Dam Induced Flood Disaster · Kerala

Role of dams in Kerala’s 2018 floods

ABSTRACT: Many independent observers have argued that dams have played a role in increasing the proportions of Kerala flood disaster during July-Aug 2018. This article shows that Kerala dams violated many basic norms and if operated prudently, could have helped. It shows how post dam floods are different than pre dam floods. It lists the steps that would help in future disasters involving dams. The lessons are useful for all large dams of India.

In theory, every dam can help moderate floods in the downstream areas, as long as and as much as the dam has space to store water. In fact, every action that helps to store, hold, recharge (to groundwater aquifer), delay flow of rainwater from the catchment to the river would help moderate flow and hence flood in the river. Our catchments are fast losing that capacity, with continued destruction of natural forests, wetlands, local water bodies and also soil’s capacity to hold water.

Here the typicality of Kerala situation would need to be kept in mind: Kerala is almost entirely part of Western Ghats having High Biodiversity & Fragile ecology, on one side there are mountains and the other side is sea, It’s a traditionally High Rainfall state with some parts getting double monsoon, the entire state is close to equator and sea, Kerala’s 44 rivers have relatively short lengths with high slopes, It has over 60 large dams and Highly urbanised society.

In practice, this potential capacity of the dam to help moderate flood can be realized only when dams are operated with that objective in mind. When dams are not operated with that objective in mind and instead are filled up as soon there is water available, then they have no space left to store more water. Then they are left with only TINA (there is no alternative) and to release all the inflows to the downstream river. When this release happens while downstream areas are facing floods due to local rainfall or some other reasons, the dams end up increasing the proportions of downstream flood disaster.

the Periyar river from the Kalady bridge on August 26 Madhu
The Periyar river from the Kalady bridge on August 26 (Photo by Anonymous)

There any many instances of this kind, including in case of Uttarakhand (June 2013), Tehri (Sept 2010), Hirakud (2009, 2011, 2014), Damodar dams (many years), Krishna basin dams (2006, Oct 2009), Ukai (Aug 2006), Chennai floods (Dec 2015), Bansagar Dam (Aug 2016), Kurichu Dam of Bhutan (2004, 2016, others), Ranganadi (2017, others), Doyang (2018), among other dams, where wrong operation of dams created or worsened flood disasters in downstream areas.

Chalkudy Town Aug 17 2018 Photo by Madhu
Chalakudy Town Aug 17 2018 Photo from Internet

Post dam flood vs pre dam flood There is no dispute that in Kerala, most of the dams were almost full by the end of July 2018. The Central Water Commission report on Kerala floods[i], however, says (p 34): “From the analysis it has been found that the dams in Kerala neither added to the flood nor helped in reduction of flood, as most of the dams were already at FRL or very close to FRL on 14 August 2018, due to more than normal rainfall in the months of June to July 2018.” Such statements, in an effort to absolve the dams from any blame, assume and imply that the flood in the river downstream before and after the dam are same. This is totally misleading and wrong assumption. The flood in the downstream area from water released by the dam is very different than the flood in the undammed river, for a number of reasons, including the following.

  • Flood in river before the dam could be most of the times be seen gradually rising, so people could get prepared, could save lives and valuables. Flood from water released by dams comes much more suddenly, leaving little time to respond.
  • The damage potential of water suddenly released from dam is much greater than the damage potential of gradually rising flood in the river.
  • The river downstream, its flood plain and even the river bed, not used to having regular floods, may have changed, with false sense of security that people are given/ they get. The carrying capacity of the downstream river may have changed. The river immediately downstream of Idukki dam has seen no flows for 26 years, the last time the gates were opened was in 1992. The flood carrying capacity of Tapi river downstream of Ukai dam has reduced from about 8.5 lakh cusecs (cubic feet per second) earlier to about 4.0 lakh cusecs and to possibly less than 2 lakh cusecs now.[ii]
  • The water released from the dam is either relatively silt free or carrying too much silt, if released from bottom sluices. In either case, it’s different than normal flood and would have a very different damage potential.

So Dam operators cannot be exonerated based on claim that they have not added to the incoming flood.

The real question is: Have the dam operators done everything possible to moderate the flood in the downstream area? The CWC report does not even ask that question.

So what could the dam operators have done to moderate the floods in Kerala this monsoon?

Two weeks before the flood – 26th July 2018 Water spilling over the gates of Poringalkuthu Reservoir, Chalakudy River, Kerala Madhu
Two weeks before the flood – 26th July 2018 Water spilling over the gates of Poringalkuthu Reservoir, Chalakudy River, Kerala Photo Internet

Almost all Kerala dams violated the Rule Curve Every dam is supposed to have a dam specific rule curve, that tells, among other things, how the dam is supposed to be filled during the monsoon, to optimize flood moderation for the downstream area, while ensuring that the dam is filled up only closer to the end of the monsoon. Almost all the dams in Kerala were almost full by the end of July. This was in complete violation of the rule curve, as end of July is just half through the South West Monsoon and large parts of Kerala also gets benefit from the North East Monsoon, that follows SW Monsoon. So to fill up the dams by end of July was sure invitation to disaster.

The CWC report is clearly designed to save the dam operators from any blame so it does not say that Kerala dam operators followed or violated the rule curve. However, the very first recommendation of the report is: “It is essential to review the rule curves of all the reservoirs in Kerala. The rule curves need to be formulated for both conservation as well operations during the flood, particularly for the reservoirs having the live storage capacity of more than 200 MCM in order to create some dynamic flood cushion for moderating the floods of lower return periods particularly in the early period of monsoon.”

Screen Shot 2018-10-04 at 4.37.32 PM

The Kerala dams clearly failed to provide this flood moderation during Kerala floods in August 2018 as they were already full when the floods came.

The CWC recommends that the rule curves of Kerala dams need to be reviewed. Some of the factors that would be required for such review of rule curve include: carrying capacity of the river downstream of dams, changed rainfall pattern in the upstream and downstream, changed live storage capacity of the dam due to siltation, changed flood profile due to degradation and reduced flood absorption capacity of the catchment area and changed situation of upstream and other basin dams.

Screen Shot 2018-10-04 at 4.40.47 PM
Source: CWC Report, Sept 2018

Operation of Dams during monsoon Some of the factors that are necessary to be kept in mind to achieve the objective of optimum flood moderation due to dam operations during monsoon include: Updated Rule curve for the reservoir, Storage situation of the reservoir being operated, Inflows into the reservoir, outflow capacity, River flow in the upstream, Storage position and releases from upstream dams, Down stream river flow situation, including from downstream tributaries and situation of dams if there are any in the downstream and their inflow-outflow regime, updated Downstream river carrying capacity, Down stream high tide situation, Downstream inundation maps for different releases, evacuation plans, Catchment (U/s and D/s) rainfall in last 24-72 hours, depending on travel time in the catchment, Forecast of rainfall in the catchment (U/s and D/s) over the next 1-5 days.

The Bureau of Indian Standards code for Reservoir Operations[iii] (IS 7323:1994) have very clear stipulation in this regard: “…the flood control schedules would consist of releasing all inflows up to the safe channel capacity.” But CWC report on Kerala floods does not even mention if there exists assessment of safe channel capacity downstream of various dams in Kerala and if there was any attempt to even follow them.

As CWC[iv] and CAG[v] reports have noted, each state has to prepare for each large dam, a Dam operation manual that also includes Emergency Action Plan (EAP), here emergency does not mean only mean dam break event, but all kind of crisis situations, Determination of potential inundation area, preparation of Inundation Maps and notification of emergency, set up a Hydrological Unit for preparation of Inundation Map, set up emergency control room for each dam to coordinate crisis situation. None of the Kerala dams had almost any of these: No manuals, no EAPs, no inundation maps.

SANDRP Coordinator invited by NIDM to give a lecture on Reservoir Operations in the context of Flood Risk Management On Sept 8, 2018, National Institute of Disaster Management invited Himanshu Thakkar of SANDRP to speak on “Reservoir Operation in the context of Flood Management in India”. Here is the full Video of the event, including the lecture and the question answers.  https://www.youtube.com/watch?v=-e7GB4711bI

Some specific dam situations during Kerala floods

Poringalkuthu Dam Post flood Aug 21 2018 Photo by Madhu
Damaged Poringalkuthu Dam Post flood Aug 21 2018 Photo Internet

Chalakudy Basin Dams Kerala officials have been saying[vi] in their defense that it was such an unprecedented deluge that no one could have forecast it. While this is true, it may be useful to point out that a letter was sent, well before the worst floods struck Kerala during the second week of Aug 2018, by Dr Madhusoodhanan (a Ph D from IIT Mumbai) on July 18 to district collector of Thrisur and on July 20 to district collector of Ernakulam, warning about “alarming water levels and current operational patterns of the dams in the Chalakudy basin”, “an imminent possibility of dam induced floods in Chalakudy river” and also suggesting steps to start dealing with the situation. He wrote: “The river is flowing bank full owing to the huge spill discharge from the Poringalkuthu dam and heavy rainfall in the lower catchment. Except Kerala Sholayar, all the 5 reservoirs are full. TN Sholayar and Poringalkuthu reservoirs are already discharging spill water to the downstream.” The collectors, others did nothing! No response. Chalakudy was one of the major affected basins, and dams here played significant role.

Poringalkuthu Spillway clogged Aug 20 2018 Photo by Madhu
Poringalkuthu Spillway clogged Aug 20 2018. Photo from Internet

Idukki Dam Idukki and Idamalayar are the only Kerala dams having live storage capacity over 1000 Million Cubic Meters (MCM). Idukki Dam live storage was already 25% full even before the monsoon started on May 31, 2018, reducing available storage capacity to that extent. Idukki is a hydropower dam; it can use the water only for hydropower generation. It has six units of 130 MW each. One unit was out of operation since Aug 2017. Another went out of operation on June 26, 2018, for annual maintenance! So one third of it’s water use facility was not available during peak flood season. Before 2018, the Idukki dam has NEVER been full anytime in the SW monsoon, since it was commissioned in 1975. The only two times its gates were opened (1981 & 1992) was in NE monsoon. That dam, this year, not only gets filled up for the first time ever in SW Monsoon, but filled up by over 90% by end of July, just halfway through the SW Monsoon. That should have been a big wake up call.

On July 31, KSEB was prepared to open the gates of Idukki dam, downstream people were alerted through orange alert, NDRF persons were stationed, gate-opening was tested. But than they decided against opening the gates, due to, as James Wilson[vii] (special advisor to state government on inter-state water) wrote, inflows going down. In fact, even power generation at Idukki dropped after July 31!

CWC report does not even mention about number of dams or the water control/ regulating mechanisms in any of the basins they studied. In the Periyar river basin alone there are about 20 dams and 17 reservoirs. Apart from the inflow from the free catchment and Mullaperiyar dam spill, Idukki reservoir is augmented by diverting water from 6 diversion dams in and around Idukki.  These dams also augmented the inflows into Idukki during floods. James Wilson gave a glimpse of it in his article dated Aug 13, 2018[viii]: “The Kallar and Erattayar diversion dams in the Periyar augment Idukki reservoir.” Kerala State Electricity Board[ix] that owns and manages some 33 hydropower dams in Kerala including Idukki, lists the augmentation schemes to increase inflows into Idukki dam: 1. Kuttiyar Diversion; 2. Vadakkepuzha Diversion; 3. Azhutha Diversion; 4. Narakakkanam Diversion; 5. Kallar Diversion and 6. Irattayar Diversion. This only shows how the hurriedly prepared CWC report missed taking into account key aspects.

Alternative operation scenario for Idukki Dam Now let us see how Idukki dam, if operated more prudently, could have reduced floods. The lowest gate level of Idukki dam is at 2373 ft, which corresponds to live storage of around 69%, the dam reached at this level around July 17, 2018. It would have been prudent to keep water level managed around this level at least till August end, considering the history of this dam and Kerala situation. At this level, the power generation would have continued very close to peak level and it would have provided flood moderation space of about 440 MCM. This flood cushion could have been used to absorb the flows above the safe carrying capacity of the downstream channel and release the additional water whenever inflow would have reduced. If this was the situation say till say Aug 8 and then Aug 15, when highest intensity rainfall struck Idukki dam catchment, then the dam would have about 400 MCM of flood cushion during peak flood period.

According to CWC report: “During the rainfall event of 15-17, August 2018, the total release during three days from Idukki reservoir was about 345 MCM (spill) and 30 MCM (power house going to Muvattupuzha river) against the inflow volume of 435 MCM.” What this means is that if Idukki project was operated as suggested above, there would have been no need for any water release from the dam at all during this three-day period, the full inflow of 435 MCM, minus 30 MCM power house use, would have been absorbed by the flood cushion of 400 MCM. However, the dam was earlier from Aug 10, releasing about 750 cubic meters per second or cumecs (65 MCM per day). If we were to limit the releases to say 500 cumecs during Aug 10-20, then this flood cushion would have done that. This means that the peak outflow from Idukki would have remained at 500 cumecs, a third of the 1500 cumecs it released. This kind of operation of other dams in Kerala would have similarly helped reduce the flood in the downstream rivers.

Mullaperiyar Did Mullaperiyar dam, upstream of Idukki dam in Kerala, but controlled by Tamil Nadu for power generation and diversion of water to Vaigai basin for irrigation, play a role in increasing the proportions of Kerala floods? Yes, says Kerala Chief Secretary in affidavit before the  Supreme Court: “Mean time, the Secretary, Water Resources, Government of Kerala addressed her counterpart in Tamil Nadu Government as well as the Chairman, Supervisory Committee on Mullaperiyar Dam, herein after called Supervisory Committee, urging the commencement of controlled releases of water from the Mullaperiyar Dam without waiting for the water level in the reservoir to reach its FRL.” While Tamil Nadu does seem to have violated the basic reservoir operation principles, the Kerala Chief Secretary, by this charge, imply Kerala’s violations on the same count for about forty dams. While there is evidence to show that Mullaperiyar dam generated power at peak capacity during say July 20 to Aug 20, there is no official data to substantiate that TN diverted at peak capacity of 2200 cusecs during that period, since peak power generation needs about 1600 cusecs of water discharge. More water TN had diverted during that period, greater help it would have been for Kerala.

There is also the flood hydrograph from CWC for Vandiperiyar site on Periyar river, just downstream from Mullaperiyar dam. This shows that during Aug 15-20, water level here went to unprecedented 3.5 m above the Highest Flood Level recorded at this site and remained above HFL for over 4 days. Tamil Nadu started using water from Vaigai dam only after Aug 20, why they did not use it earlier is also a bit of mystery.

16 Aug Vendiperiya
CWC Hydrograph for Vandiperiyar site during 14-16 Aug, 2018

Here this conclusion of CWC report is noteworthy: “The worst affected districts noticed were Wayanad (Kabini sub-basin), Idukki (Periyar sub-basin), Ernakulam (Periyar and Chalakudi) sub-basins, Alleppey and Pathanamthitta (both in Pamba sub-basin).” It’s educative to note that there was role of dams in each of these sub basins. And in each case, the dams did not follow rule curve, did not have emergency plans, inundation maps, and violated other basic norms of reservoir management.

Puthenvellikkara village flood level Photo by Madhu
Puthenvellikkara village flood level. Photo from Internet

Lessons for dams from Kerala floods Even the CWC report, which is essentially trying to defend the dams and dam operators during Kerala floods, agrees that dams need to review the rule curves and CWC officials have made public statements that dams should follow rule curve. Here are some key lessons from this experience. Kerala needs to update or formulate where it does not exist, rule curve for each large dams of Kerala and ask Tamil Nadu to do the same for the four Kerala dams that TN controls.

For each dam, there should be a study of downstream channel carrying capacity and removal of illegal encroachments where necessary.  There should be mapping of inundation areas and formulation of Standard Operating Procedures for different flood scenarios, including control room, identified officer in charge, emergency action plans and coordination mechanisms. There should be flood forecasting that takes into account both for upstream and downstream areas, the various river flows, dam storages and releases, actual rainfall that has happened over last 3-5 days, rainfall forecast for next 3-5 days, among others.

All of this, for each dam should be in public domain each day, say on designated website and should remain on the website at least for next five years. In addition, there should be a dam management committee for each dam in which about half the persons should be non government persons with independent standing and community representatives. All of this should be statutory requirement say under Dam Safety Act that Kerala has, only one of the two states in India that have such an Act. Immediately, Kerala should set up an independent panel to review what happened during the floods and how different agencies responded, with an objective to learn lessons for future. Another panel should be set up for creating a long term set of recommendations of how to deal with the fragility of Western Ghats that Kerala is part of.

Business as usual is not an option for Kerala.

Himanshu Thakkar (ht.sandrp@gmail.com, https://sandrp.in/)

NOTE: An edited version of this was published in ECONOMIC AND POLITICAL WEEKLY, Vol. 53, Issue No. 38, 22 Sep, 2018 see: https://www.epw.in/journal/2018/38/commentary/role-dams-keralas-flood-disaster.html, https://www.epw.in/system/files/pdf/2018_53/38/CM_LIII_38_220918_Himanshu_Thakkar.pdf

POST SCRIPT: With IMD predicting Red Alert in three Kerala districts on Oct 3, 2018, it was interesting to see Kerala government, KSEB and others promptly talking about prudent dam management and need to release water in advance, see: http://www.newindianexpress.com/states/kerala/2018/oct/04/clouds-gather-in-sky-kerala-state-electricity-board-stays-guarded-1880743.html. This means that Kerala has learnt lessons and also acknowledges that their dam operations earlier, as narrated in this article was a major factor in increasing the proportions of disaster.


Central Water Commission (Sept 2018): “Study Report: Kerala Floods of August 2018”, Ministry of Water Resources, River Development & Ganga Rejuvenation, Government of India, New Delhi. http://cwc.gov.in/main/downloads/KeralaFloodReport/Rev-1.pdf

Central Water Commission (April 2005): “Real Time Integrated Operation of Reservoirs”, Ministry of Water Resources, River Development & Ganga Rejuvenation, Government of India, New Delhi. http://cwc.gov.in/main/downloads/Real%20Integrated%20Operation%20of%20Reservoirs%20.pdf

Patel Chandresh G and Gundaliya, Dr P J (March 2014) “Calculating Discharge Carrying Capacity of River Tapi”, International Journal of Engineering Research and Technology, Vol 3, Issue 3, pp 2075-2078.  https://www.ijert.org/phocadownload/V3I3/IJERTV3IS031843.pdf

Bureau of Indian Standards (Nov 1994) “Indian Standard: Operation of Reservoirs – Guidelines (First Revision)”, New Delhi. https://ia800204.us.archive.org/12/items/gov.in.is.7323.1994/is.7323.1994.pdf

Central Water Commission (Jan 2018) “Guidelines for Preparing

Operation and Maintenance Manual for Dams”, Ministry of Water Resources, River Development & Ganga Rejuvenation, Government of India


Comptroller and Auditor General of India (July 2018), “Report No.4 of 2017 – Performance Audit of Flood Management and Response in Chennai and its Suburban Areas Government of Tamil Nadu”, New Delhi https://cag.gov.in/content/report-no4-2017-performance-audit-flood-management-and-response-chennai-and-its-suburban

Comptroller and Auditor General of India (July 2017), “Report No.10 of 2017 – Performance audit Union Government Schemes for Flood Control and Flood Forecasting Reports of Ministry of Water Resources, River Development & Ganga Rejuvenation”, New Delhi


Wilson, James (Aug 30, 2018) “In Kerala, there’s no reason to damn the dams”, National Herald, New Delhi. https://www.nationalheraldindia.com/india/in-kerala-theres-no-reason-to-damn-the-dams

Wilson, James (Aug 13, 2018) “Understanding the 42-year-old Idukki dam which is now saving Kerala”, The Print, New Delhi. https://theprint.in/opinion/in-monsoon-battered-kerala-idukki-dam-has-stood-tall-to-prevent-floods/97579/

Kerala State Electricity Board (Nov 2015) “Periyar Basin Hydro Electric Projects”, Trivendrum, Kerala. http://www.kseb.in/index.php?option=com_content&view=article&id=69&lang=en


[i] http://cwc.gov.in/main/downloads/KeralaFloodReport/Rev-1.pdf,  revised report dated Sept 11, 2018.

[ii] http://cwc.gov.in/main/downloads/Real%20Integrated%20Operation%20of%20Reservoirs%20.pdf pp 46 and https://www.ijert.org/phocadownload/V3I3/IJERTV3IS031843.pdf

[iii] https://ia800204.us.archive.org/12/items/gov.in.is.7323.1994/is.7323.1994.pdf

[iv] https://damsafety.in/ecm-includes/PDFs/Guidelines_for_Preparing_O&M_Manuals_for_Dams.pdf, http://cwc.gov.in/main/downloads/Real%20Integrated%20Operation%20of%20Reservoirs%20.pdf

[v] https://cag.gov.in/content/report-no4-2017-performance-audit-flood-management-and-response-chennai-and-its-suburban, https://cag.gov.in/content/report-no10-2017-performance-audit-union-government-schemes-flood-control-and-flood

[vi] https://www.nationalheraldindia.com/india/in-kerala-theres-no-reason-to-damn-the-dams, https://www.thehindu.com/todays-paper/tp-national/tp-kerala/what-caused-the-floods/article24859826.ece

[vii] https://twitter.com/jamewils

[viii] https://theprint.in/opinion/in-monsoon-battered-kerala-idukki-dam-has-stood-tall-to-prevent-floods/97579/

[ix] http://www.kseb.in/index.php?option=com_content&view=article&id=69&lang=en

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