The 2018 Kerala Floods: A Dam Rule Curve That Was Never Followed
Kerala's dams, including the giant Idukki reservoir, were meant to hold a flood cushion in reserve and warn of releases in time to protect people downstream. A CAG-directed IISc study of the August 2018 floods, which killed over 480 people, found the flood cushion went unused, no advance rain or inflow warnings were issued, and sudden gate openings turned a severe monsoon into a catastrophe.
The Promise
“The sudden releases from the Mullaperiyar Dam ... forced us [Kerala] to release more water from the Idukki reservoir, downstream of Mullaperiyar, which is one of the causes of this deluge.”
— Government of Kerala, State government, in an affidavit filed before the Supreme Court of India · 24 August 2018
Kerala's own affidavit to the Supreme Court, made while defending its handling of dam releases during the floods, itself acknowledged that reservoir-release decisions contributed to the disaster's severity — a claim later examined in detail by an independent academic study commissioned at the CAG's direction.
The Standard
Dam operation that reserves a flood cushion below full reservoir level ahead of forecast heavy inflows, issues advance warnings of large releases to downstream authorities and the public, and coordinates release timing among cascading reservoirs (Mullaperiyar-Idukki-Periyar) to avoid compounding a flood peak.
Central Water Commission dam operation and flood-forecasting norms; Kerala's own dam rule-curve and reservoir operation guidelines
In force from 1 August 2018
The Reality
A study by the Indian Institute of Science, Bengaluru, carried out at the direction of the Comptroller and Auditor General, found that faulty dam management aggravated the August 2018 Kerala floods, which killed more than 480 people and displaced over a million. Although Idukki dam's operating protocol stipulates it be used for flood control as well as power generation, the study found it was operated primarily for power generation, and during the critical 14-18 August 2018 period, the reservoir's flood cushion of 110.42 million cubic metres — the buffer between full storage and the maximum permissible water level — was not utilised; had it been used, the study concluded the first phase of gate releases could have been avoided. The study also found no advance rain warnings or inflow forecasts had been issued to dam operators ahead of the extreme rainfall, hampering release planning. Kerala's own Supreme Court affidavit acknowledged that sudden upstream releases from the Tamil Nadu-controlled Mullaperiyar dam forced larger downstream releases from Idukki, compounding the flooding — a claim that intersected with, but did not resolve, longstanding Kerala-Tamil Nadu disputes over Mullaperiyar's operation. The episode renewed long-running allegations, including from activist groups, that the floods were substantially "man-made" through dam mismanagement rather than purely a natural disaster.
As of 30 March 2021
The Gap
Bars share a single zero-based scale. No axis truncation is used to exaggerate or minimize the gap between the two figures.
Timeline
- AnnouncementExtreme monsoon rainfall begins over Kerala
Unusually heavy and sustained monsoon rainfall begins across Kerala's river catchments, rapidly filling reservoirs including Idukki and Mullaperiyar.
- DelayCritical reservoir period begins without flood-cushion use
Between 14 and 18 August, Idukki's flood cushion of 110.42 MCM goes unused even as inflows rise, per the later IISc study; gates are opened as levels approach capacity.
- MilestoneKerala floods peak
Flooding across Kerala peaks, ultimately killing more than 480 people and displacing over a million, in what is described as the state's worst flood in nearly a century.
- StatusKerala's Supreme Court affidavit cites Mullaperiyar releases
Kerala tells the Supreme Court that sudden releases from the Tamil Nadu-controlled Mullaperiyar dam forced larger downstream releases from Idukki, contributing to the deluge.
- StatusIISc study finds dam mismanagement worsened floods
The CAG-directed IISc study concludes that failure to use the available flood cushion and the absence of advance rain and inflow warnings aggravated the 2018 floods.
Legal Status
This is a governance and reservoir-operation failure documented through an academic study commissioned at the direction of the CAG and Kerala's own Supreme Court submissions, not a criminal case. No dam official or minister has been criminally prosecuted specifically over the 2018 release decisions; the interstate Mullaperiyar dispute with Tamil Nadu remains a separate, long-running legal matter before the Supreme Court.
Verdict
An academic study commissioned at the direction of India's constitutional auditor found that Kerala's dam operators, including at the flagship Idukki reservoir, did not use the flood-cushion buffer their own operating protocol allowed for, had no advance rainfall or inflow warning system feeding into release decisions, and that the resulting late, sudden gate openings compounded a severe monsoon into one of Kerala's deadliest floods in a century.
The IISc study's findings are corroborated across multiple independent reports, and Kerala's own Supreme Court affidavit corroborates the causal role of upstream releases. Confidence is not higher because this entry has not directly reviewed the IISc study or the CAG's underlying audit, and because dam-management responsibility for the 2018 floods remains contested between Kerala and Tamil Nadu authorities and among independent researchers.
What remains incomplete
- This entry has not directly reviewed the IISc study or the CAG audit that commissioned it, relying on secondary reporting of their findings.
- The extent to which Mullaperiyar dam operation (under Tamil Nadu's control) versus Idukki's own management (under Kerala's control) was primarily responsible for the flood severity remains disputed between the two states and has not been independently adjudicated in this entry.
- No specific individual accountability findings or disciplinary action tied to the 2018 dam release decisions have been confirmed.
Sources
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