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Lesson plan Grade 5 Health & Consumer Science

Redbank Cove Beach Advisory: Rain Totals and Safe Swimming

A grade 5 health lesson in which students add and compare decimal rainfall totals to decide whether a fictional town's swimming beach stays open after a storm.

Objectives

  1. Students will add decimal rainfall amounts to hundredths to find two-day and five-day totals.
  2. Students will compare a decimal rainfall total to a stated closing amount and decide whether a beach is open.
  3. Students will explain why rain that fell earlier can still affect whether lake water is safe for swimming.

Vocabulary

Key words: advisory, runoff, rain gauge, decimal

Teacher overview

Many lake and river beaches post swimming advisories after heavy rain, because stormwater running off streets, yards, and parking lots carries germs into the water faster than the lake can dilute them. This lesson uses the fictional town of Redbank Cove, whose parks department closes its swimming beach whenever the rain measured over the past two days totals 0.75 inch or more. Students add and compare decimal rainfall amounts, then decide what the rule says for each pair of days. The misconception addressed here is that clear-looking water is automatically safe water; the rule depends on what rain has washed into the lake, not on how the surface looks.

Procedure

Launch (5 min): Show the rain gauge and ask students how they would tell someone the amount of rain in it if the water stopped between two marks. Establish that rainfall is reported with decimals, and read a few sample amounts aloud, naming the tenths and hundredths places.

Mini-lesson (8 min): Introduce the Redbank Cove rule: the beach closes when the past two days of rain add up to 0.75 inch or more. Model one two-day total that students will not see again on the handout, 0.18 inch plus 0.24 inch, lining the decimal points up vertically to get 0.42 inch, then state the decision aloud: 0.42 is less than 0.75, so the beach stays open. Record the example in a class rainfall chart with columns for Day 1, Day 2, Total, and Decision.

Class practice (7 min): Work one more pair together with student input, 0.60 inch plus 0.30 inch, and ask for both the sum, 0.90 inch, and the decision, which is closed. Take a thumbs-up, thumbs-down poll on the decision before revealing it. If fewer than three quarters of thumbs match, rebuild the comparison on a number line marked from 0 to 1 in hundredths before students work alone.

Independent handout (15 min): Students complete the eight-question handout individually. Circulate and watch question 5, where an amount greater than one inch is added to a hundredths amount, and question 7, where five decimals are added in sequence.

Debrief (5 min): Collect the handouts and ask two or three students to read their answer to question 8 aloud. Close by noting that the parks department also tests the lake water, and the rain rule is a fast way to make a decision while test results are still coming back.

Redbank Cove Beach Advisory: Rain Totals and Safe Swimming — Grade 5 Health & Consumer Science
Name: ____________________________ Date: ______________

Student Handout

Redbank Cove is a fictional town. Its beach closes when the rain over the past two days totals 0.75 inch or more.

  1. On Monday, 0.30 inch of rain fell at Redbank Cove. On Tuesday, 0.45 inch fell. What was the two-day rain total?
  2. The two-day total for Monday and Tuesday was 0.75 inch. The beach closes when the two-day total is 0.75 inch or more. Was the beach open or closed?
  3. On Thursday, 0.12 inch of rain fell. On Friday, 0.20 inch fell. What was that two-day rain total?
  4. The Thursday and Friday total was 0.32 inch. The closing amount is 0.75 inch. How much more rain would it have taken to close the beach?
  5. On Saturday, 1.15 inches of rain fell. On Sunday, 0.05 inch fell. What was the two-day rain total?
  6. The Saturday and Sunday total was 1.20 inches. The closing amount is 0.75 inch. How much greater was the total than the closing amount?
  7. Over five days the Redbank Cove gauge recorded 0.30 inch, 0.45 inch, 0.12 inch, 0.20 inch, and 1.15 inches. What was the five-day total?
  8. Write one or two sentences explaining why rain that fell two days ago could still make lake water unsafe for swimming today.

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: 0.75 inch. Add the two amounts: 0.30 + 0.45 = 0.75.
  2. Answer: Closed. The total of 0.75 inch equals the closing amount, and the rule closes the beach at 0.75 inch or more.
  3. Answer: 0.32 inch. Add the two amounts: 0.12 + 0.20 = 0.32.
  4. Answer: 0.43 inch. Subtract the total from the closing amount: 0.75 - 0.32 = 0.43.
  5. Answer: 1.20 inches. Add the two amounts: 1.15 + 0.05 = 1.20.
  6. Answer: 0.45 inch. Subtract the closing amount from the total: 1.20 - 0.75 = 0.45.
  7. Answer: 2.22 inches. Add in order: 0.30 + 0.45 = 0.75, plus 0.12 is 0.87, plus 0.20 is 1.07, plus 1.15 is 2.22.
  8. Answer: Rain washes dirt and germs off streets and yards into the lake, and the water needs time before those germs die off or spread out, so the lake can still be unsafe a day or two later. Accept any answer that connects runoff carrying material into the lake with the time the lake needs to recover.

Differentiation

Support

Give these students a decimal place-value chart with columns for ones, tenths, and hundredths, and have them write each rainfall amount into the chart before adding. Provide a number line from 0 to 1.50 marked every 0.05 so the comparison with the closing amount is visual rather than symbolic.

Extension

Ask students to write a two-day rainfall pair that would leave the beach open by the smallest possible amount using hundredths, and a pair that would close it by exactly one hundredth of an inch. Students should show both sums and explain how they chose the numbers.

ELL supports

Pre-teach "advisory," "runoff," and "gauge" using the physical rain gauge and a picture of water flowing from a street into a lake. Post the sentence frame "The two-day total is ____ inches, so the beach is ____," and allow students to answer question 8 orally to a partner before writing it.

Extensions

Students can keep a five-day rainfall log for their own community using a school rain gauge, apply the Redbank Cove rule to their data, and report which days would have closed a beach. A short follow-up discussion can compare their totals with the ones on the handout.