Cyclone Okchi: CWC asks TN to monitor Ponnaiyar river, dams

The Central Water Commission (CWC) has asked authorities in Tamil Nadu to closely monitor the Ponnaiyar river for the next five-seven days after a shutter of the Krishnagiri dam got damaged recently, forcing release of water downstream, and in view of Cyclone Okchi.
The reservoir on the river is located near Periyamuthur village, about 10 km from Krishnagiri town in the state's Krishnagiri district.
The dam reached its full reservoir level (FRL) in September this year due to "very heavy rainfall" in the upper catchment of the Ponnaiyar river in Karnataka and Andhra Pradesh. It started releasing water downstream. Due to this, its downstream reservoir, the Sathanur dam, neared its FRL.

In such a situation, one of the shutters of the Krishnagiri dam got damaged and water started flowing through it on November 29, the CWC said in its report.
The CWC, however, has inferred that the peak flow from the Krishnagiri dam to downstream has already passed through the damaged spillway and that there will be reduction in the outflow "in case there is no further aggravation in the damage caused to the reservoir".
"However, the effect of rainfall in Karnataka area if any in association with cyclonic storm Okchi is to be monitored closely.

"The inflow to Sathanur dam will be mostly moderated around the outflow from Krishnagiri dam other than that through the intervening catchment rainfall," the CWC said in its report.

Referring to the forecast that the area is likely to receive around 25-50 mm rainfall over the next two days, the CWC said it might increase the inflow into the Krishnagiri dam, prompting release of more water.
"This should be monitored carefully," it added.
The commission further advised that the effect of the releases from Sathanur dam as well as the tidal effect from sea near the confluence have to be monitored carefully.
In addition to that, local rainfall in association with "another brewing system" in the Bay of Bengal has to be monitored, it said.
"There should be very close monitoring of the entire Ponnaiyar system for the next five-seven days in view of the likely development of severe rainfall producing systems," it added.