There was one area of my property that was always wet. You could count on getting a tractor stuck there about every year. I decided about 12 years ago to dig a lake in that spot. I don't have a background in engineering, but I do have a background in carefully plotting out actions and making the appropriate contacts to allow me to achieve the proper engineering and calculations.
I have a 1 1/2 acre lake there that is 20 to 22 feet deep at the deepest and carries a 7' average depth. I calculated that I moved something like 35,000 cubic yards of dirt when I dug that lake. That is quite a bit of dirt to move, but it becomes more when you figure that every yard had to be trucked to a different area of my property and then spread and levelled. That means that I basically had to handle the dirt twice; moving around 70,000 cubic yards of dirt.
Anyway, even with a mild natural spring feeding the lake, I will still lose about 1' of water every month during the hot summer months if we don't have any rain. We have had droughts where we have not had any measurable rain in over 4 months; last year being one of those years. My lake was down right at 4'. I used that opportunity to line the banks on one side with rip rap rock.
Taking standard calculations and measurements, that would mean that I would have roughly 3,421,425 gallons of water in my lake at any given time. Based on the apparent rule of thumb of losing about a foot a month, and knowing that one acre foot of water is equal to 325,850 gallons and my lake is 1 and 1/2 acres in size, I'm losing about 16,293 gallons of water a day to evaporation in summer months. In the winter months, the evaporation rate seems to be practically nil.
In your case, with a 1 acre lake/pond (some call it a pond and some call it a lake - I don't care), and for calculation sake assuming that you will have about the same evaporation rates I have, you will lose about 10,862 gallons of water per day. Just rounding up to accomodate for the continued evaporation during water replacement, that means during the hottest dry season that you will need to replace water at a rate of roughly 500 gallons per hour, or about 8 and a half gallons per minute.
Whew! Hopefully that all makes sense to you. The formulas and calculations are all based on scientific fact other than the evaporation rate. That has too many variables for me to be able to give you any accurate measurement other than what I experience. The rate will vary with the hours of sunshine, the relative humidity, the average temperature of your water, the average ambient temperature of your air, the wind speed, as well as the amount of algae and even the turbidity of your water; complicated to say the least. Anyway, hopefully that will answer your question.
Oh yeah, this is all based on my lake which does have a small natural spring feeding it. I have no idea how much water is put out by that spring. Since you are in a generally hotter climate and you made no mention of a spring feeding your pond, take my calculations at a bare minimum for your needs. Also, I am familiar with the estimated evapotranspiration calculations using the Priestly-Taylor method, the Penman method, the DeBruin-Keijman method and the Papadakis method. However, for my response here, I opted to use my actual measurements of evaporation loss method. /forums/images/graemlins/wink.gif There are just too many variables in any particular method to give you an accurate guide for your particular pond.
