Dam Interesting
September 17, 2017 5:52 AM   Subscribe

A dam fusegate is a non-mechanical method for automatically triggering water release when a reservoir fills to capacity. Basically a very large pivoting metal or concrete bucket that is tripped by inlet flow at high water, it’s like an electrical fuse, only for water, and can be bigger. Much, much, bigger, as the can be seen at the Terminus Dam Spillway of Lake Kahweah in California.

A little more information available in this document, page 3-46 on.
posted by carter (29 comments total) 26 users marked this as a favorite
 
Ack, extraneous "the " in the description ...
posted by carter at 5:53 AM on September 17, 2017


What is the advantage they offer over a simple fixed concrete spillway ( I mean one where when water behind a dam reaches a certain height, it starts spilling over)? Is it that you can vary the amount of flow or that you can vary the height at which the water starts to flow?
posted by Bee'sWing at 6:31 AM on September 17, 2017 [1 favorite]


How is this "non-mechanical"?
posted by falsedmitri at 6:35 AM on September 17, 2017 [12 favorites]


Perhaps because there are no gears or levers? Sounds like the fusegate is just one piece.
posted by grumpybear69 at 6:43 AM on September 17, 2017


Bee'sWing, think of it this way: The fuse gates don't replace the normal spillways; they supplement them. The standard spillways are designed with specific flow patterns in mind. But let's say you have a particularly heavy rainfall, such that the reservoir floods and rises much too quickly, and you need to bleed off the excess water to prevent damaging other systems.

The fusegates act as a no-human-interaction-needed method of ensuring the primary spillways don't get overloaded, by "tripping" like an electrical breaker and releasing excess water very quickly down the emergency spillway. And it's not just that no action need be taken by an operator -- they also require no other moving parts (gears, valves, etc.) other than the concrete of the gate itself being flipped on its side when the fuse "trips."

They are normally installed in a series, with increasing tolerances, so that only the necessary number of "tripped" gates need open to release flood waters, thus reducing the risk further down the ecosystem.
posted by mystyk at 6:44 AM on September 17, 2017 [12 favorites]


Perhaps because there are no gears or levers? Sounds like the fusegate is just one piece.

Water flowing is fluid mechanics. The fusegate tips over, that's definitely mechanics.

A chemical reaction, an electrical system with no moving parts or some quantum magic would qualify as non-mechanical at my normal operating level of pedantry.
posted by Dr Dracator at 6:52 AM on September 17, 2017 [13 favorites]


Here (2-page pdf) is a good illustration and explanation of how they operate, for those still uncertain.
posted by mystyk at 6:52 AM on September 17, 2017 [6 favorites]


So the idea is that the dam can store the maximum amount of water (this would make sense in California) with these installed, but if there was a flood, these would trip and let out excess water.
posted by Bee'sWing at 7:04 AM on September 17, 2017


A smaller version in action
posted by TedW at 7:13 AM on September 17, 2017 [2 favorites]


I think I get it now, these offer additional spillways when needed. We saw what happened a little while back when a spillway was overloaded and had a huge hole eroded into it in Oroville.
posted by Bee'sWing at 7:18 AM on September 17, 2017 [2 favorites]


There's a dam a few towns over from me that has a similar system built in the 1960s using siphons. There are vertically arrayed pipes on the upstream side of the dam which go up and "over" the the flood-stage level of the dam to discharge at a point much lower on the downstream side. The idea being that when the water gets to flood stage, the siphons kick in automatically and drain the water to a much lower point--the bottom of the upstream siphon pipes--than normal capacity.

It's pretty neat. And the siphons have no moving parts and require little if any maintenance. And when they're running, they have this really deep and creepy gurgling sound.
posted by RonButNotStupid at 8:01 AM on September 17, 2017 [2 favorites]


Wikipedia has a clear and concise explanation of their purposes:

Fusegates are a mechanism designed to provide the controlled release of water in the event of exceptionally large floods. The design consists of free standing blocks (the fusegates) set side by side on a flattened spillway sill. The Fusegate blocks act as a fixed weir most of the time, but in excessive flood conditions they are designed to topple forward, allowing the controlled discharge of water. Multiple fusegates are generally set up side by side, with each fusegate designed to release under progressively extreme flooding, thus minimizing the impact of the floodwater on the river downstream. The System is developed and patented by Hydroplus from Paris, France. It has been installed on more than 50 dams around the world with sizes ranging from 1 m to more than 9 m in height. Fusegate are typically used to increase the storage capacity of existing dams or to maximize the discharge potential of undersized spillways.
posted by Bee'sWing at 8:13 AM on September 17, 2017 [2 favorites]


I was wondering how come I'd never seen these fusegates, considering how much of my early life was spent on boats on this very lake. I had to read to find out they are new. Sadly you'd be hard pressed to either float a boat on Kaweah Lake in recent years, much less need to use fuse gates. Let's hope they get another couple years of atmospheric rivers and these things get plenty of use.
posted by Conrad-Casserole at 8:40 AM on September 17, 2017


An even smaller version.
posted by eye of newt at 9:30 AM on September 17, 2017 [2 favorites]


I wish there was footage of a fusegate exceeding the balancing point and then toppling over as designed. Seems like it would be a pretty scary thing to witness one or more of those giant buckets flip over. The photos appear to show Lake Kaweah at spill over capacity, but not at tipping capacity. It also appears that each fusegate may not actually be fixed to its pivot point. Is it correct to assume a fusegate is a one time use device? It's not clear to me, but it looks like each fuse gate rests in place solely by its own weight, and when tipped over, designed to get pushed out of the way by the water by virtue of not actually being fastened down at the pivot point.
posted by 2N2222 at 11:29 AM on September 17, 2017


"Once the flood is over, a winch or a jacking system is used to raise the pannel up again."

So, nota one time use device, but not one that automatically resets itself.
posted by JiBB at 11:35 AM on September 17, 2017 [2 favorites]


Seems like it would be a pretty scary thing to witness one or more of those giant buckets flip over.

Seeing as it's supposed to happen during a major flood, you'd be probably be pretty busy in the witnessing scary things department.
posted by Dr Dracator at 1:04 PM on September 17, 2017 [5 favorites]


I am so used to seeing the -gate suffix used in a political context that at first I thought this post was about a scandal named "fusegate".
posted by Pyry at 1:51 PM on September 17, 2017 [1 favorite]


Well, these are water gates.
posted by Bee'sWing at 1:59 PM on September 17, 2017 [8 favorites]


ಠ_ಠ
posted by Johnny Wallflower at 2:01 PM on September 17, 2017 [3 favorites]


Without being pedantic about it, it's definitely a mechanical system, being at a minimum a kind of inverted gate that tips forward on what amounts to a hinge, in other words it's a lever, one of the fundamental simple machines. The tipping, though, seems to be of two different types. In one form the gate is lifted and pushed forward by water pressure fed from underneath to disrupt its balance. The Hydroplus gate is held up by an articulated arm; water pressure fed from underneath folds the arm and the gate drops. Fusegates as described in the usbr.gov paper are not fixed in place; when they tip they're carried partway downstream to minimize obstruction, returning them to service requires dragging them back upstream, which sounds like a bit more work than just using a crane to tug it up.
posted by ardgedee at 4:52 PM on September 17, 2017


I'm speculating, but maybe what they meant by non-mechanical was that you don't need human intervention to open the gates? It would have to be a translation issue.
posted by Bee'sWing at 5:06 PM on September 17, 2017


Seems that this is a specialized solution for a few cases that have geographical limitations. For most dams, they have an emergency spillway that is just a flat, level concrete lip that is hundreds of feet wide. If the water reaches that level in an emergency, then water is released by flowing across hundreds of feet of space. A completely passive emergency system with no moving parts.

If the geology limits the width of the emergency spillway, as in a narrow canyon, then they need to release a lot of water in a very narrow space. That means opening up a big, deep plug. That is the situation that might benefit from these fuse gates. But for most dams this would be an unnecessary expense.
posted by JackFlash at 7:39 PM on September 17, 2017


I guess these would be cheaper than gates and have lower maintenance requirements. I mean, lifting it every decade to keep it from sticking? That's pretty rad, keeping something like the Folsom Dam incident in mind.
posted by Standard Orange at 8:32 PM on September 17, 2017


@JackFlash Thank you! I was having a real problem trying to imagine why it wouldn't just be preferable to have a system that just drains excess water as it comes up, much like a glory hole.
posted by qwip at 9:16 PM on September 17, 2017


JackFlash, remember reservoirs are like beer pitchers, they are wider (and hold more) at the top. If the most important job of the dam is to store drinking water (as would be true in California) then a few more meters above the spillway sill could really be a boon.
posted by Bee'sWing at 11:37 AM on September 18, 2017


I usually try and avoid thread sitting, but many thanks to all who have contributed Useful and Informative Comments as to how these things work. It has greatly improved this post. Thank you!
posted by carter at 12:54 PM on September 18, 2017 [1 favorite]




I wonder if some kind of metal gasket could prevent the concrete from bonding. hmmm
posted by Megafly at 3:20 PM on September 18, 2017


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