Mettur Dam Opened for Irrigation: 45-Day Release Plan Faces Water Sustainability Test
Chief Minister C. Joseph Vijay on Tuesday (September 1, 2026) opened the Mettur dam for irrigation, marking the start of the release of Cauvery water for the Samba cultivation season. The government plans to maintain the release for an initial period of 45 days, but the exact duration will depend on the storage position and the inflow from Karnataka in the coming weeks.
At the time of the opening, the water level in the dam stood at 91.56 feet, with storage at 54.45 thousand million cubic feet (tmc ft). The dam's full reservoir level is 120 feet, and its total capacity is 93.47 tmc ft. Authorities are expected to release about one tmc ft per day.
Based on current storage, and after setting aside about 10 tmc ft for environmental flows, drinking water and dead storage, the release can be sustained for roughly one and a half months even if no further inflow arrives. That calculation broadly matches the 45-day plan announced by the government.
However, the actual duration will also hinge on inflow from the Cauvery catchment in Karnataka. Data from the Cauvery Water Management Authority shows that during the southwest monsoon season of 2026-27, the quantum of water received up to August 30 was far below the stipulated amount. The total required by the Supreme Court's February 2018 judgment was 84.8977 tmc ft for June to August, but the realised flow at Billigundulu on the inter-State border was only 27.6517 tmc ft — a shortfall of 57.246 tmc ft.
In specific fortnightly periods, the variation was mixed. Between July 29 and August 11, the authority had prescribed a release of 4.234 tmc ft, but the realised amount was 8.27 tmc ft. In the following period, August 12-24, the stipulated quantum was 13.478 tmc ft, against which 11.464 tmc ft was received. Between August 25 and 30, the prescribed release was 4.67 tmc ft, while the actual inflow was 4.34 tmc ft.
Looking ahead to September, the average inflow at Billigundulu over the last 30 years has been about 36.8 tmc ft. Given the current monsoon deficiency of about 47 percent in the catchment, the State could expect nearly 20 tmc ft in the next month. If that materialises, it may be possible to extend the release by about two weeks.
Even under the worst-case scenario, the lowest September inflow recorded since 1974 has been around 10 tmc ft. For instance, in September 1987, the State received 10.57 tmc ft. Even in the drought years of 2003-04 and 2023-24, when annual realisations were below 100 tmc ft, September flows were 13.385 tmc ft and 13.5857 tmc ft respectively.
Another factor in the government's planning is the northeast monsoon, which normally accounts for about half of the State's annual rainfall. It is expected to set in around October 20, within a deviation of seven days on either side. A timely monsoon could replenish reservoirs and ease pressure on the Cauvery system.
An official explained that the release was started now because it takes about three weeks for the water to reach the tail end of the river system. If the release were delayed, the Samba crop would suffer, he said. The government is therefore proceeding with the release while continuously monitoring storage levels and upstream inflow.
