Lesson plan Grade 11 Science
Wystan Gorge and the New Deal Dams: Hydropower Trade-Offs
A grade 11 science and history lesson on why the New Deal built giant dams, how hydropower works, and the cost-benefit trade-offs of a fictional dam proposal.
Objectives
- Students will explain how resource needs and federal policy drove large dam construction in the New Deal era.
- Students will calculate hydropower output using nameplate capacity and capacity factor and weigh a dam's trade-offs.
Vocabulary
- 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.
- 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: nameplate capacity, capacity factor, multipurpose dam
Teacher overview
Large federal dams reshaped the American West and South, and several of the best known, including Grand Coulee, Bonneville, Fort Peck, and the first Tennessee Valley Authority dams, were begun in the 1930s as part of the New Deal response to the Great Depression. This lesson connects the science of hydropower to that history, then asks students to evaluate a fictional modern proposal, the Wystan Gorge Dam, the way an agency board would. Hoover Dam's power plant has a capacity of about 2,080 megawatts, a useful anchor for the energy math. A common misconception the lesson corrects is that a dam's nameplate capacity equals its actual yearly output; students learn that real generation is the nameplate capacity scaled down by the capacity factor.
Procedure
Hook (5 min): Project a 1930s construction-era image or description of a large dam and ask: during the worst years of the Great Depression, why would the federal government spend enormous sums building dams in remote canyons? Collect predictions about jobs, power, and water without confirming them yet.
Direct instruction, the history (15 min): Explain that the federal government pursued large multipurpose dams through agencies such as the Bureau of Reclamation and, in the Southeast, the Tennessee Valley Authority. Hoover Dam, begun in 1931 and completed in 1936 on the Colorado River, is the signature example. These projects served several goals at once: flood control, irrigation water for agriculture, electric power, river navigation, and direct employment during the Depression. Tie this to government: Congress funded the projects, federal agencies built and still operate them, and the electricity was sold to repay construction costs. This is why access to a river became a driver of where people lived, farmed, and worked.
Direct instruction, how hydropower works (10 min): Water held behind a dam has gravitational potential energy; as it falls through turbines, that energy becomes electricity. Define nameplate capacity, the maximum power a plant can produce, and capacity factor, the fraction of that maximum the plant actually averages over a year. Worked anchor: suppose Hoover Dam ran at its full 2,080 megawatt capacity for one hour; it would generate 2,080 megawatt-hours, which is 2,080,000 kilowatt-hours. Stress that real output is lower because flows vary; the Bureau of Reclamation reports that years of drought and low Lake Mead levels have cut Hoover Dam's power generation by about 30 percent.
Guided practice and discussion (10 min): Shift to today's trade-offs. Dams block fish migration, trap sediment that would rebuild downstream habitat, and flood land upstream, which is why some communities now debate dam removal. List benefits and costs in two columns on the board, and frame the choice as a cost-benefit comparison against alternatives such as solar, wind, or conservation.
Independent practice (12 min): Students complete the Student Handout, computing the output of the proposed Wystan Gorge Dam and comparing it to Hoover Dam.
Closure and exit ticket (3 min): Students answer on a card: "Name one benefit and one cost a board should weigh before approving a new hydropower dam." Confirm that at least 80 percent list a genuine benefit and a genuine cost before dismissal.
Student Handout
Use the fictional Wystan Gorge Dam for every question.
- The Wystan Gorge Dam has a nameplate capacity of 200 megawatts. If it runs at full capacity for 24 hours, how many megawatt-hours does it produce that day?
- Convert your item 1 answer to kilowatt-hours.
- Real dams rarely run at full output. If Wystan Gorge actually averages a capacity factor of 0.35, how many megawatt-hours does it produce in a day?
- Hoover Dam's capacity is about 2,080 megawatts. About how many times larger is Hoover Dam's capacity than Wystan Gorge's 200 megawatts? Round to the nearest whole number.
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: 4,800 MWh.
Energy = power x time = 200 megawatts x 24 hours = 4,800 megawatt-hours. - Answer: 4,800,000 kWh.
4,800 megawatt-hours x 1,000 kilowatt-hours per megawatt-hour = 4,800,000 kilowatt-hours. - Answer: 1,680 MWh.
Actual output = nameplate output x capacity factor = 4,800 megawatt-hours x 0.35 = 1,680 megawatt-hours in a day. - Answer: 10 times.
2,080 megawatts / 200 megawatts = 10.4, which rounds to about 10 times larger.
Differentiation
Support
Provide the energy formula, energy equals power times time, already written, and give item 1 with the multiplication set up (200 x 24). Offer a two-column benefit-and-cost chart with two examples already filled in for the discussion.
Extension
Have students estimate how many average homes the actual Wystan Gorge daily output from item 3 could supply if each home uses about 30 kilowatt-hours per day, and write a short paragraph on whether that output alone justifies the dam's ecological costs.
ELL supports
Pre-teach nameplate capacity, capacity factor, turbine, and reservoir with a labeled cross-section of a dam showing water falling through a turbine. Provide sentence frames for the exit ticket: "One benefit of a dam is ___. One cost of a dam is ___."