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Lesson plan Grade 7 Science

Lindenmoor School Rain Garden: A Grade 7 Stormwater Runoff Lesson

A 50-minute grade 7 lesson where students calculate roof runoff and compare pavement to planted ground to design a school rain garden that cuts stormwater.

Objectives

  1. Students will calculate roof runoff from area and rainfall using the 0.623 conversion.
  2. Students will compare runoff from pavement and planted ground using runoff coefficients.
  3. Students will explain how a rain garden reduces the stormwater leaving the school.

Vocabulary

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, impervious, runoff coefficient

Teacher overview

When rain falls on a roof or a paved courtyard, most of it runs off instead of soaking in, and that runoff has to go somewhere. At the fictional Lindenmoor School, a paved courtyard floods after every storm, and this lesson has students calculate how much water runs off and design a rain garden to catch it. A common student misconception is that a small patch of planted ground cannot make a real difference; the runoff-coefficient comparison in this lesson is built to correct that by showing pavement sheds several times more water than planted ground.

Procedure

Hook (5 min): Describe or show the flooded Lindenmoor courtyard after a storm. Ask students where all that water goes and why it puddles on pavement but not on a lawn. Record ideas without correcting them yet.

Direct instruction (12 min): Define runoff, impervious surfaces, and green infrastructure. Teach the roof-runoff formula: gallons = roof area (square feet) times rainfall (inches) times 0.623. Point out that this gives all the rain that falls on the roof, and that a real gutter and rain garden collect somewhat less. Then introduce the runoff coefficient from the rational method: pavement has a coefficient of about 0.9 and planted ground (lawn) about 0.2, meaning pavement lets far more water run off. Explain that a rain garden is a shallow planted basin that soaks up runoff, which is one way to monitor and reduce the impact of paving over land.

Guided practice (13 min): Work handout items 1 through 3 together as a class, modeling how to substitute numbers into the runoff formula and how to compare the two runoff coefficients. Have students check each step with a partner before moving on.

Independent practice (12 min): Students complete handout items 4 through 6 on their own, then compare answers with a partner and resolve any differences.

Closure and exit ticket (8 min): Each student writes one sentence naming a way the rain garden reduces the runoff leaving Lindenmoor. Collect the tickets and scan for whether students connect planted ground to lower runoff; if most of the class does not make that link, reteach the coefficient comparison next session.

Lindenmoor School Rain Garden: A Grade 7 Stormwater Runoff Lesson — Grade 7 Science
Name: ____________________________ Date: ______________

Student Handout

Lindenmoor School is a fictional school. Use gallons = area times rainfall times 0.623 for roof runoff, and the runoff coefficients pavement = 0.9 and planted ground = 0.2 where asked.

  1. The school roof is 2,000 square feet. A storm drops 1.5 inches of rain. How many gallons run off the roof?
  2. A later storm drops 2 inches of rain on the same 2,000-square-foot roof. How many gallons run off?
  3. Pavement has a runoff coefficient of 0.9 and planted ground 0.2. For the same area and rainfall, how many times more runoff does pavement produce than planted ground?
  4. The class replaces a 400-square-foot strip of pavement (coefficient 0.9) with rain-garden planting (coefficient 0.2). By how much does the runoff coefficient drop for that strip?
  5. Express that coefficient drop as a percent decrease from 0.9. Round to the nearest whole percent.
  6. The finished rain garden can hold 1,900 gallons. Can it hold all of the roof runoff from the 1.5-inch storm in item 1? By how many gallons is it under or over?

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: 1,869 gallons.
    2,000 square feet times 1.5 inches times 0.623 equals 1,869 gallons.
  2. Answer: 2,492 gallons.
    2,000 square feet times 2 inches times 0.623 equals 2,492 gallons.
  3. Answer: 4.5 times.
    0.9 divided by 0.2 equals 4.5, so pavement produces 4.5 times as much runoff as planted ground.
  4. Answer: 0.7.
    0.9 minus 0.2 equals a drop of 0.7 in the runoff coefficient.
  5. Answer: About 78 percent.
    0.7 divided by 0.9 equals about 0.778, which rounds to a 78 percent decrease.
  6. Answer: Yes, with 31 gallons to spare.
    The roof runoff in item 1 is 1,869 gallons. The rain garden holds 1,900 gallons, and 1,900 minus 1,869 equals 31 gallons of extra room.

Differentiation

Support

Give students the runoff formula with the first step already filled in for item 1 (2,000 times 1.5), and provide a calculator. Pre-label the two coefficients on the handout so students do not confuse pavement with planted ground.

Extension

Have students design a second rain garden for the 2-inch storm in item 2, calculate the volume it would need to hold, and explain why a garden sized for the smaller storm might overflow.

ELL supports

Pre-teach "runoff," "pavement," and "soak in" with a simple demonstration: pour water on a tray and on a damp sponge. Provide a sentence frame for the exit ticket: "The rain garden reduces runoff because ___."