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Abstract
Reducing evaporation losses from open water storages is of paramount importance for water security in arid countries. In many parts of Australia, the annual average evaporation exceeds the annual precipitation by more than 5 times. High capital and maintenance costs of manufactured products are a significant barrier to implementation. Single and multilayer floating modular devices as a potential evaporation mitigation method has been investigated extensively from the coastal to the arid zone of Australia for the first time. Systematic reduction in evaporation is demonstrated, approximately linearly proportional to the covered surface. Evaporation is reduced by approximately 40% at the maximum packing densities achievable for a single layer of floating recycled bottles. Increasing device thickness to 5 layers of plastic bottles assemblies have shown that they can effectively mitigate evaporation loss by between 52-79% depending on the boundary conditions. Plastic spheres can reduce evaporation loss by 54%.
Thus study also provided the opportunity to capture long term measurement of the Droplet size and fall velocity distributions of natural rainfall. Formal expressions that link droplet size distribution, intensity, fall velocity and kinetic energy of natural rainfall are developed for both the sites. These are reconciled between different recent studies and compared with data collected from both the locations. Measurements of terminal velocity at both the sites show that raindrops of all size class fall at significantly lower speeds than the classical terminal velocities of distilled water in stagnant air. Fall velocities of droplets in a certain size class have been found normally distributed and the width of the distribution increases with increasing rainfall intensity for both the sites. The energy of rain is approximately constant at intensities higher than 80 mm/hr both at the coastal and arid site.