Water Systems
The Water Cycle, Streams, and
Ground Water
Earth’s Water Supply
Water Cycle
• movement of water between the atmosphere, the land,
and the oceans.
Evaporation
• Water changing from liquid phase to a gaseous
phase(water vapor) without boiling.
• Surface 2/3 Water
• 500,000 km3 /year
• Evapotranspiration – evaporation from plant
leaves.
Condensation
• change of state from a gas to a liquid
• When water vapor rises in the atmosphere, it
expands and cools.
• As the vapor becomes cooler; some of it
condenses back to liquid
• High – Clouds
• Low – Fog
• Surface - Dew
Precipitation
• Any form of water that falls to Earth’s surface (rain,
snow, sleet, and hail)
• Most precipitation falls on Earth’s oceans.
• The rest falls on land and becomes runoff or
infiltrates the soil to become groundwater.
Runoff
• Rain that falls to the ground and is not
absorbed
• Moves along the surface of the land until it
flows into a stream system
• Causes erosion.
Factors Affecting Runoff
•  Rate of rain  Runoff
•  Slope  Runoff
•  Buildings  Runoff
•  Plants Runoff
River Systems
• watershed (AKA basin) the area of land that is
drained by a river system
• The ridges or elevated regions that separate
watersheds are called divides.
• tributaries streams that flows into a lake or into a
larger stream
• A river system is made up of a main stream and
tributaries.
Mississippi River Basin
Moosehead
Lake
Watershed
Contains:
• 31 lakes
• 549 m2 of land
•400 miles of rivers and
streams
•empties out into the
Atlantic Ocean
River Systems
• Channel - Depression that a stream follows as it
flows downhill
• Banks - The edges of a stream channel that are above
water level
• Bed - The part of the stream channel that is below the
water level
• A stream channel gradually becomes wider and
deeper as it erodes its banks and bed.
River Systems
stream load - Sediment carried by a stream
• Stream load takes three forms
– suspended load
– bed load
– dissolved load
Stream Load
River Systems
Stream gradient the change in elevation over a given
distance
• Near the headwaters, or the beginning of a stream,
the gradient generally is steep.
• As the stream nears its mouth, its gradient often
becomes flatter.
• The characteristics of streams with different gradients
are very different
Gradient
River Systems
• River systems change continuously because of
erosion.
• Depending on the slope of the land, streams
have three stages of development. Young,
Mature, and Old
• These differing streams support different types
of organisms
Young Streams
• Flow swiftly through a steep valley.
• Lots of whitewater and waterfalls because
they have not yet eroded all the material in
their way.
• Young streams erode most on the bottom
and less on the sides.
Qualities
•
•
•
•
Fast Moving
High oxygen
Cold
Little Nutrients
Stream Merging
• Many young streams join together to form
larger streams.
• Depending on the slope of the land and the
amount of water they will form either
mature or old streams
Mature and Old Streams
• Mature and Old Streams flow through
floodplains.
• floodplain an area along a river that forms
from sediments deposited when the river
overflows its banks
• Occurs when water levels increase
depending on the amount of rainfall and
snowmelt in the watershed.
Floodplains
Mature Streams
• Curving streams that flow down a gradual
slope
• Erode more on their sides than on the
bottom.
• This leads to the creation of meanders
(curves in a stream)
Qualities
• Lots of sediment/nutrients
– Erosion from young streams
• Slow moving
– Algae can grow
Evolution of Mature Streams
meander
• When a river rounds a bend, the velocity of the
water on the outside of the curve increases.
– Increase erosion
• On the inside of the curve, the velocity of the
water decreases.
– Increased deposition
• Causes curves to widen
Stream Flow
Horseshoe
Bend
of the Colorado River
near Page, AZ
Oxbow Lakes
• The curve enlarges while further erosion takes place
on the opposite bank, where the water is moving
more quickly.
• Meanders can become so curved that they almost
form a loop, separated by only a narrow neck of land
• This can eventually become separated into an oxbow
lake
Old Streams
• Old streams flow very slowly through a
broad flat floodplain.
• Usually they have lost their meanders and
flow more straightly.
Deltas and Alluvial Fans
• Fan-shaped masses of sediment deposited as a
stream slows
• Deltas occur where streams meet oceans
• Alluvial fans result where streams loose
energy as the slope decreases rapidly.
Groundwater
• Water that absorbs into the ground and is
located in the spaces between sediments
(pores)
• These pores are connected and allow water
to flow through them.
Permeability
• Ability of a material(rock/sediment) to
allow water to flow through it.
• Permeable rock/sediment layers allow water
to pass through easily
• Impermeable rock/sediment layers resist the
flow of water.
• Depends on size and shape of sediment
Zone of Saturation
• Ground water fills the pores in the permeable
rock/sediment layer creating an aquifer.
• The area of the soil where all of the pores have
completely filled with water is referred to as the
zone of saturation.
• The upper limit of this zone is called the water
table.
Wells
• Holes that are dug below the water table.
• Water has been filtered by sediment.
• If water table drops (drought) it can dry up the
well.
• Too many wells in one area can also lower the
water table
Artesian Wells
• Special kind of well where water is pushed up to
the surface naturally.
• Require a special kind of geography where an
aquifer is sandwiched between impermeable
layers and the layers change in elevation.
• Gravity creates pressure that forces water up
artesian wells.
Springs
• Springs can exist where the groundwater
reaches the surface
• Some times cracks allow natural artesian
wells to form.
• Freshwater springs exist along coasts where
fresh ground water enters the ocean.
Hot Springs and Geysers
• Occur where groundwater is stored near hot
rocks
• Hot springs - near boiling water leaks up to
the surface.
• Geysers - boiling water and steam is
periodically released causing a stream of
hot water to shoot out of the ground.
Caves and Sinkholes
• Form as carbonic acid dissolves limestone.
• Caves are structurally stable and do no collapse.
• If soil above a cave is weak and it collapses into a
sinkhole.
• People pumping water out can turn caves into sink
holes
Stalactites and Stalagmites
• Little CO2 in caves, carbonic acid breaks down,
can’t hold dissolved limestone.
• Limestone accumulates as water drips
• Stalactite - ceiling of the cave
• Stalagmite - ground of the cave
QuickTime™ and a
decompressor
are needed to see this picture.
Adaptations
• Animals must have special adaptations to
deal with living in a cave
• Dark
• No plants
• Wet
• Dangerous Chemicals