Dams: last 100-200 years, make floods worse, an environmental disaster, most will soon be past their lifespan

Within the next 20 years, 85% of U.S. dams that cost taxpayers $2 trillion dollars will have outlived their average 50-year lifespan, putting lives, property, the environment, and the climate at risk unless they are repaired and upgraded.  Thousands of aging dams should be repaired or destroyed, at a cost of billions.

Dams only last 100-200 years

  • Dams don’t last because all dams fill up with sediment at a rate of between half a percent and one percent of the dam’s storage capacity.
  • Usually this sediment can’t be removed, even if it can, it’s very expensive — $3 per cubic meter or more

More water can evaporate from a dammed reservoir than they store

  • This is due to evaporation, which consumes 5 to 15% of the fresh water in reservoirs
  • This is why the Rio Grande and Colorado rivers don’t reach the sea anymore
  • It would be better to keep the water in clean aquifers than dammed reservoirs, but farming irrigation is depleting groundwater faster than it can accumulate

Dams are an environmental disaster

  • By restraining sediment, dams accelerate erosion below
  • Precious topsoil crumbles into rivers and either gets trapped by dams or flows out to sea
  • Dams pollute and alter the chemistry and biology of rivers. They warm the water and lower the oxygen levels which favors invasive species and algae blooms while blocking and killing native species both down and upstream
  • Rivers have more endangered species than any other ecosystem, with many important species, such as pacific salmon and southern freshwater mussels facing extinction almost entirely because of dams
  • Dams also pollute the air – only 2% generate clean power, the rest worsen climate change because of methane releases – up to 4% of human total warming from the 52,000 large dams (over 50 feet high) and 25% of human-caused methane emissions, and even more than that if the smaller dams were taken into account

Dams can make floods worse

  • Dams initially designed for flood control may actually make floods more destructive because people have moved into downstream floodplains
  • Upstream watersheds can no longer absorb and control extreme storms
  • Mild rainstorms in October 2005 & may 2006 caused 408 over-toppings, breaches, and damaged dams in just 3 states alone
  • Only half of dams even have emergency action plans

Dams fail eventually

  • As they age, they crack, rot, leak, and eventually collapse
  • There’s very little money to maintain public or private dams.
  • The American Society of Civil Engineers gave U.S. dams and water infrastructure a grade of D
  • It would cost up to $36.2 billion to fix NON-federal dams
  • Cash-strapped states are doing almost nothing – dozens of states have only one full-time employee per 500 to 1,200 dams to check on their safety
  • Owners of old dams litigate and lobby against safety rules, or walk away – 11% of dams are abandoned now

There are

  • 2.5 million dams in the United States
  • 79,000 of these are so large they need to be monitored
  • Worldwide there are 800,000 substantial dams


  • The world’s 8th largest economy
  • generates 13% of U.S. wealth.
  • Needs another $6 billion in dams to store water because high temperatures, low rainfall, and a growing population have created a water crisis
  • 1,253 dams are risky enough to be regulated
  • 50 times that many unregistered small dams
  • $200 million dollars is the cost of removing 4 dams on the Klamath rive

Large Dam history in North America:

  • 13% for flood control
  • 11% for irrigation
  • 10% for water supply
  • 11% for hydropower
  • 24% for some other single purpose such as recreation or navigation
  • 30% for a mix of these purposes.

Today, the primary reason is drinking water storage and, to a far lesser extent, hydropower and irrigation.


James G. Workman. 9 Oct 2007. How to Fix Our Dam Problems. Thousands of aging dams should be repaired or destroyed, at a cost of billions. A cap-and-trade policy could speed the process and help pay the bills. Issues in Science and Technology. National Academies of Sciences.

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