charlie_grumbles wrote:hunjoh wrote:charlie_grumbles wrote:Actually you have to get (more than) deep enough to make the pressure balance. Otherwise it draws from the Atlantic into the basin. That has been calculated already to be 1km deep.
Could you explain this? I don't understand.
Ignore for a moment the salinity question (saline is denser than fresh). A siphon pumps water from the "short" side to the "long" side because of the extra water's weight in the longer "long" side tube. That is why you can't siphon uphill, only downhill. So, if you throw a siphon over a dam, water will run from the high water side of the dam to the low. If you make the siphon tubes longer (on either side) below the water line, it won't change that. And that is what you get if you just put the Med side of the siphon a bit below sea level.
So, to make this whole saline siphon work, you have to get the "high" side on the Med side. But it doesn't have to be high in altitude, just high in pressure. So make your tubes really long on both sides, so that on the Med side you reach heavier, denser water, but not on the Atlantic side. That gives you the higher pressure to overcome the difference in height since you have "lighter" water in the Atlantic. But it takes (apparently, I'm trusting the estimates given earlier) 1km of depth to get there. But you have to balance that on the Atlantic side as well.
Let's take your dam example. I get the "high" side of the pipe under the water behind the dam. Going deeper doesn't help, I just need to make sure that the siphon tube won't suck air. But on the "low" side, the lower I go, the more pressure I develop at the outlet.
Explanation: On the "high" side it doesn't matter how deep I go because the density inside the pipe and outside the pipe are the same. So there will never be a pressure differential. On the "low" side the density outside the pipe is lower than inside the pipe, therefore the lower the pipe extends the greater the differential pressure is. Am I missing something here?