The Water Cycle

 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!

 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.

  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.

The Water Cycle Process  The water cycle collects, purifies, and redistributes the Earth’s 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.

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!)

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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!

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

Water Poster Assignment 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!