Effect of Artificial Aeration on Evaporation Inhibition under Floating Balls Cover

Evaporation from reservoirs in arid plains is a significant concern. To mitigate this, covering the water surface with anti-evaporation materials, such as floating balls, can effectively reduce evaporation and enhance the utilization of water resources. However, during the hot season, the high net radiation absorbed by the surface of the floating balls is converted into sensible heat, which in turn warms the upper layer of the water. This warming effect leads to temperature stratification in shallow water, which reduces the effectiveness of the anti-evaporation materials in inhibiting evaporation. There is a lack of research on strategies to mitigate the surface water warming caused by these materials during the hot season. This study suggests that the reduced performance of evaporation suppression in summer, coupled with the resulting temperature stratification, may pose potential hazards to the aquatic environment. Five groups of evaporators were installed at the top of the reservoir dam, consisting of both covered and uncovered units, with and without aeration and at varying aeration frequencies. These units were designed to eliminate thermal stratification in the upper water column, lower surface water temperatures, and improve the effectiveness of evaporation suppression. The findings indicate that artificial aeration can effectively reduce evaporation in the floating balls cover group, but only during the period of water temperature stratification (May to September). Decomposition coupling calculations of the energy balance for evaporating surfaces under different aeration modes showed that aeration reduced the sensible heat flux of the evaporating surfaces by approximately 9.74% for continuous aeration and 3.42% for intermittent aeration, as well as the latent heat flux by 6.94% and 3.61% respectively, during the hot season, thereby reducing water evaporation. Continuous aeration enhances the anti-evaporation performance by approximately 6.36%. Intermittent aeration, while slightly less effective in improving evaporation inhibition at 4.05%, can effectively mitigate the temperature rise of the bottom water due to the mixing of upper and lower water layers and inhibit the diffusion of sediment pollutants into the overlying water. Current research on the evaporation of covered water surfaces in flowing water bodies at reservoir sites, considering varying times and frequencies of aeration, is still limited and requires further investigation.