Shmuel Assouline, 

Kfir Narkis

To accommodate the increase in irrigation water demand, millions of reservoirs were built during the last decades all over the world, but half of the stored water is lost to evaporation. Opaque floating elements are used to cover the reservoirs and suppress evaporation. However, they limit light transmission and oxygen exchange, thus preventing the coupling of fish farming with irrigation. The concept of open, lattice-like, structures that suppress evaporation while allowing transfer of light and oxygen to the water is presented here. Experimental results under laboratory conditions show that the structure studied has reduced the wind speed above the free water surface, and has suppressed evaporation by 40%–60%. The performances of the lattice-like structure were compared to those of floating balls. In the absence of wind, the balls that cover ∼90% of the water surface with opaque material are much more efficient in suppressing evaporation than the lattice structure that leaves ∼90% of the water surface uncovered. When the wind blows, the balls-cover is still more efficient in suppressing evaporation than the lattice structure. However, the ratio between evaporation from the basin covered with the lattice structure and the one covered with balls is higher than 0.75. That shows that the performances of the investigated structure are equivalent to opaque elements covering 50%–85% of the surface. This emphasizes the high efficiency of the proposed concept to achieve significant evaporation suppression while ensuring transfer of light and oxygen, thus allowing efficient management of dual reservoirs.