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Worksheet Grade 7 Social Studies & Civics

The Twin Rivers Compact: Allocating Water in Acre-Feet

A grade 7 worksheet using a fictional two-state river compact to practice acre-foot conversions and multistep percent problems tied to interstate water allocation.

Objectives

  1. Students will convert a water allocation from acre-feet into gallons and cubic feet using standard conversion factors.
  2. Students will calculate a percent decrease in water allocation between a normal year and a drought year.
  3. Students will explain why river basins and political boundaries do not always match, and why compact negotiations use public hearings.

Vocabulary

Interstate compact
A formal deal between states about how to share a river that crosses their borders. Congress approves these agreements, and they can last for a century.
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.
Watershed
A watershed is all the land where rain that falls will drain to the same stream, river, or lake. Everyone lives in a watershed, no matter how far from the water they live.

Also: allocation, deliberation

Teacher overview

Rivers rarely stop at a state line, so when two or more states share one river basin, they typically negotiate a compact that divides the water among them by law, the way several real river basins in the United States are governed today. This worksheet uses a fictional two-state compact, between the states of Cascadia and Rio Alto, to give students practice converting a water allocation from acre-feet, the unit water planners commonly use for a share this large, into gallons and cubic feet. A common misconception this worksheet is built to correct is the idea that a fixed percentage split guarantees each state a fixed amount of water no matter what happens; because the basin's total yield changes from year to year, each state's actual water changes too, even though its percentage share stays exactly the same.

The Twin Rivers Compact: Allocating Water in Acre-Feet — Grade 7 Social Studies & Civics
Name: ____________________________ Date: ______________

Student Worksheet

Suppose two fictional states, Cascadia and Rio Alto, share a river system. It is called the Twin Rivers Basin. Under the fictional Twin Rivers Compact, the two states split the basin's water each year. The split uses a fixed percentage: Cascadia gets 60 percent of the water. Rio Alto gets 40 percent. Use these facts for all problems:

  • One acre-foot equals 325,851 gallons.
  • One acre-foot equals 43,560 cubic feet.
  • In a normal year, the Twin Rivers Basin produces 900,000 acre-feet of water.

  1. How many acre-feet does Cascadia get in a normal year? (Find 60 percent of 900,000 acre-feet.)

  2. How many acre-feet does Rio Alto get in a normal year? (Find 40 percent of 900,000 acre-feet.)

  3. Convert Cascadia's normal-year share to gallons. Round to the nearest tenth of a billion gallons.

  4. Now suppose a drought hits. The basin's total yield drops to 720,000 acre-feet. The two states still split the water 60/40. How many acre-feet does Cascadia get in the drought year?

  5. Compare item 1 (the normal year) and item 4 (the drought year). By what percent did Cascadia's share decrease?

  6. Convert Rio Alto's drought-year share to cubic feet. Round to the nearest tenth of a billion cubic feet.

  7. Rio Alto's normal-year share equals 117.3 billion gallons. Add that number to your answer for item 3. This gives the whole basin's normal-year yield in gallons. Round to the nearest tenth of a billion.

  8. A compact can split water by a fixed percentage, or it can promise each state a fixed number of acre-feet. Explain why the percentage method treats both states more fairly during a drought.

  9. Before states sign a compact like this one, they often hold public hearings. Residents, farmers, and city water managers can speak at these hearings. Name one advantage of allowing public comment before a compact is finalized.

  10. A river basin has a natural boundary. This is the line where rain drains into the river on one side, and away from it on the other. That line does not match the political border between Cascadia and Rio Alto. Explain in one or two sentences why a river basin's natural boundary might not match a political boundary.

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: 540,000 acre-feet.
    60% of 900,000 = 0.60 × 900,000 = 540,000 acre-feet.

  2. Answer: 360,000 acre-feet.
    40% of 900,000 = 0.40 × 900,000 = 360,000 acre-feet, which checks against item 1 since 540,000 + 360,000 = 900,000.

  3. Answer: 176.0 billion gal.
    540,000 acre-feet × 325,851 gallons/acre-foot = 175,959,540,000 gallons, which is about 176.0 billion gallons when rounded to the nearest tenth of a billion.

  4. Answer: 432,000 acre-feet.
    60% of 720,000 = 0.60 × 720,000 = 432,000 acre-feet.

  5. Answer: 20 percent.
    The decrease is 540,000 − 432,000 = 108,000 acre-feet. As a percent of the original: 108,000 ÷ 540,000 = 0.20 = 20%. This matches the drought's overall 20% cut to the basin (720,000 is 80% of 900,000), because a fixed-percentage split means every party's share falls by the same percent as the total.

  6. Answer: 12.5 billion cu ft.
    Rio Alto's drought-year share is 40% of 720,000 = 288,000 acre-feet. Converting: 288,000 × 43,560 cubic feet/acre-foot = 12,545,280,000 cubic feet, about 12.5 billion cubic feet rounded to the nearest tenth.

  7. Answer: 293.3 billion gal.
    Cascadia's normal-year share in gallons (item 3) is about 176.0 billion. Rio Alto's normal-year share, 360,000 acre-feet × 325,851 gallons/acre-foot, is 117,306,360,000 gallons, about 117.3 billion. Adding: 176.0 + 117.3 = 293.3 billion gallons, the whole basin's normal-year yield.

  8. Answer: A fixed percentage split adjusts automatically to how much water actually exists that year, so both states absorb a drought's losses in proportion rather than one state absorbing the entire shortfall while the other still receives its full fixed amount.

  9. Answer: Public hearings let the people who will be most affected by the compact, such as farmers and city water managers, raise concerns or share local knowledge before the agreement becomes permanent, which can prevent disputes later and make the final compact more workable for everyone who depends on the river.

  10. Answer: A river basin's boundary is set by the shape of the land, specifically by which direction rainwater drains, while a political boundary was drawn by people for reasons that often had nothing to do with drainage patterns, so the two lines rarely line up exactly.

Differentiation

Support (below grade level)

Provide a printed conversion card listing "acre-feet × 325,851 = gallons" and "acre-feet × 43,560 = cubic feet" alongside a worked example using a third number (not 540,000 or 288,000). Allow a calculator for all multiplication and division steps, and pre-fill the basin's normal-year total (900,000 acre-feet) and the two states' percentages directly onto the student's page.

Extension (above grade level)

Ask students to design a three-state version of the Twin Rivers Compact with percentages that sum to 100, choose their own basin total, and calculate each state's allocation in acre-feet, gallons, and cubic feet, showing every conversion step.

ELL supports

Pre-teach "compact," "allocation," and "watershed" with a simple diagram showing two states and a shared river with an arrow splitting into two flows labeled with the percentages. Allow items 8, 9, and 10 to be answered with a labeled sketch plus a short phrase instead of a full paragraph, where the standard permits.