A method of evaluating the effect of a monomolecular film in suppressing reservoir evaporation

Abstract

Evaporation from a water surface may be reduced by the application of a monomolecular film. Because of possible seasonal variations in evaporation‐pan coefficients, computed savings in evaporation may be unreliable if based upon evaporation‐pan records. A more reliable measure of the evaporation reduction is obtained by the solution of equations based upon energy budget and heat and mass transfer theory. The rise in water‐surface temperature caused by application of the film can be computed.

Review of literature on evaporation suppression

“…Harbeck and Koberg (134) conclude that a better method of assessing the suppression of evaporation may be obtained by using a combination of the ene^gy-budget and mass-transfer evaporation measurement techniques.…”

“…The following have reported on their progress: Southwest Research Institute (101,102,103,169,249), the U.S. Bureau of Reclamation (77, 291, 292, 293, 307, 308, and 309), the U.S. Geological Survey (133,134), and others (248,276,277).…”

Evaporation control research, 1959-60

“…During the studies the level of the lake remained above that of the excavated area. EVALUATION METHOD In the field tests, the Harbeck and Koberg (1959) method was used to determine the effectiveness of the film in reducing evaporation. This method uses a combination of the energy-budget and masstransfer evaporation measurement techniques.…”

“…The energy contributed to storage, as a result.o-f the film, complicates the problem of evaluating the reduction in evaporation by the Harbeck and Koberg (1959) technique. If a film could be applied in such a manner so that it would continually cover the entire water surface for an indefinite time, a period could be selected, for the above mentioned evaluation technique, that would start and end at any time after the temperature of the water surface had completed its rise as a result of the film.…”

“…However, present methods of applying and maintaining the film for most reservoirs have never been completely successful in obtaining complete coverage and, even if complete film coverage is obtained, it can be maintained only for a short, duration of time. Therefore, in using the Harbeck and Koberg (1959) evaluation technique to determine the reduction in evaporation, periods should be selected, if possible, when the energy stored in the reservoir as a result of the film is not significant.…”