Encroachments expose Periyar banks to flood risk

The rare phenomenon of simultaneous opening of the shutters of Cheruthoni and Idamalayar dams may result in the discharge of larger volumes of water, thus increasing the impact of flooding in low-lying areas along the banks of Periyar.

The peak power generation coupled with drop in intensity of rain in its catchment areas may have enabled the authorities to withhold the issue of second warning in the case of Idamalayar dam. All shutters of Bhoothathankettu dam remain open to facilitate the smooth flow of water to be released from Cheruthoni dam.

Besides, the shutters of all regulators in Chalakkudy and Periyar rivers have been opened to prevent holding up of water. “With the release of water from the Cheruthoni dam, there will be an unavoidable inundation of low-lying areas from where people will have to be evacuated till water recedes. Aluva, Kadungalloor, Karumalloor, Kunnukara, Kalamassery, and Puthenvelikkara are among the areas that are likely to be affected in the district,” Irrigation Department sources told
The Hindu

The department is expecting the shutters to be opened by August 4 or 5.

The release of small quantity of water is unlikely to cause much of a flood, since the water level in the Periyar has subsided from what it was after the heavy rain that lashed the district recently.

A good share of the inflowing water to Idamalayar dam is being used for power generation, and the excess inflow over and above power generation is what forces the opening of shutters. Compared to Idamalayar, Idukki dam uses only one-third of the inflow for power generation, sources said.

“The flow of water up to Aluva will be relatively smooth. The problem arises in the branches and sub-branches of the Periyar infested with encroachments and weeds hampering the smooth flow of water further downstream. This causes the water to hold up, inundating low-lying areas.

“The accumulation of mud may have also caused widespread undergrowth, which would have by now taken deep roots in the mud and cannot even be removed using floating excavators but will have to be removed using cutters,” a senior official said.

Unhampered flow of water along the full width of the Periyar, which has an average width of 180 metres, is unlikely to cause flooding following the opening of the dam shutters, as the water level may not rise in excess of 60-70 cm, though the exact volume of the release of water is not known, he added. There will be no sudden release of water.

Since flooding caused by opening of dam shutters has not happened for over a quarter century, many may have built houses in low-lying areas.

The release of water from Cheruthoni dam may also have its impact on the water treatment facility in the Periyar. Water turbidity may lead to greater settling time of suspended particles consequently consuming more time for treatment. The plant will also have to be cleaned after a few rounds of treatment if the turbidity is greater, the official said.

With the release of water from the Cheruthoni dam, there will be an unavoidable inundation of low-lying areas from where people will have to be evacuated till water recedes

Irrigation dept

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