Our Garden, Our Watershed Full Lesson

Lesson Title: Our Garden, Our Watershed

Lesson Summary: How does a garden model a healthy watershed? Students will explore the impact that permeable and impermeable surfaces have on rainwater filtration through this hands-on garden lesson. They will learn that the permeable surfaces in their garden naturally absorb and filter rainwater that would otherwise collect pollutants on impermeable surfaces, flow into the sewer system, and then into natural waterways, where it could cause harm to members of those ecosystems. They will determine how much rain water (liters/gallons) is being absorbed and filtered in their garden by using local rainfall data and calculating the cumulative surface area of their garden beds. The goal is to help students understand that the ecological benefits of the garden include improved water quality for the surrounding watershed.


Students will be able to 

-Construct an argument to show the key role rain filtration plays in their regional watershed.

-Describe the impact of permeable and impermeable surfaces on the natural process of rain filtration and water quality.

-Determine the amount of rainwater the school garden beds are filtering by calculating the total surface area of school garden beds.


Standards Met:


  • Solve real-world and mathematical problems involving area, volume and surface area of two- and three-dimensional objects composed of triangles, quadrilaterals, polygons, cubes, and right prisms.


  • Use variables to represent quantities in a real-world or mathematical problem, and construct simple equations and inequalities to solve problems by reasoning about the quantities.

Ecosystems: Interactions, Energy, and Dynamics

  • LS2-4. Construct an argument supported by empirical evidence that changes to physical or biological components of an ecosystem affect populations.
  • LS2-5. Evaluate competing design solutions for maintaining biodiversity and ecosystem services.

Earth and Human Activity

  • ESS3-3. Apply scientific principles to design a method for monitoring and minimizing a human impact on the environment.



Formative: Ask students what it mean to filter something?  Where have they seen filters before?

How might unfiltered water be harmful in the environment?

After introducing the concept of P/I surfaces have the students estimate the number of different impermeable surfaces they can see from the courtyard, and describe them. Challenge them at this point to guess where the slope goes, where the runoff will likely go.

Summative: After students have had time to investigate the different surfaces in their garden and calculated how much rainwater is filtered by their garden plots ask students to discuss how different surfaces impact the ability of water to filter in a watershed?

What can we do to help slow down rainwater so that it has time to filter?

Have students revisit the map of their garden area to chart the direction in which their rainwater runoff flows at a later time.

Potential Big Picture Mind Mapping: How are the functions of a watershed present in the garden?


Exit Ticket Questions:

  1. Describe an example of a permeable surface and an impermeable surface.
  2. Describe how permeable surfaces aid natural rain filtration.
  3. Describe how unfiltered rainwater can harm the environment.
  4. Describe how you used technology as part of learning about filtration.
  5. Give an example of how your class can help protect the watershed by improving rain filtration.


The lesson:

Hook:  Draw students in with a quick demonstration of permeable surfaces and impermeable surfaces.  This can be done inside with watering cans, or inside using permeable/impermeable paper demonstration.

Imagine for a moment a single rain drop falling from the sky.  The drop can either land on a permeable surface (show plain paper) or an impermeable surface (show paper with holes).  This impermeable surface is solid.  Anybody want to take a guess as to which surfaces in the city that are solid? Yeah, we’ll start with a piece of paper, which represents pavement and this empty cup will represent a gutter.  Take a second to make a quick prediction as to what will happen if I pour water on this surface?


**Pour water on impermeable paper gutter and capture it in the empty container**


Now imagine a rain drop falling from the sky.  The drop has landed on a permeable surface has tiny holes like a sponge.  What kind of surfaces in a city are permeable? Predict what will happen when I drop the rainwater across this surface?

**Pour water on permeable paper and capture it in the container**

Ask students to describe where water goes in a rainstorm on the playground’s impermeable surface.

What surface the rain falls on determines whether it will soak in or flow across the land.  Which of these surfaces demonstrated the rainwater flowing over the ground? Which surface demonstrated water soaking into, or filtering, into the soil?

A watershed is an area of land where all of the water that drains off of it, or under it as groundwater, flows into the same river, basin, or ocean! When water soaks into the ground it slows down, spreads, and is filtered by the soil. Water is filtered through layers of soil, sand, and rock, and other natural materials like leaves. When water flows across the ground as it does on pavement it picks up pollution (car oil, fertilizers, detergents, and pesticides) and litter and carries it to a storm drain unfiltered where it eventually ends up in a larger body of water.

This is a great video to show the impact of I/P surfaces and introduced the use of rain gardens as a way to positively impact the health of the watershed.

Vimeo Video: http://vimeo.com/77811268


Introduction to filtration calculation and garden map activities in garden:

Today, we are going to be looking at how your garden is a part of your watershed. Which parts of your garden courtyard would you expect to be permeable?  We’ll have one group mapping out the garden and testing what surfaces are permeable and impermeable. The other group will calculate how much rainwater is being filtered by each raised bed garden and construct a rain gauge to put near the garden beds.


Collecting Your Data in the Garden

What data you need to collect:

How much rain has fallen in inches? We can measure this ourselves using a tool called a rain gauge, or we can search for rainfall data for this area online.

What is the surface area of each raised bed garden? The surface area being just the surface and not the depth (imagine an orange peel vs. the orange itself). Calculate this by Length * Width= SA.

The amount of water a single square foot of permeable surface can filter. 0.623 gallons or 2.36 liters.


Calculate Water Filtration*


For Gallons:

(g) Permeable surface in square ft. x (rainfall amount in inches x 0.623) = approximate gallons of water filtered

For liters:

(g) Permeable surface in square ft. x (rainfall amount in inches x 2.36) = approximate liters of water filtered.

These formulas are based on 1 square foot of permeable surface filtering 0.623 gallons or 2.36 liters of water. These figures have been checked by Nature Conservancy scientists.  Please note however that many factors will affect the amount of water that your garden filters including transpiration by plants, soil type and quality, grade of the land, depth of the soil, etc.  Your resulting data will therefore not be 100% accurate but is designed to be used as a teaching tool.


Mapping Out the Garden

Students will see how an impermeable surface allows water to flow quickly and unfiltered into the watershed, while a permeable surface of soil and vegetation not only slows the water flow but also absorbs and filters much of the water.

Draw a map of your garden, include all raised beds, greenhouse, and any other structures in space.  After you have a map drawn, shade in the impermeable vs. permeable surfaces with colored pencils.

Permeable surfaces — all surfaces that contain soil, garden beds, planters, pots, etc. Impermeable surfaces — concrete or stone surfaces, metal structures, paved areas, etc. Students should also consider what makes these surfaces permeable or impermeable.


Pour water in a select few impermeable areas of your garden.  Draw arrows on your map to indicate which direction the water is flowing.  Consider where this water might go and what that means for the watershed. What could result from water not being filtered before it enters a larger body of water?


Transfer of Learning:  

Present your group’s observations during this activity.  What did you find? Was it surprising? What connection can you draw between the garden and your watershed? In the video we watched earlier the phrase “lots of little things…add up to a big effect.” How does this apply to your garden? What about your community and other gardens in this area?  What about gardens across the country?


Possible Extensions:

Track rainfall and drainage over a longer time period.

Use the “Nature Works Everywhere” page to track your gardens rainfall data.


References: Adapted from “Gardens Filter Rainwater” https://www.natureworkseverywhere.org/#your_garden


Created by Liesel Benecke on May 11th, 2017.




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