Evaluation of Using Physical Floating Covers in Reducing Evaporation Loses from Small-Reservoirs Water Surface in Arid and Semi-arid Regions

The lack of water resources in arid and semi-arid regions like our country and the high volume of water losses through evaporation have made the importance of appropriate and practical methods to reduce evaporation from water reservoirs to be more and more clear day by day. Water is one of the most essential human needs. Evaporation is one of the climatic phenomenon in lakes and open space water loss. Different types of decreasing evaporation varied according to regional and economic conditions and environmental issues. On the other hand, in Iran the research conducted regarding reducing and controlling evaporation from water reservoirs is limited. Therefore, the current research is carried out with the aim of using new, economic, and appropriate to climatic conditions and accessible methods to reduce evaporation from water reservoirs, especially agricultural water reservoirs, in the Semnan region.

The efficiency of 6 physical covers (white plastic balls, empty bottles, bottles filled with straw and stubble, green canopy net with 50% density, green canopy net with 80% density, and white canopy net with 50% density), after preparation on the sunken Colorado evaporation pans, is evaluated in four periods of about 30 days in fall 2018 and winter of 2019 and spring and summer of 2021. Measuring the amount of evaporation from pans during 4 periods of approximately 30 days in different seasons of the year are done daily at 10:30 in autumn and winter and at 9:30 in spring and summer. It should be noted that the water temperature is also measured using an alcohol thermometer at the same time as the water level reading.

Based on the results of measurements, the rate of evaporation from the treatments of white plastic balls, empty bottles, bottles containing straw and stubble, green canopy net with 50% density, green canopy net with 80% density, canopy net White with a density of 50% and the control is equal to 259, 320, 213, 277, 369, 283 and 754 mm, respectively in four periods, which clearly shows a significant reduction in the evaporation of the applying six covers to the amount of 66, 58, 72, 63, 52 and 61 percent compared to the control treatment.

In general, according to the efficiency of all the treatments in this research and the application of these covers, taking into account the economic, social conditions and the feasibility of implementation, in order to reduce evaporation from open water reservoirs, especially agricultural water storage pools, it is evaluated as efficient and suitable. Generally, among the methods used, the most efficient related to the bottle filled with straw and stubble, followed by plastic ball treatments and green canopy netting with a density of 80 are evaluated as the most appropriate methods.