Fresh Tremors Mullaperiyar Dam

Mullaperiyar Dam, 

The “To Be” Or “Not To Be”

On Nov 18, the tremor-prone Idukki district woke up to the latest rumbles with the strongest registering an intensity of 3.1 on the Richter scale. India Meteorological Department (IMD) located the depth of the same at five km below the surface and close to the Idukki dam, housing the largest hydro-electric project in the State. Tremors were felt across the high-ranges at Idukki, Kumali, Kulamavu, Moolamattom, Mullaperiyar, Pashupara, Vagamon, Vandiperiyar, Topramkudi and Upputhara in Idukki district. They were also felt at Erattupetta.

Many people were woken up by this tremor at 5:45 a.m. A cold shiver felt down the spine of every keralite. Dark and foreboding thoughts of an impending catastrophe loomed large.


 The politicians still played the flute.

It is now time for a wakeup call

The Mullaperiyar dam is one of the oldest dams in service in the World. We are talking of safety of the 105-year-old dam when the average life span of well designed and well built dams is generally considered to be about 50 to 60 years by International experts. The safety issues relating to Mullaperiyar are heavily interlinked with the safety of the dams of the Idukki project downstream. The fact that the failure of the Mullaperiyar dam could lead to failure of the Idukki dam increases the magnitude of the risk associated with the continued use of the Mullaperiyar dam.

Talking about life span of storage dams, the Dam engineers and dam owners may not always have a clear idea about the life-span of their projects. Similar to other major infrastructure projects, the design life-span of the dam body is given as a time-span varying between the concession period and typically 100 years. However, the life-span of hydro mechanical steel structures, electromechanical equipment and control units is shorter than that of the main civil/structural components and are specified by the suppliers, who also provide instruction manuals describing operation and maintenance. For the civil parts of a water storage facility, however, there are often no manuals on maintenance, although there may be guidelines on regular visual inspections and dam monitoring. It has to be recognized that there is a direct relationship between dam safety and its life-span, i.e. if the dam is unsafe its life-span has expired.

Safety criteria for assessment of the life-span of dams

The life-span of any dam is as long as it is technically safe and operable! In view of the high damage potential of large storage dams, the safety has to be assessed based on an integral safety concept, which includes the following elements.

• 1. Structural safety (main elements: geologic, hydraulic and seismic design criteria; design criteria and methods of analysis may have to be updated when new data are available).

• 2. Safety monitoring (main elements: dam instrumentation, periodic safety assessments by dam experts, etc.)

• 3. Operational safety (main elements: reliable rule curves for reservoir operation, training of personnel, dam maintenance, sediment flushing, engineering back-up etc.).

• 4. Emergency planning (main elements: emergency action plans, water alarm systems, evacuation plans, engineering back-up etc.).

Therefore, as long as the proper handling of these safety issues can be guaranteed according to this integral safety concept, a dam can be considered as safe.

With the number of people living in the downstream area of a dam and the economic development the risk pattern may change with time, calling for higher safety standards to be applied to the project.

affecting life-span oFactors f dams

The main factors, which have an impact on the service life and which may call for upgrading of a dam are the following:

• (i) Changes in the design criteria (hydrology and seismic hazard) based on new information obtained since the initial design of the dam.

• (ii) Changes in methods of analysis and new safety

• (iii) Results of risk assessments (new risks and change in risk acceptance criteria).

• (iv) Ageing of construction and foundation materials and components.

As any changes in the above items are reviewed periodically, effects such as climatic change on floods etc. can be taken care of. As a matter of fact, this has been done and is being done for other hazards, such as earthquake action, which has not been considered at all in the design of older dams. To adapt an old dam to new seismic design and flood safety criteria is often more drastic than the rather long-term changes in the floods.

Ageing and its impact on the life-span of concrete dams

One of the important safety concerns is ageing of the concrete and of the foundation rock, i.e.

• (i) Chemical processes ( sulphate attack, leaching etc).

• (ii) Physical and mechanical processes (thawing-freezing and drying-wetting cycles, cracking due to seismic actions or non-uniform foundation movements etc).

• (iii) Biological processes (growth of plants in cracks, mussels etc).

• (iii) Seepage in the foundation and the dam body (dissolution of material, weakening of conglomerate, change in uplift of the dam and the foundation).

The ageing processes have to be followed by periodic visual inspections, tests and by monitoring of the dam, but not everything is visible or measurable.

Life-span of dams and components

The service life of a well-designed, well-constructed and well-maintained and monitored embankment and concrete dams can easily reach 100 years. Hydro mechanical elements such as gates and their motors have to be replaced after 30 to 50 years. The life-span of penstocks is 40 to 60 years.

The service life of electro-mechanical equipment varies from 20 to 60 years and electronic control units and software may have to be exchanged as frequently as office computers as they may become technologically outdated and maintenance may no longer are available.

The life-span of a dam is as long as proper maintenance can be guaranteed. This statement does not capture all aspects of safety, but it clearly indicates that a dam, which is safe at the time of completion, does not automatically remain safe. Unfortunately, quite a few still believe that a dam, which was safe at the time of its completion, will always remain safe. Some of them even abandon monitoring of the dam structure if instrumental data have remained the same for several years. Neglecting civil maintenance will unequivocally lead to a shortened life-span, which signifies an economic loss, and in a loss of confidence in the safety of dams by the affected people. Maintenance of the electro-mechanical and hydro mechanical components is more common than civil maintenance as component failure and corrosion are more common phenomena, which have direct consequences, e.g. on the operation of the power plant. In the large dam structures internal deterioration and deficiencies are often not as readily visible as in the usually accessible hydro mechanical and electro-mechanical components.

In the case of Mullaperiyar the main risk factor arises from its age itself, not many dams of this age are in service in the World now.  It is a dam built using old technology and naturally was not based on modern parameters for design of dams. Much of the binding material (lime) has leached out over the years. No effective or sustained and systematic maintenance had been carried out in its proper meaning. Apart from maintenance, monitoring is an important aspect of keeping a dam safe. The Central Water Commission had suggested installation of a definite pattern of instrumentation at Mullaperiyar to monitor the condition of the dam. However, no systematic monitoring has also been done and no reliable results have been made public. An old dam left without any monitoring itself is a serious matter

There is monitoring failures in the case of Idukki dam also. Some of the instruments embedded in the dam were either not working or giving unreliable readings for several years. The Kerala State Electricity Board (KSEB) defaulted on taking regular readings and publishing the data. There is also no indication of sufficient preparedness from the part of the Board for emergency measures such as the opening of the spillways. According to the expert committee, the spillways at Idukki do not have the capacity to handle even the probable maximum flood discharge from Mullaperiyar not to speak of a breach of the Mullaperiyar dam. 

Failure of the dam can occur due to the following causes: 
1.Liquefaction of the materials used in the dam.
2.Liquefaction in the foundation soil
3.Wrong estimation of the peak ground acceleration due to wrong assumptions on seismic potential of the area in terms of magnitude, intensity and methods followed for estimating effective Peak Ground Acceleration
4.Prediction of deformations and stresses from earthquake loading
5.Inability to make necessary modifications in the size of the dam that will provide an acceptable response in case the predicted deformations or stresses are intolerable due to revised increases in seismicity of the area during project construction.
6.Inability to estimate performance of the dam and foundation characteristics by comparison with case histories of dam failures 
Other modes of dam failures include:
7.Slope failures induced by ground motions
8.Sliding of the dam on weak foundation materials
9.Disruption of dam by major fault movement in the foundation
10.Loss of freeboard due o differential tectonic movements
11.Loss of freeboard due to slope failures or soil compaction
12.Piping failure through cracks induced by the ground motions
13.Overtopping of dam due to seiche in the reservoir
14.Overtopping of dam due to slides into the reservoir
15.Overtopping of dam due to failure of spillway or failure of dams upstream.

Solution to the Mullaperiyar issue lies in the expert analysis of the causes, its relevance with present context and a realistic approach. Emotional or hysterical utterances over the issue by vested interested people should be ignored. Malignancy should be treated by physicians and not by onlookers. The administrators should face the reality and show their metal rather than shying away for minimal gains.

To put in right perspective, it must be noted here that, there is a limit to the number of years one can keep dams in service through maintenance and strengthening measures. One day, it has to be rebuilt, or the dam will give way. Visionary leaders should accept this and act accordingly. Realization of the fact and timely decision should not be delayed.