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Topic 1. Water – Nature's Magician
Chapter 1B: The hydrologic cycle
To the teacher
Purpose
To review the hydrologic cycle and emphasize the endless and continuing motion of water molecules.
Subject areas
Language Arts, Environmental Studies, Social Studies, Math, Art, Science
Procedure
- Using the diagram in the Student Information section, review the concept of the water cycle. If this is new to students, discuss tricycles, bicycles, seasonal cycles, or their school time table cycle.
- Go over the vocabulary of the hydrologic cycle.
- Review with students that the three primary kinds of water include atmospheric water or vapour, surface water, and groundwater. Ask them if they can name some of each, for example:
- atmosphere – vapour, snow, rain, hail
- surface – oceans, icecaps, wetlands
- groundwater – aquifers, artesian wells
Each kind of water is part of the hydrologic cycle.
- Ask if there is more water around today than there was 100 years ago.
Point out that the water here today is the same water that their great grandfathers used 100 years ago; and the same water has been here for approximately 4 billion years since the earth was formed. This water keeps going around and around in one of nature's cycles.
- Use a world map to point out to students where British Columbia, Brazil, and Bangladesh are located. Emphasize that the same water we use has travelled to a lot of places – a Canadian living in any province or territory has likely been rained on by water drops that fell on other countries.
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Vocabulary
- condensation
- disperse
- evaporation
- evapotranspiration
- groundwater
- hydrologic cycle
- percolate
- precipitation
- prehistoric
- recycling
- saturate
- transpiration
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References
Student information
It's Monday morning. Very early. And you hear your Social Studies teacher say something to the class about looking at the hydrologic cycle.
You're probably not quite ready for something too new right now. But relax. It's the water cycle being recycled with a new name, the hydrologic cycle. The question is, how much do you know or remember about the water/hydrologic cycle?
Let's refresh our memories with the following diagram.
The hydrologic cycle
How the hydrologic cycle works
If you observed or performed Activity 7 from the last chapter, you saw how heat changed water from liquid to steam, and from solid to liquid. In the same way, water molecules in the atmosphere need the sun's power or energy to keep moving and changing. After all, if there were no heat from the sun, the water would be frozen and we would not be here reading about it.
 Water molecules group together to form clouds (this is called condensation), and these clouds are moved about the earth by air currents. As these clouds become saturated, or full of water, precipitation occurs and the water droplets fall to earth.
When water reaches the earth, the drops disperse. Some run off as surface water and others percolate through the ground to become part of the groundwater supply.
Once again, the sun's energy works on the surface water changing the water to vapour, a process called evaporation. This vapour rises into the atmosphere to form new clouds and continue the hydrologic cycle. Water also enters the atmosphere from the leaves of trees – this is called transpiration.
And round and round the water goes, showing why this process is called a cycle.
How old is water?
A very interesting fact about water is that it doesn't go away. The same water molecules running down your drain or resting in your water glass might be the very ones that your great, great, great grandfather used to water his crops many years ago. Or, some prehistoric animal may have drunk the very same molecules that you are preparing to drink right now.
Think about it. Use your imagination to consider the stories one drop of water could tell if it could talk. It's difficult to believe that we are still recycling the same water that a young dinosaur might have frolicked in millions of years ago.
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Did you know?
The water cycle maintains a very delicate balance on a global scale. For every drop of precipitation which falls, an equal amount must disappear into the atmosphere through evaporation or transpiration. When this balance is disturbed, water can become unfriendly and we may get floods or droughts.
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The well-travelled water molecules
Because of wind currents and climate changes, water molecules get to visit all parts of the earth. Parts of the same rain which fell on you yesterday in Canada, may fall on the Brazilian and British Columbian rainforests next month, or they may seep into the ground through percolation and spend the next three years finding their way to the ocean or ending up in somebody's well.
Some water molecules might spend the next 10 000 years in the underground water supply or frozen in a northern glacier!
Just think about your glass of water again. These water molecules might have been part of floods that rushed from the Himalaya Mountains and down the Ganges River to Bangladesh causing people to lose their homes, their crops and livestock, and sometimes their lives. Or, the water molecules may have just come back to the surface water supply after having spent a thousand years frozen in the Arctic ice.
We may not be exactly sure of where and when water first appeared, but we do know two facts:
- water has been in motion constantly since it came; and
- practically the same amount of water that was here at the beginning is still with us today – being recycled time and time again through the hydrologic cycle.
Learning activities
Activity 1 – Science, Environmental Studies
You can show how a hydrologic cycle works with a simple demonstration in your classroom or at home. Try one of the following experiments:
- Set up a terrarium.
- Put soil in the bottom of a large glass jar and plant a few small plants.
- Water the plants and cover the mouth of the jar or terrarium with plastic wrap.
 Watch your terrarium for a couple of weeks.
- Write down what you observe. How do you think this relates to life on the planet Earth?
- Show how plants use and transpire water within the hydrologic cycle.
- Take a potted plant and put a plastic bag over it. Use tape to keep the bag in place and use sticks to keep the bag from touching the leaves.
- Set the plant in a sunny window.
- Record what happens.
- What conclusion would you make from this experiment?
- Make a very simple model of the water cycle.
You will need:
- a small glass jar – a baby food jar will do
- a small rock to fit in the bottom of the jar
- water that has been coloured with food colouring
- plastic wrap or lid to seal the jar
What to do:
- Place the rock in the jar and partially cover it with the coloured water. (Make sure you mark the level of the water on the outside of the jar.)
- Seal the jar, then place it in the sun.
- Come back to the jar after it has been sitting in the sun for a day. Record your observations.
- Move the jar back into the shade. What happens?
- What conclusion would you make from this experiment? Write your conclusion down.
Activity 2 – Social Studies, Language Arts
 You probably wouldn't mind being able to travel to some of the exotic places that the water molecules travel to, but you wouldn't be so crazy about some of their other travels.
Take one of the following story topics and develop a story about a water molecule in motion. Give your water molecule a catchy name.
- You are a water molecule who lives in the north and you are really keen to catch a ride to the sunny south. It takes you a whole year to get there and it is a lot of hard work. Describe what happens to you during the year.
- A dirt cycle? You are a speck of dust lying in the yard minding your own business when the wind disturbs you and lifts you into the air, taking you higher and higher.
You bump into a cloud where you meet millions of other specks, just like you, and you kind of enjoy this life on cloud nine, drifting around in the blue before you find yourself being covered by moisture.
Something drastic happens to disturb your peaceful life. What is it? Tell about your awful experiences.
- Back in the 1890s you were frozen into a glacier and you have just now been released back into the atmosphere. You don't understand what has happened to the earth in the past 100 years. Everything has changed. You try to find out from others; and you try to tell them what happened to you. Some molecules are helpful, others are not. Write about one of your conversations or write a play.
Activity 3 – Art
Now that you know how the hydrologic cycle works, why not prepare your own colourful diagram showing in detail how it works. If you are feeling really creative, give your diagram some texture with cotton wool for clouds and other fabrics or materials for sand, grass, trees, and water.
Activity 4 – Science, Math
As you saw in the diagram of the hydrologic cycle, trees send moisture back into the air through transpiration. How can you measure approximately the amount of water one tree sends back? First of all, you have to start small – begin your measurement with one single leaf over twenty-four hours and calculate the rest.
 You will need:
- a plastic sandwich bag
- a small pebble
- some string
- a set of scales
- and, last but not least, a tree with a broad leaf such as a maple or oak
What to do:
- Place the pebble in the bag.
- Weigh the bag, pebble, and string carefully. Record the weight.
- Tie the bag (with the pebble in it) around a leaf on a tree. Be careful not to disturb or damage the branch.
- After twenty-four hours, carefully remove the bag from the tree and weigh it again.
- How many milligrams of water do you have in your bag?
- Make up five math questions you could ask another person based upon what you have just learned about one leaf. For example:
- If a tree has 10 000 leaves, how much moisture will it transpire in a day? In a month? In a year?
- If you had 20 trees in your backyard, how much moisture would they transpire?
- How would you go about calculating the number of leaves on one tree? You really don't want to count them all, do you?
Activity 5 – Language Arts
Create your own word search.
This chapter uses vocabulary that you may not be familiar with.
- Read back over the information and select words to make your own word search. (You must know the meaning and spelling of every word you include!)
- Ask your teacher for graph paper to keep your lines straight.
- Remember, the words can go in any direction – forwards, backwards, up, down, and diagonally. You can also use other water words to fill in smaller spaces.
- Whichever words you use should be included in a list underneath your puzzle.
Activity 6 – Language Arts
Another word sometimes used to mean transpiration is the long word, evapotranspiration. As you can see, it is a combination of evaporation and transpiration. Try one or both of the following exercises:
- How many four-letter words can you get from evapotranspiration? List them. Remember, you are not allowed to use a letter more times than it appears in evapotranspiration, for example, you cannot use "tattle" because there are only two "t"s in evapotranspiration.
- Make a list of the three- and four-letter words you get from evapotranspiration that relate to environmental issues. (Make a side bet with your neighbour.)
Activity 7 – Art, Storytelling
You may be surprised to learn that raindrops are not tear-shaped. Rather they are shaped like small hamburger buns. Combine your artistic and storytelling skills and create your own comic strip character on a journey through the hydrologic cycle.
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