Conservation of water from open storages by minimising evaporation
Creators: name: Burston, Ian
Publisher: name: RMIT University
Year: 2024

description: The development and refinement of methods for determining evaporative loss from large open water storages dates back to the 1930's. However, it was some 20 years later before documented methods for minimising the losses first appeared, and, despite considerable research into the problem since, no practical or commercial solution was identified then. The need to conserve water in many parts of the world to support increasing demands placed on water resources by growing populations competing with environmental requirements is becoming more evident with time. This has fuelled interest to look more closely at ways to minimise evaporative losses from open storages. <br><br>In this research, the process of evaporation from a water surface and the impact of evaporation on exposed water storages have been investigated together with global and local water balances. Evaporation from irrigation storages within Australia has been estimated as well as the economic benefit to the rural sector of reducing storage evaporation. While the figures can only be used as a guide, it would appear that it is worth considering evaporation reduction methods in which a reduction of greater than 50% can be achieved. <br><br>Methods to estimate and measure open storage evaporation have been discussed as well as the means by which evaporation may be minimised. The most effective methods for reducing evaporation have been identified as those in which the driving forces for evaporation, i.e., solar energy and wind, are minimised by use of reflective floating barriers. <br><br>A floating barrier method, referred to as Aquacap modules, originally investigated by RMIT University has been further developed and field tested in purpose built evaporation ponds at the University's Bundoora East campus and at the premises of Pyramid Salt at Pyramid Hill in north-central Victoria. Industry funding and assistance from Sainty and Associates and Land and Water Australia has enabled the extensive study to be undertaken. A Steering Committee comprising representatives from the water industry, water users and academia provided valuable input to the research program. <br><br>Results from the field studies have shown that the free-standing modules are a practical solution to the problem for large water surface areas and are stable while in the water with winds gusting to 70 kilometres per hour. With the modules covering 84% of the water surface area, the average gross evaporation reduction compared with a control pond was found to be in the order of 75%. During periods of high evaporation, this reduction was found to increase to a maximum of 89%. Other advantages of the principle are the reduction of turbidity due to reduced wave action and reduced concentration of salts due to reduced evaporation. The reduction of temperature stratification resulting from the modules may also be an advantage in reducing the incidence of algal blooms. <br><br>Economic considerations indicate that the principle would be best suited to high value water applications. Preliminary investigations indicate that application of the Aquacap principle would cost in the order of $16 per square metre of water surface area when 80% of the water surface is covered. Assuming an annual evaporation rate of 2.0m if uncovered and a payback of 5 years, the water cost would be in the order of $2300 per megalitre at the above mentioned Aquacap cost per square metre. <br><br>A mathematical correlation has been used to model the rate of evaporation reduction during diurnal climate changes and to predict the change in evaporative loss with change of water temperature. The water temperature has been related to radiant transmission through the dome of the module. <br>It is evident that further research would benefit the commercialisation opportunities of the principle. Areas to be addressed are material selection and manufacturing principles to reduce the module cost; water quality issues relating to the application of the modules to potable water storages; and issues relating to water management and the economics of the principle.