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How Different Spillway Gates Work

Jan 05, 2023

How Different Spillway Gates Work

In the heart of Minneapolis, Minnesota on the Mississippi River is the picturesque Upper Saint Anthony Falls Dam and Lock, which originally made it possible to travel upstream on the river past the falls beginning in 1937. It is a famous structure with a fascinating history, plus It has this striking overflow

spillway

with a damper basin at the foot that protects the underlying sandstone from erosion. But there is another dam just downriver, which is a little less well known and a little less picturesque, aptly named the Lower St. Anthony Falls Lock and Dam. Interestingly, the

spillway

of the lower dam is less than half the width of the upper one, even though they are on exactly the same stretch of the MississippiRiver, subject to the same conditions and the same floods.
how different spillway gates work
That's partly because, unlike suprima upstream, the Lower Saint Anthony Falls dam is equipped with

gates

, which provide greater control and capacity for the flow of water through the dam. In fact, dams around the world use

gates

to control the flow of water through

spillway

s. If you ask me, there is almost nothing on this blue earth more fascinating than the water infrastructure. Also, I have always wanted to have a 3D printer for the store. So, I took out the acrylic channel, put some sparkles in the water, and printed a few types of doors so we can see them in action, talk about the engineering behind them, and compare their pros and cons.
how different spillway gates work
And I even made a type of door that is designed to lift and lower with almost no added force. But this particular type of door became famous in 2019, so we'll talk about that too. I'm Grady, and this is Practical Engineering. In today's episode, we're talking about

spillway

gates

. This episode is sponsored by Henson Shave. More on them later. Almost all dams need a way to release excess water when the reservoir is full. If you've ever tried to build a reservoir across a small stream or canal, you know how powerful even a small amount of flowing water can be.
how different spillway gates work
Modern

spillway

s are usually the most complex part of a dam due to the high flow velocities. If not managed carefully, that fast-flowing water can quickly tear a dike apart. The incredible damage at Oroville Dam in 2017 is a striking example of this. Although many dams use uncontrolled

spillway

s where water flows naturally once the reservoir rises to a certain level, gated

spillway

s provide more control over flow, and therefore may allow us to build smaller, more cost-effective structures. There are countless arrangements of mechanical devices that have been used throughout the world and throughout history to manage water flow. But, modern engineering has been fused with variations in only a few

different

types of doors.
how different spillway gates work
One of the simplest is the ridge gate consisting of a drop-leaf above a

spillway

. A primary benefit of the ridge gate is that ice and debris flow right over the top, since there is nothing for the flow to get trapped. Another advantage of ridge

gates

is that they provide a lot of control over the upstream level, as they act as a weir with an adjustable top. Therefore, you will often see crest

gates

used in dams where the upstream water level must be kept within a narrow range. For example, here in San Antonio we have the RiverWalk downtown.
how different spillway gates work
If the water gets too low it won't be very attractive, and if it gets too high it will spill over the sidewalks and flood all the restaurants. So most of the dams that manage the flow of water in the downtown San Antonio River use steel

gates

like this one. Just down the road from me, Ladybird Lake (formerly Town Lake) is held back by Longhorn Dam in downtown Austin. Longhorn Dam has vertical lift

gates

to pass large floods, but the center

gates

of the dam that handle daily flows are crest

gates

. Finally, the dam that retains Town Lake in Tempe, Arizona, uses a series of crest

gates

that are lowered during flooding.
how different spillway gates work
Ridge

gates

are attached to some type of arm that raises or lowers the sash as needed. Most use hydraulic cylinders like the one at Tempe City Lake Dam. The ones here in San Antonio actually use a large nut on a long threaded rod like the emergency jack that comes on some cars. You may notice I'm using a passthrough with a metal hook to open and close the model ridge gate, but most internals aren't strong enough to hold a crest gate on a real dam. In fact, one of the most significant disadvantages of ridge

gates

is that the operators, whether hydraulic cylinders or something else, not only have to handle the weight of the gate itself, but also the hydrostatic force of the water behind the gate. , which can be huge.
Let's do some quick math to illustrate what I mean: The

gates

at Tempe Town Lake are 32 meters or about 106 feet long and 6.4 meters or 21 feet high. If the upstream water level is at the top of one of these

gates

, that means the average water pressure in the gate is about four and a half pounds per square inch, or about 31,000 newtons per square meter. It doesn't sound like much, but when you add up all those square inches and square meters of a door this big, you get a total force of almost one and a half million pounds or 660,000 kilograms.
That's the weight of almost two fully loaded 747s, and by the way, Tempe Town Lake has eight of these doors. The hydraulic cylinders that support them have to withstand these enormous forces 24 hours a day, 7 days a week. That's a lot to ask of a hydraulic or electromechanical system, especially since when the operating system fails at a crest gate, gravity and hydrostatic pressure tend to open the gate, leaving all the water behind and potentially creating a dangerous condition downstream. The next type of

spillway

gate solves some of these problems. Radial ridge

gates

, also known as Tainter

gates

, use a curved face connected to struts that converge downstream toward a hinge called a trunnion.
A hoist lifts the gate using a set of chains or cables, and water flows under it. The fact that my model is made of plastic means that it stays where it is placed due to friction, but full-scale radial

gates

are sufficiently too heavy to close under its own weight. That's a good thing, because unlike most ridge

gates

, if the hoist breaks, the gate won't close. The hoist is also mainly simply lifting the weight of the door itself, with the trunnion supporting the hydrostatic force of the water behind it. These features make radial

gates

so reliable that they are used in the vast majority of gated

spillway

s in large dams around the world.
If you're going to visit a dam or see a swooping aerial shot of a majestically flowing

spillway

, there's a good chance that water is flowing under a radial gate. The trunnion that retains all that pressure while still allowing the door to rotate is a pretty impressive piece of engineering. I mean, it's a big metal pin, but the anchors that hold that pin to the rest of the dam are pretty impressive. Water pressure acts perpendicular to a surface, so the hydrostatic pressure in a radial gate acts directly through this. pin. That keeps the force off the hoist, providing a low-friction motion.
But it's not completely friction-free. In fact, the design of many older radial

gates

neglected the frictional force within the trunnion and needed modification later on. I mentioned the story of California's Folsom Dam in a previous video. That one wasn't so lucky to get a structural upgrade before disaster struck in 1995. Operators were attempting to raise one of the

gates

to make a release through the

spillway

when the struts buckled, releasing a wave of water downstream. Folsom Reservoir was half empty when they closed the opening created by the failed gate. How they did it? Stoplogs, another feature you are likely to see in most large dams around the world.
Like all mechanical devices that could cause dangerous conditions and tremendous damage during failure,

spillway

gates

need to be regularly inspected and maintained. That's hard to do when they're submerged. The inspection part is possible, but it's hard to paint things underwater. In fact, it is much simpler, safer, and more cost-effective to perform most types of dry maintenance. So we put doors on our doors. Usually these are simpler structures, just beams that fit into slots upstream of the front door. Stoplogs cannot generally be installed in running water and are only used as a temporary measure to drain water from the front door for inspection or maintenance.
I put some stop register slots in my model so you can see how this

work

s. I can place the stoplogs in the slots one by one until they reach the level of the reservoir. Then I open the door and the space drains. You can see there is still some leakage from the stop registers but that is normal and those leaks can be bypassed quite easily. The main thing is that the upstream face of the door is now dry so it can be inspected, cleaned, repaired or repainted. And if you look closely, it's not just my model toplogs that are leaking, but the

gates

as well.
In fact, all

spillway

gates

have at least a little bit of leakage. Usually not a big problem, but we can't let them leak too much. After all, there's not much point in having a door if it can't hold water. Steel components in

spillway

gates

do not mount directly against the concrete surface of the

spillway

. Instead, they are fitted with gigantic rubber seals that slide on a steel plate embedded in the concrete. Even these seals have a lot of engineering going into them. I won't read you the entire Hydraulics Lab Report #323: Radial Gate Seal Testing or the US Army Corps of Engineers manual on

Spillway

Tainter

Gates

design, but suffice to say we've tried a lot in

different

ways. of keeping the doors airtight over the years and having it mostly sealed up to a science now.
Most

gates

use a J-bulb seal that is oriented so that upstream water pressure pushes the seal against the recessed plate, making the door more watertight.

Different

shapes of rubber seals can be used in

different

locations to allow all parts to move without letting water through where you don't want it. In fact, there is one more type of

spillway

gate I want to share where seals are particularly important. Beartrap doors are like ridge doors in that they have one bottom-hinged leaf, but beartrap doors use two overlapping hinged leaves, and open and close in a completely

different

way.
The theory behind a bear trap door is that a pressurized chamber can be created between the two leaves. if you present upstream water in this chamber, the resulting pressure will float the lower sheet, pushing it upwards. That, in turn, raises the top sheet. The upstream water level rises as the gate rises, increasing the pressure inside the chamber between the

gates

. The two leaves are usually tied in such a way that, once fully opened, they can be locked together. To lower the

gates

, the conduit to the upstream water is closed, and the water in the chamber is allowed to drain downstream, relieving upward pressure on the bottom sheet so that it can slowly fall back to its rest position.
Sounds simple in theory, but in practice this is quite difficult to get right. I built a model of a bear trapdoor that mostly

work

s. If I open this valve on the upstream side, I put the chamber under the pressure of the upstream water. Under ideal conditions with no friction and tight seals, this would create enough pressure to lift both blades. You actually need a little help from the inner hook. but you can see that, as the water level rises upstream, the bottom sheet also floats up. When the doors are fully open, the leaves lock together to be self-supporting. some old bear trap

gates

used air pressure in the chamber to help the

gates

rise.
I tried that on my model and it

work

ed like a charm. It took a few tries to figure out how much pressure to send, but I finally got it. It's not just my model bear, however, the trap door is finicky. Despite the great benefit of not requiring a significant external force to raise and lower the doors, this type of system has never been widely used. This chamber between the leaves is the perfect place for silt and sand to settle. They were also quite difficult to inspect and maintain because the entire chamber had to be dewatered and the flows had to be redirected.
And because they weren't widely used, there were never any off-the-shelf components, so whenever something was neededIt'll fix, it was a custom job. The world got to see a rather dramatic example of the challenges associated with maintaining the old bear trap

gates

in 2019 when one of the

gates

at Dunlap Dam near New Braunfels, Texas completely collapsed. This dam was one of five on the Guadalupe River built in the 1930s to provide hydroelectric power to the area. But for nearly a century that followed, energy became much cheaper, and aging dams became much more expensive to replace. Since the dam was not built with maintenance in mind, it was nearly impossible to inspect the condition of the door's steel hinges.
But that lack of vigilance reached the owner on the morning of May 14, 2019 when a security camera at the dam captured the dramatic failure of one of the gate hinges. The lake behind the dam quickly drained and started a chain of legal battles, some of which are still going on today. Fortunately, no one was injured as a result of the failure. Eventually, homeowners around the upstream lake banded together to tax themselves and rebuild the structure, a task that is nearly complete now more than three years later. Of course, there is much more to this fascinating story, but it is a great reminder of the importance of

spillway

gates

in our lives and what can go wrong if we neglect our water infrastructure.
And this is what can go wrong if you shave when you don't look good with a beard. My New Year's resolution is not to try to grow facial hair, and I think it might as well be my wife's resolution. Last year, Henson offered to sponsor an episode and I told them I wanted to try the razor first. They sent one and I tried it. And I don't even know where my old razor is now because I never used it again after that. The Henson razor was born from a machine shop pivot away from aerospace parts during the pandemic slowdown, and it shows.
It's just a piece of craftsmanship. And here's the thing: Is a new razor going to change your life? Probably not. But, shaving is a chore. A mundane task for most of us. And using a precision tool, at least for me, makes it feel less mundane and instead a small part of my day that I actually look forward to. I had never used a safety razor before this, but found it easier to use because it doesn't clog and the blade sits across the full width, so it's less likely to cause a rash. I also thought $70 was a bit steep for a straight razor until I did the math on how much it was to spend to replace cartridge blades and realized that, for most people, it will pay for itself within a year.
Henson razor blades are so cheap you could probably put in a new one for every shave and still save money. And actually, if you buy a razor, put the 100-blade pack in your cart, and use my code PRACTICAL ENGINEERING at checkout, those blades are on me. and 100the blades will last you a long time. There is no subscription service or monthly fee, it's just a cool shaver that I really like and I think you will too. Again, use my code PRACTICAL ENGINEERING at checkout to support the channel and get 100 blades for me. Thanks for looking and let me know what you think.
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