Influence of Air-Bubble Plumes and Effects of Climate Change on Reservoir Evaporation

Abstract

It is estimated that open water reservoirs in Australia lose around 40% of their total water storage capacity per year to evaporation. This can be attributed to the country’s dry climate, with high temperatures and strong winds. To further exacerbate this issue, temperature increases have been recorded during the past decades, and this is predicted to continue over the coming years in Australia. This has been directing even greater concern to how much water will be lost from Australian reservoirs in the future through the evaporation process. For several decades, Australia has been investigating mechanisms to minimize evaporation from reservoirs. These include the use of physical and chemical covers, windbreaks and even modifying the reservoir shape in order to reduce its surface area. Most of these techniques however, have been shown to be ineffective, as in the example of windbreaks; to be excessively expensive, as in the example of physical covers and modifying the reservoir shape; or to impose potential risks to the water quality, as in the use of chemical covers. Destratification by air-bubble plumes, which involves pumping compressed air into the interior of a reservoir, thereby allowing the resultant bubbles to rise and carry cold bottom water to the surface, is one technique that deserves further investigation. Air-bubble plumes have been suggested in literature as a potential mechanism for reducing evaporation from reservoirs due to their potential effects on water temperature change. The primary aim of destratification by air-bubble plumes is to maintain or improve the quality of the reservoir water, specifically by increasing dissolved oxygen in the water. The potential of these systems to reduce evaporative losses is related to the change in water temperature attributable to mixing. The intuitive principle is that cold hypolimnetic water is lifted by the air bubbles, and once at the surface, this water mixes with the lighter epilimnetic water, reducing its temperature and consequently, evaporation rates.