This video shows a different side of dams, what many think of as clean hydroelectric power. Many points are made about the negative effects dams have on their surrounding environment. This is important given that only 3% of U.S. dams create hydroelectric power. From and Earth science perspective, an important impact of dams is that they stop the flow of natural sediment, causing it to build up in the reservoir behind the dam.

Why Watch This Video

  1. Have you ever wondered if there are any negative side-effects to generating power through hydroelectric dams?
  2. Would you like to know how geology relates to dams?
  3. Have you ever wondered how long dams can last?

Key Terms

  1. Hydroelectric Power – Electrical power that is generated through the force of flowing water.
  2. Sedimentary Rock – Rock formed through the deposition and solidification of sediment, usually moved via water.
  3. Sediment – Particles formed from the weathering and erosion of rocks

Loose Ends

  1. How is sediment captured in dams, and how much? Sediment is captured in the reservoirs next to dams and can trap 90-100 percent of the sediments carried by a river.
  1. What does this mean for dams that so much sediment is captured? The sediment that should be making it past the dams is supposed to help build up marshes and wetland. This isn’t working, though, so lands are more prone to rising seas. This means we have to search for new ways to combat the rising seas. (Robbins, 2017)
  1. How can we stop dams from trapping sediment? For further reading, this paper by Kondolf et al. (2014) explains ways people are combatting the impact of dams on sediment transport.

Self-Test Questions


Mathias Kondolf, et al. (2014) “Sustainable management in reservoirs and regulated rivers: Experiences from five continents”. Earth’s Future

Robbins, Jim. “Why the World’s Rivers Are Losing Sediment and Why It Matters”. YaleEnvironment360. June 2017.

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