Evaporation (Pan) 2

[ccampttu]

I am trying to determine a rough volume for the daily evaporation from a reservoir using evaporation pan data. I have been looking through several textbooks which only discuss using pan data in relation to reservoirs by referring to the correction factor Cp for the rate. The data I have for the pan is the evaporation rate in in/day. There is no discussion on the area over which this rate occurs. I am trying to determine how to calculate the volume per time that is lost from a reservoir of a certain size. Just for argument sake the (factored) evaporation rate is 0.24 in/day and the reservoir is 2 acres. Is the rate from the pan data over the area of the pan? is it over a square inch? a square foot?

Thanks
Curt

 

[Ron]

Just as rainfall is considered as a "loading rate", evaporation is considered an "unloading rate"....in inches/time. The pan rate is over the whole pan...the area is irrelevant if the same conditions apply to the whole area in question.

 

[ccampttu]

what would be the volume of evaporation over the 2 acre reservoir per day in ac-ft? The purpose of this evaluation is to determine how much make-up water should be introduced to maintain a required working pond volume.

 

[hokie66]

(0.24 in/day) x (1/12 ft/in) x 2 acres = 0.04 acre-ft. Is that all you are asking?

 

[cvg]

correction factor is to relate the small pan to a larger reservoir. obviously the water in the pan will evaporate at a different rate (faster) due to temperature differences. commonly used coefficient is 0.75.

 

[hokie66]

He did say the rate was factored. These things are all just estimates, varying a lot with atmospheric conditions, and then it rains...

 

[ccampttu]

Thanks hokie66. That is what I was doing, it just felt too simple.

 

[hokie66]

You are welcome. Simple is best.