Science Experiment: Modeling Beach Erosion

This science project is great to help 6th graders understand how water works.

Setting the Scene: Disappearing Beaches

Beaches are some of our most important and valuable assets, one of the first things people think of when someone says “Florida.” However, this long-standing symbol of Florida may not be so enduring after all. Many of our beaches are shrinking before our eyes. The state has spent almost a billion dollars to restore precious beaches, but the problem – some might even say the disaster - continues. The problem is erosion. To find the causes of erosion, we must look not seaward, but toward the land.

The Basic Science: The Forces of Erosion

Erosion isn’t a difficult concept. Forces of nature - wind, rain, and surf – move rock, soil, and sand from one place to another. Most often erosion works with gravity to move materials downhill, from a higher elevation to a lower one.

You may have learned about soil erosion if you studied the Nile River in Egypt or our own Mississippi River. Long before humans were cultivating fields or cutting forests, rain washed soil into these great rivers, which transported it downstream. When the flow of the river slowed near the mouth of the river, the soil settled out. This sediment formed great deltas of low-lying, fertile land. Vast amounts of soil were moved hundreds, even thousands of miles.

Beach erosion often occurs when storms bring great waves ashore to loosen the sandy soil of the coastline and wash it into the sea. Florida’s beaches were stable for thousands of years. While storms may have taken some coastal materials seaward, the waves also brought sand ashore. Nature’s balance of forces created and sustained our famous beaches. So why is there a problem now? What has changed?

Beaches In Your Community

Stand at your favorite beach, and imagine how it looked a thousand years ago. Now compare that mental image with the appearance of the beach today. What’s the biggest difference?

There were no buildings, roads, or parking lots near our beaches. Even a hundred years ago, we had few buildings near the shoreline. The single greatest change in our beach environment is human development. The effects of coastal development are causing sand to wash out to sea far faster than nature can replenish it. Nature’s equilibrium has been disturbed.

Just how does development hasten beach erosion? Experts point to the increased area of land now covered by impermeable surfaces (which are surfaces through which water cannot flow). Roads, roofs, parking lots, and sidewalks don’t allow rain to soak into the ground. Instead, they often channel all the water from a large area to a single discharge point or a series of drains. Before development, much more water soaked into the ground, and much less was channeled into streams. With that altered flow of water, erosion has become more severe.

You can study the phenomenon of erosion using some simple materials. 

Materials

To build a model showing the effects of beach erosion, you will need the following materials:

• A rectangular plastic container
• A sharp knife or scissors
• Sand
• Aquarium gravel
• A large plastic drinking cup with holes punched in the bottom.

Procedure

NOTE: Put your model inside a larger container, such as a plastic tray, to contain whatever mess you may make. Also, work hard to prevent sand from going down the drain because it may settle in traps and cause plumbing problems.

1. Cut one end out of the plastic container, fill it about 1/3 full with sand or gravel. Prop up the other end, so everything flows downward. You have created a little beach. By simulating rain and surf, you can observe how the sand erodes. To recreate the rain and surf, use plastic (or paper) cups. For rain, punch holes in the bottom. For hard rain, make the holes bigger. For surf, slosh the water onto the beach.
2. Keep changing your experimental conditions, such as the type of sand or gravel and the length and intensity of the rain. Make careful observations and measurements of exactly what you do, what happens, and what changes.
3. What happens to the sand on the slope as the rain falls on it? Does it stay in place or move? How much of it moves? Experiment with different slope angles to see the effect.
4. You can simulate roads, buildings, and parking lots by covering part of your beach with plastic wrap or other material that water will not pass through. You can simulate drains by channeling the water that falls on this "impermeable" material to a single release point. On a roof, that models a downspout; on a road, it models a storm drain.
5. What other things might you try with your model? What is the effect of changing the size of the sand (perhaps by using the aquarium gravel instead)? Measure the amount of erosion to compare the effects of design changes.

Other Ideas

1. Find an agency or interest group in your area that is concerned with beach erosion. That might be as simple as looking for signs to find out what agencies are responsible for your beach. You could search for newspaper or other articles; these might lead you to individuals you could interview.
2. Is beach erosion inevitable, or are there things we can do to move back toward nature’s balances? Research such innovations as permeable parking lot material that enable rain water to percolate through the pavement into the ground.
3. Adopt a beach near you and observe changes in the beach after heavy rains, high winds, or very high, rough tides.
4. Find maps of the shoreline in your community from previous historical periods. See if you notice any changes. If you can find maps that show building structures and roads from previous periods, can you connect changes in the shoreline to that development?

Putting it Together

When you have perfected your model of beach erosion, make a demonstration model to present to others. Make posters or other visuals that show in detail how each of these forces of rain, surf, and human development have affected beaches. Display charts showing your results, with a descriptive paragraph. Write (or deliver orally) a recommendation about how to protect beach erosion in your community.