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Hydroelectric Energy: Classroom Activities

Local Stream Drainage


To develop a better understanding of how a river is part of a network of streams feeding a single stream that empties into the ocean.

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Background Information

Rivers form from precipitation that falls onto the land surface. This water flows across the surface, under the influence of gravity, as runoff. This water flows down slopes and is concentrated by topography into creeks or small streams. These streams flow downhill and join together to form larger streams. Larger streams merge into large rivers that flow to the oceans. It is the flow of this water that is harnessed to produce hydroelectricity.

The amount of electricity a hydroelectric power plant can produce is related to the volume of water available to flow through the dam and the rate at which the water flows. The larger the volume of water in the reservoir and the faster it flows through the dam, the more electricity the plant can produce. The best sites for building hydroelectric power plants that use dams to generate electricity plants are fast-moving rivers or streams and areas with consistent rainfall. This ensures that the flow of water is adequate to fill the dam. In addition, a strong flow of water compensates for water that is lost from the reservoir due to evaporation and seepage into the ground.

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Activity Overview

Students use local topographic maps to describe stream drainage in their community.

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Materials and Equipment

topographic map of your community or a nearby community. If one is not available, use the topographic map of Ragged Mountain included in this activity (below).

Ragged Mountain Topo map
Source: The American Geological Institute, EarthComm: Project-Based Space and Earth System Science, 2nd Edition, Armonk, New York: It's About Time, 2012, pg. 387.


  1. Provide students a topographic map of your community. If you do not have a river or stream in your community, use a topographic map from a nearby community. Alternatively, you can use the following map:
    Ragged Mountain Topo map
    Source: The American Geological Institute, EarthComm: Project-Based Space and Earth System Science, 2nd Edition, Armonk, New York: It's About Time, 2012, pg. 387.
  2. Ask students to find a stream on the map that flows into or joins another stream. Have them answer the following:
    1. What do you notice about its size relative to the stream that it flows into?
      Be sure that streams that can be identified appear on the maps. Maps will often show larger versus smaller streams by width or color.
    2. In which compass direction does it flow?
      There are various ways to determine the direction of streamflow from a topographic map: (i) contour lines hook, or "V," upstream as they cross streams; (ii) the elevation decreases downstream, as indicated by the labeling of the contour lines where they cross the stream; (iii) at confluences, the angle between the two streams that meet at the confluence is usually less than 90°. Then use the north arrow in the map legend to determine in which compass direction the stream flows.
    3. Describe how the relative sizes of streams can be used to determine the direction in which a stream flows.
      Smaller streams flow into larger streams.
    4. Contour lines on a topographic map show elevation above sea level. What is the highest elevation along the course of the stream you chose? What is the lowest elevation? Record these values in your log.
      Answers will vary.
    5. How can you use contour lines to determine the direction in which a stream flows?
      Streams flow from higher to lower elevations. Elevation can be determined by looking at the labels on the contour lines.
  3. Provide students a photocopy of the topographic map (or a clear overlay).
  4. Tell students to trace the pattern of streams. Have them devise a way to show small streams, medium streams, and large streams.
  5. Have students count the number of streams of each size and make a data table for their results.
  6. Ask students to describe any relationships and patterns they observe between smaller streams and larger streams.
    Smaller streams flow into larger streams.
  7. Have students identify the best location on their map to build a dam for use in a hydroelectric plant.

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