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Hydroelectric Energy: Classroom Activities

The Water Cycle


Goal

To understand how water changes state and moves through the Earth System and how this movement can be used to produce electricity.

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Background Information

Water is constantly moving through a vast global cycle called the water cycle. Solar energy heats water in the Earth's lakes and oceans, causing it to evaporate. This water condenses into clouds and then falls back onto the continents as precipitation. The water flows through streams and rivers back into the oceans, where it evaporates and begins the cycle over again.

The water cycle is important to the production of hydroelectricity. Hydroelectric energy uses the kinetic energy of moving water, as it passes through the water cycle, to make electricity. The most common method for doing this is to manipulate the cycle by constructing a dam across a river. The dam blocks the flow of the river and creates a reservoir of water behind it. Water from the reservoir travels through the dam and applies pressure against the blades of a turbine, causing them to spin, which drives a generator to produce electricity.

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Activity Overview

Students construct a diagram that illustrates how water moves within the hydrologic cycle.

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Materials and Equipment

Water Cycle diagram (below) - color copies or projected, several blank sheets of paper, scissors, ruler or straightedge, poster board, markers, removable tape, colored pencils (blue, red, green)

Diagram of the water cycle
Source: The American Geological Institute, EarthComm: Project-Based Space and Earth System Science, 2nd Edition, Armonk, New York: It's About Time, 2012, pg. 373.

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Activity

  1. Show students the following diagram that shows a simplified version of the water cycle:
    Diagram of the water cycle
    Source: The American Geological Institute, EarthComm: Project-Based Space and Earth System Science, 2nd Edition, Armonk, New York: It's About Time, 2012, pg. 373.
  2. Explain to students that the total volume of water near Earth's surface is almost constant and that this water is in constant motion. Tell them that that the water cycle describes how Earth's water moves from place to place in an endless cycle. Review with students the following list of the components of the water cycle. Review some of the definitions as well. Explain how the list is divided into two parts: reservoirs (places where water is stored) and processes (ways that water is moved from place to place).
    Reservoirs: Processes: Definitions:
    • oceans
    • atmosphere
    • louds
    • glaciers
    • soil moisture
    • groundwater
    • lakes
    • rivers
    • vegetation
    • evaporation from the ocean surface
    • precipitation onto the ocean surface
    • evaporation from the land surface
    • precipitation onto the land surface
    • precipitation onto glaciers
    • condensation to form clouds
    • melting of glaciers
    • calving of glaciers
    • surface runoff into rivers
    • surface runoff into lakes
    • infiltration of surface water
    • groundwater flow
    • river flow
    • transpiration from plants
    • uptake of water by plant roots
    Calving: Some glaciers end in the ocean. As the glacial ice moves forward into the ocean water, it breaks away from the glacier in huge masses, to float away as icebergs, which gradually melt.

    Groundwater: Some of the liquid water at Earth's surface moves downward through porous Earth materials until it reaches a zone where the material is saturated with water. This water flows slowly beneath Earth's surface until it reaches rivers, lakes, or the ocean.

    Infiltration: Some of the rain that falls on Earth's surface sinks directly into the soil.

    Soil Moisture: Water, in the form of liquid, vapor, and/or ice, resides in Earth's soil layer. It is the water that remains in the soil after rainfall moves downward toward the groundwater zone. Soil moisture is available for plants. What is not used by plants gradually moves back up to the soil surface, where it evaporates into the atmosphere.

    Surface Runoff: Some of the rain that falls on Earth's surface flows across the land surface, eventually reaching a stream, a river, a lake, or the ocean.

    Transpiration: Water taken up by the roots of plants is delivered to the leaves. Some of this water is used to make new plant tissue, and some is emitted from the leaves in the form of water vapor, by a process called transpiration.
  3. Have students draw and cut out nine rectangular boxes with dimensions less than about 2.5 cm. Have them draw and cut out fifteen circles with diameters of less than about 2.5cm.
  4. Ask students to write the name of each reservoir in a box. Ask them to write them name of each process in a circle.
  5. Have students draw the following on a poster board:
    1. A horizontal line lengthwise across the middle of a poster board to represent Earth's surface in a vertical cross-section view.
    2. On the left half of the poster board, some mountains to represent a continent.
    3. On the right half of the poster board, a small island or a sailboat to represent a large ocean.
  6. Instruct students to tape the boxes and circles on the poster board where they think they belong. They should use the simplified version of the water cycle diagram to help them.
  7. Instruct students to use colored pencils to draw arrows between the various boxes and circles to show the movement or transport of water from place to place on or near Earth's surface. Remind them that a circle (process) will be located in the middle of an arrow between two different boxes (storage places). Ask them to think about whether the movement or transport is in the form of liquid water, water vapor, or ice (or two or three of these at the same time). They should use blue for liquid water, red for water vapor, and green for ice.
  8. Have students answer the following:
    1. Is there net movement of water vapor from the oceans to the continents, or from the continents to the oceans? Explain your answer.
      Student should note that because there is a net excess of evaporation over precipitation over the oceans, there must be a net transport of water vapor from the oceans to the continents. Make sure that the students realize that water vapor nonetheless moves in both directions: from the oceans to the continents at some times and in some places, and from the continents to the oceans at other times and in other places.
    2. Is there net movement of liquid water from the oceans to the continents, or from the continents to the oceans? Explain your answer.
      Students should note that there is net movement of liquid water from the continents to the oceans, resulting from the flow of streams and ground water into the oceans. Water does not flow out of the oceans onto land.
    3. How does the nature of the water cycle vary with the seasons?
      Student responses will vary. Some possible seasonal variations in the water cycle might include:
      • an increase in evaporation and transport of water vapor from the ocean to the continents during the summer months (relative to the spring, for example).
      • lower amounts of transpiration from plants during the winter relative to the spring and summer.
      • lower amounts of freshwater runoff from the continents to the oceans during the winter months (relative to the spring, for example) when water is stored on the continents in the form of snow and ice.
      • an increase in freshwater input to the oceans from the continents during the spring thaw.

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