The situation is set to worsen and Hanoi has to pay due attention, they add.
In the last week of February, the Red River section that flows through Lao Cai Province in northern Vietnam has become so clear that there are some shallow areas towards the banks where the river bed can be seen at a depth of one meter. This is a highly unusual development because the Red River is known for its reddish or pinkish hue.
Dao Trong Tu, head of the executive board of the Vietnam Rivers Network, said one possible reason for the changes seen in the Red River is rooted in China. A series of hydropower plants and reservoirs operated by China further upstream could have held back alluvium, he said.
The Red River, over 1,100 km long, originates in China and flows through 26 localities in northern Vietnam including Lao Cai, Yen Bai, Phu Tho, Vinh Phuc and Hanoi, with a combined population of more than 26 million. The river section that flows through Vietnam is about 510 km long.
Tu said that of Red River’s total water volume of 133 billion cubic meters, China contributes 39 percent, the rest is from Vietnam (60 percent) and Laos (1 percent). The amount of alluvium that comes in from China is huge, at around 160 to 200 million tonnes per year.
The Red River has three tributaries in Vietnam – the Da, Lo and Thao rivers. In upstream parts of these rivers, China has completed several of 52 planned hydropower plants.
China’s dams are likely holding a large amount of sediment, stopping it from flowing downstream to Vietnam.
“Consequently, agriculture activities in the Red River delta are strongly affected,” Tu said.
The lack of alluvium might have caused the riverbeds to sink lower, preventing water from flowing into farmers’ fields. Authorities are, therefore, forced to release around three to five billion cu.m of water every year from dams in Hoa Binh and Tuyen Quang provinces for irrigation.
Agreeing with Tu, Nguyen Lan Chau, Deputy Director of Institute of Mechanics and Environment Engineering, under the Vietnam Union of Science and Technology Associations, said China’s hydropower plants could be considered a key reason for the drastic reduction in the amount of alluvium in the Red River.
Chau said the river water in Lao Cai has been getting clearer after China began operating two major power plants on the upstream part of Thao River.
The first one is Nanshan, with holding capacity of 300 million cu.m of water and the second one is Madushan, which can hold more than 550 million cu.m. The two dams are 140 km and 100 km away from the Vietnamese border.
Chau said her studies show that the river’s clear color in Lao Cai has been randomly seen in recent years, especially in the dry season. Water flow in the river has also been reduced, she added.
She said Beijing has begun operating 12 of 29 dams planned in the upstream area of the Thao River, 11 among 12 on the Da River, and eight plants on the Lo and Gam rivers.
“The lower amount of alluvium from the upper Red River makes it hard for Vietnam to cultivate, and increases erosion along rivers in downstream sections,” Chau said.
Floods and droughts
Numbers that indicate flood levels on the Red River under the Long Bien Bridge, Hanoi, August 2020. Photo by VnExpress/Giang Huy.
Tu said China’s dams typically cause floods in Vietnam in the rainy season, when Beijing needs to release water to ensure the reservoirs’ safety. The water flow in this season accounts for 70 percent of the whole year’s flow due to geological and climatic conditions.
“This creates the situation where Vietnam is constantly bombarded by floods.”
He also said the risk of dam collapse is a possible disaster that people downstream cannot ignore.
Chau said Vietnam has suffered many times from flash floods caused by China. In 2015, there was a flood with an amplitude of three meters in Lao Cai; in 2006, the flood amplitude was over 10 meters in a section of the Da River in Muong Te District, Lai Chau Province; another flood the same year, which was caused by a broken dam in the upper part of Thao River, surpassed alarm level 2 (82 meters), and left two people dead. In 2007, the flood amplitude was over four meters in the Nam Na River in Lao Cai’s Bat Xat District.
In August 2020, authorities in China’s Hekou Yao County informed their Lao Cai counterparts that the Madushan Dam would open its floodgates as heavy rains had caused the dam to reach its maximum capacity. They did not provide a specific figure, only saying that water levels in the Red River would be higher, prompting Vietnam’s northern localities to take precautions without really knowing what to prepare for.
The third problem, Tu and Chau said, is drought during the dry season, when dam operators store water in their reservoirs.
Chau’s studies have shown that in January and March 2007, the water flowing into to Hoa Binh hydropower plant in Vietnam was at the lowest level in a century, at 140 cu.m and 145 cu.m per second. Additionally, China’s night and day regulation mode made for huge fluctuations of water levels in the Da, Thao, and Lo rivers, leading to a higher risk of riverbank erosion.
Tu said he was very worried that Vietnam does not have a bilateral mechanism for cooperation with China on the Red River despite Hanoi’s attempts to reach one. Tu and his colleagues have visited China to discuss this issue, but things haven’t changed.
One possible mechanism that should be considered is similar to that of the Mekong River Commission (MRC), where some riparian countries’ leaders exchange information and views regularly.
Tu said that when China does not provide detailed information, Vietnam could not have good preparation to react in urgent cases. For example, in 2020, China announced when it would release water from its dams, but did not say how much. Vietnam did not know how to measure the impacts on economic and civil activities in order to prepare an adequate response.
He said the situation will only worsen in the future if no agreement is reached on joint management of rivers that flow through both countries.