Reading passage Grade 3 English Language Arts
How Hoover Dam Turns Moving Water Into Electricity
A grade 3 informational reading passage explaining how Hoover Dam uses moving water and spinning turbines to make electricity, with text-evidence questions.
Objectives
- Students will describe how a dam uses moving water to make electricity.
- Students will answer questions about an informational text using evidence from the passage.
Vocabulary
- Dam
- A strong wall built across a river to hold back water. Dams store water for people and farms, help prevent floods, and can make electricity.
- Turbine
- A machine with blades that spin when water rushes past, like a high-tech waterwheel. Spinning turbines turn generators that make electricity.
- Reservoir
- A human-made lake, usually created by a dam, that stores water for later. Reservoirs supply cities and farms and help control floods.
Also: electricity
Teacher overview
Hoover Dam sits on the Colorado River, between the states of Nevada and Arizona, and it does two jobs at once: it holds back a huge lake of water, and it uses that water to make electricity. This passage explains how a dam turns moving water into power that travels to homes and cities far away. It traces electricity from the wall outlet back to the water pushing through machines called turbines.
Passage
A dam is a thick, strong wall. It is built across a river. Hoover Dam is one of the largest dams in the United States. It crosses the Colorado River. The dam holds back so much water that a giant lake formed behind it. The lake is called Lake Mead.
Water behind a dam does not just sit still. Workers built large pipes inside Hoover Dam. Some of the lake's water flows through these pipes. The water rushes downward fast. It pushes against big spinning machines. These machines are called turbines. Each turbine looks like a giant fan. It has wide blades.
The rushing water spins a turbine. The turbine turns a generator. A generator is a machine. It changes spinning motion into electricity. More rushing water pushes the turbine harder. A harder push makes more electricity. Hoover Dam's turbines can make about 2,080 megawatts of electricity. That is enough power for many homes and businesses in three states: Nevada, Arizona, and California. But there have been many dry years. Lake Mead now holds less water than it used to. With less water, the dam has been making less electricity.
The water does not disappear after it spins the turbines. It flows out the bottom of the dam. It keeps moving down the Colorado River. Farms and cities use that water too. Other dams use it further down the river.
Workers built Hoover Dam in the 1930s. Many people needed jobs at that time. Thousands of workers built the dam by hand. They used early machines too. They poured huge amounts of concrete. The wall had to be very strong. It needed to hold back the whole river. Today, people can visit Hoover Dam. They can look down from the road on top and see the power plant far below.
Electricity from Hoover Dam travels a long way. It moves along wires for many miles. Then it reaches a light switch or a refrigerator. The next time a light turns on, think about where the electricity started. It may have started as water rushing past a spinning turbine, deep inside a dam.
Questions
- What two jobs does Hoover Dam do at once?
- What is the name of the lake behind Hoover Dam?
- What happens when rushing water pushes a turbine?
- What does a generator do?
- About how much electricity can Hoover Dam's turbines make?
- Why does more rushing water make more electricity? Use a clue from the passage.
- Why did workers need to pour so much concrete? Use a clue from the passage.
- Why might a big dam make more electricity than a small dam on a small stream? Use the passage to explain your thinking.
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: It holds back a huge lake of water, and it uses that water to make electricity. The first paragraph describes holding back the lake, and the second and third paragraphs describe making electricity.
- Answer: Lake Mead. The passage names the lake that formed behind the dam.
- Answer: The water pushes against the turbine and makes it spin. The passage describes the water rushing through pipes and pushing the turbine's wide blades.
- Answer: A generator changes spinning motion into electricity. The passage states this directly after describing the turbine.
- Answer: About 2,080 megawatts. The passage gives this number when describing how much electricity the turbines can make together. This is the most the turbines can make; the Bureau of Reclamation reports that years of drought and low water in Lake Mead have cut the dam's actual power generation by about 30 percent.
- Answer: Answers will vary, but should connect that more rushing water pushes the turbine harder, and the passage states that a harder push makes more electricity.
- Answer: Answers will vary, but should reason that a dam wall has to be extremely strong to hold back an entire lake of water, which the passage supports by describing the wall as thick and strong.
- Answer: Answers will vary, but should reason that a large river carries much more water than a small stream, and the passage explains that more rushing water pushes the turbines harder, which makes more electricity.
Differentiation
Support
Read the passage aloud in two shorter chunks, pausing after paragraph three to check understanding with a quick question ("What just happened to the water?") before continuing.
Extension
Ask students to think through, using only the passage, how a dam's job of holding back water might also help a town's water supply during a dry summer, and write two sentences explaining their idea.
ELL supports
Pre-teach "dam," "turbine," and "generator" with a simple three-step picture sequence (water flowing, a spinning fan-shaped wheel, a light bulb turning on) before reading. Allow questions 1 through 5 to be answered with short phrases copied from the passage.