It was all over the news. How is it possible to be sucked through a pipe and spit out the other end without passing through an impeller or turbine blades or something?
So, the answer is the pool is below sea level and the water just flows in due to gravity? Must be a pretty deep pool if the intakes are already 30’ down.
No, the SURFACE of the pool just has to be lower than the surface of the ocean.
And given a large diameter pipe, my WAG is just a few foot difference would make for one hella of a flow rate.
But only for a short period of time, we’d need “one hellava” flow rate back out of the pools too.
That’s what the pumps at the other end of the pool that pump water back out into the ocean are for.
Well, that’s not what they are FOR. But it is what they do.
For a 1 foot/sec flow rate in a 16 foot diameter pipe I come up with about 200 cubic foot/sec, or 25 gallons/second. Would 1 foot/sec suck a diver in?
It would be marginal.
Have you ever tried to swim “fast” in full scuba gear? I have. Under such conditions “fast” is a certainly a relative term.
It doesn’t take much of a current to be a victim of going with the flow whether you like it or not.
I just remembered a real life experience that is related.
A few year back I was canoeing the Sante Fe River in Florida…or maybe it was the Swannee.
Anyway, at one point there was a large spring off to the side. It formed a pool/bay sorta thing in a U shaped cliff area. The water from that pool came down maybe a dozen or two foot long “flume” into the river. I’d be surprised if that pool was a full 2 feet above river level. It was probably more like a foot IIRC.
It took every bit of speed I could muster in that canoe to get up it. IIRC I’ve clocked myself at like 5 or 6 mph full out for short distances before using a GPS. And I can paddle WAY faster than I can swim in scuba gear 
It does not take much of a level difference for water to get up some serious speed.
200 cu-ft/sec = ~1500 gal/sec.
Pipelines are also generally going to have a higher velocity than 1 fps. I’d guess in the 3-10 fps range. A higher pipe velocity means less chance of debris settling and lower cost (since a smaller diameter pipe can be used).
Likelihood of getting sucked in would also depend on whether he’s conscious of the direction of flow. If he’s “full frontal” in facing the flow, drag forces will be higher, and it’ll be harder to resist the flow. If he’s not swimming directly against the flow, energy will be wasted, and it’ll be harder to sustain swimming in the opposite direction.
[hangs head in shame]
Ignoring friction in the pipe, a 1-foot drop will give you a flow rate of about 8 ft/sec. Friction will obviously cut that down, but it still doesn’t take a very big height differential to create a flow in a 12-foot pipe that a person can’t swim against.
I am not sure what the ponds were for. Were they supplying water to the power plant condensers? Or is the pons used for storing fuel rods?