The Mekong River Under Threat

Since the 1980s, the character of the Mekong river has been steadily transformed by China’s dam-building program in Yunnan province. The important changes that had taken place on the course of the river since 1980 and up to 2004 were outlined in the Lowy Institute Paper, River at Risk: The Mekong and the Water Politics of Southeast Asia. In 2010 three hydroelectric dams are already in operation and two more very large dams are under construction and due for completion in 2012 and 2017. Plans exist for at least two further dams, and by 2030 there could be a ‘cascade’ of seven dams in Yunnan. Even before that date and with five dams commissioned China will be able to regulate the flow of the river, reducing the floods of the wet season and raising the level of the river during the dry. In building its dams, China has acted without consulting its downstream neighbours. Although until now the effects of the dams so far built have been limited, this is set to change within a decade, as discussed below.
For despite the limited environmental costs of the dams China has so far completed, and of the river clearances to aid navigation, this state of affairs will change once China has five dams in operation. And the costs exacted by the Chinese dams will be magnified if the proposed mainstream dams below China are built.

Even if no dams are built on the mainstream below China, the cascade to which it is committed will ultimately have serious effects on the functioning of the Mekong once the dams are used to control the river’s flow. This will be the case because the cascade will:

• alter the hydrology of the river and so the current ‘flood pulse’, the regular rise and fall of the river on an annual basis which plays an essential part in the timing of spawning and the migration pattern. This will be particularly important in relation to the Tonle Sap in Cambodia, but will have an effect throughout the river’s course;

• block the flow of sediment down the river which plays a vital part both in depositing nutrients on the agricultural regions flooded by the river and also as a trigger for fish migration — at present well over 50% of the river’s sediment comes from China;

• at least initially cause problems by restricting the amount of flooding that takes place most importantly in Cambodia and Vietnam; and

• lead to the erosion of river banks.

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