For the past few years thanks to Southwest Monsoon seeing fairly robust seasonal rainfall numbers, in particular over Peninsular India Cauvery basin dams were mostly seeing good times with almost all the dams including Mettur overflowing more than one occasion in the same season. While this year models were early on indicating a possibly weak Southwest Monsoon for the Southwest Coast of Peninsular India, which is primarily the catchment area for Cauvery Basin, things dont look great for the storage at the biggest dam in the Cauvery Basin. Mettur with a storage of nearly 93.5 Mcuft can store nearly 80% of the total storage possible across the 4 major Cauvery Basin Dams in Karnataka namely KRS, Hemavathi, Kabini & Harangi.
In a strange turn of fate as of yesterday the storage in Mettur dam at 29.42 Mcuft is lesser than the current storage of 29.85 Mcuft at Bhavanisagar dam. While it could be an interesting exercise to plot all those occasions when such an event happened during peak Monsoon period, it is only fair to say not often one sees the storage of Mettur lesser than Bhavanisagar during the 4th week of August. With the Tamil Nadu government sticking to traditional date of June 12th to open Mettur dam, 2nd successive year in a row, for the benefit of delta farmers it has created a catch 22 situation now for the water managers of the state with storage now at the Crossroads. The current storage is less than half of the storage at same time last year and just 1/3rd of the overall storage capacity.
With just about 5 weeks of Southwest Monsoon season left, though the actual withdrawal over Peninsular India may be around 7 / 8 weeks from now the weather models are not very enthusiastic of any major / extreme inflows into the three major river basins of Peninsular India, Cauvery, Krishna & Godavari, during the rest of the Southwest Monsoon Season. With Mettur dam storage at the end of Southwest Monsoon having ramifications that extend well into the start of the next irrigation year in the form of opening the dam for subsequent cropping season a very large cloud of uncertainty is now hovering over the end of the season storage for Mettur Dam.
While we are not in a position to offer a solution to this question we end this post with hope resting on a fairly good Monsoon withdrawal season thunderstorms over South Interior Karnataka & adjoining areas of Northwest Tamil Nadu, catchment areas downstream of Krishnaraja Sagar, and a robust Northeast Monsoon for the delta farmers reducing their dependence on Mettur waters in the days to come.