How can I break the surface tension on my waterfall spillway rock so
that the water falls straight down instead of running underneath the
rock and falling about 3-4" back from the lip.

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Request for Question Clarification by tutuzdad-ga on 22 Oct 2005 17:38 PDT

Like pouring milk from a cup and having it dribble down the side
because you didn't tip it at the right angle, you'll need to correct
the problem by tilting the fall edge downward a bit further. You can
probably do this by placing a wedge of some sort under the pool end of
the rock. It may caused your pol level to rise a bit from what you are
accustomed to but I suspect it will also do the trick. Would a
solution like this work for you?

tutuzdad-ga

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Request for Question Clarification by cynthia-ga on 22 Oct 2005 17:42 PDT

luckyduck22,

I used to own a carpet and upholstery cleaning company. This is
actually relevant, because the chemistry of cleaning requires you to
understand an important concept:

Surfactant
http://en.wikipedia.org/wiki/Surfactant

In cleaning, one adds a "wetting agent" to the water to remove the
surface tension --allowing the dirt to "fall in" and become suspended
in the water. Although many products have wetting agents, in cleaning
the "wetting agent" is called detergent, and it is added to the water.
A carpet cleaner only uses enough detergent to make the water feel
"slippery" --I think this will work for you.

I would look for a non-sudsing detergent, not surprisingly, these can
be found at professional carpet cleaning supply stores. I'd make a
personal appearance, talk to them, they are knowlegable and can advise
you as to what products conatining surfactants might be best for your
application. ALso, you want to take them a sample of the water so they
can test the PH. The starting PH, and compisition of it will determine
how much to use. It will also be helpful to tell them how many gallons
are circulating and the kind of pump you use.

If you find this is helpful information and wish me to be compensated,
please let me know and I will repost this information in the Answer
box.

~~Cynthia

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Clarification of Question by luckyduck22-ga on 23 Oct 2005 02:54 PDT

Tutuzdad:  Thanks, but I tried that already and the angle needed is
too steep to be practical or attractive.

Cynthia:  I am concerned that if I add a surfactant, it would
compromise the health of the pond residents (fish, snails, plants et
al) But thanks.

Myoarin:  Adding the concrete edge might work, but you're right, it
would detract from the beauty of the spill stone.  Tried a larger pump
but it looked like projectile vomiting...not a nice relaxing look.  I
don't want to start chipping away at the spill stone unless I am
absolutely sure that that would answer the problem.  Thanks.

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Request for Question Clarification by tutuzdad-ga on 23 Oct 2005 09:39 PDT

Perhaps your solution would be to find a stone cutter to customize a
stone specifically for the volume, flow and pitch your pond. Maybe
even a mason who could fabricate a realistic-looking, man-made stone
for such a purpose. I know that many of the modern masons can create
stones of any shape using a syrofoam or fiberglass structure cut to
specification and then overlay it with a hardening surface coat that
very closely resembles stone or concrete. This would allow you to
achieve precisely the physics you are hoping for without having to
travel the globe in search of just the right stone for the job.

tutuzdad-ga

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Clarification of Question by luckyduck22-ga on 23 Oct 2005 11:37 PDT

Tutuzdad:  I should have added that I like this particular natural
stone, and I'm not willing to have someone hack away at it unless: 1.
I was guaranteed that they wouldn't break it, and 2. that it would
work.  But thanks for the thought.

Traducer:  I think you have something there.  My neighbor, a
chemist/MD, suggested the same thing this morning, explaining that
silicone is hydrophobic.  I think I'll use a different stone to try it
on....I'm off to Ace Hardware.  Thanks!

Y'all are right, of course, but I think the problem is that the lip of
the fall is too gentle, rounded, relative to the flow of water.  Maybe
this is what Tutuzdad was considering.
If the flow of water could be increased, I think that it would stop
following the curve of the lip, curling back under it.  You probably
can't or don't want to do this.  The alternative is to break the curve
so that there is a sharper edge to the lip.
How?   One could add to the lip a layer of cement with a sharp edge. 
I don't know how that would look, of course.  Or perhaps the underside
of the stone spillway could be chipped back to create a sharper edge. 
Maybe just a line chipped or cut with an abrasive disk at the right
point would do the trick.  I expect that this would be just slightly
above vertical tangent to the lip.

Does that make sense?
Myoarin

Further to myoarins comment, the water is falling a couple of inches
further back along the underside of the spillway because there is no
physical resistance to the water moving in that direction. May I
suggest as a workaround that you apply a 'ridge' of silicone sealant
to the underside of the spillway lip as a trial (the silicone can
easily be removed if it proves unworkable - its only an experiment to
see if it copes with the volumes of water) this will break the smooth
passage of the water along the underside and cause it to 'drop' where
you want it.
If this works then a more permanent solution can be found that is
slightly more elegant although it should be hidden by the spill-water
anyway.
Just a thought...