The devastation wrought by the Kerala floods of August could not be attributed to the release of water from dams, says a computer-simulation of flood storage and flow patterns by a team of researchers.
Scientists from the Indian Institute of Technology-Madras and the Purdue University, United States, say that the odds of such floods were “0.06%” and no reservoir management could have considered such scenarios.
Previous analyses of the Kerala floods had not incorporated a simulation of water flows and relied only on measurements of water levels at dam sites, according to the authors of the study.
Kerala has 39 major dams. and they are maintained by the Kerala State Electricity Board and the Water Resources Department.
All 39 dams in the State had reached their full reservoir level by July-end, and were incapable of absorbing the torrential volumes in August leaving dam-managers with no choice but to release them. The scientists analysed different scenarios with combinations of reservoir storages (85%, 75%, 150% and 25%) at different time periods (end of June and end of July), along with different soil moisture conditions, which has a bearing on river flows.
What they found was that in the hypothetical scenario that there were no dams in the Pamba River Basin (PRB) — there are 17 dams and barrages — the “peak discharge” at locations downstream of the Idukki reservoir would have been “reduced by 31%.” This, however, wasn’t a reduction enough to have prevented the inundation, according to the researchers.
“The major share of the total flood flow was by Perinjankutty (3,500 m3/s), which is a near uncontrolled tributary, while the 14 controlled releases from Idukki had contributed only 1, 860 m3/s… the results indicated that the role of releases from the major reservoirs in the PRB to cause the flood havoc was less,” the authors say in the study to be published in a forthcoming issue of the peer-reviewed Current Science .
A simulation of the section of the Periyar river at Neeleswaram showed that even if reservoirs were emptied out to their dead-storage levels of 25%, it still would have meant flows far in excess of the maximum capacity that could have been contained with the river banks. “Most dams are designed to store as much water as possible to the full reservoir level for hydropower planning,” said K.P. Sudheer, Professor, Department of Civil Engineering, IIT-M. “So, maintaining 25% storage beats the point of having a dam in the first place.”
For future planning, authorities must put in place an “integrated flow management” system, that is, view dams as critical to managing floods and not merely a fount for producing electricity. Additionally, weather forecasting agencies ought to be giving more quantitative forecasts — of the likelihood of water volumes rather than descriptions of ‘extreme events’ — regarding expected water levels during possible floods, Mr. Sudheer added.