Following a night of relentless rain and significant inflows, the floodgates of Chennai’s two crucial reservoirs, Chembarambakkam and Poondi, were further opened on Wednesday, October 22, 2025. This action was taken to meticulously control water levels and mitigate any potential flood threats.
A well-defined low-pressure system lingering over the southwest Bay of Bengal, just off the Tamil Nadu coast, has been the catalyst for these intense downpours across various parts of the state. Currently, the 90 major water bodies in Tamil Nadu collectively hold an impressive 87.7% of their total storage capacity, which amounts to 224.34 thousand million cubic feet.
Likelihood of Depression
The Regional Meteorological Centre (RMC) in Chennai anticipates that this weather system will continue its northwestward trajectory. It is projected to gain strength, potentially evolving into a depression over the southwest and adjacent west-central Bay of Bengal, off the coasts of north Tamil Nadu and south Andhra Pradesh, by Wednesday evening. The system is expected to traverse across north Tamil Nadu, Puducherry, and the south Andhra Pradesh coasts within the next 12 hours.
Managing Water Bodies
Chembarambakkam reservoir, a vital source of drinking water for Chennai spanning 25.51 square kilometers, received a substantial inflow of 2,170 cubic feet per second (cusecs). This figure includes water diverted from Poondi reservoir via a link canal. Water Resources Department officials have noted that the upstream water bodies feeding Chembarambakkam are rapidly reaching full capacity. On Wednesday, October 22, the reservoir’s water level stood at 20.84 feet, a notable increase from 18.52 feet recorded on October 18. With its storage capacity reaching 2,815 million cubic feet (mcft) against a total of 3,645 mcft, the department proactively escalated the water discharge into the Adyar river from 100 cusecs to 500 cusecs on Wednesday morning. This measure aims to balance storage and effectively manage the heavy inflows. Consequently, flood warnings have been issued for areas downstream and along the Adyar river.
Similarly, the Poondi reservoir has seen its water release intensified to 4,500 cusecs. This increased discharge is critical for maintaining its water level at 33.05 feet, which is two feet below its full capacity.
Significant Rainfall Received
The Northeast monsoon has vigorously impacted several districts throughout the state. Periyakalapet in Puducherry experienced exceptionally heavy rainfall, recording 25 cm within the 24 hours leading up to 8:30 a.m. Numerous weather stations and rain gauges in and around Puducherry, Villupuram, and Cuddalore also reported very heavy rainfall.
Widespread and intense rainfall also drenched other districts, including Chennai, Kallakurichi, Tiruchi, Karur, and Chengalpattu.
Current Forecast
In its latest nowcast, the RMC forecasts light to moderate rainfall across the northern districts of Tamil Nadu, including Chennai, Ranipet, and Cuddalore, as well as Kanniyakumari district and Puducherry, until 1 p.m. The RMC has revised its forecast, narrowing the red alert specifically to Ranipet and Tiruvallur districts until 8:30 a.m. on Thursday, October 23. Meanwhile, many other north Tamil Nadu districts, including Chennai, remain under an orange alert for the same duration.