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?

Water retention Infiltration

EvapotranspirationRunoff

Water is trapped on the Earth’s surface as

snow or ice.

Water “seeps” or infiltrates into the

soil.

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

The steeper the slope, the less likely water

will infiltrate into the ground.

Slop

e of

the

Land

Rate of Infiltration

What factors can affect infiltration?

Vegetation and Land Use

Infiltration tends to be higher in areas where vegetation covers the

soil (ie: grasses, shrubs, trees).

Amou

nt o

f la

nd u

sed

by

peop

le

Rate of Infiltration

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).

Rate of Infiltration

Amou

nt o

f ve

geta

tion

Soil SaturationZone of aeration: Area of the soil in which space between soil particles is partially filled with air

and partially filled with water.

Zone of saturation: Area of the soil in which all of space

between soil particles is filled with water (GROUNDWATER).

Water Table: The interface between the zones of

aeration and saturation.

Soil SaturationAs 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

Soil

Satu

ratio

n

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.

Poro

sity

Rate of Infiltration

pore space

Some soil types have a high porosity

due to the size and shape of

the soil particles.

Factors that affect Porosity ShapeRound soil fragments have

a higher porosity than angular soil fragments.

Round fragments

High Porosity

Angular fragments

Low Porosity

Factors that affect 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).SortedHigh

Porosity

UnsortedLow

Porosity

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 soilHigh

Porosity

Packed soilLow

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.

Capillarity 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.

Particle Size

Capi

llarit

y

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.

What factors can affect the runoff of water on Earth’s surface?

Rate of Precipitation Soil Saturation

Slope of the land Rate of Evapotranspiration

If the rate of precipitation is higher than the rate of infiltration, runoff will occur.

If the slope of the land is steep, runoff will occur.

If the rate of evapotranspiration is low, runoff will occur.

If the soil is saturated with water, runoff will occur.