The Water Cycle
Water vapor was “out gassed” during
Earth’s cooling process some 4.5
billion years ago.
This volume of water has been
recycled ever since.
What happens to precipitation
that reaches the Earth’s surface?
Infiltration
Water retention
Water is
trapped on
the Earth’s
surface as
snow or ice.
Runoff
Water
“seeps” or
infiltrates
into the
soil.
Evapotranspiration
Water moves
across the
surface of the
Earth to a large
body of water.
Water is
evaporated
and/or
transpired
back into
the
atmosphere
What factors can affect the
infiltration of water into the soil?
Slope of the land
Slope of the Land
The steeper the slope,
the less likely water
will infiltrate into the
ground.
Rate of Infiltration
What factors can
affect infiltration?
Vegetation and Land Use
Infiltration tends to be poor in areas
where the land has been used by
people (ie: compacted soil of farms
and/or city landscapes covered by
asphalt).
Amount of
land used by
people
Amount of
vegetation
Infiltration tends to be
higher in areas where
vegetation covers the
soil (ie: grasses,
shrubs, trees).
Rate of Infiltration
Rate of Infiltration
Soil Saturation
Zone of aeration: Area of the soil
in which space between soil
particles is partially filled with air
and partially filled with water.
Water Table: The interface
between the zones of
aeration and saturation.
Zone of saturation: Area of the
soil in which all of space between
soil particles is filled with water
(GROUNDWATER).
Soil Saturation
Soil Saturation
As the ground becomes
saturated with water, the
water table rises. As the
water table rises, the
chance of water infiltrating
the soil will decrease.
Rate of Infiltration
Porosity
Porosity: The amount of “open
space” (pore space) between soil
particles compared to the total
volume of soil.
If the amount of “pore space”
between soil particles is high, then
water will infiltrate the soil more
easily.
Some soil
types have a
high porosity
due to the size
and shape of
the soil
particles.
Porosity
pore space
Rate of Infiltration
Factors that affect Porosity
Shape
Round soil fragments
have a higher porosity
than angular soil
fragments.
Round
fragments
High Porosity
Angular
fragments
Low Porosity
Factors that affect Porosity
Sorted
High
Porosity
Unsorted
Low
Porosity
Sorting
Soil fragments that are
roughly the same size and
shape (sorted) will have a
higher porosity than those
that are not the same size
and shape (unsorted).
Factors that affect Porosity
Packing
Soil fragments that are loosely
packed will have a lot of pore space
and will have a high porosity.
Soil fragments that are compacted
will have a small amount of pore
space and will have a low porosity.
Loose soil
High
Porosity
Packed soil
Low
Porosity
Permeability
Permeability: The ability of
a material to allow a fluid to
pass through it.
Different soils have different
levels of permeability – or the
rate at which water can move
through the soil.
Which soil type do you think has the
highest permeability?
Sandy soil has the highest permeability.
Which soil sample below has
the smallest particle size?
The clay soil sample has the
smallest particle size. The
clay shows the best evidence
of capillarity as seen by the
highest upward rise of water
in the sample.
Capillarity: The upward migration
of water in soil against the force of
gravity.
Capillarity is commonly found in
soils with loosely packed, small
particle size.
The larger the particle size of the
soil; the lower the rate of capillarity.
Capillarity
Capillarity
Particle Size
What factors can affect the runoff of
water on Earth’s surface?
Rate of Precipitation
If the rate of
precipitation is
higher than the
rate of
infiltration, runoff
will occur.
Slope of the land
If the slope of the
land is steep,
runoff will occur.
Soil Saturation
If the soil is
saturated with
water, runoff will
occur.
Rate of Evapotranspiration
If the rate of
evapotranspiration
is low, runoff will
occur.