So if you have a 100' weir in a straight line, and the water is 1 inch higher, it will leave the reservoir (spill) at 100 inches per unit of time (second, maybe?). If you have a 300' weir, it will spill at 300 inches per second. If you make that 300' weir zigzag and accordion it into the same space as the 100' straight weir, it will still spill at about 300" per second.
One of those links I put up somewhere mentions having to run pipes with more water to the downstream side of the weir, and they blast water up to break up that suction/cause turbulence or something to keep the water from backing up.
People rage about dumping runoff into the ocean but the salinization of the delta is a big problem too.
Some of the levees around there are breaking because they've been so dry for so long (among other reasons). They're building "turnouts" along the San Joaquin and the aqueducts to flood some pretty large acreages to help recharge the aquifer and store water below ground. But the downstream monopolies are going to complain about that too.
There is a lot of thermodynamics in Laminar and turbulent flow models and equations. It's crazy stuff, and a lot of it is really non-intuitive. Like Kurt's scruffy surfboards and why golf balls have dimples. One of my physics profs said something along the lines of 'the universe is trying to kill us by sucking out all the heat, and it has plenty of time to wait us out'.
So if you have a 100' weir in a straight line, and the water is 1 inch higher, it will leave the reservoir (spill) at 100 inches per unit of time (second, maybe?). If you have a 300' weir, it will spill at 300 inches per second. If you make that 300' weir zigzag and accordion it into the same space as the 100' straight weir, it will still spill at about 300" per second.
One of those links I put up somewhere mentions having to run pipes with more water to the downstream side of the weir, and they blast water up to break up that suction/cause turbulence or something to keep the water from backing up.
People rage about dumping runoff into the ocean but the salinization of the delta is a big problem too.
Some of the levees around there are breaking because they've been so dry for so long (among other reasons). They're building "turnouts" along the San Joaquin and the aqueducts to flood some pretty large acreages to help recharge the aquifer and store water below ground. But the downstream monopolies are going to complain about that too.
I'm also coming to understand the difference between a dam that's mostly for flood control, and a dam that's for hydro or irrigation etc. We see all these images of California reservoirs during the drought, and assume it's terrible. It's not good, but they don't want them to fill up. Our irrigation reservoir in Cody goes over the spillway almost every year, but it's a feature not a bug. They used to crank the outflow down so far that trout were dying—they wanted the reservoir full at all costs. But they eventually passed an in-stream flow minimum, and I think that's standard now. But it still fills up eventually. Hmm now a PK Weir. PK="Piano Keys" Check out the cool one they're building at Lake Isabella
That's pretty cool. Applying hydrodynamics and surface drag knowledge to influence the water flow. Similar to how drag works on boat hulls and surfboards. In the mid 60's we learned about how much the finish on a surface can influence drag. It was found that a hard shiny finish actually attracted a thicker layer of water than a fine sanded matte finish allowing water to pass more quickly over the surface because of less friction / drag.
This is creating more surface area to affect the water flow by thinning out the overall layer that creates drag that slows it down. The same volume is spread out over a wider area making it easier to flow if I'm getting this. Or not.
About California's water system ... Back when it was designed and built under the first Gov. Brown, Jerry's dad, it was never intended to store water for long durations or flooding for that matter. The primary purpose was to move water from NorCal and the Colorado River into SoCal via aqueducts for immediate use. Reservoirs were not a consideration It was very short sighted as we have come to find out, but then again the population has nearly quadrupled since its design and build. There is usually plenty of water if managed and properly stored. But most runs off into the ocean when it storms. Or worse, diverted to areas less in need for strange reasons found only in California.
I'm also coming to understand the difference between a dam that's mostly for flood control, and a dam that's for hydro or irrigation etc. We see all these images of California reservoirs during the drought, and assume it's terrible. It's not good, but they don't want them to fill up. Our irrigation reservoir in Cody goes over the spillway almost every year, but it's a feature not a bug. They used to crank the outflow down so far that trout were dyingâthey wanted the reservoir full at all costs. But they eventually passed an in-stream flow minimum, and I think that's standard now. But it still fills up eventually.
Check out the cool one they're building at Lake Isabella
As a scientist I, of course look down at engineers but that's unfair, especially when it comes to people who are thinking up creative new design principles.
The overlap is when someone thinks they can design around hydrologic and hydrogeologic reality. A geology professor I know pointed out that the reservoirs in Australia for flood control do very little to control floods. Basically, there is no way for them to hold enough water to have much impact on a big flood. Yeah, they might prevent minor flooding if they are nearly empty but afterall you are in a wet period so they probably aren't. But then the weather forecast says, "Oh Shit!" and you can't dump the water fast enough to empty it and besides more water flows in from the whole catchment than it can hold. But they try to dump water anyway and, guess what? Minor flooding anyway, probably followed by major flooding. He's been right more often than not over the past couple of years.
eta: Used to use V-notch weirs to measure flow down streams by relating water level behind the notch to the amount of water that can flow through the notch. There are other designs but the V is good because you can measure low flows pretty well but as more water comes down it has a larger area to flow through and the rate can be calculated with some complications - because physics. One trouble was that there has to be a free-drop on the downstream side of the weir so the water isn't backed up. That means that the bottom of the weir needs to be set in a little dam and you don't get a measurement until the pool fills up to the notch. I came up with a system to use high-resolution laser topography measurements to calculate the pool volumes at different levels as water rises up to the notch and calculate the inflow. Of course the real problem was the debris caught in the weir and the yabbies (freshwater crayfish) digging tunnels underneath.
That's pretty cool. I read something recently about some other kind of toothed overflow thingy, maybe for a different situation. Thought, "Nice. Don't understand it really but these civil engineers seem to have fun."
Our local reservoir overflowed this year but the conventional spillway worked. Took out a road downstream (and flooded most of a town). Of course they are repairing the road the same way it was rather than raising the bridge. Mainly because there were a lot of roads damaged and they don't have the money to do it right.
I'm also coming to understand the difference between a dam that's mostly for flood control, and a dam that's for hydro or irrigation etc. We see all these images of California reservoirs during the drought, and assume it's terrible. It's not good, but they don't want them to fill up. Our irrigation reservoir in Cody goes over the spillway almost every year, but it's a feature not a bug. They used to crank the outflow down so far that trout were dyingâthey wanted the reservoir full at all costs. But they eventually passed an in-stream flow minimum, and I think that's standard now. But it still fills up eventually.
...about a Labyrinth Weir. The Terminus Dam at Lake Kaweah, above where Justine's from, is approaching the (literal) tipping point of its fusegates too, so that'll be interesting.
So a dam that's overtopped by an inch will have an inch of water pouring over it along its entire length. If that's a 100' dam, then math people can figure out how much water per hour it can drain.
âââââââââââââââââââââââ
But if they make that edge look like a giant sawtooth,
}_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{
they can increase the length of the edge that water can pour over, doubling or tripling the volume per hour.
At Terminus Dam, the "teeth" of that weir are designed to tip over if the water gets too high. Water will first pour into a shaft that will then apply upward pressure and tip a giant cube of concrete over, where it will fall off the dam and break up, leaving an Alfred E. Neuman* gap for the water to pour through.
*
That's pretty cool. I read something recently about some other kind of toothed overflow thingy, maybe for a different situation. Thought, "Nice. Don't understand it really but these civil engineers seem to have fun."
Our local reservoir overflowed this year but the conventional spillway worked. Took out a road downstream (and flooded most of a town). Of course they are repairing the road the same way it was rather than raising the bridge. Mainly because there were a lot of roads damaged and they don't have the money to do it right.
...about a Labyrinth Weir. The Terminus Dam at Lake Kaweah, above where Justine's from, is approaching the (literal) tipping point of its fusegates too, so that'll be interesting.
So a dam that's overtopped by an inch will have an inch of water pouring over it along its entire length. If that's a 100' dam, then math people can figure out how much water per hour it can drain.
âââââââââââââââââââââââ
But if they make that edge look like a giant sawtooth,
}_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{
they can increase the length of the edge that water can pour over, doubling or tripling the volume per hour.
At Terminus Dam, the "teeth" of that weir are designed to tip over if the water gets too high. Water will first pour into a shaft that will then apply upward pressure and tip a giant cube of concrete over, where it will fall off the dam and break up, leaving an Alfred E. Neuman* gap for the water to pour through.
*
good to know
i find terminus to be a weird dam name
it's probably me...
...about a Labyrinth Weir. The Terminus Dam at Lake Kaweah, above where Justine's from, is approaching the (literal) tipping point of its fusegates too, so that'll be interesting.
So a dam that's overtopped by an inch will have an inch of water pouring over it along its entire length. If that's a 100' dam, then math people can figure out how much water per hour it can drain.
âââââââââââââââââââââââ
But if they make that edge look like a giant sawtooth,
}_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{ }_{
they can increase the length of the edge that water can pour over, doubling or tripling the volume per hour.
At Terminus Dam, the "teeth" of that weir are designed to tip over if the water gets too high. Water will first pour into a shaft that will then apply upward pressure and tip a giant cube of concrete over, where it will fall off the dam and break up, leaving an Alfred E. Neuman* gap for the water to pour through.
I bought a cool tricked out candy apple red tricycle there once. Drove that sucker to work for years.
Until some drunk kid in a radio flyer t-boned me at a stop sign. I had a cervical convection in my pants!
