Question
Hello,

I am hoping that you can help me answer the following questions:

How much water loss due to evaporation and/or splashing can be expected or considered acceptable in (gallons and inches) during mid-summer days when the temperature is in the high 80's to mid 90's?  

Also is it true that waterfalls and streams contribute to water loss due to evaporation and/or splashing because of the water turbulence that they create?
 

The pond specs are as follows:

The pond is oval 14'6" Wide x 19'6" long.
The depth slopes from 3'8" to 2'8"
It contains 3150 gallons of water.  Measured using a hose bib meter when filling.
Head Height is 5'
The skimmer pump is rated at 6,000/hr at a head height of 5'
I have 35' of stream approximately 24" wide  (the streambed is covered with 1"-3" Delaware Boulders) The stream has 3 waterfalls that are each approximately 16" high The first waterfall originates directly from the bio-falls then there is 6'of stream (then waterfall) then 8'of stream (then waterfall) then 21'of stream to the pond equaling 35' of stream.

Thank you for your time.

Answer
Yes water loss would be greater for the splashing.
The temperature range given by indicate a loss of approx 7mm per day. This is a estimation only it will depend on following factors wind velocity,velocity of water and vegetation around the water body.
Alternatively you can visit this the following link and get the answer

http://www.engineeringtoolbox.com/evaporation-water-surface-d_690.html