Water Loss by Evaporation From Partially Covered Water Bodies

Fresh water is a very precious commodity in most parts of the world; and mch of it is held in lakes and reservoirs. Yet significant amount of this water is continuously lost due to evaporation, especially during hot seasons. One way to reduce this loss is to cover the water surface. However, due to its often large size, it is not practical to cover it totally. Furthermore, environmental considerations (like access to the water for water birds, not turning the water bodies into "hot soup", etc.) would render such attempt at total cover very undesirable. Instead, it is proposed here to partially cover these water bodies with floating covers which are of manageable size and easy to manufacture. They are supported by floats and leave an air gap (for environmental reasons) above the water surface. In this work, the covers are of hexagonal shape; and when used they together cover about 60% of the water surface area. Measurements have been conducted in situ of day-time evaporation levels from covered and uncovered water tanks, along with weather data (wind speed and direction, air temperature, solar radiation, and humidity) during a summer season (excluding rainy days) at a Sydney suburb. Results have shown that depending on the weather, reduction of evaporation in the range of 5 - 30% has been achieved with the covers. Results from this work also helps with understanding the evaporation process from lakes and reservoir, and the design of better covers