Outflow into Kosasthalaiyar river will be stored in 12 checkdams before reaching the sea
The Water Resources Department (WRD) doubled the outflow from the Poondi reservoir in Tiruvallur on Monday as the waterbody received inflow from upstream waterways for the second day.
This is the first time in a decade that water had been discharged before the onset of the northeast monsoon. Officials of the WRD recalled that the reservoir’s floodgates were opened under similar circumstances once in 1996 and then in 2011.
“We had to step up outflow to nearly 2,000 cubic feet per second (cusecs) as the reservoir received inflow from one of the arms of Nagari river through Pallipet. Water from Ammapalli Dam in Andhra Pradesh and catchment areas flowed through Nagari river. Surplus water of two tanks upstream also flowed into the reservoir through Nandi river,” an official said.
As on Monday, the Poondi reservoir has 2,840 million cubic feet (mcft) of water, which is 88% of its capacity. The department plans to maintain the water level below 34 feet against the full level of 35 feet this month as more inflow is expected during the ensuing northeast monsoon.
Water released into Kosasthalaiyar river would take four or five days to drain into the sea. “Water discharged into the river will be stored in 12 checkdams downstream of Poondi before it reaches the sea. A minimum of 500 mcft will be saved in these checkdams and water will be transferred to the Cholavaram reservoir through Tamaraipakkam anicut with regulator arrangements,” an official said.
Moreover, well fields along the course will be recharged and another 500 mcft of water will be harnessed through groundwater recharge, the official added.
At present, Kosasthalaiyar river carried 2,000-2,500 cusecs, which was far less than its capacity of 70,000 cusecs. Flood warning was issued for villages along the river’s course, including Thirukandalam, Pudukuppam and Bandikavanur, and those in the city’s merged areas, such as Manali, Sadayankuppam and Ennore.
“We plan to maintain a minimal discharge of 200-300 cusecs into the river to keep the Poondi reservoir’s water level below 34 ft even if inflow decreases. The flow in the river will help groundwater recharge and maintain river ecology. Residents of areas close to the river will also remain alert ahead of the monsoon,” an official said. The two other major reservoirs in Red Hills and Chembarambakkam have a storage of 87% and 78% respectively.
“We are monitoring the water levels. Inflow for two or three days due to incessant rains will be needed to open the floodgates,” the official added.