Mekong Damming: What are The Environmental and Social Impacts?

Blogs - Mekong: June 13, 2018

The Mekong river is one of the worlds longest rivers and traverses six Southeast Asian countries, acting as a natural boundary between territories. Its estimated length of 4,350 km runs from its sources in the Tibetan Plateau down through China’s Yunnan Province, Myanmar, Laos, Thailand and Cambodia, until it meets the sea in a vast delta on the southern coast of Vietnam.

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The river acts as a major trade route through these countries and also buoys local economies by supporting neighbouring communities, fisheries and agriculture along its banks and tributaries, with wild captured fish making up a major portion of local dietary protein.

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The river and its surroundings also support a rich biodiversity, with many fascinating and several endangered species, such as “Cantor’s giant softshell turtle”, a freshwater stingray that grows beyond 5m in length and 1.9m in width, and the freshwater Irrawaddy dolphin, now with only near 80 individuals remaining.

In 1995, Laos, Thailand, Cambodia and Vietnam established the Mekong River Commission (MRC) to manage and coordinate use of the Mekong’s resources. In 1996, China and Myanmar became “dialogue partners” of the MRC and the six countries now work together in a cooperative framework.

Video source: mrcmekongorg

Hydropower along the Mekong

Recent developments have seen numerous hydropower dam projects along the Mekong. China already has several hydropower dams completed, with many more already under construction, planned or proposed. Laos has two dams currently under construction and another seven planned or proposed, the Xayaburi dam in Northern Laos raising “serious concerns” with NGOs and scientists. Cambodia has two dams planned/proposed, one in particular, the Sambor dam, attracting some criticism as the “worst possible place” to build a major dam following a three-year study commissioned by the Cambodian government in 2014 from the National Heritage Institute (NHI), a US-based research and consultancy firm. These projects will not have a direct impact on Vietnam, but indirectly river silt flow will be affected and coastal erosion and marine inundation will probably result along the coastline. Fish stock could also be impacted.

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Beyond the obvious benefits of large hydropower supply for help in developing these areas economically, significant drawbacks have been noted and commented upon concerning not only the environmental changes and loss of habitat, but also upon the speed of change in the river system itself and the knock-on consequences of building consecutive dams. China’s construction of dams on the Upper Mekong has had impacts on downstream communities where fish migratory patterns have been disrupted and water level fluctuations have also affected ground irrigation and agriculture.

Video source: mrcmekongorg

One Study on Sustainable Management and Development of the Mekong River including “Impacts of Mainstream Hydropower Projects”, points out positive benefits of hydropower projects, such as an increase in economic benefits, navigation opportunities, flood protection and drought management, and more dry season flow for irrigation expansion, but these development projects also bring along negative impacts, including food security issues, fish stock depletion, reduction in sediment and nutrient transport downstream.

Another study on the planned developments in Laos makes recommendations for a further study period when the results of current negative impact mitigation measures can be better evaluated.


Alternative models for developing power generation have been considered and may in fact prove more cost-effective, but no doubt they will have their own environmental impact. One proposal is to install large floating arrays of solar panels on existing reservoirs for electricity generation (a technology already successfully utilised in China and India).

Environmental and Social impact

According to the NHI study, the proposed Sambor Dam and the reservoir in Cambodia would create a barrier that would be devastating for the migratory fish stocks in the Mekong and its tributaries, disrupting the reproductive cycle. At least 86 species are long-range migratory species in the Cambodian part of the Mekong River, and all would become endangered by a Sambor dam. Irrawaddy river dolphins, which are critically endangered, also use the Sambor corridor for refuge and breeding grounds. Dam construction at or near Sambor places the remaining 80 dolphins at high risk of extinction in the Mekong.

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Any impact on the fisheries and fish stocks that exist along the Mekong, including Vietnam, is expected to have a direct effect upon the riverside communities, were fisheries-related employment and indeed subsistence living relies on the free fish in the river as well as farming along the river banks. Large dam projects will have an immediate impact resulting in displacement of a large number of communities upstream of the dam, and an equal if more gradual impact on fishing and farming communities downstream of large dams, resulting in a dramatic change in the social and economic prosperity of these areas. Modern developments and relocation from rural community life and work to an urban and factory work life will likely bring significant societal change.

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Additional Complexity

More complicated issues associated with damming of large rivers is that of sediment supply (river-borne silt). As the dams limit flow and seasonal flooding, silt build-up accumulates in the more sedate main river channel and may require dredging to maintain a navigable waterway. Dredging becomes another significant threat to fisheries, disrupting fish spawning rounds as well as affecting the irrigation of adjacent agricultural lands. Of particular concern in the river delta area, the resulting reduction (possibly by as much as 90 percent) of river silt and sediment accumulation in the delta could lead to further loss of habitat and increased inundation of land areas by the sea during storm events, leading to an eventual loss of overall land area to the sea.

Modelling of overall effects on the entire river is far from simple, and the still poorly understood systems being affected are best observed and studied over long time periods as development progresses. As mentioned above, current recommendations are to observe the outcomes and impacts of existing dam construction and the efforts at problem mitigation, and to gather data for a more complete study before proceeding with further development of major river dam projects.

The NHI study reports that the proposed Sambor Dam would capture all of the bedload (particles transported along the river bed) and 60% of the suspended sediments that are needed to maintain and replenish the Mekong Delta in Vietnam, which according to the IPCC (Intergovernmental Panel on Climate Change) is one of the three major delta systems in the world most vulnerable to sea level rise, through storm surges and salt water invasion/salinisation. The resilience of the delta to the effects of climate change depends directly on the continued replenishment of sediment.

The Future

Thanks to the internationally coordinated efforts of the MRC, the onward and further development of the Mekong River will continue with due caution and regard for all parties with continued participation in the agreed regional decision-making procedures called the “Procedures for Notification, Prior Consultation and Agreement” (PNPCA).

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Whatever the outcome on the immediate forward plans of the individual and coordinated governments, the immediate prospect for the Lower Mekong and its habitats and environment is one of certain change, and as with the Yangtze River Dolphin in China, now functionally extinct, the Irrawaddy Dolphin and perhaps other species will cease to exist in the mighty Mekong.

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