کاهش تبخیر از مخزن‌‌ آب سد‌‌ها

Total renewable water resources in Iran is about 105 billion m³ that is about 0.3% of the world total fresh water; whereas, the land area and population of Iran is 1.1% of the world. Furthermore, the per capita water resources in Iran is about 1300 m³ that is lower than that in many other countries in the world. Therefore, shortage of water resources in Iran is higher than that for other countries. The total capacity of dam reservoirs in Iran is about 48 billion m³ from which about 34 billion m³ is regulated water and may be used for agriculture, industry and domestic. Due to dry air and high air temperature the evaporation water loss from the dam reservoirs is high; therefore, it should be reduced to save the stored water resources. In this study it is shown that the magnitude of evaporated water is important (4.2%-14.3% of total capacity of the stored water in dams). The amount of evaporated water, on average (10%) is 4, 8 billion m³ that should be reduced in drought and water crisis conditions and the saved water should be used in agriculture, industry and domestic. Different methods for reduction of water evaporation from reservoirs are used in the world, among which emulsion and powder chemicals and covering water surface are suitable ones that can be used in Iran. Application of emulsion and powder on the water surface produces monolayers that cover the water surface to reduce the evaporation losses. However, wind and water wave disrupt the monolayer and reduce its effects on the evaporation reduction; therefore, it should be applied continuously by 1-2 day intervals. One of the evaporation reduction chemicals in the world is “Watersaver” that its use is safe for environment. Application of this chemical can reduce the water evaporation by 40%. Covering materials that can be used are floating white Styrofoam or floating light hollow concrete blocks that reduce the evaporation loss by 80%. Economic analysis indicated that evaporation reduction and water conservation by these chemical and materials are compatible to fresh water production by desalinization of saline sea water and wastewater treatment.