WSP10994

• File Number: 8210.470
• Description: Pacific Southwest Interagency Committee
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 3/1/1962
• Author: PSIAC
• Title: Stock Water Facilities Guide - March 1962
• Water Supply Pro - Doc Type: Report/Study

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The most widely us ed compound is a,cetyl alcohol, hexadeconal,
a waxlike solid, insoluble in water, but forming a film on the water sur-
face one molecule in thickness when dispensed in the water. Several
other related compounds have been tested, the most common being two
additional cetyl al cohols, octadecanol, and dodecanol (Crus e and Harbeck,
1960). A number of different methods for dispensing the materials to
form a film on the water have also been tried and new ones are currently
being developed.

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It is well documented thattbe,filr'ns suppress evaporat ion but great
difficulty has been experienced in maintaining the film over bodies of
water expos ed to the wind. Under laboratory conditions where the film
can be maintained continuously, reductions in evaporation up to 40 percent
have been obtained but in open water the reductions are much less. In the
Lake Hefner, Oklahoma, experiments, as reported by,the Senate Select
Committee on Water Resources (1960), the measured, reduction was 9 per-
cent over an 86-day period with a maximum saving of 14 percent during
one weekly period. Although intensive efforts were made to maintain the
film during the experiment, this was only pa-rtly successful due to breakup
of the film caus ed by wind. The, same difficulty has been encountered in
other similar tests and appears to be responsible for the low reduction 'in
evaporation obtained under field conditions.

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Koberg (1961) has reported on measurements of evaporation reduc-
tion from stock ponds located in southern Texas made, in,cooperation with
the Texas Department of Agriculture and the Southwest Research Institute.
Nine tests were conducted on the stock ponds us Lng hexadecanol, dodecanol,
and octadecanol applied either in solution, us Lng several different solvents,
or in dispersed form. Four types of dispersing equipment were tested and
intensive efforts were directed toward maintaining a film over the ponds.
Savings in evaporation wer e calculated, us ing energy budget or mass trans-
fer methods to determine what the evaporation would have been without
the film. The maximum reduction in evaporation for a 2 -week period was
27 percent, but in most of the tests extending over several days the savings
ranged from 7 to 12 percent, and in one test there was no discerniblesav-
ings. The invetigators concluded that at present the economics of suppres-
sing evaporation in stock tanks is questionable because of the great difficulty
in maintaining a film on the water surface.

These tests were conducted under carefully controlled conditions,
and the savings obtained probably exceed by a considerable amount those
which would be expected under ordinary field operations. Bas ed on the
experience of thes e investigators, the conclus,ion seems inescapable that
until additional progress has been made in applying and maintaining the
film or until new methods have been developed, there is little reason to
believe that savings in evaporation from stock ponds located in the Pacific

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