FACE OFF: What if the wall was to break
Jan 24, 2002
An NGO director warns Sri Nakarin Dam could collapse while an Egat director says it's for 1,000 years.
Sri Nakarin Dam, an allpurpose dam which is part of the Mae Klong River Basin development, is located in Baan Chao Nane, Tambon Tha Kradan of Kanchanaburi�s Sri Sawat District. Built by the Electricity Generating Authority of Thailand, the dam became operational in 1980 and is used mainly for irrigation, covering 4 million rai of farmland, as well as flood prevention and desalination. It also has the capacity to generate 1.25 kilowatts/hour of electricity. The earth-filled dam, which measures 140 metres in height, 610 metres in length and 15 metres across, has a 419squarekilometre reservoir and can hold a maximum of 17.7 billion cubic metres of water.
Chainarong Sethchua, director of the Thai chapter of Southeast Asia River Network:
We demand a thorough examination of the Sri Nakarin Dam following news reports quoting the Electricity Generating Authority of Thailand�s engineering division that the dam had shifted about 16.5 centimetres from its original location, and that if no measures are taken to stop this, the dam might collapse within 10 years.
The dam was built right across the Sri Sawat Fault, an active geological fault which causes frequent earthquakes.
On April 22, 1983 an earthquake of the magnitude of 5.8 on the Richter scale took place near the reservoir behind the Sri Nakarin Dam, causing a fourkilometrelong split in the ground and tidal waves in the reservoir.
The Southeast Asia River Network has been trying to raise public awareness on failing dams and the risks associated with defective dams for some time. The intention is to persuade Egat to take precautionary measures to minimise those risks.
Sri Nakarin Dam is not the only dam that has this problem. The Khao Laem Dam in Kanchanaburi�s Sangkhla Buri District is built on another active geological fault called the Three Pagodas Fault. There are signs that this dam is shifting just like the Sri Nakarin Dam.
Both Sri Nakarin and Khao Laem dams were designed and built to withstand earthquakes, which resulted in an escalation of the construction cost by over 200 per cent. Even so, there are still serious risks involved in the event of major earthquakes.
The problem is, Egat has no experience in dealing with earthquakes and the effects on its dams. What if one or more of the dams collapses? It has been estimated that if the Sri Nakarin Dam broke it could cause catastrophic flooding, with 27 metrehigh water in downstream areas for between two and six days. That�s why Egat needs to come up with emergency plans, including evacuation and contingency relief operations.
The oldest dam in the world is less than 200 years old and no longer functioning. Most dams in Thailand are falling apart, with huge cracks showing, in just decades since their completion.
We want a neutral committee, such as the National Safety Centre, to examine the dam and to provide training for evacuation if the dam fails. A 1985 paper by Peerawat Pumthong, of the Asian Institute of Technology, says the dam is threatened by three factors: an active geological fault that passes near the dam, earthquakes and mudslides.
Chalermchai Rattanalak, deputy governor of Egat:
We insist that the Sri Nakarin Dam, which has shifted by about one half of a foot, remains structurally sound and will continue to serve its purposes for a long, long time. The construction of the dam met the highest international standards in dam building.
Egat has carried out yearly examinations of all the dams. The last time that we checked on Sri Nakarin Dam was in April 2001. In the first five years since the dam was completed, it was found that it had shifted by only 59 centimetres, while the dam was designed to anticipate shifting of up to 150 centimetres. Despite all this, the foundations of the dam remain intact.
There has been no shifting whatsoever taking place in the past several years.
Building a dam is not all that different from building a road. When you build a dam by compressing earth and stones together, there is bound to be some shifting taking place, particularly after the construction has been completed. Engineers in charge of designing and construction of the dam had anticipated this. As it is, the shifting of 40 centimetres is considered normal when the allowable shifting has been set at 150 centimetres.
As for the earthquakes near the dam area, it must be stressed that Egat has taken the issue very seriously. Our dam has been built to withstand earthquakes, even major tremors. The Sri Nakarin Dam can withstand serious earthquakes of up to 7.5 on the Richter scale.
Another thing that members of the public tend not to be aware of is that sometimes the construction of a dam can induce earthquakes. That is because the tremendous weight of water in the reservoir could cause shifting or movement of the bedrock and earth crust underneath. But this kind of earthquake generally subsides and can stop altogether several years after the construction is completed.
Newspapers either misquoted or misinformed the public when they claimed that some Egat engineers had warned about a possible collapse of the Sri Nakarin Dam in 10 years. I have checked and no Egat engineer has said anything to that effect.
The Sri Nakarin Dam is 100 per cent safe and its structural integrity has never been compromised. There are no indications that suggest the dam is unsafe.
As to the question of how long will the Sri Nakarin Dam last, all I can say is that it is going to last a long, long time. The useful working life of a dam is determined by the level of silting behind the dam. Judging from the current level of silting at Sri Nakarin Dam, the dam will still be functioning for another 1,000 years.