Do the dams attenuate or amplify floods?

A case study on the Role of Dams on the River Periyar during the 2018 Kerala Floods

kerala floods

Note:  This analysis of the 2018 Kerala Floods, completed in September 2018 could not be published due to health and other reasons. The first phase of the 2018 floods before August 15 was more due to mismanagement or hoarding of water in the reservoirs on the River Periyar, while the second phase was due to a once-in-a-century rainstorm on 15-17 August 2018.  The State also experienced lower intensity floods in 2019 also. There can be floods in 2020 also and if it happens before the State solves the corona-virus crisis, the mitigation would be almost impossible.  Hence this delayed release of the report, some 100 days before the next flood season.


In July-August 2018, the coastal State of Kerala in peninsular India experienced landslides and floods of epic proportions, directly affecting 5.5 million people.  The state received higher than normal rainfall during June-August, the first three months of the South West Monsoon.  Almost all the 36 major reservoirs with a storage capacity of 4643 million cubic meters (MCM) of water were filled to their brink.  Floods were caused due extreme rainfall events and spillages from the dams.  As the flood subsided, a new narrative that floods were the result of heavy rains and release of water from dams from a neighboring State has gained traction. The narrative says, the dams owned by the Kerala state electricity board Ltd (KSEBL) attenuated the floods by storing water during the days of heavy downpour.  Since the floods were not a single event, but multiple events with varying intensity, spread, depth and duration of inundation, it is not proper to club them together and link them all to one or two causes.  Each of these events should be studied individually to know the causes and effects.  The present study is an attempt to understand the roles – positive or negative- of three dams on the upper reaches of the River Periyar in the flood events of Ernakulam district during 10-20 August 2018. The specific questions asked are,  (a) did the dams attenuate or amplify the flood and (b) if they amplified the flood effects, would a different management strategy have changed the course of events.  The findings are (a) the dams amplified the floods (b) in the absence of a flood cushion, the reservoir could not accommodate the normal inflows of two days, which lead to the abrupt and unplanned spillages (c) Idukki reservoir swelled so fast due to idling of the generators during January- July 2018 and (d) under a safety oriented strategy, the spillages from 09 to 16 August could have been avoided.


According to the India Meteorological Department (IMD), during 01 June- 17 August 2018, Kerala State received 2443 mm of rain, which is 126% of the normal.[1] Rainfall was not uniform across the State; there were spatial and temporal variations.  Almost all the dams were filled before the first week of August.  Prolonged and repeated extreme rain events, release of waters stored behind the dams and landslides are thought to be the main causes for this ‘once in a hundred years disaster’.   According to the Government of Kerala, the events killed 483 persons, affected 5.5 million people directly and 1.45 million people moved to 3879 relief camps. More than 8,000 cattle, 3,297 goats, and 47 dogs, most of them tethered, also died.  The deluge destroyed about 10,000 km of roads and damaged thousands of homes. A World Bank (WB)-Asian Development Bank (ADB) team estimated that the reconstruction of the flood-ravaged economy and infrastructure would cost Rs 250 billion. Everyone praised the rescue operations coordinated by the Government of Kerala, which significantly reduced the death toll. About 4,500 fishermen with their 669 Noah’s Arks rescued about 65,000 people, and the Indian Navy rescued of 17,000 people using Gemini boats and helicopters.[2]

Backgrounder -Floods in Ernakulam district

Ernakulam district in Central Kerala has an area of 3068 sq km and a population of 3.3 million, 70% of whom are urban. (2011 Census). Twenty five percent of its geographical area is flood-prone.  The lifeline of the district, the River Periyar, has three large and eight small reservoirs upstream with a cumulative storage of 2920 MCM of water.  For the 750 km2 flood-prone area, the stored water is equal to an inundation depth of 4 meters.  Ernakulam is the biggest urban agglomeration and the industrial and financial capital of the State. Several hazardous industries- including the thorium-processing mill of the Indian Rare Earths Ltd (IREL), the pesticide manufacturer- the Hindustan Insecticide Ltd (HIL), synthetic rutile manufacturer -the Cochin Minerals and Rutiles Pvt Ltd (CMRL) and the Fertilizers and Chemicals Travancore Ltd (FACT) are located in the flood-prone low-lying areas of the district.

Floods are almost an annual ritual in the low-lying areas of Kerala.  Ernakulam district experienced the first bouts of ‘routine’ floods since the beginning of July 2018 which subsided during the fourth week. Then came the big ones on 9 August, the day the dams started their spillages and lasted until 21 August 2018.

Though the floods affected all districts of Kerala, there were differences in inundation depth, duration and the number of people and establishments affected. The number of people forced into the relief camps can be treated as a proxy for the magnitude of the disaster.  The camps in the district sheltered 532,000 people, more than a third of the 1.4 million people in the entire State.

Backgrounder- Dams on the River Periyar

There are three major dams on the River Periyar – Mullaperiyar, owned by the Government of Tamil Nadu, Idukki and Idamalayar both owned by the KSEBL.  All these have a catchment area of 1714 km2 and effective storage of 2,780 MCM. About 2.5 people live in Ernakulam district, the target area of these three dams. Details of the dams are given in table 1.

Table 1:  Details of Major Dams on the River Periyar

Name of Dam Catchment Area km2 Storage MCM Spill cap M3/sec Spillage/ MCM/day
Mullaperiyar 637 300 3455 298
Idukki 605 1460 5013 433
Idamalayar 472 1020 3013 260
Total 1714 2780 11481 992


The Idukki reservoir, commissioned in 1975, is bound by three dams, Idukki, Cheruthoni and Kulamavu. The Idukki dam, one of the highest arch dams (169 m) in Asia is one of the 53 vulnerable reservoirs in the world, due to reservoir-triggered seismicity.[3] The dams are located in seismic zone –III, where earthquakes of magnitude 6.5 on Ritcher scale are expected.

Water from Mullaperiyar is taken through a tunnel and stored in Vaigai dam in Tamil Nadu. Water above the full reservoir level (FRL) is spilled through the sluice gates, which will flow through several villages before draining to the Idukki reservoir, 30 km downstream. Though its spillages will submerge villages in Kerala, the people or the Government of Kerala have no control over the dam.

Inventing a new narrative – Controlled spills attenuated the floods.

The people saw the visuals of water columns gushing out of the dams, uprooting trees and buildings in their course and inundating roads, bridges and buildings in real time on their televisions.  The alerts issued by the government had forewarned about the spillages and floods downstream. On 23 August 2018, the Government of Kerala invented a new narrative that the controlled spills by the KSEBL-owned dams, in fact played a positive role in attenuating the floods. An affidavit, submitted by the Government in the Supreme Court has more details:

“The State was managing the spate by controlling the spill and letting a major portion of the flood waters to escape to the sea by a strict operational control over the spill of the two largest reservoir systems of Idukki and Idamalayar, but the sudden releases from the Mullperiyar, the third largest reservoir (on 15 August 2018) in the Periyar basin forced us to release more water from the Idukki reservoir, which is one of the causes of the deluge.”[4] (Emphasis added)

A hurriedly prepared study report by the Central Water Commission (CWC) also considers 15th August as the beginning of the floods and underlines that “about 60 MCM of flood runoff was absorbed by Idukki reservoir during 15-17 August” which attenuated the floods.  SP Ravi and colleagues of the Forum for Policy Dialogue on Water Conflicts in India have published a detailed critique of the CWC Report in The Hindu Business online.[5]   The same chronology is given in a Wikipedia article, which says, “Beginning in 15 August 2018, severe floods affected the south Indian state of Kerala, due to unusually high rainfall during the monsoon season”.[6]

Box 1 : Sources of data.

The dam-related data used in this study have been downloaded from the websites of the Kerala State Load Dispatching Centre (SLDC-, an outfit of the KSEBL, and the Southern Regional Load Dispatch Centre (SRLDC-, which comes under the Power Operation Corporation Ltd (POSOCO), a Government of India enterprise.  The data like the rainfall, inflow, outflow, storage and water level in all hydroelectric dams in the State, uploaded daily by SLDC is available for the period 01 June 2018 until date.  SRLDC site has data of water level and generation of electricity of main generating units from the year 2004 onwards.  The data on inflow and storage of water given in million units (MU) of electricity by these agencies have been converted to million cubic meters (MCM). 

Reliability of data.

Data for the spill on 15 August 2018.  The spillage from Idukki on 15 August was shown as 390.5 MCM on 26 August, but now it is 111 MCM in SLDC website. The affidavit submitted to the Supreme Court by the Government of Tamil Nadu also says “on 15 August 2018 the quantity spilled was 390.5 MCM which is evident from data available in the website of KSEB” This analysis uses the amended value of 111 MCM.  

Spills on 14 and 15 August 2018.  Wilson James, an expert on the dams, a member of the core group managing the dam during the crisis, says in his tweet that spill from Idamalayar on 14 Aug 2018 will be 620 cumecs.  SLDC report shows nil spillage on that day.  In another tweet dated 15 August, Wilson says that the Bhoothathankettu, (the last barrage on the River Periyar, which receives spills from Idukki and spills and powerhouse discharge from Idamalayar) now discharges around 5,000 cumecs. If this rate was valid for the whole day, the total spillage should be 430 MCM. The spillage of the date reported by SLDC for all three dams is 195 MCM. 

Rainfalls during the first 75 days of the water year 2018

The IMD predicted a normal rainfall during the South-West Monsoon for Kerala State. However, the catchment areas of almost all dams received above average rains during June-July 2018. The cumulative rainfall received in the catchment area of Idukki dam as reported by SLDC was 2404 mm on 31 July 2018 and 2903 mm on 10 August 2018.

On 15 July 2018, all the hydroelectric-power reservoirs in Kerala had enough water to generate 2,830 MU, as against the average of 1,321 MU for the years 2014-17 on the same day.   In 2008, the best-inflow year of the century, the storage as on 15 July was 2,180 MU equivalent. Vimal Mishra et al report that “the 2018 rainfall (till August) in Kerala is lower than the observed rainfall in 1924 and 1961”[7].  Extreme rain events, which are the main causes of  heavy flooding, during this season in the catchment area of Idukki reservoir and in Kerala State are given in table-2. (Columns (3) and (4) show the inflows to and outflows from the reservoir. The precipitation on these days in the dam area is twice that of Kerala State.  Moreover, while the State as a whole witnessed one episode of extreme rain events for continuous 10 days, there were two such episodes in Idukki this year.

Table- 2: Highest rainfall and inflow days-Idukki and Kerala State

No of days Period Inflows Outflows Rainfall in mm Probabi-lity %
MCM MCM Idukki Kerala*
(1) (2) (3)©© (4) (5) (6) (7)
One day 15-August 168 168 295 120 1.4
Two days 15-16 August 326 326 530 236 0.5
Three days 15-17 August 442 442 711 294 1.0
Ten days 7-16 August 833 633 1342 592 0.5
Ten days 9- 18 July 790

Sources:   Idukki – SLDC       Kerala – Mishra et al (ref 7)

Filling of and Spilling from the Dams

On 18 July 2018, the Dam Safety Organization, which is in charge of 58 dams of the State, said that “heavy rain in the catchment areas has forced the dam operators to open the shutters, though it meant flooding downstream areas”.[8]  Water levels in all three dams on the River Periyar were also increasing in tandem since mid-July 2018.  Idamalayar was rising faster than Idukki from 25 July 2018 onwards.  The percentage of effective storage in Idukki and Idamalayar from 15 July to 10 August is given in Figure-1.


Figure 1: Percentage of Effective storage  In Idamalayar and Idukki dams

The Scheme that did not work

As several places in the State were reeling under the flood since the middle of July 2018, the people living on the banks of the river were demanding controlled releases of water from the reservoirs.  Blue alert (first level) was issued on 25 July for Idukki.  A high-level meeting chaired by the Chief Minster on 27 July decided the future course of action.  On 29 July 2018, the chairman of the KSEBL announced the timeline[9]:

  • Orange Alert will be issued if the water level (in Idukki) touches 2,395 ft (storage 91%),


  • Water will be discharged in a controlled manner at 2,397 ft for four hours to assess the condition of the channels and impact on their banks,


  • Red alert will be issued at 2398 ft and water will be released 24 hours after issuing the alert.”


The chair said nothing about Idamalayar dam, which was filling faster than Idukki.  Orange alerts were issued for Idukki on 30 July 2018 and Idamalayar on 1 August 2018, when their storages were 91% and 95% respectively.

In its advisory dated 1 August 2018 on Idukki spillage, the Kerala State Disaster Management Authority (KSDMA) said that the level of flooding in Periyar would be the same as that of 2013, when the spillways of Idamalayar were opened. (This was on 6 August 2013 and the spillage was 900 cumecs). No alert was issued before the spills, and there was no mention about the simultaneous releases from both the dams. They repeatedly reassured the people that the level of flooding would be the same as that of August 2013 and there was no reason to panic.  Several honest citizens, who pay their taxes regularly, did take the reassurance seriously and refused to move out of their water front apartments, until the first floor of their houses was flooded and the fishermen arrived with their rescue boats.

While issuing the red alert for Idamalayar on 8 August 2018, the KSEBL said that spillage of 164 cumecs of water will start at 06:00 hrs on 9 August, which is expected to raise the water level of the River Periyar by 1 to 1.5 meter.

The Chairman’s scheme mentioned above did not work.  The water level in Idukki reached 2397 ft at 14:00 hrs on 08 August, but the trial run (controlled release) did not happen on that day. On this, the Chief Minister’s Face Book post says, “the shutters of Idamalayar dam were opened on August 8 and the thinking at that point was that it would be devastating if both the dams were opened at the same time”.[10]  If trial runs of Idukki and real runs of Idamalayar together would be devastating, what would be the effects of the real runs of both the reservoirs together, which happened during the next 10 days?

Red alert for Idukki was issued on 9 August 2018, when the water level had already reached 2401 ft. The trial run of controlled release started at 12:30 hrs, after the issue of red alert.  As the uncontrolled release started a couple of hours after the trial runs, there was no time to assess its impacts downstream.

The ‘Controlled Spillage’ and the Deluge Downstream

The sluice gates of the Idamalayar and the Idukki dams were opened on 09 August 2018 and the total spillage on the day was 65 MCM (718 cumecs). Nine hours after the opening of the shutters of Idamalayar dam, the Manorama Online reported that (a) the rate of spillage was 600 cumecs as against 164 cumecs planned earlier and (b) the spillage and the previous day’s incessant rains has intensified the floods in the River Periyar.[11] On the next day, The Hindu reported that over 2,000 people moved to the relief camps in Ernakulam district.  From 9 to 14 August, the two dams spilled 518 MCM of water into the river.

Government of Kerala’s affidavit in the Supreme Court says: “At 11:00 hrs on 14 August, the district administration of Idukki was frantically evacuating people from the downstream of Idukki Dam, where spillway releases were increased gradually from 25 cumecs to 450 cumecs.”[12]  James Wilson (@jamewils) tweeted at 11:48 hrs on 14 Aug 2018 “District Collector, Idukki informed that evacuation of people from downstream of Mullaperiyar Dam is completed.”

At 00:00 hrs on August 15, 2018, The Hindu reported that “many people of “North Paravur were shifted to relief camps following the increase in water level in the Periyar by 23:00 hrs and a high alert was issued after the authorities informed the public that water discharge from Idamalayar dam has been increased to 600 cumecs”[13].  As per the SLDC report, the average spillage on 15 August 2018 was 972 cumecs.

On 15 August, the Mullaperiyar dam also joined the party and spilled 35 MCM of water.  The total spills (reported by SLDC) from all three dams on the day were 195 MCM.  At 17:41 hrs on 15 August 2018, The Times of India reported that 18,000 people were living in 117 camps in the district.[14]  Spillages from all three sources during 15-17 August were 625 MCM, which is about 43% of the total spillage during 9 -21 August.  Details of spillages during 9 to 21 August from three dams are given in table.  Columns (c), (d), (h) and (i) have spills from Idukki and Mullaperiyar separately.

Table 4: Spill from Idamalayar, Idukki and Mullai- in MCM and Cumecs


Date Idama-layar Idukki Mulla-Periyar Idukki+ Mullai All three
(a) (b) ( c) (d) (e) (f)
9-Aug-18 62 3.3 0 3.3* 65
10-Aug-18 52 53 0 53 105
11-Aug-18 13 65 0 65 78
12-Aug-18 28 65 0 65 93
13-Aug-18 35 51 0 51 86
14-Aug-18 46 0 46 46
15-Aug-18 84 76 35 111 195
16-Aug-18 118 70 57 127 244
17-Aug-18 71 91 24 115 185
18-Aug-18 0 47 24 71 71
19-Aug-18 31 35 24 59 90
20-Aug-18 25 32 24 56 82
21-Aug-18 17 43 43 60
Total 535 676 188 864 1400
Percent 38.2 48.3 13.4 100

Note:  Data of spillage from Mullaiperiyar is from the Government of Tamil Nadu affidavit in the Supreme Court.  Data for Idukki shows the spillage reported by SLDC minus the Mullai spillage.   *  Idukki on 9 Aug 18 – Trial run for four hours.

Two phases of the floods during 9 to 18 August 2018

Based on the inflows into and spillages from the dam, the August event can be partitioned into two phases, viz., 8 to 13 Aug 2018 and 14 to 18 August 2018.  During the first phase, the average rainfall, inflow and spillage of Idukki were 84 mm, 51 MCM and 47 MCM respectively.  During the second phase, these were 203 mm, 123 MCM and 106 MCM respectively. The inflows into the Idamalayar reservoir also showed a similar pattern with 83 MCM/day during the first phase and 212 MCM/day during the second phase.  Details for Idukki dam are given in table 5.

Table 5: Daily average rainfall, inflow and spillage

During two phases of the floods – Idukki dam


Phases Rainfall mm Inflow MCM Spill MCM
8 – 13 August 84 51 47
14 -18 August 203 125 106

The CWC Report says that during 15 – 17 August 2018, there was a rainstorm with its eye above Peerumedu in Idukki, which was similar in intensity with the rainstorm of 16-18 July 1924, with its eye above  Devikulam, also in Idukki district. The Devikulam storm is considered as the cause of the 1924 Floods, known as the “Floods of 99”.

Attenuation or Amplification by Dams?

During 10 – 21 August, the Idukki dam drained 861 MCM through its spillways and discharged 121 MCM from the power house; the total outflow being 982 MCM.  During the same period, the inflow was 964 MCM, which means an excess burden of 18 MCM to the river.  The total inflows and outflows from the Idamalayar dam were 487 MCM and 562 MCM, an excess outflow of 75 MCM.  In short, during the floods, both the dams spilled 93 MCM of water, captured during the normal days.

The Cushion they did not have

India’s National Water Policy of 2002 recommended to provide adequate flood cushion in water storage projects to facilitate better flood management.[15]   According to the affidavit submitted by the Government of Kerala in the Supreme Court, the Idukki  reservoir has  two ‘cushions’ to absorb the flood waters and they are “left open so that dam managers would have sufficient maneuverability to negotiate extreme flash floods.”   The first one, between the height of 731.2 to 732.4 m (2399-2403 feet), can absorb 69 MCM and the second one between 732.4 -734.1 m (2403 – 2408 feet) can absorb 179 MCM. Since the spillage started when the water level was 732 m (2401 ft), it appears that the second cushion is imaginary.  Even the first cushion is only for use in the Court; it looks like an after-thought as the events of 7-8 August reveal.

On 30 July 2018, Idukki reservoir had 1330 MCM and a cushion of 130 MCM.  Orange alert was issued on 31 July.  The same day, the minister for water resources  said there was no need for a trial run of opening the  sluice gates, as the “water level was rising only by 0.02 feet an hour”.[16] The storages on 31 July and 6 August were 1,339 MCM and 1,345 MCM respectively, and the average inflow and outflow (powerhouse discharge) were 11 MCM and 10 MCM respectively.  They still had a cushion of 115 MCM, which would have lasted for more than hundred days, under the inflow regime of the first week of August.

The inflow started increasing on 7 August and the net gain to reservoir on 7, 8 and 9 August were 7, 30 and 43 MCM respectively. The cushion available on 9 August was 35 MCM.   The CWC report says that the level of water in Idukki dam at 24:00 hrs on 9 August was “731.82 m, 0.61 m below FRL and the inflow was 649 cumecs”, or 57 MCM/day.  Without spilling, the water level would have crossed the FRL by midday on 10 August.

The methodology used for fixing the cushion is not known.  Leave alone managing the inflows during flood days, the cushion available was not even sufficient to accommodate the inflows of two normal days.

The Genesis of Crisis – Hoarding Water

There are six turbine-generators (TG) with installed capacity of 130 MW each at the Moolamattom Power House, the underground generating station of the Idukki dam.  Each one of these can generate 3 million units (MU) of electricity a day. As one TG has been on a long-term refurbishment since June 2017, the maximum capacity now is 15 MU.  For generating 1 MU of electricity, 0.68 MCM of water is required.

On 01 June 2018, the first day of the water year, the Idukki reservoir had 365 MCM of water, which was 25% of its effective storage. The storage on 1 June 2017 was 165 MCM.  The higher reserve in June 2018 was due to gross underutilization of the generators during Jan-May 2018, when the total generation was 896 MU or a daily average of 5.9 MU.  Using the ‘excess’ reserve of 200 MCM of water, they could have generated an extra 296 MU during the peak-demand months of Jan-May.

The under-utilization continued until 23 July 2018.  Idukki’s total generation during the first 53 days of the water-year was 209 MU, as against the maximum capacity of 795 MU.  The volume of water saved due to non-generation of 586 MU during 01 June- 21 July 2018 was 388 MCM.  Incidentally, during the peak demand months of Feb-June 2018, the second unit of the Kudankulam Nuclear Power Plant, the only other source of cheap power for the KSEBL, was also under a forced shutdown.

If all the five generators were put on work during Jan-July 2018, the powerhouse could have utilized 588 MCM (200 during Jan- May and 388 during June-July) of stored water and the storage in the reservoir as on 8 August would have been 794 MCM.  The total spillage during 9 to 17 August, which includes three days of super-flood plus Mullaperiyar release, was 635 MCM.  The reservoir could have absorbed all these and the storage as on 18 August, the last day of the Peerumedu storm, would have been 1430 MCM, 30 MCM less than the storage at FRL.

The catastrophe averted on 14 August 2018

Incidentally, water was not the only element received by the reservoir during the high inflow days.  The rivers also carried the products of the landslides like entire villages, building and trees along with the torrent.  These could have obstructed the spillways, leading to the overtopping of the dams.  That could have been beginning of the end.

On 14 August 2018, an insider tweeted:

“No one is sleeping tonight. All senior secretaries, SDMA people, KSEBL chairman, chief engineers of KSEBL and irrigation dept, police, revenue. We all are in the loop, each minute is updated and collective decision-making is happening. Revenue Additional Chief Secretary and Chairman, KSEBL are not even blinking. We all are brainstorming how to handle this deluge. Kerala’s bureaucracy is setting example here.”

Were the CMD and his team working hard to prevent a dam break? The website of the Kerala Legislative Assembly ( says, “Studies commissioned by Kerala Government have shown that such probability (of dam break) exists” for Idukki.  SK Mishra and colleagues from the Indian Institute of Technology (IIT), Roorkey had done a Dam Break Analysis for Idukki and Mullaperiyar dams in 2012 under a contract from the Government of Kerala.[17]  Quotes from an article available at

“two to three hours time will be taken for overtopping of dams at Idukki.  In case of failure of Idukki dam, the Lower Periyar dam and the Bhoothathankettu Barrage will be washed away… Theoretically, a concrete gravity dam like Cheruthoni will topple if water level exceeds the maximum reservoir level. … The depths of flows at different locations will vary from 5.43 meters near Arabian Sea to 163.78 meters just below the Lower Periyar Dam. This means that Greater Kochi can be under 6 meters of water.[18]

While portions of the report on Mullaperiyar dam break is available[19], nothing much is known about the report on Idukki.  Two years ago, the Government of Kerala had informed the Comptroller and Auditor General (CAG) that no dam-break analysis was conducted in respect to any of the 61 dams in the state.” It appears that the Government of Kerala wants to deny the existence of SK Mishra study.

Summary of findings and recommendations

  1. Idukki and Idamalayar dams did not attenuate the floods. They amplified it due to the excess of outflow over inflow from both the dams.
  2. The reservoirs did not have the cushion to accommodate the expected inflow of even one day. During the fortnight before the beginning of the spillage and deluge, the management forgot that we were in the middle of a vigorous monsoon and there were about 30-40 rainy days ahead.
  3. The under-utilization of the generators during January-July 2018 was the main reason for the swelling of Idukki reservoir. About three-fourth of the water spilled from Idukki during the flood days was part of the inflows of the last year and June-July this year.
  4. The releases from the dams significantly contributed to the flooding in Ernakulam and Thrissur districts.
  5. This disaster has revealed several deficiencies in the management of dams, like no inundation studies, no emergency action plans, no co-ordination between the dam owners and other functionaries, and no free-flow of useful information for the people at the receiving end.
  6. The probability of extreme rain events is very alarming considering their impacts. The large number of reservoirs in the State can attenuate the flood effects, if they keep sufficiently large cushions.  This requires a radical change in the attitude and practice of the dam owners.
  7. All the three large dams on the River Periyar are High Hazard Dams, defined as a “dam whose failure would cause the loss of life and severe damage to homes, industrial and commercial buildings, public utilities, major highways, or railroads”.[20]
  8. An objective and impartial assessment of the Periyar floods with the involvement of all stakeholders will help us learn the new lessons for prevention and/or mitigation of future disasters and unlearn the old lessons which have brought us here.


During the 3-days continuous extreme rainfall event, the reservoir at Idukki received 440 MCM of water.  The effective storage of Mullaperiyar is 220 MCM.  In other words two Mullai reservoir flowed in and flowed out of the reservoir in three days.  The inflows during 15-17 August into the Idukki reservoir could be highest ever in its forty years of service.  During one month after the flood events, there have been several high rainfalls in small areas of Idukki.  A yellow alert for ‘heavy’ rainfall was issued for Idukki on 24 September 2018.  Exceptional rainfalls can also occur during the North East Monsoon (October- December).  So there is no time for complacency.  The damages, destructions and disruption in the flooded areas were unprecedented.  The State cannot afford another catastrophe of this magnitude.    Naming the event as one-in-a-century or blaming the nature or the neighbor will not take us too far.  The days of doing business as usual are over.

VT Padmanabhan is a researcher working on health effects of ionizing and non-ionizing radiation, nuclear safety, coastal zone management, corona-virus pandemic etc.  He has published his findings in Counter Currents, peer-reviewed journals.  Most of his papers are available at the

Abbreviations and Acronyms

Cumecs           : Cubic meters per second

MCM              : Million cubic meters

CWC               : Central Water Commission

KSEBL           : Kerala State Electricity Board Ltd

KSDMA         : Kerala State Disaster Management Authority

CAG               : Comptroller and Auditor General

IMD                : India Meteorological Department

SLDC              : Kerala State Load Dispatch Centre

SRLDC           : Southern Regional Load Dispatch Centre

MU                  : Million Units (of electricity)

FRL                 : Full Reservoir Level



[2]  2018-08-27

[3]            Rajendran, K., Rajendran, C. P., Kesavan, S. and Naveen, R., Recent microtremors near the Idukki Reservoir,

Kerala,  South India Curr. Sci., 2012, 102, 1446–1451.

[4]        Supreme Court of India, Affidavit filed by the Government of Kerala dated –Aug 2018, MA No 2219 of 2018,   Writ Petition (Civil) No. 878 of 2017.

[5]        SP Ravi, KJ Joy and  Neha Bhadbhade, 2018,  Dams did exacerbate Kerala’s floods .


[7]        Vimal Mishra et al, 2018,  The Kerala flood of 2018: combined impact of extreme rainfall and reservoir storage,  Hydrol. Earth Syst. Sci. Discuss., Manuscript under review for journal Hydrol. Earth Syst. Sci.


[9] basis-1850396.html








[17]      SK Mishra et al 2012, Dam break analysis Mullaperiyar dam to Idukki Reservoir – Vol 1 Vol II – Idukki Idukki Dam, Cheruthony Dam, Kulamavu Dam; Lower Periyar Dam; and Bhuthathankettu Barrage and the propagation of flood wave from Mullaperiyar Dam to the Arabian Sea



[20]      Central Water Commission Ministry of Water Resources, River Development & Ganga Rejuvenation Government of India Guidelines for Safety Inspection of Dams,  June 2017.



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