Kerala has experienced a devastating flood during the month of August 2018. While an extreme rainfall was the primary reason for this flood, there were critisism at various levels that unproffesional management of dams were also magnified the impact of flood. IIT Chennai conducted a case study in one of the worst affected basins during the flood, Periyar River Basin(PRB) that received a 145 year return period rainfall.
The analysis suggested that reservoir operations could not have helped in avoiding the flood situations as only 16-21% peak attenuation was possible by emptying the reservoir in advance,as the bulk off runoff to the flooding was also contributed by the intermediate catchment without any reservoirs to control. And also the attenuated flood peak due to advance emptying of the reservoir would still be almost double the safe carrying capacity of the river.
In addition, the reliability of the rainfall forecast is also a concern for the reservoir operations. It is also noted that the probability of Extreme Rainfall Events(EREs) of this kind in the month August in PRB is very small(0.6%), and therefore any planned operation could not have helped in reducing floods of such magnitude.