Worksheet Grade 6 Social Studies & Civics

Acre-Feet on the Cobb Ditch: Sharing a Creek's Water

A grade 6 worksheet on how a ditch company divides a creek by shares, with acre-foot conversions to gallons and cubic feet and a dry-year cut to all shareholders.

Grade: Grade 6
Subject: Social Studies & Civics
Material: Worksheet
Time: 40 min
Prep: No prep
Materials: None

Standards

6.RP.A.3 Common Core Math

Use ratio and rate reasoning to solve real-world and mathematical problems, e.g., by reasoning about tables of equivalent ratios, tape diagrams, double number line diagrams, or equations, including finding a percent of a quantity and converting measurement units.

How this material aligns: Students convert acre-feet to gallons and cubic feet with a single given rate and find each shareholder's percent of the total, which is the real-world ratio and percent work this standard names.

All materials for 6.RP.A.3 →

D2.Geo.4.6-8 C3 Framework

Explain how cultural patterns and economic decisions influence environments and the daily lives of people in both nearby and distant places.

How this material aligns: Questions 11 and 12 ask students to argue how a dry-year cut would fall differently on households and on farms in the same valley, connecting a shared economic rule about water to daily life in a dry place.

All materials for D2.Geo.4.6-8 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-09-03.

Objectives

Students will convert a quantity in acre-feet to gallons and to cubic feet using a given rate.
Students will find each shareholder's percent of a ditch company's total water.
Students will apply a dry-year percent cut to two different shareholders.

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.

Also: ditch company, share, shareholder, irrigation, dry year

Teacher overview

Across much of the western United States, a ditch company divides a creek among its members by shares rather than by the gallon, and the unit written on the paperwork is the acre-foot. This worksheet uses the fictional Thistlecombe Valley, where the Cobb Ditch Company splits one creek among two farms and a town. Students find each shareholder's amount, convert acre-feet into two other units using the standard conversions, and then apply a dry-year cut to see who feels it most. A common misconception is that an acre-foot is a small farm measurement; converting it to gallons shows students that a single acre-foot is a large volume, which is why western water paperwork uses it at all.

Acre-Feet on the Cobb Ditch: Sharing a Creek's Water — Grade 6 Social Studies & Civics

Name: ____________________________ Date: ______________

Student Worksheet

The Cobb Ditch Company carries water from Thistlecombe Creek in the fictional Thistlecombe Valley. The company divides the creek into shares. Each share is worth 10 acre-feet of water for the season. The table shows who holds the shares.

Shareholder	Shares held
Alder Rise Farm	12
Two Pines Farm	5
Town of Thistlecombe	3

Use these two conversions when a question asks for them. One acre-foot is 325,851 gallons. One acre-foot is 43,560 cubic feet. Show your work, and a calculator is allowed.

Alder Rise Farm holds 12 shares, and each share is 10 acre-feet. How many acre-feet does Alder Rise Farm hold?
Two Pines Farm holds 5 shares, and each share is 10 acre-feet. How many acre-feet does Two Pines Farm hold?
The Town of Thistlecombe holds 3 shares, and each share is 10 acre-feet. How many acre-feet does the town hold?
The company divides 20 shares in all, and each share is 10 acre-feet. How many acre-feet does the company divide in all?
Alder Rise Farm's 120 acre-feet is part of the 200 acre-feet the company divides. What percent of the total goes to Alder Rise Farm?
The town's 30 acre-feet is part of the same 200 acre-feet. What percent of the total goes to the town?
One acre-foot is 325,851 gallons. Change Two Pines Farm's 50 acre-feet into gallons.
One acre-foot is 43,560 cubic feet. Change the town's 30 acre-feet into cubic feet.
In a dry year the company cuts every shareholder by 25 percent. Alder Rise Farm normally receives 120 acre-feet. How many acre-feet would it receive after the cut?
The town normally receives 30 acre-feet. How many acre-feet would it receive after the same 25 percent cut?
Give one reason the town might argue that a 25 percent cut is harder on homes than on farms.
Give one reason a farmer might argue that the same cut is harder on a farm.

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

Answer Key

Answer: 120 acre-feet. Multiplying 12 shares by 10 acre-feet in each share gives 120 acre-feet.
Answer: 50 acre-feet. Multiplying 5 shares by 10 acre-feet in each share gives 50 acre-feet.
Answer: 30 acre-feet. Multiplying 3 shares by 10 acre-feet in each share gives 30 acre-feet.
Answer: 200 acre-feet. Multiplying 20 shares by 10 acre-feet in each share gives 200 acre-feet, which also equals 120 plus 50 plus 30.
Answer: 60%. Dividing 120 acre-feet by 200 acre-feet gives 0.60, which is 60 percent.
Answer: 15%. Dividing 30 acre-feet by 200 acre-feet gives 0.15, which is 15 percent.
Answer: 16,292,550 gallons. Multiplying 50 acre-feet by 325,851 gallons in each acre-foot gives 16,292,550 gallons.
Answer: 1,306,800 cubic feet. Multiplying 30 acre-feet by 43,560 cubic feet in each acre-foot gives 1,306,800 cubic feet.
Answer: 90 acre-feet. A 25 percent cut removes 30 acre-feet from 120 acre-feet, leaving 90 acre-feet. Students may also multiply 120 by 0.75.
Answer: 22.5 acre-feet. A 25 percent cut removes 7.5 acre-feet from 30 acre-feet, leaving 22.5 acre-feet. Students may also multiply 30 by 0.75.
Answer: Answers vary. Accept any reasonable argument, such as the point that homes need water for drinking, cooking, and washing every day and cannot postpone those uses, or that the town serves many households with a small share to begin with.
Answer: Answers vary. Accept any reasonable argument, such as the point that a farm's crops die without water at the right week and cannot be made up later, or that a lost crop means lost income for the whole year.

Differentiation

Support

Give these students the first row of the table already converted, and let them use a calculator for every step. Provide a labeled model showing one share as a box worth 10 acre-feet, so questions 1 through 4 become counting boxes rather than abstract multiplication. For questions 9 and 10, offer the hint that a 25 percent cut leaves three quarters of the original amount.

Extension

Have students propose a different dry-year rule, such as cutting the two farms more than the town or protecting the first 10 acre-feet for every shareholder before cutting the rest. They should calculate what each shareholder would receive under their rule and write two sentences defending it to the ditch company board, including how they would answer the shareholder who loses the most.

ELL supports

Pre-teach "ditch," "share," "acre-foot," and "cut" with a drawing of one creek splitting into three channels of different widths. Provide the sentence frame "Alder Rise Farm receives ___ acre-feet because ___ shares times ___ acre-feet equals ___." Allow questions 11 and 12 to be answered in short phrases, and accept a labeled drawing of a home and a field as part of the answer.

Extensions

Have students find whether water in their own state is divided by shares, by permits, or by rules tied to owning land beside a stream, using the state water agency's public pages. Students can then write one paragraph comparing that system to the Cobb Ditch Company and naming which system they think handles a dry year more fairly.