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u/HDauthentic 17d ago
PSI on that has to be tens of thousands, right?
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u/CaptainLegot 17d ago
This is a top down view of a radial spillgate, typically the to edge is out of the water, so it's only tens of feet of head hydraulic head. The pressure is quite low, it's just that "low" pressures don't get nearly the respect they deserve.
Based on the sediment this is probably a full depth gate that goes to the bottom of a channel, rather than a spillway at the top of a dam.
Like 50ft of head is 20ish psi at the bottom, but on a 50ft tall by 20ft wide spillgate you have 144000 square inches, which would work out to be over 700 tons of force acting on the gate.
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u/HDauthentic 17d ago
Thanks for the detailed answer, I wasn’t thinking about it in terms of total surface area
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u/g3nerallycurious 17d ago
I recently watched a video on YouTube about how natural sediment build up like this that is principally unavoidable with dams is bad for downstream life and will eventually fill up the reservoir, rendering it useless. You seem knowledgeable about dams - what are your thoughts on the youtuber’s claims?
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u/CaptainLegot 17d ago
That's Grady from practical engineering! He's an excellent educator and is 100% correct. The rivers are stronger than anything we could ever build, and they will always (when given enough time) find the path of least resistance. That path is always going to be either breaching the dam, or finding a new route. The sediment buildup is part of the process of finding a new route (which would occur whether the obstruction was natural or man-made).
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u/g3nerallycurious 16d ago
Yep, that’s the one!
Has sediment buildup like this ever rendered a reservoir obsolete? If so, how many? What would be the average lifespan of a dam if sediment buildup was the only issue considered? What kind of time scale are we talking about? How often is sediment buildup causing an issue with dam operations, and how often is the sediment displaced in some way or another?
I found it quite annoying that he basically said “here’s a fundamentally massive problem to human existence” and then said barely anything about how to avoid it or how urgent of an issue this is.
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u/CaptainLegot 16d ago edited 16d ago
I don't think there's a way to figure out the average lifespan just because it depends so much on how much sediment is picked up by the river and how much volume your reservoir has.
Some places do just dredge their reservoirs, others have low level gates that can be opened that let a little bit pass through. We have one where sediment has reduced the water capacity by like 30%, so the solution there is to build a taller dam to sink the current one and the one upstream under a super lake, basically turning the upstream dam into a massive slit trap.
This is mostly a problem because people in the past didn't know all of what they were doing, and site selection didn't consider upstream conditions to be particularly important. I think that was time goes on we'll see more dams removed permanently(which is excellent for the environment) as well as have several re-engineered to better manage the issue.
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u/g3nerallycurious 16d ago
Ok. So lack of freshwater isn’t going to be creating droughts that will kill people anytime soon - at least not due to sedimentation of dams?
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u/CaptainLegot 16d ago
Certainly not at every dam all at once. This is a relatively slow moving problem. But like with most slow moving problems the solutions are also slow moving, so it's not something we can really afford to wait to address.
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u/Majestic_Finding1182 15d ago
Many dams and basins need to be cleaned out regularly or after major storms (especially post fire). The material is removed and hauled to another location.
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u/UhOhAllWillyNilly 17d ago
ALL DAMS ARE TEMPORARY. They silt up/fill with sediment. Moving water can carry sediment along as long as it flows but as soon as the water backs up behind a dam all that silt/sediment settles to the bottom and fills up the dam with dirt.
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u/SlightComplaint 16d ago
Typically this takes like 200 years right ?
Without intervention?1
u/UhOhAllWillyNilly 16d ago
That all depends on the sediment load of the river. Muddy rivers silt up dams much faster than clear-running streams.
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u/brakenotincluded 17d ago
No, far from that, it's roughly 45psi/100' of water height so you looking at 100psi at most ?
Water is heavy and height gives it a lot of potential energy, that's all you need.
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u/SmackinGoobers 15d ago
If it was tens of thousands the water would be moving at mach 3
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u/brakenotincluded 15d ago
The whole dam would be moving XD
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u/SmackinGoobers 15d ago
Got me thinking about waterjets so had to look up the pressure used. 50,000-60,000
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u/brakenotincluded 15d ago
High pressure system are nuts, there's a lot of energy in there. I used to work in process control, we had these very nice Sno-trik (swagelok) tubing with 1/4'' OD that had 0.95 wall thickness, they had to be hardened for pressures around 60,000 if I remember correctly. The face seals where precision made and had to be treated like silk because even the tiniest scratch would be a failure.
As seen here, psi don't look like much but it's misleading, anything over 100 psi needs to be treated respectfully, even more so if it's a gas.
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u/DirtyBalm 17d ago
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u/Billy_Chill_305 17d ago
Watching this on the toilet as I haven’t pooped in a few days, it’s inspiring
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u/reaper_ya_creepers 17d ago
Would that erode the concrete?
Having that much soil and what looks like rocks must do some damage surely
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u/CaptainLegot 17d ago
It would, but if you do it infrequently it doesn't really matter. Also you can repair concrete.
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u/myaccountgotbanmed 17d ago edited 17d ago
Me after a hard night on the Guinness...
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u/countryboy351m 16d ago
Decades? Not sure what country this is in, I manage a dam in the North East US and the standards here require monthly exercising of both primary and secondary auxiliary valves. Both of my valves are 40” diameter, even at that size the hydraulic power is just incredible.
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u/camo_junkie0611 17d ago
Took me a minute to realize what I was looking at in the beginning of the clip…a huge wall of sludge. Pretty gnarly
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u/Future_Initial_3972 17d ago
It would be interesting to see the sediment load downstream once everything equalizes. Would you see a high water line or not?
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u/Charlie_Linson 17d ago
What’s the reason for doing this after so long, or for not doing it for so long?
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u/balstien97 17d ago
I was scrolling while taking a poop and saw this. I feel this video was meant for me.
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u/greentomatoegarden 16d ago
I know in some places sediment is regulated as a pollutant, I wonder if something like this would put enough sediment in the water to make a noticeable difference.
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u/drzook555 16d ago
This is why man made structure fail, all equipment should be tested on a regular scheduled basis and not decades apart
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u/Ok_Mountain3607 16d ago
Don't know why but I feel like they should have panned all that dirt for gold.
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u/DarkFather24601 17d ago
Pretty much the same thing after heavy drinking and Taco Bell late night food aftermath.
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u/TopExperience3424 17d ago
Believe it or not this is what your body will do if you start working out and drinking plenty of water 💩💩💩💩💩🌊🌊🌊🌊🌊🌊. It's very healthy to cleanse yourself every once in a while.
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u/Balshazzar 17d ago
I was unclear which way was down and was briefly very worried for the person filming