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What are reasons for decommissioning (removing and taking out) a dam? Select all that apply.

  • A. Dams have finite lifetimes and fill up with sediment
  • B. Fish passage and reproduction
  • C. Rivers become 'sediment starved' below dams, which leads to erosion
  • D. Dams contribute to coastal erosion


Dams need to be maintained properly or else they can become a safety liability. Over time, dams are subject to sediment buildup, which means that the dam's reservoir will gradually become shallower and the dam will hold less water over time. Sediment can also make the water unsafe for aquatic life, so decommissioning a dam can allow for natural sediment flow and improve conditions for fish. Damming a river can also prevent fish from swimming upstream to mate and spawn, which is an ecological detriment to the river ecosystem. Finally, sediment buildup below dams can lead to erosion and coastal erosion (if the river eventually flows into the ocean), so decommissioning a dam can prevent this from happening.