Evaporation in Ponds, Streams, Waterfalls and Fountains

Published on May 1, 2012

[img:1] *Courtesy of IPPCA*

Water evaporates. It also has been known to leak. The obvious question raised by many new water features’ owners is: “The water is going down – is it leaking?” A good general rule of thumb is that most water features will loose approximately 1 inch per week by evaporation.

HOWEVER, when there is a lower pond and a water feature such as a stream or waterfall above it, there is more to it than just looking at the lower pond and measuring the loss.
For example: An upper pond 6´ x 8´, a stream bed 15´ long and about 1´ wide of actual running water, and a lower pond that is only 10´ x 10´. If we actually had exactly one inch of evaporation it would translate to:

Lower Pond:
10´ x 10´ = 100 sq. ft., x 1/12 ft. deep = 8.33 cu. ft. x 7.4805 gal./cu. ft. = 62.3 gallons.

Streambed:
15´ x 1´ = 15 sq. ft., x 1/12 ft. deep = 1.25 cu. ft. x 7.4805 gal./cu. ft. = 9.35 gallons.

Upper Pond:
6´ x 8´ = 48 sq. ft., x 1/12 ft. deep = 4 cu. ft. x 7.4805 gal./cu. ft. = 29.2 gallons.

We now have a total evaporation of 100.85 gallons. But it is only affecting the level in the lower pond, since the pump is keeping the upper pond and streambed full. Therefore, 100.85 gallons divided by 7.4805 = 13.37 cu. ft. divided by 100 sq. ft. = .13 x 12 in./ft. = 1.6 inches of actual drop in the lower pond for each 1 inch of actual evaporation in the entire system.

 Now we have to toss the equation some real variable, such as the **“splash factor”** in the streambed and waterfall. If it is a nice hot summer day and the water is splashing small droplets onto a hot rock, chances are that it will immediately evaporate rather than run back into the stream. Some, naturally, may actually splash completely out of the system. There might also be a small stick, leaf, plant stem, etc., that for the moment is laying across the edge of the stream and that is wicking some water along it and out of the system. And, do not forget the occasional herd of deer drinking at night, the herd of small neighborhood kids playing, or the large dog taking a swim and taking water out with him.

And, a hot day with low humidity will obviously have a different evaporation rate compared with a cold and damp day.

If the system is completely covered with, for example, cheap clear plastic, making sure that it is all held down on the edges **within the system** – so that any water splashing or condensing on it will run into the pond system and not outside of it – all evaporation can be eliminated and a much truer picture of “evaporation or leak” can be seen.

IPPCA – The International Professional Pond Companies Association. Our Mission: To Promote, Protect and Advance the Pond and Waterscape Industry.

For more information about the IPPCA see their website at www.ippca.com.

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