Questions about evaporation

[cerceau]

• What is the approx. normal evaporation rate for a pond of about 80 - 90 sq. ft, in shaded area in mid-summer?

• How often do most people under similar conditions have to add water?

• Does one dechlorinate every time one raises the level by an inch or so by adding tap water to a 1,400 gal. pond (skimmer + waterfall)?

 

[JBtheExplorer]

It depends on a lot of circumstances. Heat, humidity, wind, clouds, etc.
My 800g pond is in full sun, but I'd guess, given a stretch of "average" summer weather, I usually have to fill a half inch about every 3-4 days if it doesn't rain, but on hot days I can lose a half inch in a day, and during the really hot stretches, like the "too hot to sit outside in the shade" days, I can lose up to an inch a day. I don't know what others deal with but I'm sure they'll chime in. I also don't have chlorine in my water so I'm not sure what others do about that, either.

 

[Meyer Jordan]

• What is the approx. normal evaporation rate for a pond of about 80 - 90 sq. ft, in shaded area in mid-summer?

• How often do most people under similar conditions have to add water?

• Does one dechlorinate every time one raises the level by an inch or so by adding tap water to a 1,400 gal. pond (skimmer + waterfall)?

'Normal' will first depend on geographical location.

...and time of year. (click on 'Current Bulletin and scroll to evaporation map for your area's current pan rate).

http://www.usda.gov/oce/weather/pubs/Weekly/Wwcb/

These are only close approximations for your exact location. Other factors such as air temperature,water temperature, wind, water movement etc. all determine the ever changing evaporation rate.

 

[cerceau]

'Normal' will first depend on geographical location.
View attachment 82905
...and time of year. (click on 'Current Bulletin and scroll to evaporation map for your area's current pan rate).

http://www.usda.gov/oce/weather/pubs/Weekly/Wwcb/

These are only close approximations for your exact location. Other factors such as air temperature,water temperature, wind, water movement etc. all determine the ever changing evaporation rate.

Thanks for this! How does one interpret those figures? The chart gives 0.16" a day currently (in central Missouri) — is this regardless of the area of the basin and whether it's full exposure to the sun of shaded?

 

[Meyer Jordan]

Thanks for this! How does one interpret those figures? The chart gives 0.16" a day currently (in central Missouri) — is this regardless of the area of the basin and whether it's full exposure to the sun of shaded?

These are Pan rates. These measuring basins are located in full sun and evaporation rates will vary only slightly in other different size basins in the same general geographical area.

 

[morewater]

• What is the approx. normal evaporation rate for a pond of about 80 - 90 sq. ft, in shaded area in mid-summer?

• How often do most people under similar conditions have to add water?

• Does one dechlorinate every time one raises the level by an inch or so by adding tap water to a 1,400 gal. pond (skimmer + waterfall)?

One of the largest causes of pond "evaporation" is the result of splash from the waterfall itself, whereby water is splashed onto the surrounding rockery and evaporates quickly from the rock surface.

As to dechlorination, an inch or two in a pond of that size isn't going to make that much difference, but add if it makes you comfortable.

 

[mgmine]

I lose 1/2" a day every day but I have a water falls and 45 foot stream. I keep the water level constant with an automatic feeder.