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Repairs at leaking dam create controversy

Update: April, 02/2012 - 09:35

The cause of the leakage at Song Tranh 2 Hydro-Power Plant, the biggest dam in central Viet Nam, remains a controversial issue. The accident catalysed a comprehensive examination of the country's hydro-power system. Tran Quynh Hoa reports for Viet Nam News.

Hoang Xuan Hong, head of the Science and Technology Department, the Viet Nam National Committee on Large Dams and Water Resources Development

 

Hoang Xuan Hong
I agree that there's no immediate danger in the short term for the dam at the Song Tranh 2 Hydro-Power Plant. But what the Ministry of Industry and Trade (MoIT) and EVN has done [unblocking "water holes"] has not been as effective as they claim.

Saying that leakage has been improved because water is now leaking out of the dam at a speed of 7 or 8 litres per second instead of the 30 litres before their "intervention" may comfort the layman but it has stirred harsh reactions from dam scientists.

Unblocking water holes can do nothing to stop water leakage. It's normal that water might leak out at a speed of 30 litres per second from all over a huge area of 35,000 square metres from the top to bottom of the dam. In this case, however, water leaks out from thermal gaps, which means there are major leaks at only a few sites.

Inside the thermal gaps there must be waterproof shields that completely prevent water from flowing out. Something must be wrong with these waterproof shields.

Therefore, the explanation of the MoIT and EVN is unacceptable and what they have been doing has had no effect. In other words, they have done nothing with water leakage but only direct leaked water from here to there. Instead of letting water leak out, the water holes gather leaked water into three tunnels before it is pumped out.

It should be noted that these three tunnels are not responsible for holding leaked water from inside the dam. There are six small water ditches (two in each tunnel) that are used to carry water out. The tunnels are indeed designed to measure the leakage, sinking and temperature of the dam.

In this case, however, even the tunnels are inundated in water, which is totally wrong, not to mention that the equipment in the tunnels is not working.

The MoIT and EVN should install extra waterproof shields at the locations where water is leaking. The entire concrete wall of the dam must be carefully checked since the concrete could have some small holes as a result of inappropriate construction and supervision.

To do this, water in the dam must be pumped out for the repairs. This will cost EVN lots of money since Song Tranh 2 is the major source of electricity for the central region. Alternatively, there are technologies available in the world that allow waterproof shields to be put in while the dam is still full of water. But they are also very costly. It could be millions of dollars.

The world has a lot of experience in these types of accidents. Cracks and breakage in concrete gravity-arch dams have been reported in Colombia, Venezuela and even developed countries such as the US and Switzerland. The only question is if EVN wants to confer with experts and pay for long-term repairs.

To Van Truong, former director of the Southern Irrigation Planning Institute

 

To Van Truong
The most effective and impartial way to deal with the Song Tranh 2 Hydro-Power Plant case is to invite experienced and independent consultants to join hands as soon as possible. The danger of water leaking from a dam cannot be underestimated, particularly in areas prone to earthquakes.

This incident shows a need for mechanisms and policies for independent consultancy in Viet Nam, especially in topics involving science and technology. Here people have not been willing to listen to opposing arguments. Therefore, even in some cases where independent councils are set up, they are just for show. It's time to change!

In another issue, the overall picture of hydro-power in the country needs to be re-examined. The development strategy of the power sector is currently based on untrustworthy plans of other sectors, simply parroting them to forecast growth for dozens of years ahead.

Forty per cent of power generated in Viet Nam is from hydro-power plants. Water sources for power generation depend on the weather and the operational regulations of dams are worked out by humans. We do not have a law on planning yet, so the responsibilities of different industries often overlap. In the case of hydro-power, the biggest problem is that the system creates water usage conflicts. In 2010, when we visited Yook Don National Reserve in the Central Highlands, we saw nearly 20km of the Serepok River dry out because of the Serepok 4A Hydro-Power Plant.

A stricter designing procedure must also be worked out for earthquake-prone areas such as Quang Nam and Da Nang.

Le Quang Hung, director of the Construction Ministry's Construction Works Assessment Department and member of the State Council for Assessment and Acceptance of Construction Works

 

Le Quang Hung
Of course concrete must be faulty to let water penetrate through that much. There are several types of problems, including cracks in thermal gaps or low-quality concrete at one or more places. But it does not mean drilling samples [to check concrete quality] are necessary in all cases.

The question is whether the dam is so dangerous that evacuation is necessary. The answer is no.

Responsibility for the problems belongs to the investor [EVN], the designer consultant [Electricity Construction Consultancy Company 1], and the bidder [Irrigation Construction Corporation 4]. So we need to let these organisations work out repair measures first.

For important infrastructure projects like hydro-power plants, which significantly affect local residents' lives, State organisations have to inspect, supervise and assess repair measures.

The State Council for Assessment and Acceptance of Construction Works has regularly assessed State construction works like this. The council also has independent experts. — VNS

A meeting at the site yesterday between Deputy Minister of Industry and Trade Hoang Quoc Vuong, the managers of Song Tranh 2 Hydro-Power Plant and the local governments of central Quang Nam Province and Bac Tra My District still failed to produce a final decision about how to deal with the leakage.

The Ministry of Industry and Trade (MoIT) and Electricity of Viet Nam (EVN) last week announced that removing the blockage from water holes had been an effective method to reduce leakage at the plant.

Water holes were designed to catch moisture absorbed from inside the dam's concrete walls in ditches before it could leak out, since concrete is not completely waterproof.

According to the MoIT, unblocking water holes helped bring down the leakage to 7-8 litres per second, instead of the earlier 30 litres.

Deputy Minister Vuong promised that the water leakage, which had been reported since February, would be curbed by mid-April and all repairs would be finished by the end of July – the start of the rainy season.

Initial assessments by experts from the MoIT, EVN and the State Council for Assessment and Acceptance of Construction Works showed that some water holes were blocked, resulting in water leaking from "thermal gaps" – small openings placed between concrete blocks to prevent cracking in the heat.

Vuong confirmed that the dam, with a water capacity of 729 million cubic metres — equivalent to 43 West Lakes in Ha Noi, remained safe and stable.

The dam's water level would be lowered to 140m from the current 160m to facilitate the repairs, according to yesterday's meeting.

It has been raining in Bac Tra My District over the past few days, adding 50 cubic metres of water to the dam every second.

The EVN-owned $249-million plant began operations in January 2011.

Viet Nam has some 3,000 dams but only 14 of them are concrete gravity-arch dams lke Song Tranh 2.

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