Lesson at a Glance
A lesson plan adapted from an
activity by Zeoma Tanaka, from Moanalua Gardens Foundation Teachers
Workshop, July 1987.
The class conducts experiments
comparing runoff and groundwater recharge on simple models of
vegetated and barren mountain slopes.
Key Concept
Forests protect watersheds by
preventing soil erosion and maintaining the quality of surface
water by reducing sediment and other water pollutants. Forests
absorb water which is released slowly to plants, streams, and
groundwater supplies.
Objectives
Students will be able to:
- Predict the amount of runoff
and groundwater recharge on models of vegetated and non-vegetated
mountain slopes.
- Measure the amount of water
collected in the experiment and compare it with their predictions.
- Draw pictures and write caption
contrasting the effects of rainfall on a forested and on a barren
slope in Hawaii.
Time
1-2 class periods
Materials
- 9x13 inch foil tray or pan
- 2 sponges
- 4 rubber bands
- 2 rectangular, flat vegetable
graters
- glass or clear plastic measuring
cup
- small bowl (to fit inside foil
tray)
- spray mist bottle full of water
- blue food coloring
- old towel or newspapers
- masking tape
Preparation
Use the graters to make an A-frame
with the small holes on the top. Bend one of the handles so that
the two graters will fit securely together. Cover the long, wide
holes with masking tape. Put the foil tray on an old towel or
newspapers, and then place the small bowl between the graters
in the center of the tray. Add a few drops of blue food coloring
to the water in the spray mist bottle. Wet the sponges and wring
them out in preparation for the demonstration.
Teaching Suggestions
- Explain what a watershed is.
Ask students to visualize a mountain range divided into a series
of connecting bathtubs (valleys). When rain falls on a ridge
line, it will fall into one "bathtub" or another, and
then drain to a stream at the bottom. Each "bathtub"
or valley, is a separate watershed.
- Compare a barren mountain with
the roof on a house: When it rains, most of the water washes
right down the roof, flows through the gutter, and splashes onto
the ground. Very little water remain on the roof, and the gutter
(like a stream) becomes dry soon after the rain stops. The roof
is the "watershed" for the gutter.
- Interpret the watershed model
for the class. The two graters represent mountain slopes separating
two different watersheds, and the holes are the pores in the
ground. The small bowl is inside the mountain and represents
the groundwater lens. The large pan is the ocean, and the blue
water coming from the mist bottle is rain.
- Explain that the grater "mountain"
is unforested. Ask the class to predict where most of the rain
falling on this mountain will end up--as groundwater in the bowl,
or as surface water in the ocean? Take a vote and record their
predictions on the board.
- Pump the mist bottle over the
mountain about 80 times to simulate rainfall. Allow a few moments
for the water to drain, and then pour the "groundwater"
collected in the small bowl into the measuring cup. Ask a volunteer
to read the amount collected and record the figure on the board.
Then pour the water out and repeat the procedure with the "ocean"
water that collected in the tray. compare the amounts measured
with the original predictions.
- Discuss the results and ask
students what they think will happen if spongy forest cover is
added to the mountain. Attach sponges to the grates with rubber
bands, and repeat the experiment. Before measuring the amount
of "groundwater" collected, squeeze the sponges into
the "groundwater lens" or bowl to speed up the process
of water percolating into the water table.
- Again, compare the amounts of
"seawater" and "groundwater" with the student's
predictions. Emphasize the importance of forest cover in watershed
management. Explain that in a real forest, some of the water
stored would be used by plants.
- Remind students that while forested
watersheds will help provide a steady water supply, only wise
water use and conservation will insure that the water supply
continues to meet the needs of our growing population.
- Ask students to draw a picture
comparing rainfall on a forested slope and on a barren slope
in Hawaii, and write captions for the pictures based on the results
of the watershed experiment.
Extended Activities
- Have students work in groups
to create their own models of forested and barren watershed.
Shag carpet, towels, or moss can be used to represent the forest,
while metal, plastic, or clay can represent barren slopes.
- Ask students to imagine what
Hawaii might be like now if the forests had not been damaged
by hoofed animals, or cleared for urban development. Ask them
to imagine what it would be like if the barrens slopes had not
been reforested.
- Generate a discussion about
environmental responsibility. Point out that our water supply
today is largely due to the foresight of people generations ago.
Ask students how their attitudes and actions toward the environment
today may affect the lives of their grandchildren in the next
century.
- Hold a school-wide paper drive.
Explain how recycling paper saves trees. Donate money earned
to a local or international organization that is working to save
native forests, or use it to purchase seedling and gardening
tools for your own reforestation project.
- On Arbor Day (in Hawaii, the
third Friday in November), lead the class on a tree planting
expedition. Trees can be planted on the school grounds, or in
other community areas with the appropriate permission. Be careful
about which tree species you plant. Native trees have many ecological
advantages, but some are difficult to establish. If you choose
an introduced species, make sure it is not a pest species (contact
the State Department of Agriculture if you're not sure).
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