How Rain Gardens Fight Pollution and Flooding
Summary
Overview
Students might think rain gardens are only there to make an urban area look nice. In this lesson, students will make mini rain gardens and discover how these can filter out pollution and soak up excess rainwater. Will they find how rain gardens help prevent natural disasters? Try out this fun lesson and see!
Learning Objectives
- List the problems runoff creates and understand how rain gardens mitigate these problems.
- Use data from a rain garden experiment as the one done in the lesson to support the claim "Rain gardens reduce runoff."
- Use data from a rain garden experiment as the one done in the lesson to support the claim "Rain gardens filter some pollutants out of runoff."
NGSS Alignment
This lesson helps students prepare for these Next Generation Science Standards Performance Expectations:- 3-ESS3-1. Make a claim about the merit of a design solution that reduces the impacts of a weather-related hazard.
| Science & Engineering Practices | Disciplinary Core Ideas | Crosscutting Concepts | |||
| Science & Engineering Practices | Developing and Using Models.
Use a model to test cause and effect relationships or interactions concerning the functioning of a natural or designed system.
Planning and Carrying Out Investigations. Make observations and/or measurements to produce data to serve as the basis for evidence for an explanation of a phenomenon or test a design solution. Engaging in Argument from Evidence. Construct and/or support an argument with evidence, data, and/or a model. Make a claim about the merit of a solution to a problem by citing relevant evidence about how it meets the criteria and constraints of the problem. |
Disciplinary Core Ideas | ESS3.B: Natural Hazards.
A variety of natural hazards result from natural processes. Humans cannot eliminate natural hazards but can take steps to reduce their impacts. |
Crosscutting Concepts | Cause and Effect.
Cause and effect relationships are routinely identified, tested, and used to explain change.
Connections to Engineering, Technology and Applications of Science Influence of Science, Engineering and Technology on Society and the Natural World. Engineers improve existing technologies or develop new ones to increase their benefits, decrease known risks, and meet societal demands. Connections to Nature of Science Science is a Human Endeavor. Science affects everyday life. |
Materials
For the teacher:
- Utility knife
- Hole punch
- Plastic cup
For each group of 1-4 students, and one extra for the teacher:
- One container, e.g., gallon jug, 2-liter soda bottle, disposable loaf pan, etc. The containers of all groups should be similar.
- A bottle cap or object of similar height like a rectangular eraser, a granola bar, etc.
- Clear disposable cup, 12–16 oz. Try to have all cups identical. Small plastic water bottles from which the top has been removed work well, too.
- Cup, similar in size to the disposable one.
- Metric ruler
- Clay (about 1 lb for the students, 2 lbs for the teacher)
- Rope or yarn (40 cm long)
For the class:
- Rain garden supplies. If substitutes are used, it is best to stay with organic materials as this will make it easy to dispose of the rain garden content in the compost bin.
- Potting soil or loose dirt from the garden
- Pebbles, small rocks, or substitutes such as corn kernels or dry beans
- Materials to make polluted water:
- Water
- Measuring spoon
- Cooking oil (1 cup)
- Liquid food coloring, preferably blue
- Food that floats on water, such as some cereals or popcorn (1 cup)
Background Information for Teachers
This section contains a quick review for teachers of the science and concepts covered in this lesson.Urbanization increases runoff, the excess rain-, storm-, or meltwater that flows across impervious surfaces. Runoff is caused by surfaces like concrete and asphalt (roads, sidewalks, parking lots, the roofs of buildings, etc.) that do not absorb water. Since the water cannot soak into the ground, this water runs off and picks up pollutants such as dust and dirt particles, oil (e.g., oil from leaking cars), litter, chemicals (e.g., fertilizer), and bacteria. Storm drains or lakes and rivers collect runoff. From the storm drain, it flows directly to nearby lakes and rivers, polluting these nearby bodies of water. Pollution is not the only problem with runoff; excessive runoff also leads to flooding.
Urban developers include rain gardens to mitigate the problems created by runoff. Rain gardens are designed to soak up runoff temporarily and filter out many of the pollutants. They also beautify the area.
Figure 1. Rain garden, picture from Wikimedia Commons user Rogersoh, licensed under Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0) license.
Rain gardens are typically created on the downside of a slight slope. They are usually layered: mulch at the top, planting soil to support vegetation, a sand bed, and a rock base as illustrated in Figure 2. Rain gardens typically include native plants. Plants beautify the rain garden and have roots penetrating down into the soil, making it easier for water to flow downward. The roots also suck up some of the water into the plants.
Figure 2. Cross section of a layered rain garden.
The students will create two types of mini rain gardens in this lesson, one with loose potting soil and another with pebbles. The variations section lists more options, but even these simple gardens allow the students to observe the effect of adding a rain garden. The video Build a Mini Rain Garden shows how the students will make a mini rain garden with soil.
