Waves and Currents
Form teams of 3-5 students. Each team should have at least a timer, recorder and experimenter. Look at how the waves come to the shore. Are the waves parallel to the shore or do they come in at an angle? Toss a floatable toy into the back of the swash zone. Have one of your team members stand on shore where you tossed in the toy. Watch the toy for 10 minutes to determine where it goes. Have one team member stand onshore where the toy is at the end of 10 minutes. Another one of the team can retrieve the toy (try not to get too wet). Now, measure the distance between the two team members onshore. How far did the toy move? In which direction? Compare your results with the other teams? Did the toys move about the same distance? Did they move in the same direction? What was the speed (distance/time=speed)? Collect some sand from the intertidal area, pour out any excess water, mark the sample as "intertidal" with the location and date. Keep the sample for later analysis. Scoop up some of the sand in your hand and look at it with your hand lens. Describe what you see in your notebook. Share this information with your team mates. Do you see any animals or plants in the swash zone? Scoop some sand into your sifter and dip the bottom of the sifter into the water until the sand is removed. Do you see some animals now that were buried in the sand? Describe what you see in your notebook. Compare your notes with others on your team and in the class.
Now, attach a long string with a small weight on it to a floatable toy. Toss the toy beyond the swash zone into the breaker zone; the weight will help you to throw the toy farther. The breaker zone is the place where the waves begin to break. Repeat the previous experiment. Does the toy travel at the same speed? In the same direction? Describe what you see. How do you explain this result? [teacher note: If the students have successfully thrown the toy beyond the swash area, they should see either little movement or much slower rate. In some cases, depending on the area, they may see a reversal of the direction. Waves transmit energy, not water flow. Water that is in the form of collapsed waves is moving on the shore. As water piles up along the shore, it will move along the shoreline creating the longshore current with a net transport parallel to the shore. However, beyond the area where waves are collapsing, students may see the effects of the energy transfer. This will show the toy moving up and down, but not moving significantly along the shoreline. The toy also will not move significantly closer to shore if the students have successfully tossed it beyond the breaker zone.]
If the water moves in this way, how do you think the sand moves? In a storm, more energy is transported so the waves come to shore more often and are generally higher. How do you think this might affect the longshore current? The area beyond the swash zone? [teacher note: When you return to class, these experiments give a good introduction to a discussion of building houses on barrier islands. This type of discussion can be done across grade levels. For more advanced students, you might ask them to create a webquest study (here is an excellent overview of how to develop a webquest for your class constructed mostly by teachers; of the question using the information from the class trip as well as information that they can find online.]
Next: Water clarity