Should the water level of Mullaperiyar dam be raised or lowered?

The current water level of the dam is 136 feet and the status quo is to be maintained by orders of the Supreme Court, pending final decision by the Supreme Court. Tamilnadu wants it to be raised to 142 ft and even higher to the full water level of 155 feet, to meet its water supply requirements.

Kerala wants it to be lowered to 120 feet, citing safety concerns. The dam is an endangered scheduled dam under the Kerala Irrigation and Conservation of Water (Amendment) Act of 2006. The Act fixes 136 feet as the allowable maximum water level for the dam. The provisions of the Kerala dam safety Act have been challenged by Tamilnadu in the Supreme Court. The decision of the Supreme Court concerning this, is awaited.

The Supreme Court judgment of 2006 ruled that the water level could be raised to 142 feet from 136 feet, based on the technical report of Central Water Commission on the safety of the dam. The Supreme Court then did not consider the water requirements of Tamilnadu and whether those requirements could be met at a lower level. The earlier decision of the Supreme Court is now being revisited by the current case pending before the Supreme Court.

The question is: Should the water level be raised or lowered?
Safety considerations would require that the water stored in the reservoir must be at a minimum level to reduce hydrostatic pressure on the dam. Damages arising from a potential dam collapse would be minimized if the storage level is minimized.

Can Tamilnadu's water needs be met at a lowered water level of 120 feet or lower without affecting water supply to Tamilnadu?
Tamilnadu draws water from the dam from a water level of 104 feet upwards, since the upper level of the tunnel through which water flows down to the Cumbum Valley is 104 feet. The water flows down through the rock-cut tunnel to Forebay dam near Kumili (Errachipalem) in Tamilnadu.  From Forebay dam, hydel pipe lines carry the water to the Periyar Power Station in Lower Periyar, Tamil Nadu. This is used for power generation (175 MW capacity) in the Periyar Power Station.

From Periyar Power Station, water is let out to Suruliyar, a tributary of Vaigai. Suruliyar carries the water to Vaigai Dam, from where water is distributed for irrigation, drinking water supply and industrial use through the network of water channels.

The water is thus used by Tamilnadu for power generation, irrigation, drinking water supply and industrial use.  It is not clear how much water is actually drawn by Tamilnadu to meet these requirements.
Is it not possible for Tamilnadu to draw the water through the tunnels and store them in Forebay dam and also in Vaigai dam for the intended use, without storing the water in Tekkadi reservoir? Or is it a question of 'asking for more and more' without caring for the milking cow's age and safety?

-Joseph Ponnoly

Irreparable structural damages to Mullaperiyar dam or is it an 11 year old new and safe dam?

The  Central Soil and Materials Research Station (http://mowr.gov.in/writereaddata/linkimages/anu123112470069.pdf) , on directions from the Empowered Committee appointed by the Supreme Court, found severe damages to the masonry structure of Mullaperiyar dam. They used a remotely operated underwater vehicle (ROV) for the underwater inspection on the upstream face of the dam.

Picture of ROV used for imaging the front face of the dam
(Courtesy: James Wilson)

Potholes, crevices and loosened rubble were found in the masonry structure of the dam between 95 and 106 feet from the base of the dam.
Irreparable deterioration was noticed in all 34 sections of the dam resulting from erosion of lime surki mortar from the rubble joints.  Some of the damage was caused by mistakes in the strengthening works carried out by Tamil Nadu since 1979, based on the recommendations of the Central Water Commission, according to  M. Sasidharan, retired engineer and Kerala's observer during the scanning.
Details at:
http://www.thehindu.com/news/states/kerala/article2694645.ece

This finding comes in the wake of Tamil Nadu's plea that the dam has been totally retrofitted during the period 1981 to 2000 with cable anchoring and RCC backing and that it is a new dam  replacing the 116 year old dam and is to be considered  11 years old  only, as claimed by Tamil Nadu PWD Engineer S. Suthanthira Amalraj. This was reported by 'the Hindu' at:
http://www.thehindu.com/news/cities/Madurai/article2697623.ece

In the mean time Chief Minister Oommen Chandy announced that a dam break analysis is awaited from IIT Roorkie, with whom the Kerala Government has signed an MOU for the analysis.

-Joseph Ponnoly

What is the normal lifespan of a storage dam?

Has the 116 year old Mullaperiyar dam outlived its lifespan?
What is the normal lifespan of a storage dam?

Here are some excerpts from 'Life-span of Storage Dams' by Martin Wieland

Reproduced from:

http://www.waterpowermagazine.com/story.asp?sc=2055594

Life-span of storage dams
03 March 2010
Dam engineers and dam owners may not always have a clear idea about the life-span of their projects. Here, Martin Wieland discusses the many factors which could impact on the useful life of a dam
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 hydromechanical 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 (Wieland and Mueller, 2009):
• 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 or new recommendations, guidelines, regulations or codes are introduced).
• 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 under normal and extraordinary (hydrological) conditions, 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.
Factors affecting life-span of 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 concepts (for example, n-1 rule for flood discharge facilities of embankment dams).
• (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 (e.g. during detailed five-year-inspections of large dams), 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 (swelling due to alkali aggregate reactivity (AAR), sulphate attack, leaching (Figure 1), 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 resulting in changes in the stability of the dam and abutment).
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.
Dense frost-resistant concrete should have a very long service life. Concrete dams, which do not have any steel reinforcement, have a much longer service life than reinforced concrete structures exposed to weather. The oldest concrete dams are about 120 years old. Masonry dams can be much older and still be in service. However, these are usually low structures used in irrigation projects or for water supply.
An extrapolation of concrete performance to 150 or 200 years is rather difficult as no reference projects exist. However, engineers have studied concrete mixes which would guarantee a very long life.
A service life of up to 1000 years would be possible for concrete structures made of special (low-heat) cements and stable aggregates and without steel reinforcement. It is obvious that under ideal environmental conditions (temperature, humidity etc.) the life-span of a concrete dam can be very long. But at the same time, it can also be very short if some of the safety-relevant elements are no longer functioning properly.
An example for uncontrolled safety decrease is the 272m high Enguri arch dam (the world’s highest arch dam) in Georgia, which was completed in 1984. Due to civil war in the 1990s, dam safety monitoring (cables and equipment were removed), dam maintenance and emergency plans no longer worked and within a few years it was not clear if the dam was still safe or not (Figure 2). Gates of bottom outlets were leaking, and due to a deficient grout curtain and the failure of pumps used for removing the drainage water, uplift pressure increased. Since then the safety of the dam has been re-established and a new dam monitoring system has been installed.
Due to the many factors affecting the operational condition and environment of a dam, it is not possible to give a number for the remaining service life of existing dams. This has to be assessed periodically on a case-by-case study. Quite a few concrete dams may, however, require major rehabilitation, especially those showing signs of abnormal behaviour or AAR. Also, uncontrolled sedimentation may shorten the use of the reservoir and may block intakes but does not have a serious effect on the safety of the dam structure or its life-span as long as bottom outlets and spillway gates can still be operated properly. But sediment flushing can cause serious erosion in bottom outlets and sediment flushing tunnels, and sediments can damage turbines within a short period of time.
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. Hydromechanical 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 (Figure 3).
The service life of electro-mechanical equipment varies from 20 to 60 years (Table 1) 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 be available.
A summary of service lives of structural elements and components of different hydro power plants are given by Giesecke and Mosonyi (2005).
...
Ageing also affects the foundation of a dam. With embankment dams these ageing processes can be more critical than with concrete dams because they are often founded on alluvial deposits or residual soils. Water flow through the foundation can result in strength changes over time. Particularly sensitive are clayey materials, but also rocks may reduce their strength. Water flow through the foundation can affect foundation permeability, dissolution of soluble rock, and leaching of grout curtains. Finally, seepage may wash out infilled joints or cause erosion in the soils of the foundation (especially with dispersive soils) leading to the formation of ‘pipes’. All these processes are usually very slow and only develop over a time span of many years.
The foundation is as essential for the life-span of the dam structure as the structure itself. Maintenance of a foundation is by providing it with supplementary treatment, for example by reinforcing or extending the grout curtain or by replacing it with a positive or semi-positive cutoff, by installing relief wells or any other means of drainage depending on the actual situation and its requirements.
Properly designed and constructed embankment dams can remain structurally stable and safe for centuries as long as they are not subjected to erosion processes. There are also a few landslide dams, which have blocked valleys for many years and remained stable, such as the 650m high Usoy dam in Tajikistan, which was formed by a massive landslide triggered by a magnitude 7.3 earthquake in 1911
Embankment dams are most vulnerable to floods (Figure 5), internal erosion and seismic loading. However, a well-designed and maintained embankment dam is a very resilient structure and can also sustain extreme loading conditions. However, periodic safety assessments are indispensable as they will show what measures have to be taken to maintain or even extend the life-span. Deficiencies observed after commissioning must be rectified as early as possible.
Conclusions
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 dam owners 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 hydromechanical 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 hydromechanical and electro-mechanical components.
In some cases the economical life of a storage project may be governed by other factures such as siltation of the reservoir, etc.
Martin Wieland, Chairman, ICOLD Committee on Seismic Aspects of Dam Design; c/o Pöyry Energy Ltd., Hardturmstrasse 161, P.O. Box, CH-8037 Zurich, Switzerland, E-mail: martin.wieland@poyry.com

The Threat of Piping and Seepage at the Dam's Foundation

R.P.Kulkarni, in his article 'Irrigation Engineering in India' has surveyed the engineering history of masonry dams in India including Periyar Dam (height 45 m).  He mentions thus: " It may be noted that almost all these (masonry) dams have served well without any mishap but their sections are found to be inadequate according to the modern theories."

He points to the dangers of 'piping' or the process by which water percolating under a dam has sufficient pressure and velocity to erode the foundations and undermine the dam's structure.  This was noticed in the Coleroon dam built in 1836 by Arthur Cotton, another British Engineer.  He further says, "Similar failures of other Indian river dams eventually led to the first experimental investigations of seepage under masonry dams, and the work of Beresford and Clibborn in the 1890s was able to predict the failure in 1898 of the Narora weir on the river Ganges."

The question that arises is:
Have there been investigations and monitoring of  piping along with seepage under the Periyar dam's foundation so far?
-Joseph Ponnoly

Reference:
Kulkarni, R.P. Irrigation Engineering in India. Indian Journal of History of Science, 17(1); 28-45
http://www.new.dli.ernet.in/rawdataupload/upload/insa/INSA_1/20005af6_28.pdf

Back to Basics: Why lime-surkhi mortar was used?

Engineering and Contracting, Volume 37 (1912) page 567:  records thus:
"At Periyar the use of commercial cements meant importation from Europe and long carriage through virgin jungle. "....
The method of making puzzuolan (locally made concrete) at Periyar, as described by Mr. A. T. Mackenzie,
Project Engineer, in his "History of the Periyar Project,"  is reproduced in the book thus: " Local limestone was burned in stone and clay kilns and after burning the lime was slacked and stored. Clay molded into flat tiles was under-burned in similar kilns. To manufacture the cement, the tiles roughly broken up were placed in a pan mills with a little water and ground to a fine powder. Lime was then added to this powder by degrees, with more water, and the grinding was continued until a thoroughly mixed and rather sloppy mixture resulted. This mixture was then combined with sand and stone to make mortar or concrete. "

The question is: Has not degradation of the lime-surkhi mortar used for the dam's construction 116 years ago weakened the dam's structure?

-Joseph Ponnoly

References:

Mackenzie, A.T. (1899)   History of the Periyar Project. Reprinted in 1963 by the Controller of Stationery and Print on behalf of the Govt. of Madras 

Chrimes, Mike, Ahead of the game – masonry dam design in the British colonies 1800–1900, part 2: 1872–1900,  Source: Dams and Reservoirs, Volume 19, Issue 4, pages 171 –183 , ISSN: 1368-1494, E-ISSN: 1756-8404.

J. Pennycuick. (1897) The diversion of the Periyar.. Min Procs ICE, 205