in the rocks
themselves.
►
2. Permeability: how fast
water will pass through the
soil material. The ability to
pass through sediments in
the ground.
Water table
►
►
The height of the water in the ground. Water near the
surface can evaporate, lowering the water table.
Water will infiltrate the ground when it is unsaturated and
permeable, causing the water table to rise.
Infiltration – water will seep into
ground to the water table
Permeability:
►Permeable:
water passes through fast
(gravel and sand)
►Impermeable:
water passes through
very slowly (silt and clay)
Permeability animation
Why did the water pass through the
gravel and sand faster?
Gravel and Sand: High porosity, high permeability
Because there are larger spaces between the pieces of
gravel and grains of sand where water can go through
easily.
Silt and Clay: Low porosity, low permeability
Silt and clay are tightly packed together and have very
small spaces between them.
What is the relationship between
sediment size and permeability?
► The
larger the sediment, the more
permeable because the spaces will be
bigger.
► The
smaller the sediment, the less
permeable because the spaces will be
smaller.
http://www.brainpop.com/science/earthsystem/groundwater/
Porosity:
► The
percentage of open space in a material
compared to its total volume.
 Shape –rounded particles have more porosity
than angular particles
 Packing-closely packed particle have lower
porosity
 Sorting – sorted particle have higher porosity
than unsorted
But…sorted sediments that are
equally packed have equal porosity
Capillarity
► Small
closely
packed rocks will
draw water up
against the flow
of gravity
Summary: Factors that affect runoff
and infiltration
► Permeability
of the soil- type of soil, size of
sediments, sorted vs. unsorted
► Slope
– steeper will cause more runoff, shallow
slope more infiltration.
► Saturation
of the ground – wetter ground will
decrease permeability and cause more to run off,
dryer ground will allow more infiltration, less
runoff
► Groundcover
– vegetation decreases runoff,
concrete increases runoff.
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