Ocean waves erode the coastline. The sand they remove is shifted to another location. This paradoxical effect can strip beaches in one location and create them in another. We'll observe this effect by creating a model of the shoreline.
In this experiment, students will create a model of a shoreline, observe erosion and examine how jetties prevent erosion.
- Permanent marker
- Plastic box at least 6” x 12” x 8" (bigger boxes work better – an “under bed” plastic storage contain is ideal)
- Two gallons of sand
- Small plastic toy that represents a house (can be made from Legos)
- 10 to 20 pieces of gravel
- 10 to 20 one-inch stones (if you use a larger box, they you can use two-inch stones
- Big spoon
- Working out of doors, use your permanent marker to mark the bottom of the container into nine rectangles. There should be three lines running vertically and three lines running horizontally.
- Fill the container with water so that it is 1/3 full.
- Add sand to the container. Mix the sand and the water. Pour off any cloudy water. Keep adding water, stirring and pouring off the water until the water is clear. Dump out all the water. At this point, you know your sand is clean.
- Pile up all the sand so that is covers the bottom three squares of the container. Pack it down firmly. Put your plastic toy on the sand, and scatter the gravel pebbles across the sand. This is your beach.
- Add water, pouring very carefully into the squares that do not have sand. Make sure that the water level is not so high that the top of the beach is covered with water.
- In your lab book, draw a box that is proportional to your plastic container. Divide it into nine sections, just as you did your plastic container. Make three copies of this diagram. Label two of them “With Jetties” and two of them “Without Jetties.” This will be used to make a cross section of the distribution of the sand in the box.
- Gently rock the container back and forth ten times to imitate wave action. Sketch a cross section of the sand levels on the first sheet labeled “Without Jetties.”
- Repeat step 7, rocking more vigorously to imitate storm waves. Sketch your results.
- Re-pile the sand as you had it originally in step 4. Pack it down firmly.
- Add a row of the bigger stones so that they are parallel to the beach. They should be located at the second line across the plastic container.
- Repeat steps 7 and 8. Sketch your results on the sheets labeled “With Jetties.” Consider what effect the jetties may have on beach erosion.