How Do Spillways Work?

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We typically build a dam to hold water back and store it for use in water supply, irrigation, hydropower, or flood control. But occasionally we must let some water go. Whether or not we need it downstream or the impounded water behind the dam is simply too full to store any more, almost every dam needs a spillway to securely discharge water. The spillway is a crucial part of any dam and frequently the most complex component. So how does it work?

Writing/Editing/Production: Grady Hillhouse
Thumbnail Photo: Doug Letterman (CC BY 2.0)


  1. Your trending right now congrats. Also, congrats on making 1M subscribers

  2. One of those videos of the dam with the hydraulic jump was actually gavins point dam. That was during a major flood in 2011 and it actually almost destroyed the dam. They were letting 80,000 cubic feet of water through per second and that was the most they had ever let through.

  3. Very Interesting – good video

  4. Grady, thanks for another quality video! Continuing with the water theme, you might consider a video on how canals can control water. Here in Florida, there are irrigation canals and locks everywhere, and especially around Lake Okeechobee. I think some of it has to do with draining natural swamp land so it’s prime for urban sprawl. I would love to know more about how those work.

  5. What happens if you get pulled into one?

  6. This reminds of that video where that girl screams while watching a duck go down one of those hole thingys

  7. Have you ever read David McCullough’s book on the Jonestown flood? It’s a pretty interesting and terrifying example of bad dam designs without a spillway.

  8. Some spillways make me really uncomfortable to look at closely…

  9. Black holes

  10. What are those tower those at the hover dam in the picture that was showed? Please and thank you.

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