Lesson 4: Rainbox Throw Down

Learner Outcomes

Students will engage in hands-on experiments that will serve as a basis for understanding the mechanics behind erosion and sediment control.  They will develop ideas on ways to manage these processes.

Success Indicator

Describe the experimental design process.

Skill Level

Advanced; ages 14-18

Time Needed

One 90-minute class or two 45-minute classes

Life Skills 

  • Teamwork
  • Communication
  • Sharing
  • Critical Thinking
  • Problem Solving
  • Wise Use of Resources

Materials

  • Lesson Four slides
  • 5 rainboxes (see lesson two for rainbox construction guidelines)
  • Clayey soil to fill the volume of each rainbox (about ½ of a 5-gallon bucket per rainbox)
  • Various materials to use in the rainbox throw down experiment (provided by students and teacher)
  • Hay, mulch, sod, plastic
  • Watering can
  • Large plastic container to collect runoff
  • 5, 1-quart (1000mL) jars with lids to collect runoff samples (to measure turbidity)
  • 5, 8 oz  jars with lids to collect runoff samples (to demonstrate PAM properties)
  • 5, 4 oz jars with lids to collect runoff samples (to use for Total Suspended Solids measurement)
  • 5 digital cameras
  • Video camera (optional)

Lesson Slides

Lesson Slides

Click on “File” and then select “Make a Copy ” of the lesson slide deck to use it with your youth.

Introduction

Background Information

Through research, soil scientists have developed a number of best management practices (BMPs) to control erosion and sedimentation in construction and agricultural environments.  The purpose of the rainbox experiment is for students to draw conclusions on what might be some of the best ways to minimize soil erosion.  The principles are generally similar for managing soil loss in both agricultural and construction or urban development contexts.  The measurements used to quantify the impacts of erosion and sedimentation are the same for both environments as well and focus on turbidity and total suspended solids.

Turbidity

As students collect runoff samples from their rainbox, the water might be cloudy.  The cloudiness of the water is called turbidity and is measured in nephelometric turbidity units (NTUs).  When soil is exposed during construction or agriculture activities, runoff (resulting from storm events) picks up soil particles and carries them to the nearest body of water.  Larger particles, such as gravel and sand, quickly settle to the bottom of the creek, stream, or river once the flow rate slows.  Clays and fine silts, however, settle much more slowly, staying suspended in the water, see Fig. 4-1. below.

Soil Particle

Size (mm)

Fall Time

  Gravel

  10

  1 sec

  Coarse Sand

  1

  10 sec

  Fine Sand

  0.1 (e.g. human hair)

  125 sec

  Silt

  0.01

  108 min

  Bacteria

  0.001

  180 hr

  Colloid

  0.0001

  755 days (>2 years)

 

These suspended particles make the water look muddy, or turbid.  Turbidity is the measurement of the amount of light that is scattered and absorbed by suspended soil particles.  The cloudier the water, the more suspended particles, and the higher levels of turbidity.  These particles often include sediments like fine clays or silt or fine organic matter.  In the scientific community, turbidity is measured in NTUs by a nephelometric turbidimeter or nephelometer.  For less precise turbidity measurements, a turbidity tube with a secchi disk can be used for an approximation.  A secchi disk is a circular disk with a black and white pattern that uses the transparency of water to provide a turbidity estimation. 

Turbidity tends to increase during storm events that cause increased overland flow, stream flow, and erosion. Turbid water can travel many miles in streams or keep ponds and lakes looking muddy for a long time after a storm.  Turbidity decreases water quality by reducing the productivity of the affected waters through a decrease in their recreational value and increases treatment costs for industrial or drinking water plants.

Effects of turbidity on bodies of water

image of a muddy river
Sediment in our waterways can cause significant environmental harm.
  • Negatively affects the ability of fish gills to absorb dissolved oxygen
  • Increases the concentration of pollutants that are bound to the soil particles
  • Decreases sunlight penetration and inhibits the growth of aquatic plants
  • Increases risk from toxic microorganisms that attach to soil particles
  • Decreases aesthetics
  • Reduces in long-term feeding success of fish
  • Covers habitat and spawning areas in water bodies
  • In some cases, high turbidity levels benefit some ecosystems, like the relationship between some mangroves and certain fish species

Total Suspended Solids

Like turbidity, total suspended solids (TSS) is a measurement of water quality.  TSS is the measurement of how much (mg/L) sediment is in a known volume of water. Collecting water samples, filtering those samples, and drying the sediment will give you this information. Research has found that there is a close correlation between turbidity and TSS.  So, as turbidity rises so does the amount of suspended solids in a given sample. Reducing the amount of erosion reduces both the amount of total suspended solids entering the waterways and turbidity levels.

Experience: Rainbox Throwdown

Rainbox Throwdown

The rainbox experiment can be quite messy and should be conducted outside if possible.  If it must be done indoors, protect the floor or lab benches with plastic sheeting, garbage bags, or something that will make it easy to clean a muddy mess. 

  1. Allow the students to start setting up their boxes using materials they have brought in, found outside on the school grounds, or are available in the classroom. 
  2. Distribute the “Let it Rain” handout to the students and follow the steps within the handout.  
  3. Have each of the groups present and implement their rainbox experiment and engage in a lively discussion with their peers. After each group presents, have short discussions about observations and questions. 
  4. Teachers should supplement with their own knowledge and point out key concepts along the way. For example, if students build a dam-like structure, you could point out that it is slowing the velocity of water, allowing sediments to drop out of suspension and remain in the box.  Other students may cover the box with rocks, limiting the loss of soil, but not necessarily a cost-effective means of control depending on the situation.
  5. After each rainbox experiment, using the three collection jars, have each group collect three samples of their runoff water to analyze in lesson 5.   
  6. Ask the students to observe the samples. Remind students that the cloudiness is the result of fine soil particles (clay) being suspended in the runoff water. The cloudier the water in the sample the higher the turbidity. Turbidity is a measurement of the amount of light that is scattered and absorbed by suspended soil particles. Students will be exploring this concept more extensively in the next activity.
  7. After all of the groups have finished, ask them to dispose of their materials.  Many items could be composted (mulch, leaves, hay, soil) and other materials should be thrown away. Pour the water samples on the ground outside, not in sinks or toilets, to avoid clogging drains.
  8. After the activity, use the questions in the student handout, “Let it Rain” to process the experience. Weave together the life skills students used throughout the planning and implementing of the experiment with the content they learned about erosion, sedimentation, and turbidity.

Students can tweak their initial rainbox design:

  • Were the results what students expected? 
  • What worked about their new design? 
  • Is there still something that could be changed? 

Soil Erosion Variables

  • Students can design a new experiment by looking at these questions.
  • How does slope affect soil erosion?
  • How does soil texture affect soil erosion?
  • Does rain intensity change the amount of soil lost?
  • Does rain volume affect the amount of soil lost?
  • Is wind erosion a real threat?
Let it Rain Handout

Use this student handout to guide the process of setting up the rainbox throw down.

Rainbox Design Plans

Use these plans to construct your own rainboxes.

Rainbox Materials & Pricing

Use this resource to determine what you need to be able to construct the rainbox.

Rainbox Throwdown Demonstration

If you missed this in Lesson 2, watch this quick rainbox throw down between three Richmond County 4-H’ers.

Rainbox Throw Down Jamboard

Use this jamboard to post images of your rainbox throw down and to think about other ways the rainbox throw down could be done.

Teachers/Leaders: Please go to the upper right hand corner and click on the three vertical dots and “make a copy” for your own use.

Talking it Over

Rainbox Experiment

Share …what you did

  • What happened? How did the different treatments from each group impact the runoff?
  • What did they like about the activity? How did you decide what design to choose? In what ways did students communicate their ideas and form a consensus for a design?

Reflect …on the results

  • Which group had the best design? Why? What were the key elements they used?
  • What did you learn in a group that you might not have learned alone? As students were presenting, how did they articulate their ideas?

Generalize …to your community

  • How can a design be generalized to a larger scale? Would it be practical? Is it cost-effective?
  • Why is it important to think about solutions you can implement in your own community?
  • What are some ways that you like to learn?

Apply …to your community

  • Is there an environmental impact from your design? (Are you using sustainable materials or something that would persist in the environment, but could be reused?)
  • How might you strike a balance between cost and environmental benefits? How might treatments vary between different land users? For example, how would a site being developed for recreation or wilderness differ from one being developed for commercial or residential use?
  • What would treatments for agricultural lands look like? Why do they think it is important to share their ideas with peers? What did you learn about your own skill in communicating with others?

Assessment

Assessment

REPLAY

REPLAY is an assessment that asks students to reflect on the rainbox experiment and recall why they did the experiment, explain how they did it and show they learned, and list new questions they have — essentially a verbal REPLAY of the experiment. A REPLAY helps teachers determine how well the students understood the material and spaces of uncertainty as well as ideas for new experiments that the students can do.  

Provide time after doing the rainbox experiment to have students share what they did in the lab, the objective, the results and what the results mean, ideas they are still unclear about, and new ideas on how they might adjust or change their original design as well as new variables they could test.  Students can work individually or collectively to capture their thoughts.  These ideas can inform additional teaching of concepts and give students the opportunity to repeat and experiment.

What event/moment made them change their thinking?  

Did they make a connection between any factors that cause soil erosion and controlling it?

The Daily Blog

Have students debrief on the rainbox “throwdown” experiment.  Students can include discussion points from their experiment, photos, and videos.  They might hypothesize how they would redo their experiment given the opportunity.  Students should also reflect on the life skills they might have learned or realized as part of working with their group.  Did they gain any leadership or communication skills?  Why is this important in a scientific community?  Teachers might ask the student bloggers to research information and issues regarding turbidity. Encourage students to take the time to comment on each other’s postings, asking questions or making remarks that are relevant to the posted text.

Learn More

Learn More

Macroinvertebrate Sampling

Sampling for aquatic specimens can help you understand the quality of your water body.

Clean water is vitally important to our everyday lives,  from drinking water to swimming, fishing, growing food, and operating industries.  By monitoring the quality of surface water, we can understand how we might be impacting our water supply and play a role in water conservation.  Water quality can be difficult to measure, but by using a combination of tools, we can begin to create a picture of what is happening in our community.  Scientists measure water temperature, pH, dissolved oxygen, and turbidity along with current environmental conditions to quantify water quality.  

Macroinvertebrate Sampling is another tool that citizens can use to look at the health of a stream.  Aquatic macroinvertebrates are found in streams, ponds, lakes, and marshes and maintain the health of the water ecosystem by eating bacteria and dead, decaying plants and animals. A diverse and abundant population of macroinvertebrates is an indicator of good water quality. Benthic macroinvertebrates dwell on the bottom of streams and can reveal much about the health of their aquatic environment.  Low levels of oxygen or plumes of toxic chemicals can make a stream intolerable for sensitive animals. The macroinvertebrates that can survive these conditions, like aquatic worms and leeches, are often associated with polluted waters.  Other macroinvertebrates like stoneflies, mayflies, and water pennies require high levels of dissolved oxygen and when found in abundance are an indication of good water quality.

Consider hiking down to a local stream with a friend to explore the aquatic organisms that might be present.  Take a sample and try to determine what organisms you find.  Do you think they are indicators of “good” or “poor” water quality? How do you know?  How many of each did you find?  Do quantities of organisms impact stream health?  What will you do with your findings? How can you play a role in protecting your community’s water?

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