Both research files behind this page were built as "steelmanning" exercises: presenting each state's strongest actual arguments, attributed to whoever is making them, rather than a strawman. The goal isn't to declare a winner. It's to show why this has stayed unresolved for 140 years.
Full timeline, 1886–2026
- 29 OCT 1886Lease signed: 999 years, ~8,100 acres, Rs 40,000/year, "all the waters" of the Periyar.
- 1947 / 1956Independence, then Kerala's formation under the States Reorganisation Act. Kerala later argues the lease lapsed; Tamil Nadu argues Section 108 of the Act continues it.
- 29 MAY 1970Two Supplemental Agreements: rent raised to Rs 30/acre, Tamil Nadu gets hydro rights, Kerala keeps fishing rights. Signed by Kerala's executive without Assembly ratification, later a point of contention, though no court has found it was signed under duress.
- 1979CWC inspection finds structural weakness and lime leaching; level cut from 152 ft toward 136 ft. Kerala's Assembly passes its first resolution raising safety concerns.
- 2001Mullaperiyar Environmental Protection Forum files Writ Petition 386/2001, seeking to raise the water level. This is the case that starts the modern Supreme Court litigation chain. An Expert Committee reports in March that 142 ft is hydrologically, structurally and seismically safe.
- 27 FEB 2006Mullaperiyar Environmental Protection Forum v. Union of India, (2006) 3 SCC 643. Supreme Court permits raising the level to 142 ft, calls the 1886 deed an "ordinary," "wholly non-political" lease.
- 18 MAR 2006Kerala passes the Irrigation and Water Conservation (Amendment) Act, capping the level at 136 ft by statute, directly overriding the Court's ruling three weeks earlier. Tamil Nadu responds with its own Article 131 suit challenging the Act.
- 2010–2012Empowered Committee, chaired by former CJI A.S. Anand, reviews the dam and finds it "structurally, hydrologically and seismically safe."
- 7 MAY 2014State of Tamil Nadu v. State of Kerala, (2014) 12 SCC 696. Constitution Bench strikes down Kerala's 2006 Act as unconstitutional, permanently enjoins Kerala from blocking 142 ft, creates the permanent Supervisory Committee.
- AUG 2018Catastrophic Kerala floods; Supreme Court orders the level temporarily down to 139 ft. Kerala blames sudden Tamil Nadu releases; Tamil Nadu disputes this.
- 2020–2022Dr. Joe Joseph v. State of Tamil Nadu, a public-interest petition alleging the Supervisory Committee had gone non-functional for years. Leads directly to the Dam Safety Act, 2021 (in force 30 Dec 2021), and the safety-audit process still running in 2026.
- NOV 2021Kerala's own Forest Department grants Tamil Nadu permission to fell trees near the "baby dam" for court-mandated strengthening work. Within days the Kerala Cabinet revokes it after local political backlash. Both states cite this single episode as proof of the other's bad faith: Tamil Nadu calls it obstruction, Kerala calls it its own environmental law working as intended, applied to any party equally.
- 3 AUG 2024Supreme Court agrees to try 11 fresh issues in Tamil Nadu's own Original Suit No. 4 of 2014, including whether the 1886 lease deed itself remains valid, and whether the Union of India, not Tamil Nadu, is the true legal successor.
- 19 FEB 2025Court remarks Kerala and Tamil Nadu are "fighting like school children," orders a new Supervisory Committee.
- 13 OCT 2025Court issues notice on a Kerala NGO petition seeking outright decommissioning and a new dam.
- MAY 2026Political change in both states: Congress-UDF's V.D. Satheesan becomes Kerala CM; TVK's Vijay becomes Tamil Nadu CM, ending decades of DMK–AIADMK dominance.
- 5 AUG 2026Tamil Nadu's budget announces intent to raise the level toward 152 ft. Kerala's new government protests immediately.
- 20 AUG 2026Southern Zonal Council: Satheesan offers to fully fund a new dam, ceding design/location/construction to Tamil Nadu. Vijay rejects it, reiterates the push to 152 ft.
Who actually owns it
The 1886 lease reads like an ordinary English-style property lease: rent, a fixed term, an arbitration clause between "Lessor" and "Lessee." The Supreme Court itself confirmed this reading in 2006, calling it an "ordinary," "wholly non-political" agreement. That implies the standard structure: Kerala, as Travancore's successor, keeps underlying title; Tamil Nadu, as Madras's successor, holds a time-bound leasehold interest.
But it isn't fully settled. The Court's 2024 decision to try Tamil Nadu's Original Suit No. 4 of 2014 reopened the more basic question of whether the Union of India, not Tamil Nadu, is the true successor, since the original lessee was a Crown/central authority, not the Madras Presidency government specifically. One argument that doesn't hold up on inspection is adverse possession. Tamil Nadu's possession of the dam has always been permissive and rent-paying, the opposite of the "hostile" possession that doctrine requires. Tamil Nadu's real footing is contractual right plus Kerala's own 1970 re-signing, which the 2006 Court treated as a fresh ratification.
A related jurisdictional question the 2006 judgment addressed directly: Article 363 of the Constitution bars courts from hearing disputes over certain pre-Constitution political treaties signed by princely rulers, precisely so former rulers couldn't re-litigate the terms of their integration into India. Kerala argued this should bar the Court from even hearing challenges to the 1886 lease. The Court rejected that reading, holding that Article 363 was never meant to cover "ordinary agreements such as lease agreements, agreements for use of land and water, construction works," the same "wholly non-political" characterization the lease gets throughout this page.
Kerala's own counter-argument for retained sovereignty rests less on constitutional doctrine and more on continuous conduct. The leased land has been under Kerala forest and wildlife law without interruption since 1899, first as a royal reserve, later the Periyar Wildlife Sanctuary and Tiger Reserve, and it's precisely because of that ongoing jurisdiction that Tamil Nadu has repeatedly had to seek Kerala's forest-department permission for routine maintenance work, including the November 2021 tree-felling episode above. A state that had genuinely relinquished all interest in the land, Kerala's argument goes, would have no such ongoing regulatory leverage to assert.
For comparison, Kerala owns and Tamil Nadu operates another dam under nearly the same arrangement: Parambikulam, agreed the same year (1970) as Mullaperiyar's Supplemental Agreement, so this isn't a one-off. Most other Indian interstate river infrastructure (Bhakra-Beas, Tungabhadra) instead uses a joint statutory board, which may be part of why Mullaperiyar specifically has proven so hard to resolve administratively.
Tamil Nadu's case, at its strongest
Argued by Tamil Nadu
"The 1886 lease survived independence and reorganisation as a matter of law, not our say-so. The Supreme Court has confirmed it twice. The 2014 judgment grounded this directly in statute: Section 177 of the Government of India Act, 1935 substituted Madras (and so Tamil Nadu, as its successor) as lessee, and Section 7(1)(b) of the Indian Independence Act, 1947, which lapses political treaties between the Crown and princely rulers, simply doesn't apply, because this was never a political treaty to begin with. Every court-appointed technical body that has examined the dam, the 2001 Expert Committee, the 2010–12 Empowered Committee chaired by a former Chief Justice of India, the ongoing Supervisory Committee, has found it safe. Kerala's 2006 Act was Kerala trying to legislatively overrule a judgment it had just lost, and the Court called that out in exactly those terms."
- Comparable masonry dams show old masonry can last with maintenance: Spain's Almansa (500+ years), Wales's Vyrnwy (138 years), Karnataka's own Krishna Raja Sagara (built the same way, similar age).
- Five districts, a century of irrigation, a lease Kerala's own government freely re-signed in 1970 at higher rent.
- Counsel's position to the Court: "no limits are specified for the life of a dam." Age alone isn't an engineering safety criterion.
- A consistent cross-party, cross-decade line. Jayalalithaa called Kerala's fears "baseless" in 2010 and the 2014 judgment "a victory for the people of Tamil Nadu." Stalin told Kerala's CM in 2022 the dam is "safe in all aspects." Vijay rejected Kerala's 2026 funding offer on the same grounds. In April 2026, opposition leader Edappadi Palaniswami even criticized the outgoing Stalin government for not pushing hard enough to raise the level, evidence the safety consensus crosses party lines, not just governments.
Where this case is weaker
The masonry-dam longevity comparisons are real, but they don't establish that Mullaperiyar's specific documented deterioration, the 2011 underwater survey, the lime leaching Tamil Nadu itself acknowledges, is equivalent to those better-maintained structures' actual condition. No Tamil Nadu statement located in this research substantively rebuts the CSMRS or IIT Roorkee findings on their technical merits, as opposed to characterizing Kerala's concern as political theater.
Kerala's case, at its strongest
Argued by Kerala
"'Repeatedly certified safe' leaves out a parallel record of warnings. Our own Centre for Earth Science Studies found in 1979 the dam wouldn't survive a magnitude-6+ earthquake. IIT Roorkee found in 2009 it could be damaged by a 6.5 even at the lower 136 ft level. The independent R.N. Iyengar Committee found the dam becomes structurally weak at high water levels even without any earthquake at all. A 2011 underwater survey, ordered by the same Empowered Committee that later cleared the dam, found deterioration in all 34 sections examined. The Supreme Court's own 2021 order found the dam's basic instrumentation plan still unresolved, seven years after the 2014 clearance. 'Certified safe' and 'currently, verifiably safe with modern monitoring' are not the same claim."
- The only other Indian dam built the same way, Tungabhadra, had a gate fail outright in 2024, attributed partly to age.
- We've offered, repeatedly, to fully fund a replacement, and Tamil Nadu has declined every version without substantive counter-engagement. This isn't just rhetoric: Kerala's own Irrigation Design and Research Board produced a costed Detailed Project Report in 2011 (Rs 600 crore, four-year build), revised in 2021 by Tata Consulting Engineers to roughly Rs 1,500 crore.
- A UN University report names Mullaperiyar alongside five other aging dams worldwide. Every other one has already been removed or put under a funded rehabilitation program. Mullaperiyar is the only one still unresolved.
Where this case is weaker
Kerala's own 2006 Act, attempting to override a Supreme Court finding by unilateral legislation, is a real, unflattering data point for Tamil Nadu's "Kerala changes the deal" argument that Kerala hasn't fully answered on the "should it have" question. But Kerala did have a legal theory for it, not just political will: the Act was framed as a valid exercise of the state's Entry 17 (State List) competence over water and its basic police-power duty to protect its own residents, on the argument that the entire Periyar catchment sits inside Kerala, making this arguably an intra-state safety matter, not a genuine inter-state river dispute at all. The Court rejected that framing in 2014, but Kerala's own defense of the Act deserves to be stated, not just its defeat. And the widely-circulated "35 lakh deaths" figure has no credible technical basis (see If It Breaks). Using it undermines Kerala's better-evidenced population-at-risk arguments by association.
Both sides, in one line each
Tamil Nadu documents a real safety clearance record more convincingly than it rebuts the specific deterioration findings against it. Kerala documents real unresolved uncertainty more convincingly than it proves the dam is currently unsafe. Neither side has produced a comprehensive, independently-modeled dam-break economic and casualty study to settle the question either way.
The path not taken: a second tunnel
Buried in the 2014 judgment is a third option neither state is currently discussing: a second tunnel at roughly 50 feet elevation (below the existing 106.5 ft intake), first raised by Prof. C.P. Roy, then chairman of the Mullaperiyar Samara Samithi, the same Idukki activist group usually associated with the "decommission it" position, and studied for the Empowered Committee by its technical members Dr. C.D. Thatte and D.K. Mehta. The idea was to enable faster emergency drawdown and access reservoir water currently unusable below the existing tunnel's intake level. The Court itself suggested it could function "as good as decommissioning the dam" without cutting Tamil Nadu's supply.
Over a decade later, no technical feasibility study, cost estimate, or formal state position on this proposal has ever been produced. Its only quantified cost claim is the judgment's own qualitative line that it would be "meagre compared to building a new dam." No rupee figure exists anywhere in the public record. It has simply fallen out of the political conversation, replaced by the current binary fight: Kerala's new-dam demand vs. Tamil Nadu's push to 152 ft.
Current status, September 2026
142 ft remains the legally operative ceiling. A new Supervisory Committee (Feb 2025) is the primary oversight body. Original Suit No. 4 of 2014, reopening the 1886 lease's basic validity, remains pending, still at the document-production stage as of the most recent reporting found. The Save Kerala Brigade's decommissioning petition remains pending. Both state governments, under entirely new leadership since mid-2026, remain publicly at odds with no resolution in sight.
Sources
- Mullaperiyar Environmental Protection Forum v. Union of India, (2006) 3 SCC 643
- State of Tamil Nadu v. State of Kerala, (2014) 12 SCC 696
- Verdictum: "State of Tamil Nadu v. State of Kerala," 3 Aug 2024 (the 11 framed issues)
- Bar & Bench / LiveLaw: Mullaperiyar case coverage, 2021–2026
- India Together: "Mullaperiyar: Is the light in the tunnel itself?" (the second-tunnel proposal)
- UNU-INWEH: "Ageing Water Storage Infrastructure: An Emerging Global Risk" (2021)
- The News Minute, Onmanorama, The Hindu, Deccan Herald: 2021–2026 news coverage