RELATED STORY

• Changing River Flows Disrupt Fisherfolk's Culture
  

OTHER STORIES

• It's Gambling Time Again, but Locals Still in Poverty
• As Hordes of Tourists Come, Heritage Goes
• Villagers Count Costs of Dam in Vietnam
• Criss-crossing Lives
• Highways, Logs, Hydropower and the Remnants of War
• Two Stops Along the Economic Corridor
• HIV/AIDS is Far and Near

The once-quiet gorges between Lincang prefecture and the Dali Bai autonomous prefecture in south-west China's Yunnan province buzz with the sound of construction. Workers are busy building the Xiaowan hydropower station on the Lancang river, which runs through the gorges.

While the project is China's second largest, smaller only than the Three Gorges project on the Yangtze river, Chinese experts said that the impacts of the 292-metre-high dam on the lower reaches of the river will be modest.

Originating in the Qinghai-Tibet plateau, the river runs 4,880 kilometres through China, Laos, Thailand, Myanmar, Cambodia and Vietnam. Lancang is the name for the river's 2,160-kilometre upper and middle reaches running through China, while the lower reaches outside China are known as the Mekong.

From 1986 onwards, China began to build eight hydroelectric dams and two reservoirs on the waterway in Yunnan, where the Lancang traverses more than 1,000 kilometres, to lift the backward western region out of poverty.

The first dam at Manwan, was finished in June 1995. The second, at Dachaoshan, began in August 1997 and will be completed in 2003. The 2.7 billion U.S. dollar Xiaowan project, with a total installed generating capacity of 4.2 million kilowatts, is scheduled to be completed in 2012.

Ma Hongqi, chief engineer of the Yunnan Lancang River Hydropower Development Co Ltd, the major developer of these projects, said that Chinese scientists made a comprehensive analysis of the Xiaowan project's potential impacts on the lower reaches of the Mekong river before construction of the dam began in January 2002.

"We concluded that the Xiaowan project will have limited impacts on the lower reaches of the river," said the engineer at the Chinese Academy of Engineering. "Instead, the dam project will help with irrigation and navigation in the lower reaches," Ma said.

After its completion, the Xiaowan dam will create a 15 billion cubic-metre reservoir with an area of more than 190 square kilometres. The reservoir can ease water shortages in the lower Mekong during the dry season, which usually lasts from November to the following May. On average, water flow to the lower reaches will increase by 39.7 percent, officials said.

This will help improve the efficiency of flood diversion projects along the lower Mekong, Ma said. The increased flow of water will also help prevent intrusions of saline water from the South China Sea, he added.

In June 2001, the Mekong river was opened for commercial navigation simultaneously in China, Laos, Myanmar and Thailand. Thus far, only small vessels weighing under 300 tonnes could reach Laos from China.

When the Xiaowan dam begins operation, the increased flow of water in the dry season will benefit navigation on the river, Ma explained.

According to him, the Xiaowan reservoir will have a 1.1 billion cubic-metre capacity for flood adjustment. During the flood season, it will store more flood water rather than discharge it, which will decrease flooding in the lower Mekong region. "But the impact is actually very limited."

Only 13.47 percent of the Mekong's flow at its mouth in Vietnam originates in the Lancang river, and monsoon rains in the lower Mekong contribute much more precipitation than that in the Lancang drainage area.

The reservoir will cool the water flowing downward from April to September, Ma said, as still water in a reservoir is cooler than running water in the summer and is warmer than it in the winter. The cooler water can cause some negative impact on the environment. "It's not good for the growth of crops and warm-water fish species," he said.

However, the largest drop in water temperature at Xiaowan, which occurs in June, is estimated to be only 2.7 Celsius (the average temperature is 23.1 degrees Celsius). From the dam, the cooler water will flow for more than 550 km out of the country and run through the 230 km that includes tropical gorges between Laos and Myanmar.

"When the water reaches irrigation projects in the lower reaches, its temperature can return to normal," Ma said. "So the construction of the Xiaowan dam will have little negative impact on agriculture in the lower Mekong."

According to data from the Kunming Animal Research Institute at the Chinese Academy of Sciences, there are 127 species of fish in the drainage areas of the Lancang river. Among them, only four belong to migratory species.

They migrate from the lower Mekong to the Puyuan river, a tributary of the Lancang river in Xishuangbanna, a region downstream of the Xiaowan dam site, to spawn. Therefore the dam will have no impact on migratory fish, Ma said.

As the Manwan, Dachaoshan and Xiaowan dams block the Mekong river, the amount of sediment reaching the Mekong's lower reaches will be decreased by about 10 percent as well, helping prevent soil erosion along the Mekong. But this may decrease the food supply for fish living at the mouth of the river, Ma said.

China has also launched a comprehensive environmental protection project in the Lancang river drainage area with the aim of preserving the river's purity.

The project began with a major afforestation drive in 1999. Its goal is to increase the forest coverage in the area from 38 percent at present, to 50 percent in 20 years.

According to Ma, the latest statistics from hydrological monitoring stations show that the water quality of the Mekong meets the international standard for drinking water. "We are building three sewage treatment plants at the dam site to purify sewage from the construction," he said. "We have confidence the river will be clean."

This story, written under the IPS/Rockefeller media fellowship programme, 'Our Mekong: A Vision amid Globalisation', was published in 'China Daily' in Beijing.