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

Dam Safety Threat Factors for Mullaperiyar Dam

Risk /Threat Factors

• Age of the dam: The dam is 116 years old as of 2011. It has outlived its expected life span of 50 years. Strengthening the existing dam has its limitations and may not prove to be effective in the event of a disaster as seen in the Morvi Dam disaster of 1979.
• Elevation of the dam: The dam is situated approx. 3000 ft above msl and holds 15 tmc of water at full capacity (at 155 feet water level). The gravitational potential energy of the dam under these conditions is 3000 million joules. The height of the water column is 155 feet at full capacity and 1200 ft length at the crest. The damage that such a water mass can cause, in the event of a dam failure, is disastrous.
• Structural weaknesses: The dam was constructed using stone ruble masonry with lime mortar grouting following prevailing 19th century construction techniques that have now become archaic. Seepage and leaks from the dam have caused concern. Structural weaknesses of the foundation and weaknesses of the lime-surkhi ruble masonry core of the dam, need to be assessed.
• Earthquakes: The dam is situated in a seismically active zone. An earthquake measuring 4.5 on the Richter scale occurred on June 7, 1988 with maximum damage in Nedumkandam and Kallar (within 20 kms of the dam). Several earthquake tremors have occurred in the area in recent times. These could be reservoir-induced seismicity, requiring further studies according to experts. CESS (Centre for Earth Sciences, Thiruvananthapuram), IIT Roorkee and IISc (Indian Institute of Science) Bengaluru,  have reported that the dam cannot withstand earthquakes of magnitude above 6 point on the Richter scale.
• Floods and Landslides: Global warming and changing weather patterns leading to torrential rains and flooding can lead to overflow and collapse of the dam. Determination of the Probable Maximum Flood and Probable Maximum Precipitation parameters for the dam, considering current hydrological, meteorological and seismic data, is important to ensure dam safety.
• Safety maintenance and safety monitoring of the dam: Continuous safety monitoring is required to prevent disasters and to detect dam failure. Disaster Management schemes have to be in place to contain damages resulting from dam failure.

Only a formal risk assessment can identify all the threat factors and the probability of threat events happening. Similarly a disaster impact analysis would be required to determine the impact of a dam failure.

-Joseph Ponnoly

Dam Breach Parameters - Technical References

US Bureau of Reclamation Dam Safety Office Publication titled 'Prediction of Embankment Dam Breach Parameters', published in July 1998 can be seen at:

http://www.usbr.gov/pmts/hydraulics_lab/pubs/DSO/DSO-98-004.pdf

This publication deals with dam break analysis and prediction of water flow process and  overflow during extreme floods and routing of the flow after the dam breach.
This research report contains relevant literature review and also deals with case studies of dam failures with relevant data. The prediction parameters include prediction of peak outflows and dam breach prediction models.

The report focuses on 'embankment' dams. But the flood flow parameters are equally applicable to  gravity dams.

Of particular interest to Mullaperiyar Dam would be the various tools currently available for analyzing and predicting dam failures listed on page 5 of the report.  The mostly widely used ones are:

• National Weather Service (NWS) Dam-Break Flood Forecasting Model (DAMBRK)  (most widely used) and its successor FLDWAV
• The US Army Corps of Engineers Hydrologic Engineering Center Flood Hydrograph Package HEC 1
• NWS Simplified Dam-Break Forecasting Model SMPDBK.

It is suggested in the report that SMPDBK can be used as a screening tool and DAMBRK for more detailed analyses.

Analysis of the routing of the dam-break flood is particularly important to determine the post-break impact.
NWS BREACH model can be used to simulate the breach formation process in detail.

This report can guide the Engineers in analyzing and forecasting dam break parameters for Mullaperiyar dam. They can use simulation software such as Flow3D or OpenFOAM to simulate the water flow within the reservoir and downstream.
-JP

What if Mullaperiyar dam breaks?

The crucial question to be answered is:
What if Mullaperiyar dam breaks, in spite of all the strengthening done so far, with the dam burst resulting from torrential rains or earthquakes or due to structural weaknesses of the aging 116 year old dam?

The dam holds 15 tmc of water (at its full capacity) at an elevation of approx 3000 ft from msl. The water level has a height of 155 feet at its maximum level and length of 1200 feet at the top and 139 feet at the base.

If the dam breaks, what is the rate of flow of water downstream? What will be the height of the column of water and the force with which it will strike Idukki Dam, 45 kms downstream?
Even if Idukki Dam is able to hold the 15 tmc of water, will it sustain the force of the gushing waters and the waves formed in the Idukki reservoir?

How much time will it take to traverse the 244 km course of Periyar River to reach Arabian Sea?
Considering the topography of the mountain range through which the gushing waters have to pass through, where are the possibilities of new ribs or new rivers (flow channels) being formed? Which areas in Kerala will be most affected by this scenario?

What will be the impact on 11 other dams downstream and the waters held by them?

Assume the spillways are able to divert some of the water.

Consider the main dam and baby dam also breaking.

-Joseph Ponnoly

Is a new dam the solution to the problem? -What the experts say

What the experts say:
Dr D.K.Paul IIT Roorkee 's 2009 report on 'Structural Study of Mullaperiyar Dam considering the Seismic effects':
The dam will not withstand earthquakes measuring 6 point or above on the Richter scale.

Dr C.P.Rajendran, Seismologist, IISc, Bangalore:
Construction of a new dam at Mullaperiyar is the solution to most of the problems related to this century old dam

Tamilnadu stand:
The dam has been well maintained and reconstructed

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