Lesson A River Ran Through It

Learning Objectives

After this lesson, students should be able to:

• Describe the energy transformations that occur in a hydroelectric power plant.
• Describe some of the environmental effects of hydropower.
• Identify how engineers are involved in designing and constructing hydropower systems.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

International Technology and Engineering Educators Association - Technology

State Standards

Worksheets and Attachments

Introduction/Motivation

Do you think water is a source of energy? Let's think about it. Energy is when something can do work. Can you think of an example in which water does work? How about a waterwheel? People have been using water for power for a long time. More than 2,000 years ago, farmers used waterwheels to grind wheat into flour. Waterwheels spin around as a stream of water hits their blades. The gears of the wheel ground the wheat into flour. Water is definitely a source of energy, and not only that, it is a source of renewable energy!

Modern waterwheels are found in hydroelectric power plants. What do you think hydroelectric means? Let's break it down. Hydro means water and electric is electricity; so, hydroelectric means using water to create electricity. Did you know water could help us produce electricity to run our televisions, refrigerators, and homes? Well, it can! Worldwide, hydroelectric power plants produce about 19% of the world's electricity and supply more than 1 billion people with power. Utilities in the U.S. operate about 2,400 hydroelectric power plants, making hydropower the largest renewable energy source in the country. Hydroelectric power plants take in water energy and use simple steps to change that energy into electricity. Hydroelectric power plants use some basic technology: water flowing through a dam turns a turbine, which turns an electric generator. The kinetic energy of the moving water turns the blades of a turbine, which rotates magnets inside coils of wire, producing electricity.

How do we get the water to flow through a waterwheel? Fast flowing rivers are one way, but some waterwheels run off the water stored up by a dam. In the U.S., engineers have been involved with the construction of about 80,000 dams. On average, one dam has been completed each day since the signing of the Declaration of Independence! If the water needed to run the waterwheel is stored up on one side of the wheel with a dam, then it can be made to flow through the waterwheel at a particular rate. Engineers help create dams so water can flow through a hydroelectric plant at a certain speed to produce the most electricity. Meanwhile, the reservoirs or lakes created by dams are used for boating and fishing, and often the rivers beyond the dams provide opportunities for whitewater rafting and kayaking. Students can create their own waterwheels in the associated activity Waterwheel Work: Energy Transformations and Rotational Rates to investigate the transformations of energy involved in turning the blades of a hydro-turbine into work, and experiment with how weight affects the rotational rate of the waterwheel.

The rate of construction of dams has slowed in recent years. In fact, these days, civil, structural and environmental engineers are more likely to be redesigning dams or taking them apart. Sometimes dams kill fish that are trying to migrate. For instance, in the Columbia River, salmon must swim upstream to their spawning grounds to reproduce, but the series of dams blocks their way. Different approaches to fixing this problem have been used, including the construction of "fish ladders" that help the salmon "step up" the dam to the spawning grounds upstream. Dams also change the local habitat by storing water where it may not have been stored before. Engineers often redesign existing dams to be more fish-friendly. In a dozen cases, dams have been removed entirely to restore wildlife habitats.

Sometimes engineers help to evaluate whether a dam is worth keeping. In other cases, engineers plan the best way to remove a dam. After a dam is removed, environmental engineers monitor sand and debris as it flows downstream, and help to restore the wildlife habitat. After dams are removed, much of the original wildlife returns to the area. Also, logs are salvaged from the bottom of the dam for use to build furniture, musical instruments and other products.

Water is a source of renewable energy and has many benefits. Hydroelectric power does not produce much pollution, and dams can be used for flood control as well as providing the stored (potential) energy for hydroelectric plants (Refer to the associated activity Falling Water for students to explore how potential energy is converted to kinetic to power these devices). Water can also be used to irrigate farms and for recreation. On the other hand, dams can destroy animal habitats and be expensive to build properly. If a dam breaks, flooding can destroy the entire surrounding area. Engineers consider all these advantages and disadvantages when designing and developing technologies that use water energy. Following the lesson, students can engage their creative thinking in the literacy based associated activity A Case of Innovation: Technical Writing about River Current Power where they write about emerging technology and its accompanying challenges to engineers!

Lesson Background and Concepts for Teachers

See the attached reading, Hydropower — Energy from Moving Water, for an even more in-depth look at hydropower. (This article is not an appropriate reading material level for fourth-grade students.)

How is electricity generated in a hydropower plant?

Dam placement takes into consideration the natural water cycle. For most hydropower plants, dams are built on rivers at locations at which rain and snowmelt provide a plentiful and reliable supply of water flow. The geology of the area around a dam is also important for engineers to understand; if water seeps around the sides of the dam or underneath it, the dam could fail catastrophically.

The basic components of a hydropower plant are a dam, intake, turbine, generator, transformer, power lines and outflow. Most hydropower plants rely on a dam that holds back water, creating a large reservoir. Dams are some of the largest man-made structures on Earth. Large dams are vital for large-scale hydropower, but dams of all sizes are also used for flood control, water storage and irrigation throughout the world. When gates on the dam open, gravity pulls the intake water through the penstock, a pipeline that leads to the turbine. The water builds pressure as it flows through this pipe. Then the water strikes and turns the large blades of a turbine, which is attached to a generator above it by way of a shaft. As the turbine blades turn, so do a series of magnets inside a generator. Giant magnets rotate past copper coils, producing alternating current (AC). A transformer inside the powerhouse takes the AC and converts it to higher-voltage current that is carried on high-tension power lines. The used water is carried through pipelines, called tailraces, and this outflow re-enters the river downstream.

The water in the reservoir is considered stored energy. When the gates open, the water flowing through the penstock has kinetic energy because it is in motion. Several factors determine the amount of electricity generated; two of those factors are the volume of water flow and the amount of hydraulic head. The head refers to the distance between the water surface and the turbines. As the head and flow increase, so does the electricity generated. The head is usually dependent upon the amount of water in the reservoir.

A few hydropower plants are of a special design called pumped-storage plants; they are used to store energy until it is needed. In our homes, schools and workplaces, we tend to use much more electricity during the day than late at night. Some power plants, such as coal-burning generators, work more efficiently close to their peak capacity, so power from these plants is sent to a pumped-storage plant. Using a reversible turbine, the pumped-storage plant pumps water up from a lower reservoir into a high reservoir. During peak demand hours, water flows back down through the turbines and generates electricity, just like a conventional hydropower plant.

Most people are familiar with large-scale hydropower, but the energy of moving water can be captured on a much smaller scale, called micro-hydropower. In micro-hydropower small to mid-size generators are placed in rivers and streams to provide electricity for a few buildings or other smaller applications. See the literacy activity, A Case of Innovation, for information on a technology that generates electrical power from turbines placed in water currents.

How Do Dams Affect Ecosystems?

While dams are important for flood control and electric power generation, they have a significant effect on fisheries and river ecosystems. Dams can disrupt migratory fish patterns and spawning habits, especially for species like salmon. This can have devastating effects on both the fish population and people whose livelihoods depend on these fish.

Early engineering efforts to help salmon focused on designing systems that allowed the fish to bypass either the turbines or the dam itself. The most common method of bypassing the turbines is by releasing water over the dam to provide an alternate path for the passing fish. In most dams, the turbine intake is fitted with a screen that acts to guide the fish away from the turbine and towards the open spill gates. However, spilling water is less than ideal because the long fall is often traumatic for the fish. Also, the tumbling water increases dissolved gas concentrations that lead to a condition called gas bubble disease. At some dams, the government implemented transport programs in which young ocean-bound salmon are collected and barged or trucked downstream to avoid the dams. Scientists raised concerns over the trucking and barging of young salmon downstream because adult salmon that were not allowed to swim downstream as juveniles may have difficulty finding their way when they return to spawn.

The less-than-spectacular results of these earlier salmon conservation efforts led engineers to design a more fish-friendly dam. Because most salmon deaths occur as the fish pass through the turbines, engineers focused their efforts on designing new turbines. To get a better understanding of the forces felt by fish traveling through the blades, the Army Corps of Engineers used sensor fish — fish-sized plastic tubes containing instruments that measured the conditions fish would experience. They released the sensor fish into the turbine intake and collected them on the other side of the dam. They downloaded the sensor data into a computer and used it to gain insights into the cause of death for salmon passing through the turbine. With this research, engineers developed more efficient and safe turbine designs.

The most significant change in turbine design was the elimination of gaps between the turbine blades and the turbine hub, and between the outer edge of the blade and the wall of the turbine housing. Those gaps had provided places for salmon to be trapped or cut by the spinning blade. The elimination of the gaps also resulted in a smooth surface for water flow and greatly reduced turbulence. Smoother surfaces on all turbine parts protect against injuries resulting from fish colliding with abrasive turbine surfaces, while new lubricant formulations allow for smooth turbine operation without contaminating passing river water. The new designs allow for survival rates as high as 97%.

Associated Activities

• Falling Water - Students drop water from different heights to demonstrate the conversion of water's potential energy to kinetic energy. They see how varying the height affects the splash size. They take measurements, calculate averages and graph results. In seeing how falling water can be used to do work, they also learn how this energy transformation figures into the engineering design and construction of hydroelectric power plants, dams and reservoirs.

  Watch this activity on YouTube

• Waterwheel Work: Energy Transformations and Rotational Rates - Students explore kinetic energy by creating their own experimental waterwheel from a two-liter plastic bottle. They investigate the transformations of energy involved in turning the blades of a hydro-turbine into work, and experiment with how weight affects the rotational rate of the waterwheel.

  Watch this activity on YouTube

• A Case of Innovation: Technical Writing about River Current Power - In this literacy activity, students write a white paper about an alternative hydro-electrical power generation technology, and gain an awareness of the challenge and promise of technological innovation that engineers help to make possible.

Lesson Closure

Today, we have learned about the energy from water. Our word of the day is hydroelectric. What does that mean? (Answer: Using running water to create electricity.) How can the energy of moving water be used to do work? (Answer: By building structures that are moved by the water and cause something else to move, such as waterwheels and hydroelectric generators.) How does energy move through a hydroelectric power system? (Answer: The kinetic energy of the moving water turns the blades of a turbine, which rotates magnets inside coils of wire, producing electricity.) What are some advantages and disadvantages that engineers consider when working with hydroelectricity? (Answer: Advantages include: Does not produce a lot of pollution, can provide the stored [potential] energy for hydroelectric plants, can be used for irrigation and recreation. Disadvantages include: Destroying animal habitats, a potential for flooding, and expensive to build properly.)

Vocabulary/Definitions

dam: A barrier constructed across a waterway to control the flow or raise the level of water.

energy: The ability to do work.

generator: A device that transforms mechanical energy into electrical energy.

hydraulic head: The difference in depth of a liquid at two given points; the pressure of the liquid at the lower point expressed in terms of this difference.

hydroelectric power plant: A power plant that uses water turbines to generate electricity.

hydroelectricity: Electricity produced by the energy of running water.

kinetic energy: The energy of motion. For example, a spinning top, a falling object and a rolling ball all have kinetic energy. The motion, if resisted by a force, does work. Wind and water both have kinetic energy.

penstock: A pipe or conduit used to carry water to a waterwheel or turbine.

potential energy: Potential energy is the energy stored by an object as a result of its position. For example, a roller coaster at the top of a hill, or water being held behind a dam.

renewable energy: Energy made from sources that can be regenerated. Sources include solar, wind, geothermal, biomass, ocean and hydro (water).

reservoir: A natural or artificial pond or lake used for the storage and regulation of water.

rotor: The rotating part of an electrical or mechanical device.

tailrace: A pipeline below a waterwheel or dam through which the spent water flows.

turbine: A machine in which the kinetic energy of a moving fluid is converted into mechanical energy by causing a series of buckets, paddles or blades on a rotor to rotate.

waterwheel: A wheel propelled by falling or running water and used to power machinery.

Assessment

Pre-Lesson Assessment

Discussion: Ask the students if they have ever seen a beaver dam at the zoo or on a hike. Ask them to suggest reasons why the beaver builds these dams (Possible answers: To hold back water, create a home, etc). Engage them in discussing how the dams must be strong to hold back all that water.

Post-Introduction Assessment

Brainstorming: As a class, have students engage in open discussion to come up with what they think are the positives and negatives of creating dams. Remind them that in brainstorming, no idea or suggestion is "silly." All ideas should be respectfully heard. Take an uncritical position, encourage wild ideas and discourage criticism of ideas. Have students raise their hands to respond. Write their ideas on the board. Compare their ideas with the advantages and disadvantages provided in the table in the Lesson Background & Concepts for Teachers section.

Lesson Summary Assessment

For or Against: In 2019, half (50%) of the total U.S. hydroelectric capacity for electricity generation was concentrated in three states (Washington, California and New York) with approximately 24% in Washington, the location of the nation's largest hydroelectric facility—the Grand Coulee Dam. Have the students discuss why this is. Have them determine if there is a place in your city or state that might be good for a hydroelectric plant. Would they want one built nearby to them? Why or why not? What factors would engineers consider if building a hydroelectric plant in your area (wildlife, river flow, etc.)? If time, hold a debate about this topic, with half the class debating for the building of the plant and half debating against the plant.

Lesson Extension Activities

Explore the Renewable Energy Living Lab, which provides real-time U.S. Geological Survey stream flow data to educate students about what it takes to maintain our precious water supply. See: http://www.teachengineering.org/livinglabs/

References

Copyright

Contributors

Supporting Program

Acknowledgements

The contents of this digital library curriculum were developed under grants from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation (GK-12 grant no. DGE 0338326). However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.