Water for Schools
Menu

Lesson plan Grade 6 Science

Kettle Hollow's Runoff Problem: Designing Green Infrastructure

A 55-minute grade 6 science lesson where students calculate roof runoff and design green infrastructure to cut stormwater in a fictional downtown.

Objectives

  1. Students will calculate stormwater runoff from a roof or paved area using area, rainfall, and a runoff constant.
  2. Students will propose a green-infrastructure design and state its criteria and constraints.

Vocabulary

Stormwater
Stormwater is rain or melted snow that flows off roofs, streets, and parking lots. In most towns it goes into storm drains and flows to a stream without being treated, carrying whatever it picked up.
Green infrastructure
Green infrastructure uses soil and plants, like rain gardens, green roofs, and street trees, to soak up rainwater where it falls instead of piping it away. It copies the way nature handles rain.
Rain garden
A rain garden is a shallow planted dip in the ground that catches rain running off a roof or driveway and lets it soak slowly into the soil. Its deep-rooted plants help clean the water.

Also: runoff

Teacher overview

When rain falls on a roof or a parking lot, the water cannot soak in, so it runs off fast and can flood streets and overload a creek. Green infrastructure, such as rain gardens and rain barrels, catches some of that water so less of it rushes away. This lesson has students calculate runoff for Kettle Hollow, a fictional town with a paved downtown, then design a way to reduce it. A common misconception is that rain simply disappears into the ground everywhere; the runoff calculation shows students that hard surfaces send most of the rain straight to the creek instead.

Procedure

Hook (5 min): Pour a cup of water onto a flat tray tilted over a sink, then onto a sponge, and ask students which surface let the water run off and which soaked it in. Connect this to a paved downtown versus open ground.

Direct instruction and worked example (12 min): Give the runoff rule: runoff in gallons equals roof area in square feet times rainfall in inches times 0.623. Model the worked example: a 1,000 square foot roof in 2 inches of rain gives 1,000 times 2 times 0.623 = 1,246 gallons. Point out that this is a lot of water from a single small roof in one storm.

Guided practice (13 min): Work handout items 1 and 2 with the class, checking that students multiply all three factors. Introduce two green-infrastructure tools: a rain barrel that holds 55 gallons and a rain garden that soaks up 400 gallons, and explain how each keeps water out of the creek.

Independent practice (15 min): Students complete handout items 3 through 7 on their own, showing each step. Circulate and confirm that students divide correctly in item 3 and find the percent in item 5 by dividing the amount captured by the total runoff.

Closure and exit ticket (10 min): Each student writes one green-infrastructure choice for Kettle Hollow and states one criterion and one constraint for the design on an exit card. Collect and scan for a criterion (something the design must do) paired with a constraint (a limit such as budget or space).

Kettle Hollow's Runoff Problem: Designing Green Infrastructure — Grade 6 Science
Name: ____________________________ Date: ______________

Student Handout

Use these figures for every item. Kettle Hollow is a fictional town.

  • Runoff rule: runoff (gallons) = area (square feet) times rainfall (inches) times 0.623.
  • A rain barrel holds 55 gallons.
  • A rain garden soaks up 400 gallons in a storm.

  1. A downtown roof is 500 square feet. In 1 inch of rain, how many gallons run off it?

  2. A parking area is 2,000 square feet. In 1.5 inches of rain, how many gallons run off it?

  3. About how many 55-gallon rain barrels would it take to hold all the runoff from the 500-square-foot roof in item 1? That runoff is all the rain that falls on the roof; a real barrel system would catch somewhat less. Round up to a whole number of barrels.

  4. Look back at the 1,246-gallon example roof from the lesson. If one rain garden soaks up 400 gallons, how many gallons still run off?

  5. What percent of the 1,246-gallon runoff does one 400-gallon rain garden capture? Round to the nearest whole percent.

  6. Name one green-infrastructure choice for Kettle Hollow's downtown and explain how it reduces the stormwater reaching the creek.

  7. Kettle Hollow has a small budget and little open space downtown. Give one criterion the design must meet and one constraint that limits the choices.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

  1. Answer: 311.5 gallons.
    500 times 1 times 0.623 = 311.5 gallons.

  2. Answer: 1,869 gallons.
    2,000 times 1.5 times 0.623 = 1,869 gallons.

  3. Answer: 6 barrels.
    311.5 divided by 55 = 5.66, which rounds up to 6 whole barrels.

  4. Answer: 846 gallons.
    1,246 minus 400 = 846 gallons still run off after one rain garden.

  5. Answer: 32 percent.
    400 divided by 1,246 = 0.321, which rounds to 32 percent.

  6. Answer: Accept any green-infrastructure choice with a clear reason, such as: a rain garden holds runoff and lets it soak into the ground slowly, so less water rushes to the creek during a storm, or a rain barrel stores roof runoff for later use instead of sending it down the street.

  7. Answer: Accept one criterion (something the design must do, such as capture a set amount of runoff or fit in a plaza) paired with one constraint (a limit, such as a small budget, little open space, or keeping sidewalks clear). A strong answer clearly separates the goal from the limit.

Differentiation

Support

Provide the runoff rule with the three factors already labeled, and give item 1 partly worked (500 times 1 shown) so students finish the last multiplication. Allow calculators and provide the division set-up for item 3.

Extension

Ask students to design a two-part plan for the example roof that captures at least 800 of its 1,246 gallons using a mix of barrels and a rain garden, then show the math proving their plan reaches the goal.

ELL supports

Pre-teach stormwater, runoff, rain garden, and criterion with simple pictures (rain on pavement, a planted basin). Provide the frame "My design is a ___; it helps because ___," and allow the closure response to be given orally or as a labeled sketch.