Final Evaporation Control in reservoirs

6.7.2
 
Demerits of Chemical WERs 
The fatty alcohols used as WERs are not readily available and are costly. Historically, fatty 
alcohols were produced only by sperm whales or by sodium reduction of animal oils and fats. 
It was only after the development of high-pressure hydrogenation process that good quality 
fatty alcohols are now commercially available. However, this is a very advanced technology, 
and requires trained and skilled staff to operate. 
The other short-term method for control of evaporation is by covering the water surface for 
protection against rise in temperature of water surface and effects of air currents. This 
method cannot, however, be employed on large storage bodies. The use of plastic floating 
materials has been found to be quite effective and useful, although this method is also cost 
prohibitive. Floating spheres of poly-steryl can be effectively employed. White colour 
spheres have the added advantage of reflecting solar energy, thus reducing the evaporation in 

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a more effective manner. Floating covers constructed of low density (110-130 kg/m
3
) closed 
cell synthetic rubber sheeting (EFDM) can also be used. The covers can be fabricated from 
6.4 mm thick sheeting bonded together with contact adhesive. The life of such covers may be 
around 8 years, if the material and methodology as adopted by Dean (1930) and Dedrick 
(1976) is used. The size of covers should be slightly larger to accommodate shrinkage. These 
methods can be used to cover water storage tanks. The other floating materials tried are 
wheat husk, paddy husk, wooden blocks, thermocol boards etc. Thermocol board has been 
found to be more effective than straw, dust and wooden blocks. However, mass scale use of 
these materials is not recommended till results providing their economic and utility are 
available.