Wednesday, 18 January 2012

To Dam or Not to Damn the Yarlung Tsangpo

Due to its rising power shortages coupled with increasing international pressure to reduce its carbon emissions, China has dammed all the major rivers originating from Tibet. The most recent case is the damming of the untapped upper reaches of the Yarlung Tsangpo (Brahmaputra). 

A major hydropower project in Tibet at rZam (Tib:ཛམ་; Ch: Zangmu), which began in November 2010, is the first of at least 6 dams proposed on the Yarlung Tsangpo that have been approved. The most ambitious of their project is a 38,000 MW mega dam at Metog (Tib: མེ་ཏོག; Ch: Motuo) on the great bend of the mighty Tsangpo, where the river descents ~2000 m before entering India (Fig. 1). This mega project has the potential to generate output more than twice the capacity of the world's largest power station, the Three Gorges Dam.

Fig. 1 The location of dams under development, proposed and planned on Yarlung Tsangpo and its tributaries. Map source:

However, is China’s widespread dam building a correct response to reduce climate pollution and eradicate poverty, the two biggest challenges facing the country today? 

Chinese government argues that damming rivers is a greener alternative to burning coal by the country, which is the world's biggest emitter of greenhouse gases. But several studies have shown that dams impact the aquatic ecosystem including water flows, water quality, fish habitats, wetlands, and livelihood of people relying on it. Dams also causes high evaporation and loss of water and are also a globally significant source of greenhouse gases such as methane. The rotting organic matter from the vegetation and soils, and detritus that flows in the reservoir contribute to the greenhouse gas emission. According to an estimate, dams and reservoirs are responsible for almost a quarter of all human-caused methane emission. Some studies also indicate that dams cause bloom of blue algae.

Construction of widespread dams on Yarlung Tsangpo has been controversial–ecologically, socially and politically–as it involves environmental impact of altering landscape and ecosystems, and threatens the livelihood of the lower riparian communities. 

Will China’s ever increasing energy demand overwhelm Tibet’s environment?

In case of the Tibetan Plateau, the third pole, which has an extremely fragile ecology, the situation could even be worse. Due to climate change and environmental degradation, the plateau is warming at least twice as fast as the rest of the world, which is causing high rates of glacial melting which in turn leads to the formation of glacial lakes that eventually burst to cause glacial lake outburst floods. The significant and unpredictable changes in the hydrology of the glacier-fed Yarlung-Tsangpo could cause risk of dam failures and catastrophic flood releases. Any event of flash flood in the upper reaches could have a domino effect on the series of dams planned downstream of Tsangpo.

Yarlung Tsangpo has the world's deepest canyon, longer than the Grand Canyon. Largely due to its steep gradient, the river cuts deep gorges and rapidly erodes the bedrock at ~7mm every year. Tsangpo also transports an exceptionally heavy load of eroded sediments and provides nutrients down stream on which the river basin’s farmers and fish depend. The obstruction of sediment transport by dam or even tunnel could not only impact the livelihood of lower riparian communities but could cause siltation and landslides.

Fig. 2 Google earth image showing the location of dZam Dam in Gyatsa, 30 km east of the tectonically active Tsona-Chusum Rift (marked as red line).

The Tibetan Plateau due to its unique tectonic settings and active deformation, experiences high seismic activities that are frequent and often severe. Some of these dams on Tsangpo are built or planned close to major fault lines e.g. dZam dam (Ch: Zangmu) is just 30 km east of the tectonically active Tsona-Chusum rift (Ch: Cona-Qusum; Fig. 2). Moreover, the whole stretch of the Indus-Yarlung Suture experiences strike-slip motion (different blocks of landmass sliding past each other) with high seismicity. The weight of water stored in the dam has been found scientifically to be sufficient to trigger seismic events, which could further aggravate landslides and heavy siltation, posing high risk to the dam as well as lower riparian communities.

Thus, instead of simply perceiving Yarlung Tsangpo as a potential hydropower resource, China must take serious consideration to address the long-term environmental and social impacts of such a full-river development. The emission of greenhouse gases from the dams will grossly deteriorate the warming trend in the Tibetan Plateau. Therefore, China’s endeavor to save ~200m tonnes of carbon each year (by using hydro-power instead of coal) might turn into another Three Gorges Dam, a model of disaster. The cumulative effect of dam construction on this tectonically, geographically and ecologically significant region could be detrimental.

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