People and Planet - Don't Dam It!

For over a hundred years in the Pacific Northwest, the Elwha freshwater ecosystem was being disturbed by the Elwha dam. Salmon that typically spawn upstream were not able to do so.

Watch this 4:39 minute video clip titled “Restoring the Elwha”

Analysis:  

  1. How were the salmon being affected by the dam?
  2. By simply removing the dam, will the ecosystem improve? What will change?
  3. Hydoelectric power, a renewable energy source with no pollution, is an excellent alternative to fossil fuels. Removing the dam means removing a good source of power. How was the dam threatening the survival of salmon? Go to http://www.nmfs.noaa.gov/pr/species/fish/salmon.htm for more information about the impact on salmon.   Are there other threats to the survival of the salmon in the Pacific Northwest?
  4. How will the shape of the river change as the dam is removed? How will incorporating log jams improve areas for salmon to spawn? Build a model or use a stream table to simulate the Elwha river with the dam and without the dam. Add log jams. Observe the velocity of stream flow and locations of sediment deposition.

Answers - Highlight the box below to see the answers.

  1. Salmon could not move upstream to spawn
  2. The ecosystem will improve for salmon.  The river will not be blocked.   Over 90% of water shed area will be opened up to salmon.   Right now they can use only 5 miles of river.  When the dam is removed, there will be 70 miles of river available.
  3. The dam is threatening the survival of salmon because it blocks them from spawning grounds.  Other threats to survival of salmon in the Pacific Northwest are fishing and the introduction of non-native species.
  4. The riverbed now is dominated by large rocks.  There are millions of cubic meters of sediment behind the dams that will be washed downstream with the dams are removed.  Log jams will trap the sand, creating sand bars that are essential for salmon spawning. 

Source: Open Education Group Textbooks - Earth Science