Keith Nuttle wrote in message ...
I live in central Indiana, and we have experienced daytime temperatures
between 75 and 90 degrees with dew points of 55 to 65 degrees.

My pond has about 120 square feet of surface area.

Can someone give me an estimate, in gallons, of the evaporation during a
day.

Google will reveal this to be a complex thermodynamic question which
has been given much attention. One answer I have found is:

"References:
I work with an equipment for measuring
Evaporation called Evaporimeter. We have found
evaporation rates of water in 20 degrees Celsius
to be around 40 g/m2/hr.

That completely ignores humidity [or dewpoint], unfortunatly. That
quoted rate works out to about very roughly 1/8 inch/hour at 68F.

If you do not get a satisfactory answer here, google around for a good
scientific answer, besides, "Couple of inches," or inchaso."
--
Crashj