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Victoria, hold your water!

Date : 2020-Dec-12
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Recent tremors around the largest dam in Sri Lanka should alarm the authorities. When they appear to be relatively too calm about it, like the deep and dangerous waters of the Victoria dam itself, then it is a reason for people to be doubly worried. Unless you have a fresh and accurate estimation of the risk, no one can be expected to walk on the water. 


What happened in Kandy?


Nothing. But, in the last three months, areas around the Victoria dam in Digana, there have been at least 6 minor tremors. A tremor is the technical term to classify a small earthquake. The first of them was reported on 29th of August, 2020 at 20.32 and it was felt by people living in Haragama, Milapitiya, Anuragama and Kiual-Linda areas of the right bank of the Mahaweli River as well as and dwellers at Ambakote, Aluthwatte and Kengalla areas of the left bank of the river. Around the world, an estimated 100,000 tremors of this scale happen. They are sometimes not even felt by human beings living in areas where they take place.


Hazard vs Risk


Big dams bring big benefits. But they also are big hazards. History is full of dam failures. Sri Lanka has not seen any large dam breaches since 1986 Kanthale dam failure that killed at least 120 people. A hazard is the presence of something that may cause damage. But a risk is the probability of that damage actually happening. An example is that building a big reservoir with a tall dam is always a hazard. However, the real risk of that dam collapsing is a probability assessment that needs to consider so many factors. They include the nature of the ground below the dam, such as the tectonic plates, history of earthquakes in the area, and the strength of the rock underneath. They also include the design and the strength of the reinforcements and construction of the dam. Further, maintenance, possibility of flash floods, and other weather-related factors too have an impact. As such the real question here is that if the recent repeated tremors increased the risk to the Victoria dam? The authorities, such as the chief engineer of Mahaweli, Rohana Aruppola does not think so. In fact, speaking in front of a Viyathmaga banner at a press conference cum expert discussion organized by the Governor of the Centra Province’, he and others claimed that the recent tremors post no risk at all. Does he understand the difference between the hazard and the risk?


The new tectonic plate


The ThinkHazard website of the World Bank rates Sri Lanka as a country with ‘Low’ risk of earthquakes. In fact, Sri Lanka has not seen large earthquakes at all. However, recent research in geophysics does not always endorse this traditional view. A forewarning research conducted by our own academics sheds new light on this relatively neglected area of study. As early as 2005, Vidyajothi Professor Chandra Dissanayake showed that an intra-plate earthquake can strike Sri Lanka, exposing Sri Lanka to earthquake, minor tremors and even Tsunamis.  In his 2005 article to the National Science Foundation, he showed evidence of the formation of new tectonic plate boundary in the Indian Ocean, situated 400-500km from the southern shore of Sri Lanka. The new plate boundary implies a major effect to Sri Lanka. Central highland of the country consists of weak zones and faults which can be able to affect by the earthquake due to developing plate split. The reservoirs in the highland of the country should be monitored regularly by installing a seismometer in the dams. This amounts to only one thing again: a conventional approach to neglect and rule out any risk cannot be the right approach any more.


Are solutions Available?


Even the potential outbreak of a deadly virus in the form of a Corona virus from birds or pangolins had been predicted in 2008 by scientists. But no one took it seriously until it really happened. In his 2017 study on the very subject “Assessment of Concrete Arch Dam under Possible Earthquake Loading in Sri Lanka: Case Study on Victoria Dam”, Dr. Kamal Karunananda of the Open University of Sri Lanka points out:


There is a possibility of moderate earthquake happening in high amplitude which requires the investigation of seismic response in the existing structures in Sri Lanka to take adequate precaution to minimize the damages from the earthquake. Dams are massive structures and they can be subjected to severe destructive impact due to earthquake since they are located in the central high land of Sri Lanka. The consequence of major dam failure in the Mahaweli River can cause major destruction to life, properties and environment.


This study took into account the effect of three previous earthquakes on dams that had the curved structure of the Victoria dam, and proposed solutions to avoid a dam failure. They involve thickening the by 20m at the base and gradually reduce to 5m at 86m above the bottom of the dam, among other improvement downstream.

 

Neglect can be Costly


It is not for us to decide if the Victoria dam has a real risk of failure. However, those experts who were keen to rule out possible human activity being the cause of the tremors have failed to explain the real cause. Besides, why this frequently? Unless a proper and serious assessment of the risk is done, no expert should try to downplay the hazard. Because Victoria cannot fail. She holds the fate of thousands of lives with her cement wall.  

      

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