The Water Cycle

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The Water Cycle
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• The amount of water on Earth is finite (which
  means that there is a limited amount).
• All of the water present at the beginning of time
  is still present now!

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• All water on Earth is constantly
• moving.
• The natural water cycle, also known as the
  Hydrologic cycle, describes the continuous
  movement of water on, above, and below the
  surface of the Earth.

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• The water cycle is self-renewing and constant.
• The Sun provides the energy to power the water
  cycle.
• Water is always changing states between liquid,
  vapor (gas), and ice.
• These processes happen in the blink of an eye and
  over millions of years.

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The Water Cycle Process

• The water cycle collects, purifies, and
  redistributes the Earths water.
• The sun heats up the bodies of
• water it is shining on.
• The heat causes some of the water to change from
  a liquid state to a gaseous state, this is called
  evaporation.

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Evaporation

• Only pure water evaporates.
• Fact ?This is the reason why the ocean stays
  salty! Pure water evaporates leaving the salt
  behind.
• Water also evaporates from the upper layer of
  soil and from plants. Evaporation from plants is
  called transpiration (it like plants sweating!)

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Evaporation/Transpiration

• The rate of evaporation depends on a number of
  factors
• Air temperature Evaporation is much higher in
  warmer climates than in colder climates.
• Amount of moisture in the air Evaporation rates
  are lower in humid areas than in dry areas
  because humid air has little room to hold
  additional water.

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Condensation

• As evaporated water rises into the sky,
  temperatures cool and it collects around
  particles of pollution and dust to form larger
  droplets.
• The process where water vapour (gas) in the air
  turns into liquid water is condensation.
• Condensation helps in the formation of clouds.

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Condensation

• Warmer air is able to hold more water than cold
  air because there is more energy in warm air
  molecules.
• Dew Point The temperature at which condensation
  occurs. Happens when warm air masses holding a
  lot of water cool.

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Cloud Formation

• As air rises the temperature cools, and the
  ability to hold water decreases.
• Once moist air has reached the dew point
  elevation clouds are formed.
• Water vapour needs to have a surface to condense
  on. In the atmosphere the water vapour condenses
  on dust particles to form clouds.

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Precipitation

• Precipitation occurs when moist air in the
  atmosphere rises above the dew point.
• This occurs in one of 3 ways
• Convectional precipitation
• Orographic precipitation
• Frontal precipitation

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Convectional Precipitation

• As air rises it loses the ability to hold on to
  the water.
• Convection currents in the atmosphere carry water
  vapour higher in a steady state of vertical air
  flow.
• These currents only occur when there is hot air,
  thus they often occur in Canada in the summer in
  the form of thunderstorms.

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Orographic Precipitation

• In Ororgraphic, or relief precipitation, air is
  also forced to rise above the dew point, however
  it is not hot air that causes this but rather a
  change in surface elevation.
• This often occurs in mountainous regions. As air
  continues up the mountain more and more moisture
  is released. By the time the air has reached its
  highest point there the air has lost most of its
  moisture.

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Frontal Precipitation

• Frontal precipitation occurs when two air masses
  with different characteristics meet.
• Denser air masses push the air higher until the
  dew point is reached.

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Runoff

• Excessive rain or snowmelt can produce overland
  flow to creeks and ditches.
• Runoff is visible flow of water in rivers, creeks
  and lakes as the water stored in the basin drains
  out.
• If water lands on the ground and is unable to
  penetrate, it becomes surface runoff.

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Percolation

• Some of the precipitation and snow melts and
  moves downwards, percolates (filters) or
  infiltrates through cracks, joints and pores in
  soil and rocks until it reaches the water table
  where it becomes groundwater.

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Groundwater

• Subterranean water is held in cracks and pore
  spaces.
• Depending on the geology, the groundwater can
  flow to support streams. It can also be tapped by
  wells.
• Some groundwater is very old and may have been
  there for thousands of years.

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Groundwater Layers

• The layer where groundwater flows downward is the
  unsaturated zone.
• The layer where water accumulates is called the
  saturated zone.
• The level between the saturated and the
  unsaturated zone is called the water table.

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Aquifiers

• Some surface seep into the ground where it is
  held between particles of soil as groundwater or
  deep beneath the surface in porous layers called
  aquifers.

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Water Story Assignment

• Imagine yourself as a tiny drop of water what
  would your life be like?
• Create an adventure story about your life as a
  drop of water. Where would you travel? How
  would you get there?
• You must include the various parts of the water
  cycle and explain what happens to you as the drop
  of water as you travel through each of the
  different phases of the water cycle.
• This activity should demonstrate a clear
  understanding of the water cycle!

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The Three Gorges Dam

• Read The Three Gorges Dam case study on pages
  164 165 in the text book.
• Answer questions
• 1 4, page 165
• 8 page 169
• 11 a, c page 169

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Water Poster Assignment

• Create a poster depicting the path of water
  through the Water Cycle.
• Be sure to include the various stages of water
  throughout the water cycle.
• All parts of the water cycle should be included
  (evaporation, transpiration, condensation, etc.)
• Be creative! The poster should be neat, easy to
  read, organized and colourful. Remember it is a
  cycle, so it should flow that way!