The Erosion Model

The Erosion Model offers a hands-on simulation of what happens when water comes into contact with three different surfaces: 1) bare dirt; 2) ground covered by forest litter–fallen leaves, branches and twigs; and 3) soil growing deep-rooted native plants.

This activity demonstrates the impact plants have on the rate of stormwater runoff and erosion.  Participants learn that when water comes into contact with bare soil, it erodes and quickly creates murky water.  While a cover of forest litter can help to filter water, the long roots of native plants ultimately do the best job filtering and absorbing stormwater runoff and preventing erosion.

This activity pairs nicely with lessons that teach students how roots under the soil help to absorb stormwater.  It promotes awareness about healthy watersheds by introducing participants to the important environmental saying, “slow it down, spread it out, soak it in.”  The activity also serves as an ideal way to demonstrate how riparian buffers–strips of vegetation next to streams or other water bodies–help protect water quality and stream habitat.

The Erosion Model suits a wide variety of audiences and settings.  Small children through adults will benefit from seeing the immediate effects of different surfaces on erosion.  Since the demonstration does involve pouring water into containers, a pitcher of water is needed, and perhaps a towel in case of mishaps.  Suggestions for activity adaptations are available in Section 4.

Click here for a PDF.

Bare ground erodes more, creating murky water.  Leaf litter helps prevent erosion.  Plants with deep roots are the best at preventing erosion.

Suggested Books and Video to Share: Check out resources from AACPL HERE.  Chesapeake Bay Foundation, “Reducing Erosion is Good for the Bay” (Youtube). 

Hands-On-Activity: Having set up the Erosion Model, pour water over three different surfaces to observe the effect on the body of water collecting the runoff.

Optional Outdoor Activity: Walk outside and observe any places that either promote erosion or help prevent it.  Brainstorm actions that could help our local waterways.

Reflection: Ask participants to think of the kinds of surfaces in their neighborhood.  Are there opportunities to modify any surfaces to “slow it down, spread it out, soak it in”?  Ask your participants what they learned and how they can use their knowledge to take action for a healthy watershed!

* Stewards may borrow WSA's Erosion Model for this lesson.  Ideas for building your own model from simple materials may be found below.

Directions

Materials You Will Need

• 3 Surface Models

  1. Bare dirt

  2. Leaves

  3. Deep rooted plants

• Cups to capture runoff

• Plank or brick to prop model up on slant

• Pitcher of water for rain

• Towel/rag just in case!

1. Exploration / Questions for Introduction

• Ask participants to look around and describe the type of surfaces they see.

• Ask when it rains, where does that water go?  What is the closest creek or river?

• What is erosion? The transportation of material such as soil and weathered rock by wind, water, gravity, and other natural forces. Some erosion happens naturally.

• What are some human activities that can cause erosion?  (It is ok if unknown.  That is the goal of this demonstration.)

2. Background information (optional): Read a Book / Watch a Short Video.

• Check out resources from AACPL HERE.

• Chesapeake Bay Foundation, “Reducing Erosion is Good for the Bay” (Youtube).  

Every day throughout the Chesapeake Bay watershed, sediment from the ground is being washed or blown away by water and wind. This natural process is called erosion. When erosion happens too quickly—primarily due to water running off from agricultural land or excessive development in cities and towns—it can cause problems in waterways and the Bay. Too much sediment in the water makes the water cloudy, blocking sunlight from reaching underwater grasses. In addition, the excess dirt can potentially smother oysters. In this video, join CBF Educators Morgan and Matt at Maryland’s Calvert Cliffs as they explain why reducing erosion is good for the Bay.

3. Hands-on-Activity

Prior to the activity, set up the model as shown in the picture. The three surfaces– bare soil, leaves, rooted plants–should tilt towards the opening with some type of vessel to capture the runoff.  Moisten each surface with water if they are dry and hard. (Another teaching moment- have hard dry dirt and see the runoff there!) Remove the plugs so that water may pass through.

Begin by describing the surfaces.  Look around and point out where those surfaces might be found.  The container under the spout represents the creek/river/Bay that collects the runoff.  

Let’s find out what happens to the closest creek when it rains on these surfaces.  You may designate a participant to “rain” on the bare dirt model.  Suggest height from which to pour.  Have a premeasured amount of water to pour or pour to the count of five or ten, until water flows into the container.

Describe the quality and clarity of the water in the runoff.  What is the problem with muddy water? (It can carry pollutants along with it; sediment from erosion blocks sun preventing photosynthesis from aquatic plants; suffocates oysters.)

Repeat the process with the other two trays.  The leaf tray should be fairly clear, and the rooted plant might be clear, or even very little water runs out.  It is largely absorbed by the roots.

Review.  Which surface contributed to a cleaner body of water?  Why did the planted slope hold and filter the most water? (The roots helped absorb water and kept soil in place.)  

4. Continued Exploration Outside (optional) Go for a walk.  Look for evidence of erosion, or places erosion might occur.  Look for bare soil created by “desire lines,”  that cut across a patch of grass cutting a corner.  Steep slopes or running water are other places.  Point out that muddy rain water flowing down a street into a storm drain is not treated.  Since many confuse storm drains with sewage treatment, it is important for participants to understand that this water flows directly into the creek.

5. Reflection:  Get the audience thinking about what they've learned and how they can take action.  Some suggestions: planting trees, mulching bare soil paths.  Discouraging bare soil “desire lines,” and reporting violations of bare soil at construction or other sites.

Suggested Reflection Prompts for Different Age Groups

• K-2: Dramatize the rainfall.  Emphasize the effect erosion is having on animals: harder to breathe for fish and oysters, difficulty finding food.

• 3-5: Why is it important to stay on a path and not create bare dirt?

• Middle School/ High School : What can our school/community do to prevent erosion and encourage rainwater to soak in?

• Mixed Age / Families: we recommend drawing questions from our K-5 examples so that everyone will be able to participate. What can we as a family do to prevent erosion?  How does erosion harm the Bay?

Sample Lesson Plan

Sample Lesson for the Erosion Model - click the link to see a sample lesson by Watershed Steward Nan Henry. 

General Suggestions

This visual demonstration makes it appropriate for a wide variety of audiences.  When discussing the effect on the stream, refer to the stream closest to your audience to make it real.

Adaptations for Different Audiences

K-5 – Pre-measuring the water might be useful.  Get dramatic with hand gestures and sounds when it rains, and ask participants to make rain or storm noises as the water is being poured.  Emphasize the effect the runoff is having on the animals.

Middle School/ High School – Turn the activity into an experiment.  Develop a hypothesis about the runoff from the three surfaces.  Independent variable (what gets changed) - Surface. Dependent variable (what gets measured) - Clarity of water.  What needs to be constant - Amount and force of water, angle of the slope.  Emphasize the importance of having constants in the model to create a fair test of the three surfaces.  Elicit factors that could affect the outcome such as steepness of slope, velocity and amount of water, amount of moisture already in the sample surfaces.  When reviewing, ask if their hypothesis proved or disproved.

Mixed Age / Families –  we recommend drawing questions from our K-5 examples so that everyone will be able to participate. 

Adaptations for Different Formats

Indoor Classroom Setting – be sure to set expectations for making it rain to avoid a mess and take towels.

Outdoor Classroom Setting Program for a Small Audience (10 or less)  – Consider additional bottle models to represent the surfaces nearby.  For instance, use chocolate cookie crumbs to represent pet waste, or powdered drink mix to represent fertilizer.

Program for a Medium Audience (up to 20)  – If two leaders are present, take half for a walk to examine the various surfaces while the other half participates in the model.  Create a “scavenger hunt” type activity, looking for evidence of erosion and factors reducing erosion.

Program with a Club – This works nicely as an introduction or follow up to the Watershed Model.

Table at a Community Event or Festival – Depending on the length of time you have the audience, you may abbreviate the demonstration to show the importance of keeping leaves or mulch on bare ground.

Click this link for resources about erosion available at Anne Arundel County Public Libraries.

Muddy Waters: Life and Death on the Great Barrier Reef an eVideo

“By 2010, forty per cent of the world's coral reefs may be dead. By 2030, half of the Great Barrier Reef may be gone. Parts of it are already dying, but the reasons have not always been clear. Global warming and outbreaks of crown-of-thorns starfish have put extraordinary pressure on the reef. Now scientists have identified another threat - sediments, fertilisers and pesticides from agricultural run-off.”