All the 24 shutters of the Purapallikkavu regulator-cum-bridge were downed on Wednesday after days of uncertainty over saline intrusion into the Periyar.
The shutters could not be closed as large chunks of logs, branches of trees and waste materials were lying across the regulator.
The Kerala Water Authority draws water from the Periyar for most of its supply schemes in the city and surrounding areas.
The regulator was constructed to keep off saline intrusion into the river. During the floods the river had brought down lot of waste materials that blocked the working of the shutters. The shutters were closed after removing all the waste materials.
The Irrigation Department, which maintains four regulators on the river, would now be taking up the work on the Pathalam regulator, said a senior official.
KWA officials had dredged out some of the sand and silt on the side of the intake well to keep the water level optimum for drawing raw water. With the shutters closed, the water level is expected to increase.
There was some apprehension about the river losing its depth because of the sand and silt deposited downstream following the floods, the officials said.