You can expect 1/2% - 1% of the total gallons per hour, per day to be lost to evaporation

For example:

3,000 GPH pump

1/2% = 15gallons/day

1% = 30gallons/day

Make sure to estimate the flow rate after head pressure loss, 3,000 GPH pump may only supply 2,500 GPH or less, this will make a difference.

The variations are used according to the site conditions, full sun and full wind will be 1% a sheltered pond will be 1/2%.

These numbers are an average; it will fluctuate throughout the season.

This is also for the Midwest; it will work for most of the country except Arizona and other hot, dry climates.

Evaporation continues to increase as the amount of water flowing thru the atmosphere increases along with the increased splashing and vaporization of water as it crashes over boulders.

The next question or answer you need is how much water is 1" of water loss in a given pond.

11'x16' pond = 176 sq. ft. If it was a rectangle x .85 for irregular shape = 150 sq. ft.

150 x .62 gallons/sq.ft. X 1" deep = 93 gallons

3000 GPH pump x 1/2% = 15gallons x 7 days = 105 gallons/week or 1" of water loss/week.

Try it on your personal pond or other pond your familiar with to double check the calcs, adjust as necessary.