On Thu, 19 Jan 2006 13:00:14 GMT, "Koi-lo" wrote:

I'm not sure what you're trying to ask.

Let me try another way then. In caving, we generally speak of two zones,
the vadose, or what I describe as being above the water table, and
phreatic, or below the water table. As far as caves go, the vadose zone is
where erosion takes place to form passages, in the phreatic zone, solution
is the primary factor. Much cave passage is formed by solution (generally
a weak acid solution which dissolves the limestone) and then when the water
table falls, passages are enlarged (or filled) by erosion in the vadose
zone, as water makes it down to the phreatic zone. The two are not
completely distinct, but that is a general picture. Frequently we find
examples of stream erosion in the vadose zone (air filled passages) in a
section formed entirely by solution when it was in the phreatic zone. As
far as ponds go, some must be in the vadose zone (frequently requiring some
sort of physical barrier to retain the water, often a liner) and some are
"windows" in the phreatic zone, and depend entirely upon the level of the
water table for their ability to retain water. When the water table goes
down, likewise so does the level of water in the phreatic pond. The
reverse is true when the water table rises. A pond in the vadose zone,
however, will be virtually independent of what the water table does, and
the water level will be entirely dependent on how impermeable the barrier
is. (Assuming, of course, things like evaporation are ignored.) Now I can
see a whole lot of complications, such as a phreatic pond being filled by
the run off from land that is above the water table, resulting in a
phreatic pond with vadose conditions near the surface, but in the case of
an "ideal" pond, is it proper to divide them into two kinds, or is it
largely a case of a distinction without much of a difference? It makes a
fair amount of difference in speleogenesis, does it matter in regards to
ponds?

I think you're asking if an unlined
pond will eventually drain out. The answer is it depends on so many things
as you pointed out. Depth of water table, soil type, porosity of soil,
Obviously natural ponds and lakes are proof, that some can exist
perpetually, though they are often fed by rain run off, rivers or just an
incredibly shallow watertable.

Water table depth , porousness of the soil, evaporation rate, and rainfall
all impact the water level of an unlined pond. Contrary to your assessment,
these factors all play heavily into the viability of an unlined pond.
Consider that some ponders in new mexico and arizona have reported a water
loss of 1-2 inches per day from evaporation in the summer.

Natural ponds also experience similar cycles, some years they dry out
completely, other years the water level recedes drastically, other years
they flood over their banks. Call your local water district, they'll be able
to answer these questions as they relate specifically to your area.

In my area, the water district/municipality maintains an artificial pond
near my house that are designed to help refill the ground water supply. I
bet they know exactly the rate at which the water level fluctuates, and even
exactly where the water goes, evaporation or absorption into the soil.

The pond I'm fussing with seems to be entirely phreatic. Before the
bulldozer and stuff came, I pumped out the water in the pond. If, however,
I just left things alone, water would again re-enter the pond. After the
bulldozer came, I quit pumping, and now, about a week later, the pond
probably has a good four feet of water near the center. The water level
rises not as fast now, but I'd guess it is about 1/2 inch a day. I'm
guessing it has about another foot to go before it quits. Sure, we've had
a little rain here, but hardly enough to dramatically change the water
level in the pond. There is absolutely no run off into the pond, the land
surrounding the pond is a higher than the land that might possibly drain
into it. Granted, it is only a few inches higher, but that is enough.
(The land right here is like that. I noticed when I was digging post holes
for railing uprights that if I went down about a foot it got *real* damp,
and if I went much more I'd strike wet mud.)

Galen Hekhuis NpD, JFR, GWA
We are the CroMagnon of the future