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Worksheet Grade 11 Social Studies & Civics

Hoover Dam and the Colorado River: A Grade 11 Civics Worksheet

A grade 11 worksheet pairing the history of federal dam building with allocation and hydropower math for a fictional Colorado River water district.

Objectives

  1. Students will explain why building Hoover Dam required an act of Congress and an interstate compact.
  2. Students will calculate a water district's allocation use and convert acre-feet to gallons.
  3. Students will use marginal benefit and cost reasoning to evaluate large dam projects.

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.
Hydropower
Electricity made from moving water, usually water falling through a dam. It is a renewable power source that can start up quickly when the electric grid needs it.

Also: reclamation, allocation, marginal cost

Teacher overview

Hoover Dam is both an engineering landmark and a constitutional one: no single state could have financed it, and the states sharing the Colorado River had to divide the water before construction could begin. This worksheet pairs that history with the arithmetic of water allocation, using the fictional Saguaro County Water District and its Colorado River share to make the numbers concrete. Students first reason about why federal authority and an interstate compact were both necessary, then calculate allocation use and hydropower output, and finally weigh a large dam's benefits against its costs.

Hoover Dam and the Colorado River: A Grade 11 Civics Worksheet — Grade 11 Social Studies & Civics
Name: ____________________________ Date: ______________

Student Worksheet

Hoover Dam's power plant has a capacity of about 2,080 megawatts (MW). The Boulder Canyon Project Act of 1928 authorized the federal government to build the dam, and the Colorado River Compact of 1922 had already divided the river's water among the states that share it. For the calculations, use the fictional Saguaro County Water District, which holds a Colorado River allocation of 300,000 acre-feet per year and used 270,000 acre-feet last year. One acre-foot equals 325,851 gallons.

  1. Explain why building Hoover Dam required an act of Congress rather than a private company or a single state acting alone.
  2. The states negotiated the Colorado River Compact in 1922, before the dam was finished. Explain why the states wanted to divide the water before construction.
  3. What percentage of its 300,000 acre-foot allocation did Saguaro County use last year?
  4. How many acre-feet of its allocation did Saguaro County leave unused?
  5. Convert the unused allocation to gallons, using 1 acre-foot equals 325,851 gallons.
  6. Suppose Hoover Dam's plant is running at 40 percent of its 2,080 MW capacity at a given moment. How many megawatts is it generating?
  7. State one marginal benefit and one marginal cost of building a large dam like Hoover Dam.
  8. Explain how the decision to build Hoover Dam changed the environmental character of the lower Colorado River.
  9. The compact divided the river using fixed annual amounts. Explain the problem that creates for a downstream district like Saguaro County in a drought year when the river carries less water than the compact assumed.
  10. Using marginal reasoning, argue whether a growing region today should build a new large dam or invest first in conservation and reuse, citing at least one benefit and one cost.

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: The Colorado River crosses several state lines, and the dam's cost and scale were far beyond any private company or single state, so federal authority over interstate waters and the federal budget were both needed. Congress authorized it through the Boulder Canyon Project Act.
  2. Answer: Upper-basin states such as Colorado feared that faster-growing lower-basin states, especially California, would use a federally built dam to put most of the river to use first and claim senior rights under prior appropriation. Dividing the water between the basins before construction guaranteed each side a share and reduced the risk of conflict and lawsuits.
  3. Answer: 90 percent. 270,000 divided by 300,000 equals 0.90, or 90 percent.
  4. Answer: 30,000 acre-feet. 300,000 minus 270,000 equals 30,000 acre-feet unused.
  5. Answer: 9,775,530,000 gallons. 30,000 acre-feet times 325,851 gallons per acre-foot equals about 9.78 billion gallons.
  6. Answer: 832 MW. 2,080 MW times 0.40 equals 832 MW.
  7. Answer: A marginal benefit is added firm water storage, flood control, or electricity; a marginal cost is the loss of the free-flowing river reach, its fisheries, and the sediment that once moved downstream. Any reasonable pairing earns credit.
  8. Answer: The dam turned a fast, sediment-carrying stretch of river into a controlled system with a large reservoir behind it, changed downstream flows and temperatures, ended seasonal floods, and made year-round settlement and irrigation possible below the dam.
  9. Answer: Fixed annual shares assume a certain total flow, so in a drought year the river cannot deliver every state's full amount. A downstream district like Saguaro County may receive less than its paper allocation, forcing shortage-sharing rules or cutbacks.
  10. Answer: Responses vary but should weigh at least one benefit (firm new supply, power) against at least one cost (high construction cost, lost habitat, evaporation losses) and reach a defensible conclusion, ideally noting that conservation and reuse often deliver water at a lower marginal cost than a new dam.

Differentiation

Support

Provide the acre-foot conversion worked once with a different number (10,000 acre-feet) before students attempt item 5, and allow a calculator throughout. Give item 1 as a fill-in with two sentence starters naming "interstate" and "cost."

Extension

Ask students to work out, using only the figures on this worksheet, how the 90 percent use rate would change Saguaro County's options if its allocation were cut by one-fifth in a drought, and to write a short paragraph on which uses the district should protect first.

ELL supports

Pre-teach "allocation," "acre-foot," "interstate compact," and "hydropower" with a labeled diagram of a dam holding back a reservoir and releasing water and power downstream. Allow items 1, 2, 8, and 9 to be answered in short phrases or a labeled sketch.