Influence of bubble plumes on evaporation from non-stratified waters

Abstract

Air-bubble plumes have been used primarily for water quality management through destratification; however, their impact on evaporation rates is yet to be formally quantified. In this paper, the influence of these systems on evaporation from water bodies is investigated. Evaporation, temperature, humidity and wind data were collected and analysed from a laboratory experiment for various air-flow rates injected into non-stratified water. It was found that aeration by air-bubble plumes increases evaporation in their direct vicinity. The factors involved in this increase were identified, and an empirical formula to quantify the loss of water under conditions of aeration was derived. To examine their overall impact on reservoirs, a temperate reservoir in Australia was taken as example for the application of this function. While laboratory data showed that aeration plays an important role in increasing loss of water from small non-stratified water bodies (such as water tanks) for real reservoirs, the effects of aeration on evaporation increase are insignificant. This is because the area of the plume to that of the reservoir is significantly less in real reservoirs than in water tanks. Additionally, due to thermal stratification conditions in real reservoirs, aeration by bubble plumes actually causes a slight reduction in evaporation due to reduction in reservoir surface temperatures as a result of the mixing process. Therefore, the net effect of air-bubble plume aeration on real reservoirs is a reduction in evaporation. However, this quantity was shown to be minor, and does not warrant the use of these systems for the sole purpose of reducing evaporation.