Explained | Rule Curve for Mullaperiyar

The Rule Curve comes into effect between June 10 and November 30, during which the dam gets maximum inflows from the South West Monsoon. 

What is the Rule Curve?

Rule Curve is a tabulation which specifies quantum of storage of water or empty space to be maintained in a reservoir during different times of a year, based on the rainfall data for 35 years. 

It is a ready-reckoner in decision-making for officials in charge of the dam, for smooth operation of shutters, especially for moderation of flood, during monsoon times without having to seek permission from the top hierarchical ladder. 

First dam to have Rule Curve:

According to Tamil Nadu Water Resources Organisation, Mullaperiyar is the first reservoir to have Rule Curve implemented, in the country.

Water of the Mullaperiyar dam, has remained a bone of contention between Tamil Nadu and Kerala for over four decades. After a long legal battle, the Tamil Nadu Government was allowed by Supreme Court to raise the water level from 136 feet to 142 feet in 2014. However, Kerala insisted with the Supreme Court to insist that Tamil Nadu, which maintains and operates the dam, prepare a Rule Curve for flood control and flood management.

It had earlier alleged that sudden and unannounced release of flood water through Mullaperiyar dam caused severe damage to Kerala. Though Tamil Nadu Government delayed it with various reasons, it prepared the draft Rule Curve for the reservoir in consultation with Hydrology Wing of the Central Water Commission. And it was first implemented in October 2021. Water was released from the dam much before it could touch 142 feet, raising a huge hue and cry among the farmers and politicians of the State.