Transcript Chapter 11: Water

Chapter 11: Water
Section 1: Water Resources
• Some of the water we drink today
has been around since water
formed on Earth billions of years
ago
• Water is essential to life on Earth
• Humans can only survive a for
days without water
The Water Cycle
• Earth has an abundance of water in all forms: solid, liquid, and gas
• Water is renewable because it gets circulated through the water cycle
where water molecules travel between the surface and atmosphere
• Water vapor (a gas) rises into the air
• Water vapor cools as it rises through the atmosphere and condenses
into droplets forming clouds
• Water falls back down to Earth as precipitation
• Oceans are an important part because so much of water on Earth is
in the ocean
Global Water Distribution
• 71% of Earth's surface is covered
with water, but 97% of water on
Earth is salt water
• Only a small percentage is liquid,
fresh water that humans can use
• It is found in lakes, rivers, and
beneath Earth's surface
Surface Water
• Surface water is fresh water on
Earth's land surface
• It's found in lakes, rivers, streams,
and wetlands
• Throughout history, people have
built cities near reliable sources of
surface water
• Rivers, lakes, and streams provide
drinking water, water to grow
crops, food, power for industry,
and transportation
River Systems
• Streams form as water from falling rain
and melting snow drains from mountains,
hills, plateaus, and plains
• As streams flow downhill, they combine
with other streams and form rivers
• As streams and rivers move across land,
they form a flowing network of water
called a river system
• The Mississippi, the Amazon, and the Nile
are enormous river systems
• The Amazon is the largest river system in
the world
Watersheds
• The area of land drained by the
river is called a watershed
• Pollution anywhere in a watershed
may end up polluting a river
• The amount of water entering a
watershed changes throughout the
year
• Rapidly melting snow, spring and
summer rains, etc. can dramatically
increase the amount of water in a
watershed
• Communities depending on these
watersheds can be severely affected
by changes in the river system
Groundwater
• Most of the freshwater available to
humans cannot be seen because it
exists underground
• Water beneath Earth's surface in
sediment and rock formations is
called groundwater
• The point where rocks and soil are
saturated with water is called the
water table
• The water table can be at the surface
or way below the surface
Aquifers
• An aquifer is an underground formation that
contains groundwater
• The water table forms the upper boundary of
an aquifer
• Most aquifers are rock, sand, and gravel that
have lots of space for water to accumulate
• Groundwater can dissolve limestone rock
formations filling vast caves with water
creating underground lakes
• Aquifers are an important water source for
many cities and agriculture
Porosity and Permeability
• Although rocks appear to be solid, many
kinds of rocks contain small holes or
pores
• Porosity is the percentage of the total
volume of a rock that has pores
• The more porous a rock is, the more water
it can hold
• The ability of a rock or soil to allow water
to flow through it is called permeability
• Materials that allow water to flow through
are permeable; materials that do not let
water flow through are impermeable
Wells
• If you go anywhere on Earth and dig a
hole deep enough, you will eventually
find water.
• A hole that is dug or drilled to reach
groundwater is called a well.
• People dig wells because groundwater
may be a more reliable source of water
than surface water in some areas and
because water is filtered and purified as
it travels underground.
The Recharge Zone
• To reach an aquifer, surface water must travel down through
permeable layers of soil and rock
• The area of the Earth’s surface from which water percolates down into
an aquifer is called a recharge zone
• Recharge zones are environmentally sensitive areas because any
pollution in a recharge zone can also enter the aquifer
• Size of recharge zone is affected by the permeability of the surface
above the aquifer
• Structures such as buildings and parking lots can act as impermeable
layers to reduce the amount of water entering an aquifer, so recharge
zones must be managed carefully.
Copy now, answer later
• Describe the distribution of water on Earth. Where is
most of the fresh water located?
• Explain why fresh water is considered a limited
resource.
• Explain why pollution in a watershed poses a
potential threat to the river system that flows through
it.
• Describe how water travels through rock.
• Why is an underground lake an aquifer?