Introduction:
Coastal lands are constantly changing in response to wave action. As
a wave approaches the shore, it breaks and releases stored energy,
causing erosion and the transport and deposition of sediments. Waves
breaking at the base of a sea cliff can cause it to erode and
collapse into the sea, Waves breaking at an angle to the coast can
create long shore current, which transport sediment along the beach.
Rivers supply new sediment to the coast which can form deltas or be
moved along the coast by long shore currents. Coastal erosion depends
on the stability of shoreline sediments, the intensity and frequency
of storm waves, and the exposure of coastal lands. The following
activity is designed to provide students with an understanding of
coastal erosion caused by waves.
links to coastal erosion web sites for prelab exercise
Objectives:
Model and observe how waves affect the movement of sand on a
coastline.
Observe how rivers provide sand to the coast.
Observe the effect of coastline shape and manmade structures on the
movement of sand.
Materials:
Each group or team will receive one set of materials.
1. One large paint tray.
2. 1500 ml of moist play sand.
3. 50 ml of a different color or texture sand.
4. 1500 ml of water.
5. A wave maker stick.
6. One stick to act as a barrier.
7. A metric ruler.
Basic diagram of wave tank.
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Procedure:
1. Spread the 1500 ml of sand in the container, covering approximately three-fourths of the sloping part of the paint tray from the top edge of the paint tray. The sand represents a beach.
2. Add 1000 ml of water to the tray to represent the water.
3. Draw a sketch of your tray before beginning your lab. Here
sketch of your tray before beginning
lab .
4. Using the wave maker, students should take turns creating waves
in the ocean. Make approximately 20 waves at a slight angle to the
beach.
Draw a sketch of your tray, and describe how the beach has
changed.
Repeat the procedure at a different angle, how did this produce
different results?
diagram 1 - sketch of tray after first set of waves
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diagram 2 - sketch of tray after second set of waves
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5. Make a crater and a ditch in the sand. The crater should be 8 cm wide, should expose the bottom of the container and should be located at the top of the model. The ditch should be approx 1 cm wide , should expose the bottom of the container and should connect the crater and the ocean. The crater represents a lake and the ditch a river.
6. Place 50 ml of moist, different colored sand in the crater and the ditch. Slowly pour 100 ml of water into the crater until this different sand is washed down to the ocean.
7. Draw your observations and describe how the coastline changed.
diagram 3 - after emptying crater / lake into beach
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8. Reconstruct the beach exactly as it was at the beginning.
Brainstorm ways to keep the beach from eroding.
such as...using small rocks and a 10 cm stick, construct a wall,
jetty or barrier to prevent erosion.
Repeat the wave technique from step 4, making sure to use the same
angles. Diagram and record your observations.
diagram 4 -beach with jetty
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Discussion Questions.
Write out complete sentences to the following questions. Use lined paper or type your answers
1. Compare diagrams 1 and 2, from your first two attempts at beach
erosion. (step 4)
Were there any changes in the shape of the beach?
Describe these changes and the cause of the changes.
2. In which direction did the sand move?
3. The sand deposited from the river created a delta. What happened to the delta when storm waves came in contact with it?
4. Identify a major river delta in the world that has not been removes by waves. Why is this so?
5. Describe the effectiveness of your structure in reducing
coastal erosion.
Use diagrams 1 and 4 to show changes in the coast resulting from the
construction of barriers. Were any of the structures effective in
reducing beach erosion?
6. If you owned a home on the beach , which structure would you build and where would you locate it?
7. What impact would your structure have on your neighbor's beach?
8. How long would your structure last?
9. Why might homeowners prefer different methods than environmentalists?
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