Planned discharge of surplus water from the city reservoirs based on the Regional Meteorological Department’s accurate cyclone forecasts helped avert flash floods in the major rivers during the historic rain caused by cyclone Michaung.
The Water Resources Department started to gradually reduce water release from the city reservoirs, including Chembarambakkam, Poondi and Red Hills, on Wednesday. The water discharge that was as high as 8,000 cubic feet per second from Chembarambakkam reservoir on December 4 was reduced to 2,500 cusecs as rainfall has stopped over the region.
Water Resources Minister Durai Murugan inspected the reservoir on Wednesday along with various government officials. The Chembarambakkam reservoir’s storage is now being maintained at 3,459 million cubic feet (mcft) against 3,645 mcft.
Officials of the WRD said the department had shifted from its conservative approach in reservoir management this monsoon. The department had been experimenting on pre-emptying a marginal amount of storage ahead of the peak monsoon for the past two years now.
This year, it may be recalled that a minimum quantity of storage was depleted from the reservoirs be it Chembarambakkam or Red Hills ahead of the unprecedented rains. A gap of at least three feet was maintained at each reservoir feeding drinking water to the city to create more storage space.
“For instance, we had let out additional water from Chembarambakkam more than the inflow received during the initial rain spell. During peak inflow, we were able to reduce discharge and store more water in Chembarambakkam with additional storage space. Adyar river carried only peak flow from upstream stretches like Adhanur during 10 hours on the day of torrential downpour. Flash floods in Adyar river inundating neighbouring areas were averted with these balancing measures of managing discharge from Chembarambakkam,” said an official.
Such steps helped in allowing fluvial floods from various parts of the city to drain into the river. Adyar river now carried a flow of about 23,000 cusecs and can carry up to a maximum of 45,000 cusecs without spillover.
Similar measures were carried out in Poondi reservoir across Kosasthalaiyar river as well. Unlike 2015, the reservoirs continue to be filled to their brim now due to the flood routing measures. The storage in the reservoirs was brought down to 75% during the days of downpour and now again built to nearly 94% on Wednesday, officials said.