With the unprecedented flow continuing in the Cauvery, the focus now turns to whether Tamil Nadu’s realisation in the current water year (June 2022-May 2023) will exceed the 47-year high of around 455 thousand million cubic feet (tmc ft), which was recorded in 1975-76.
The pattern of flows, as registered then and now at Biligundlu on the inter-State border, indicates that the State is set to create a record. During the southwest monsoon (June-September) 47 years ago, the quantity of water realised was about 306 tmc ft. But the State received around 347 tmc ft until August this year. In the first week of September, the figure was approximately 45 tmc ft. Since June 1 till September 7, Tamil Nadu realised nearly 392 tmc ft.
(For the study, the monthly flows recorded since 1974-75, a reference period for a high-level technical team to study the Cauvery basin in October 2016, have been considered.)
If one is to go by two other parameters, the scenario is promising. The data for the last 48 years show that an average annual flow is nearly 251 tmc ft, including 107 tmc ft during the period from June to August. This means that in the remaining nine months, the State will realise 144 tmc ft. On the basis of this yardstick, the State should get a minimum of 98 tmc ft in the rest of this water year, with the deduction of 46 tmc ft received in the first five days of this month. This takes the total annual realisation to 490 tmc ft.
The other parameter is the factor of 50% dependability. This broadly means that in a block of two years, one year is good and the other is bad. Based on this parameter, the quantity of realisation for the south-west monsoon is 129 tmc ft and for a whole year, 246 tmc ft. This indicates that the State will get at least 117 tmc ft in eight months, even if one leaves out the realisation for September. In the net analysis, the annual realisation is expected to be 489 tmc ft.
