Flood in Kochi could be more devastating than in Chennai if Mullaperyar dam breaks

Thiruvananthapuram: The failure of Idukki dam can cause a flood in Kochi bigger than that faced by Chennai now.

Idukki dam could fail under certain conditions if Mullaperiyar dam fails. In case of failure of Idukk dam, the lower periyar dam and the Bhoothathankettu Barrage will be washed away.

The Dam Break Analysis done by the Indian Institute of Technology, Roorkee, in October 2012 for Chief Engineer of Inter-State Waters, Kerala, says that the depths of flows at different locations within the Periyar River reach up to Arabian Sea will vary from 5.43 metres near Arabian Sea to 163.78 metres just below the Lower Periyar Dam.

This means that Greater Kochi can be under more than 6 metres of water.  (The flooding in most parts of Chennai was of a metre or two following heavy rain and release of large quantities of water from Chembarambakkam reservoir into Adayar River.) The upper regions will face a water column of more than 100 metres in height which will devastate everything on the way. The peak of the Lower Periyar Dam break flood is estimated to be of 379446 cumecs. The breach will happen in a little over a minute when water from Idukki hits it.

The flood caused by simultaneous breach of Idukki and Cheruthoni dams at its peak is estimated to be 12.11 times the peak flood generated by breach of Mullaperiyar Dam. The water column will be as high as 161.55 metres just below the Idukki Arch Dam. It will come down to 69 metres about 20 metres downstream though that would make little difference for those living below the dam.

In case of failure of the arch dam alone, the flood will be 6.52 times the flood caused by breach of Mullaperiyar dam. The water column will be as high as 121.38 metres just below Idukki Arch Dam. Its size will come down to 36.78 metres about 20 kilometres downstream.

Breach of Cheruthoni dam will be more damaging than the arch dam with depth of peak flows ranging from 137.84 metres just below the dam site to 43.51 metres at 20.02 kilometres downstream (Lower Periyar Reservoir).  Waters from Idukki will reach Lower Periyar in less than six minutes. However, two to three hours time will be taken for overtopping of dams at Idukki.

The Mullaperiyar Dam is 36 km upstream and breach of the dam is estimated to generate depth of flows ranging from 40.36 metres just below the dam site and 20.85 metres at the end of the reach.

Note: For full details of Dam Break Analysis of Mullaperiyar Dam, visit http://expert-eyes.org. This report in News and Views merely seeks to make comparisons easy and does not assume any probability of failure of the dams as that needs to be determined by structural and other kinds of studies.  Studies commissioned by Kerala Government have shown that such probability exists. But, the Supreme Court of India has not accepted them.