Final Evaporation Control in reservoirs

6.5
 
Integrated Operation of Reservoirs 
This method is suitable for a system of reservoirs which can be operated in an integrated way.
The method consists of operating the reservoirs in such a way that total exposed water surface 
area is kept minimum for the system as a whole. Consequently evaporation loss gets minimized.
For achieving this objective water use should be planned in such a way that shallow reservoirs 
with large water spread area are depleted first. This method has been successfully practiced by 
Mumbai Municipal Corporation in their water supply scheme. Such techniques were also tried in 
the Hiran dam 1 & 2 in Junagarh district of Saurashtra region of Gujarat. The Chennai 
Metropolitan Water Supply and Sewerage Board has also been practicing integrated operation of 
Red Hills, Cholavaram and Poondi reservoirs, which supply water to Chennai City, so that the 
exposed water surface is kept minimum. 
6.6
 
Treatment with Chemical Water Evapo-Retarders (WER) 
Chemicals capable of forming a thin mono-molecular film have been found to be effective for 
reducing evaporation loss from water surface. The film so formed reflects energy inputs from 
atmosphere, as a result of which evaporation loss is reduced. The film allows enough passage of 
air through it and hence, aquatic life is not affected. The film developed by using fatty alcohols 
of different grades has been found most useful for control of evaporation. These materials form a 
film of mono-molecular layer when applied on water surface which works as a barrier between 
water body and the atmospheric conditions. These fatty alcohols used for evaporation control are 
generally termed as chemical water evapo-retardants (WERs) and these are available in the form 
of powder, solution or emulsion. 
These chemical water evapo-retardants have the disadvantage of high cost of application.
However, when adopted in scarcity period, drought, etc. the quantity of water saved by this 
method would work out cheaper than alternate means of bringing water from far off places by 
manual or mechanical transport. The economics of WERs application may however vary from 
site to site depending on local factors. The chemical water evapo-retardants have another 
limitation of the mono-layer breaking at high wind velocities. Following chemicals are generally 
used for water evaporation retardation: 
•
Cetyl Alcohol (Hexadecanol) C
16
H
33
OH 
•
Stearyl Alcohol (Octadecanol) C
18
H
37
OH 
•
Ethoxylated Alcohols and Linear Alcohols 
•
Linoxyd CS-40 
•
Acilol TA 1618 (Cetyl Stearyl Alcohol) 

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