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Riprap: It's Not Hip Hop But Erosion Stop

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Have you ever been to the Grand Canyon and seen what water can do over millions of years? When you turn on the faucet, do you see water come out, or mud? In this experiment you'll find out how engineers help prevent erosion, which keeps dirt out of our water.


Areas of Science
Time Required
Average (6-10 days)
Material Availability
Readily available
Low ($20 - $50)
No issues

Kristin Strong, Science Buddies

Adjust-A-SpoutTM is a registered trademark of HSN Improvements, LLC.


In this science project, you will build a model of a water channel and determine how best to prevent erosion in that channel.


Water has tremendous force, meaning it can carve into soil and even solid rock. As water carves, it picks up little bits of soil and rock and carries them away. This process is called erosion.

Practically any place where water and land meet-river banks, river bottoms, irrigation ditches, canals, shorelines, beaches, or farmland-you'll find civil and environmental engineers working hard to slow erosion. One way they slow erosion is by placing pieces of jagged rock, called riprap, on the land in or around waterways. This riprap blunts or dulls the force of the water so that it cannot break down the soil or carry it away as readily.

In this project you'll build a model of a waterway and see what kinds of riprap (fine or coarse, one layer or two) work best at keeping sand in the waterway and out of the water downstream.

Terms and Concepts

To do this type of project you should know what the following terms mean. Have an adult help you search the Internet or take you to your local library to find out more.



Materials and Equipment

To do this experiment, you will need the following materials and equipment:

Experimental Procedure

  1. Set-up your materials, as shown in Figure 2, first by placing the swivel-end of the extender on the box or stool and the other end on one of the liquid measuring cups. The swivel-end of the extender should be slightly higher than the end resting on the liquid measuring cup.

    One end of a rain gutter is placed above a measuring cup with the other end placed on a taller plastic bin
    Figure 2. Experimental setup.
  2. You will be testing four types of riprap, three times each. Make a data table to record your observations, as shown below:
    Riprap Type Trial 1
    Water Level
    Trial 2
    Water Level
    Trial 3
    Water Level
    Sum of Trials Average of Trials
    No Riprap, Only Sand
    Sand + Fine Gravel          
    Sand + Coarse Gravel          
    Sand + Fine Gravel + Coarse Gravel          
  3. Sprinkle sand evenly over the gutter part of the extender, as shown below in Figure 3. The amount of sand needed to evenly cover the bottom of the gutter will depend on the length of your extender. For example, a 4-foot extender will need approximately 1 cup of sand to evenly cover the bottom, while a 6-foot extender will need almost twice that. Record in your lab notebook how much sand you used so you will remember for each trial. It is important that you use the same amount of sand each time you run a trial in the experiment.

    Sand is sprinkled evenly across the inside of a rain gutter
    Figure 3. Sprinkle sand evenly along the extender.
  4. Measure out 3 cups of water into a liquid measuring cup.
  5. Pour the water all at once into the swivel-end of the extender.
  6. Wait 3-5 minutes to allow the water to completely drain out of the gutter. The exact time you wait is not critical. Just make sure you wait the same amount of time for each trial in the experiment. Record in your lab notebook about how much time you waited so you will remember for each trial.
  7. Record the water level in the liquid measuring cup at the end of the extender.
  8. Dump and rinse out the measuring cup.
  9. Thoroughly rinse off the gutter.
  10. Repeat steps 3-9 two more times using only sand on the gutter.
  11. Perform steps 3-9, this time using sand topped by 1 cup (or more, as needed) of evenly distributed fine gravel, as shown in Figures 4 and 5. Record in your lab notebook how much fine gravel you needed to evenly cover the sand. Be sure to use this same amount of sand and fine gravel each time you do a trial.

    Small gravel is spread evenly over a layer of sand in a rain gutter
    Figure 4. Sand topped with a layer of fine gravel in the extender.

    Water flows down a rain gutter that is filled with sand and small gravel
    Figure 5. Water poured all at once over the sand and fine gravel layers.
  12. Perform steps 3-9 three times, using sand topped by a layer of coarse gravel (evenly distributed). Record in your lab notebook how much coarse gravel you needed to evenly cover the sand. Again, make sure to use the same amount of sand and coarse gravel each time you do a trial.
  13. Finally, perform steps 3-9 three times with the sand topped by a layer of fine gravel, and then topped by a layer of coarse gravel (all evenly distributed). Use the same amount of sand and fine and coarse gravel for each trial, recording the amount of each in your lab notebook.
  14. Plot your results for each type of riprap on the graph paper. Which riprap type displaced the most water (had the highest water level reading)? This is the riprap type that did the poorest job at preventing erosion. Which riprap type displaced the least water (had the lowest water level reading)? This is the riprap that did the best job at preventing erosion in the channel. Did two layers work better than one?
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Ask an Expert

Do you have specific questions about your science project? Our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

Global Connections

The United Nations Sustainable Development Goals (UNSDGs) are a blueprint to achieve a better and more sustainable future for all.
This project explores topics key to Sustainable Cities and Communities: Make cities inclusive, safe, resilient and sustainable.


  • Compare smooth, round riprap vs. angular riprap.
  • Compare which sequence works best in layering-fine riprap first and coarse second, or coarse riprap first and fine second.
  • Add a layer of grass seed to any of the riprap types, sprinkle lightly with water, and let it grow until blades can be seen. After the grass has grown, do not water for 2-3 days and then repeat the trial to see if the addition of a plant mat does a better job at preventing erosion than riprap alone.


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MLA Style

Science Buddies Staff. "Riprap: It's Not Hip Hop But Erosion Stop." Science Buddies, 23 June 2020, https://www.sciencebuddies.org/science-fair-projects/project-ideas/EnvEng_p024/environmental-engineering/riprap-stopping-erosion. Accessed 28 Nov. 2023.

APA Style

Science Buddies Staff. (2020, June 23). Riprap: It's Not Hip Hop But Erosion Stop. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/EnvEng_p024/environmental-engineering/riprap-stopping-erosion

Last edit date: 2020-06-23
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