Back in 1986, when China began building the first of a series of dams on the Mekong River, hardly anyone in the downstream countries of South-East Asia paid attention. But today, as China races to finish the fourth dam for generating electricity on the upper reaches of South-East Asia’s biggest river, concerns about possible environmental impacts in the region are rising fast. Moreover, fear about antagonising China and South-East Asia’s internecine dispute might make any concerted move unlikely.
The sheer scale of China’s engineering to harness the power of the Mekong and change its natural flow is setting off alarm bells, especially in Vietnam, Cambodia, Thailand and Laos, the four countries of the lower Mekong basin where more than 60 million people depend on the river for food, water and transportation.
A report in May by the United Nations Environment Programme (UNEP) and the Asian Institute of Technology (AIT) warned that China’s plan for a cascade of eight dams on the Mekong, which it calls the Lancang Jiang, might pose “a considerable threat” to the river and its natural riches. In June, Thailand’s prime minister was handed a petition calling for a halt to dam building. It was signed by over 11,000 people, many of them subsistence farmers and fishermen who live along the river’s mainstream and its many tributaries.
Some analysts say that if the worst fears of critics are realised, relations between China and its neighbours in mainland South-East Asia will be severely damaged. But mindful of the growing power and influence of China, South-East Asian governments have muffled their concern. Meanwhile, Laos, Cambodia and Thailand have put forward plans to dam their sections of the Mekong mainstream, prompting Vietnam to object and undermining the local environmentalists’ case against China.
Although the Mekong is widely regarded as a South-East Asian river, its source is in the glaciers high in Tibet. Nearly half of the 4,880km river flows through China’s Yunnan province before it reaches South-East Asia. Since there is no international treaty governing use of trans-boundary rivers, China is in a dominant position, controlling the Mekong’s headwater. It has the right to develop its section of the river as it sees fit, and has done so without consulting its neighbours, let alone seeking their approval.
The Mekong River basin drains water from an area of 795,000 square kilometres. The Mekong River Commission (MRC), an inter-governmental agency formed in 1995 by the four lower basin countries estimates that the sustainable hydropower potential of the lower basin alone is a massive 30,000 megawatts. But it also says that there are major challenges in balancing the benefits of clean electricity, water storage and flood control from the dams against negative impacts. These include population displacement, obstruction to fish movements up and down the river, and changes in water and sediment flow.
The cascade of dams being constructed in Yunnan will generate over 15,500 megawatts of electricity for cities and industries, helping to replace polluting fossil fuels, particularly coal and oil. The eight Yunnan dams will produce about the same amount of electricity as 30 big coal-burning plants.
The fourth of China’s Mekong dams, at Xiaowan, is due to be completed by 2012 at a cost of nearly US$4 billion. Rising 292 metres, the dam wall will be the world’s tallest. Its reservoir will hold 15 billion cubic meters of water, more than five times the combined capacity of the first three Chinese dams. Since the end of 2008, when the river diversion channel of the Xiaowan hydropower dam was closed by Chinese engineers, the reservoir has been filling with water, paving the way to start the first electricity generating turbine in September. When full, the reservoir will cover an area of over 190 square kilometres. With a capacity to generate 4,200 megawatts of electricity, Xiaowan will be the largest dam so far on the Mekong.
However, by 2014, China plans to finish another dam below the Xiaowan at Nuozhadu. It will not be quite as high but will impound even more water, nearly 23 billion cubic metres, and generate 5,000 megawatts of power.
Chinese officials have assured South-East Asia that the Yunnan dams will have a positive environmental impact. They say that by holding some water back in the wet season, the dams will help control flooding and river bank erosion downstream. Conversely, releases from the hydropower reservoirs to generate power in the summer will help ease water shortages in the lower Mekong during the dry season.
However, the UNEP-AIT report said that Cambodia’s great central lake Tonle Sap, the nursery of the lower Mekong’s fish stocks, and Vietnam’s Mekong Delta, its rice bowl, were particularly at risk from changes to the river’s unique cycle of flood and drought. The Cambodian lake is linked to the Mekong by the Tonle Sap River. Scientists are concerned that reductions in the Mekong’s natural floodwater flow will cause falls in the lake’s water level and fish stocks, already under pressure from over-harvesting and pollution.
Vietnam worries that dwindling water volumes will aggravate the problem of sea water intrusion and salination in the low-lying Mekong Delta, where climate change and sea level rise threaten to inundate large areas of productive farm land and displace millions of people by the end of this century.