"Bob P" wrote in message
.net...
riverman wrote:
"Wilko" wrote in message
...
Bob P wrote:
In desperate circumstances, you're better off taking off the PFD and
diving down to follow the bottom current out of the backwash. Few
people who get in (low-head-dam) trouble have the knowledge or
composure to make that radical move, however.
I've given that some thought. Over the years, this option seems to have
surfaced on RBP a couple of times. My main concern would be what happens
after you get out of the hydrolic, and what would happen if taking off
your PFD wouldn't get you out. I'm fairly ambiguous about whether or not
that would be a smart thing to do. It's the main reason why I have a PFD
with a front zipper though... so that I can quickly take it off if
needed.

This boondoggle arises all the time.

As far as my experience goes, the old "take off your PFD and flush out
the bottom of the hole" strategy is an urban legend. Everyone knows the
rule, but afaik, no one knows anyone who has actually had to do it. Its
in the same legendary category as putting maggots in an open wound to
stymie gangrene from forming, ...

Actually, maggots are now occasionally used in hospitals to eat dead
flesh.


Yes, I know. But I was referring more to the 'Jungle Jim survival' scenario
that makes the Reader's Digest Drama in Real Life pages.



I think if you were actually trapped in a hole with sharp enough edges to
keep you in, you would be underwater and tossed around so much that you
would have no idea which way 'down' was, let alone how to crawl along the
bottom. Also, once you shed your pfd, the force of the water would almost
certainly prevent you from using the rocks along the bottom anyway, as
you'd be plastered down there at best, or slammed among them at worst...

--riverman

As I said, it's a desperation measure. If you can keep your head above
water long enough for someone to rescue you, you're better off not taking
the chance.

However... If you look at the typical water flow of a low-head, the water
first goes down and along the bed, away from the lip of the dam before it
doubles back.

Well, that's certainly the theory. In reality, the 'break line' where the
current splits surges around quite a bit (in all but the most surgically
designed dams), there are bursts and boils that erupt in various places, and
the bottom of the river is usually anything but regular. I think the
hydrodynamic model that we all look at is most accurate in man-made
spillways, with precise and consistent angles, concrete bottoms and very
clean riverbeds. And only somene with a death wish would be running
something like that: those are true killing machines. In the natural world,
there are always lots of little variations and 'irregularities' that affect
the model.

It's the only path where the water takes you to safety rather than holding
you against the top flow. I've never use it, and I certainly don't intend
to experiment, but the logic is reasonable.

Sure, if you assume that all the natural variations don't exist. All logic
is reasonable is you start with 'lets ignore any diversity to the model'.
Its like that old joke about the mathematician, the physicist and the
engineer betting on a horserace, and the mathematician says 'assume a
spherical horse'. :-)

--riverman