Monday, February 23, 2015

Morning Glory Spillways for Dams

In case you were wondering if I had lost interest in dams, I came across this link when I was Googling the Monticello Railway Museum. The 72-foot opening narrows to a 28-foot spillway.


Most of the comments are noise, and some are rather objectionable, so I summarize. Many comments were speculating that you would die because of the water pressure of a 200-foot column of water. But "AnĂ³nimo dijo... "  explains that since the water spillway is designed to accommodate the flow of water, the pressure remains around one atmosphere. But the water turbulence will rather quickly kill you.
Speaking as an ex Civil Engineer, here's the science bit:

When traversing this thing while it's active, the issue really isn't pressure.

Hydrodynamically, there are three components to the fluid's "head" at any given point ("head" is a way of expressing the total energy potential of a dynamic fluid at any point, and is expressed in metres).

1. Potential energy (height above datum). All the energy is potential at the entrance, and by the time it exits most of it is converted to...

2. Kinetic (speed). As there is negligible difference in atmospheric pressure at the entrance and exit, ignoring friction, we can assume all of the potential energy becomes kinetic as the water falls. The only way to get significant pressure on the way down would be to steal some kinetic energy by constricting or kinking the pipe, and since that would slow the water (defeating the hole's purpose) it will be a smooth ride. So there is very little head converted into...

3. Pressure. This will be pretty much 1 atmosphere throughout the system. It is designed this way precisely because this water needs to flow as fast as possible.

So no, the pressure won't kill you. What WILL kill you is turbulence and friction. Unless the water is verrrry slow, you get turbulent flow, which will buffet you around and basically bash your brains and bones all over the pipe, especially at such speeds. Given how smooth cement isn't, you'll probably also be flayed alive as you go. If the turbulence is particularly bad (although they try to avoid this so not too much speed is lost to friction), then localized pressure from vortices may burst your ear-drums.

Personally, for survival purposes, I'd wear scuba gear and go in a Zorb (a big inflatable hamster-ball) coated in kevlar. And set up a big, BIG net at the bottom to catch me :-)

By the way, the turbulence will probably still kill you, so PLEASE don't try this.


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