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Lesson plan Grade 7 Social Studies & Civics

Coldwater Valley's Drought Allocation: Sharing a Shrinking River

A grade 7 social studies lesson using a fictional irrigation district to divide a shrinking river's water between farms and a town during a drought year.

Objectives

  1. Students will calculate how a river's water is divided between farms and a town using given percentages.
  2. Students will compute the percent drop in a water supply between a normal year and a drought year.
  3. Students will compare two allocation rules and weigh their costs and benefits for different groups.

Vocabulary

Acre-foot
The amount of water it takes to cover one acre of land, about the size of a football field, one foot deep. Western states use acre-feet to measure large amounts of water.
Water right
The legal permission to take water from a river, lake, or aquifer and use it. Water rights decide who gets water when there is not enough for everyone.
Drought
A long stretch of drier-than-normal weather that leaves too little water for people, farms, and nature. Droughts build slowly and can last for years.
Irrigation district
A local organization formed by farmers to bring water to their fields. It runs the canals, sets delivery schedules, and charges its members for the service.

Also: allocation

Teacher overview

In the western United States, a single river is often shared by farms that irrigate crops and by towns that need drinking water, and the amount of water in the river changes from year to year. This lesson places students inside the fictional Coldwater Valley Irrigation District, which must divide a river's water between farms and the town of Ashford in both a normal year and a drought year. A common misconception this lesson addresses is the idea that a drought divides evenly, so that everyone simply gets "a little less"; in reality, the rule a community chooses for sharing a shortage decides who absorbs most of the loss, and students should see that the arithmetic and the fairness question are two different things.

Procedure

Hook (5 min): Project or sketch a simple map: a river flowing from farm country into the town of Ashford. Ask students, "If the river carried less water this year than last year, who should give up water first, the farms or the town? Why?" Take a few answers without settling the question.

Direct instruction (15 min): Introduce the fictional Coldwater Valley Irrigation District. Explain that water in the West is measured in acre-feet, and that an acre-foot is the amount of water it takes to cover one acre of land one foot deep. Establish the scenario numbers on the board: in a normal year the river gives the district 12,000 acre-feet, and long-standing water rights give the farms 75 percent of that water and the town of Ashford the other 25 percent. Model question 1 with the class: 75 percent of 12,000 acre-feet is 0.75 times 12,000, which equals 9,000 acre-feet for the farms. Explain that this year is a drought year, and the river will give the district only 8,400 acre-feet.

Guided practice (12 min): As a class, work the percent-drop calculation together: the supply fell from 12,000 to 8,400 acre-feet, a drop of 3,600 acre-feet, and 3,600 divided by 12,000 equals 0.30, or a 30 percent drop. Then introduce the two rules the district is considering for the drought year. Rule A keeps the same 75/25 split. Rule B protects the town's drinking water first, giving Ashford its full normal-year 3,000 acre-feet and leaving the rest for the farms. Have students predict which rule the farms would prefer before they calculate.

Independent practice (18 min): Students complete the Student Handout, which walks them through both rules and asks them to compare the results. Circulate and check that students are multiplying by the correct percentage and subtracting in the right order.

Closure / exit ticket (5 min): Each student answers on an index card: "Which rule, A or B, would you vote for as a member of the Coldwater Valley board, and give one number from today's lesson that supports your choice." Collect and confirm that each student cites a specific figure, such as the 6,300 or 5,400 acre-feet the farms receive under each rule, rather than only an opinion.

Coldwater Valley's Drought Allocation: Sharing a Shrinking River — Grade 7 Social Studies & Civics
Name: ____________________________ Date: ______________

Student Handout

Suppose you sit on the board of the fictional Coldwater Valley Irrigation District. Your job is to divide the river's water. Use these facts:

  • In a normal year the river gives the district 12,000 acre-feet.
  • Water rights give the farms 75 percent of the water and the town of Ashford 25 percent.
  • This is a drought year, and the river will give the district only 8,400 acre-feet.
  1. In a normal year, how many acre-feet do the farms receive? (Find 75 percent of 12,000 acre-feet.)
  2. In a normal year, how many acre-feet does the town of Ashford receive? (Find 25 percent of 12,000 acre-feet.)
  3. The drought supply is 8,400 acre-feet instead of 12,000. By what percent did the district's water supply drop?
  4. Rule A keeps the same 75/25 split in the drought year. Under Rule A, how many acre-feet do the farms receive? (Find 75 percent of 8,400 acre-feet.)
  5. Rule B gives the town its full normal-year 3,000 acre-feet first, and the farms receive whatever is left of the 8,400 acre-feet. Under Rule B, how many acre-feet do the farms receive?
  6. Compare your answers to questions 4 and 5. Under Rule B, do the farms get more or fewer acre-feet than under Rule A, and by how many acre-feet?

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: 9,000 acre-feet.
    0.75 × 12,000 = 9,000 acre-feet for the farms in a normal year.

  2. Answer: 3,000 acre-feet.
    0.25 × 12,000 = 3,000 acre-feet for the town of Ashford in a normal year.

  3. Answer: 30 percent.
    The drop is 12,000 − 8,400 = 3,600 acre-feet. As a percent of the normal supply, 3,600 ÷ 12,000 = 0.30 = 30 percent.

  4. Answer: 6,300 acre-feet.
    Under Rule A, 0.75 × 8,400 = 6,300 acre-feet for the farms.

  5. Answer: 5,400 acre-feet.
    Under Rule B, the town takes its full 3,000 acre-feet first, so the farms receive 8,400 − 3,000 = 5,400 acre-feet.

  6. Answer: 900 fewer acre-feet.
    Under Rule B the farms get 5,400 acre-feet, and under Rule A they get 6,300 acre-feet, so Rule B gives the farms 6,300 − 5,400 = 900 fewer acre-feet. Rule B shifts more of the drought shortfall onto the farms so the town's drinking water stays whole.

Differentiation

Support (below grade level)

Provide a partially completed handout with question 1 already worked (0.75 × 12,000 = 9,000) as a model, and give students a printed reminder that "percent of" means "multiply by the decimal." Allow calculators for every step, and let students who struggle with question 6 answer it by circling the larger of their two earlier answers before finding the difference.

Extension (above grade level)

Ask students to design a third rule, Rule C, that splits the 3,600 acre-foot shortfall so that the farms and the town each give up the same number of acre-feet. Have them calculate what each side would receive under Rule C and explain in writing how it compares with Rules A and B on fairness.

ELL supports

Pre-teach "acre-foot," "water right," "allocation," and "drought" with a simple labeled drawing (a river splitting into two pipes, one to a farm and one to a town). Provide sentence starters for the exit ticket: "I would vote for Rule ___ because the farms would receive ___ acre-feet, which is ___." Allow students to complete the handout with a partner who shares their home language.

Extensions

Have students find out where their own community's tap water comes from, using their local utility's website, and whether that source is a river, a reservoir, or groundwater that could run low in a dry year. Ask them to write two sentences connecting what they find to the sharing question Coldwater Valley faced.