How Do Spillways Work?

How Do Spillways Work?

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We normally build a dam to hold water back and store it for use in water supply, irrigation, hydropower, or flood control. But sometimes we have to let some water go. Whether we need it downstream or the impounded water behind the dam is simply too full to store any more, nearly every dam needs a spillway to safely discharge water. The spillway is a critical part of any dam and often the most complex component. So how does it work?


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

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44 Responses

  1. Qn0Bi6 says:

    Congrats to 1 million subs!!!

  2. YouTube g says:

    *_Congrats for 1M subs?_*

  3. Jake Turner FPV says:

    1 million, epic! Great video as per usual. Love from Australia <3

  4. Sam F says:

    Congratulations on getting to a million subscribers Practical Engineering!

  5. Randy Seed says:

    This is one of the best educational channels on YouTube. Great script, fantastic visuals, and excellent topics.

    Congrats on the 1 million subs! Well deserved.

  6. Rob Townsend says:

    Congratulations on 1 million subscribers. Love your videos. So educational and informative. Keep it up.

  7. Daniel Wiegert says:

    One thing I think you should include, “Then things go wrong” show example on failed structures and lessons learned by them.

    • InfernosReaper says:

      +farLander Ish. It was only built to withstand flooding of about half as much as what it ended up getting.
      I’m genuinely surprised it took pretty much 40 years for something bad to occur.

      Any one of a half dozen things could’ve been fixed and prevented Fukushima and they knew since day 1 it wasn’t up to safety guidelines.

    • Nick Nevco says:

      Feel the poster wanted to see a video about how they learned about the techniques that are present today, a history of development.

    • Bryan Dunn says:

      +ConRon The Spencer Dam on the Niobrara Broke and crumbled entirely within the past few months and Nebraska has not stopped getting hammered with rain since either. The snow melt coupled with days of heavy rainfall caused extremely fast rises in water level and in amounts never seen before caused the ancient and outdated dam to crumble to nothing. People don’t realize the extent of the damage here, There are thousands upon thousands of acres of farmland that wont be able to be farmed for YEARS. Thats grazing land for cattle, corn for ethanol, feedstock, and food, soybeans for damn near every industry…. you name it. And the near $20B disaster relief bill just got shut down again in the house of reps. The situation is far worse than most of the country realizes.

    • SuperAWaC says:

      things going wrong has been done to death a million times though, you can go watch hundreds of videos about that. i want to see things that aren’t going wrong for once.

    • Michael Cook says:

      +Mandorle21 unimaginable*

  8. ElectricGears says:

    One important advantage to note about controlled spillways is that they allow the dam to lower the level of the reservoir significantly below normal in anticipation of a large inflow. This allows them to absorb far more volume while maintaining the same outflow during the storm (or less to assist downstream dams that are picking up extra flow from the watershed between them).

    • D Coetzee says:

      Does this imply that a single dam could benefit from having both controlled and uncontrolled spillways at the same time? One to lower the level in advance and the other to catch excess volume that the controlled spillway doesn’t have the capacity to release?

    • Robbie James says:

      I think it’s more cost effective to only build one big one of each, although an uncontrolled spillway might be used as a backup for the backup spillway!

    • Brainstrain91 says:

      +D Coetzee The dam shown at 2:40 appears to be set up like this, yep. Most principal spillways are controlled, I imagine.

    • pmailkeey says:

      +D Coetzee The significant thing about an uncontrolled spillway is that there’s nothing to go wrong – no gates to get stuck shut etc. Another thing they can’t do is suddenly let water flow – by having a gate fail by being forced open if the mech breaks. Having both types is the best option.

  9. Josef says:

    came here for the plugol’, but you didn’t show enough 🙁

  10. middleman says:

    Congrats on the 1m, Grady. Fully deserved. All the best

  11. CB says:

    Morning glory spillways are so scary. Just the sheer volume of water going into those monstruous things makes me cringe

  12. ApexPredator_ says:

    5:09 “major DAMage”

    that got me lol! Nice one.

  13. Aye Lmao says:

    i suck at physics but i love these kind of videos

  14. Chamara Naveen says:

    Congrats on 1M subs.. keep making these quality stuff ??

  15. Mauno Muikkunen ja Mäyrä-Kaarlo says:

    Have you made a video about diffrent kind of fish ladders, elevators and steps? Lots of dams yes, but it affects how fish reach their breeding grounds. There is a lot of various solutions to the problem, would like to see your take on that. I would watch 🙂

    • Painmaker says:

      This would be a pretty good subject for a new video, yeah.

    • Zuaquim1 says:

      Yes, that is an interesting idea! And different structures have to be used in different situations. Tropical fish, for instance, behave differently in ladders than temperate climate ones.

  16. Pfsif says:

    ¯_(ツ)_/¯ Dam, one million subs!

  17. James Janisko says:

    I really love it when you cover new material that incorporates previous videos. That building of knowledge makes me very happy. When you talked about weirs and I didn’t have to go back to those videos because I’ve already watched them and knew what you were talking about…made me feel a bit educated on hydraulics. Can’t thank you enough for putting out such quality content.

  18. SomaliSavage0 says:

    I’m the subscriber 1 million hahaha as an engineering student I’m glad I found this

  19. ncooty says:

    Would’ve been interesting to hear you talk about some of the ecological considerations–e.g., minimum ecological flows, fish ladders, etc.

  20. David Conte says:

    All of this to avoid dam-age, Brilliant !

    Eh, I mean… Skillshare

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