Wet-season dam operations hit Mekong ecology and communities

As China celebrated the 100th anniversary of the Communist Party on 1 July, the Jinghong dam in Yunnan Province began restricting the flow of water on the Upper Mekong. Levels downstream dropped 50 centimetres in just 10 hours. By 3 July, the low levels hit the Golden Triangle at the conjunction of the Thailand, Myanmar and Laos borders. 

Hydropower dams meet higher demands for energy during the day. At night, the turbines are turned off and the release of water is restricted, resulting in hydropeaking – the rapid raising and lowering of a river’s water levels. While more transboundary data is being shared than ever before on the Mekong’s levels, operational data from China remains a source of contention.

“Hydropeaking causes frequent and rapid fluctuations of water downstream, [with] major adverse impacts on aquatic resources important for communities living downstream,” says Gary Lee of International Rivers, an NGO. “With sudden changes in water flows and levels, communities [on the Mekong] have seen their riverbanks and boats washed away, and declines in fisheries [as well as] other aquatic resources which have devastated people’s livelihoods.”

Upstream of Thailand, China has 11 hydropower dams on its section of the Upper Mekong, known as the Lancang cascade, and there are 11 more in various stages of planning and completion on the Lower Mekong, most with some level of Chinese investment in development or construction. The Luang Prabang dam in Laos is the latest to begin preliminary construction. 

Despite heavy rainfall throughout June, river levels dropped by two metres in the first week of July. By August, China and the Mekong River Commission (MRC) were at odds about the causes of fluctuating water levels in the wet season. For riparian communities living downstream, the effects of dams restricting water flow on the Upper Mekong were obvious.

What is the Mekong River Commission?

Unknown costs of hydropeaking on the Mekong

“We can see obvious impacts [of hydropeaking] on wildlife in wetland forests in the Lower Ing River, a Mekong tributary in Chiang Rai province [in northern Thailand],” says Teerapong Pomun, director of the Mekong Community Institute and Living River Siam Association. Pomun says there are 26 wetland forests along the Lower Ing. “The change of water levels in the Mekong affects the ecosystems of the forests… There are many wildlife species in the forest, including important species such as the Eurasian otter, smooth-coated otter, and king cobra.”

The smooth-coated otter is native to southern and Southeast Asia, with populations in Iraq. It is the largest otter species in Asia, and is categorised as vulnerable by the International Union for Conservation of Nature. (Image: Alamy)

The Boon Rueang wetlands in northern Thailand, which rely heavily on the regular flood pulse of the Mekong, are of particular importance to conservationists. Recent moves to turn the nearby area into a Special Economic Zone were met with public pushback for the little-studied ecosystem. 

“We believe that this is the second most important habitat of the Eurasian otter in Thailand. We found at least six haplotypes [a set of DNA variations] of Eurasian otter in the Lower Ing River, which is only about 133 kilometres long,” Teerapong Pomun says. “The change of wetland forests and fish population due to Mekong waters affects otters and other wildlife in the forest, including many migratory birds.”

The Mekong River Commission (MRC) has been attempting to work with China on studying the broader effects of hydropower dams. But a previous joint study in 2018, Gary Lee says, paid “limited attention on what the impacts are on the people who rely on the river”.

Despite promising wet-season benchmarks, when the tap was turned off at Jinghong in Yunnan province in July, the Ruak River tributary of the Mekong showed dry season sandbanks between Thailand and Myanmar. Upstream, hydropeaking also affects the Mekong’s tributaries in ways that are even less well known than those on the mainstream, with ecosystems that rely on the regular flooding and drought of the Mekong.

Information from the Mekong Dam Monitor, an online platform that uses satellite imagery to track dam reservoir levels, estimates that there were around 60 hydropeaking events between 5-7 January, and indicates that the overall effects of retention and release exacerbate seasonal problems. Due to upstream restrictions and low rainfall, Chiang Saen district in Thailand was missing 35% of its natural flow by mid-August, according to Eyes on Earth’s Natural Flow Model.

Millions of people in the Lower Mekong Basin from Myanmar rely on the fish catch from the Mekong, which supplies the largest inland fishery on the planet and determines the natural cycle of the wet and dry seasons. Recent studies claim hydropeaking on the Mekong can result in drastic changes in depth, channel morphology, temperature and flow velocity.

In addition to nutrients and sediment being held back by large hydropower dams, larval and juvenile fish are at risk from standing water and trauma caused by the force of unnatural flow. Birds that make their nests on the banks of the Mekong, some of which are endangered, are in danger having those nests flooded because of unseasonal patterns. 

“Dams [are] turning the river on and off with a switch and some knobs,” says Alan Basist, president of Eyes on Earth, noting that natural changes in the river rarely occur at the pace caused by hydropeaking. “The integrity, stability, ecology and economy are substantially impacted from these unnatural fluctuations of flow, yet it does not appear these concerns are addressed in the operations of the dams.”

The low wet-season levels for the Mekong on 2 July were first reported by the Mekong Dam Monitor (MDM), which is a cooperative effort by the Stimson Center and Eyes on Earth. The data collected by the MDM uses cloud-piercing satellites and hydrological data to predict and record Mekong levels. 

“Under normal conditions the Jinghong gauge during the dry season should gradually lower over the months of January through May, but the data shows something completely different,” says Brian Eyler, director of the Southeast Asia programme at the Stimson Center. He notes that using data from the Lancang-Mekong Cooperation (LMC)’s Yunjinghong gauge and MDM, the river rose about 3 metres between mid-February and mid-May as a result of coordinated upstream dam releases largely from upstream dams at Huangdeng, Xiaowan, and Nuozhadu.

The team also released alerts to warn downstream communities. “When the Mekong Dam Monitor team observes a 50 cm change in river level caused by a dam operation over a 24-hour period or less, an alert is issued to vulnerable communities, government authorities, civil society organisations and the media via the MDM platform, social media, and email,” says Eyler. “Since the monitor was launched in December 2020, 16 of these alerts have been issued.” 

The alerts give communities in Thailand a lead time of around 48 hours to prepare for the change in water levels. This is hopefully enough time, Eyler says, to remove boats, livestock and farming assets that might otherwise be washed away by a sudden rise. He notes that the recent LMC data portal from China and the MDM will allow for tracking the frequency and extent of hydropeaking events, and tie them to fisheries losses and loss of livelihood. 

The monitoring station at Chiang Saen in the Golden Triangle is the first monitoring station outside China to experience hydropeaking from the Lancang cascade, but the wider effects on the banks are felt further downstream, monitored at stations in Chiang Khan in Thailand and Vientiane and Nong Khai in Laos. Hydropeaking on the Mekong could also have cumulative effects as far away as Vietnam, where the lack of sediment in the river – held back by dams – combined with illicit sand mining causes river banks to collapse.  

The drastic droughts of 2019 were a catalyst for transboundary data sharing on the Mekong, and recent cooperation has provided new, near-real time data that is publicly accessible. However, while the MDM, LMC and MRC gauges broadly agree on river levels, a lack of cooperation on operational data has stymied mitigation efforts for hydropeaking. 

The MRC has no power to approve or disapprove of the building of a mainstream dam. This has always raised questions about its efficacy. Nevertheless, it continues to request operational data from China, most recently in late June 2021, for greater transparency. Others have advocated for a more action-oriented approach.

“The Thai government along with other MRC member countries should be advocating for changes in the ways the Lancang cascade is operated to reduce impacts on the river and communities,” says Gary Lee. “The dam operations should prioritise ecosystem services that are vital for livelihoods of downstream communities over power generation and commercial navigation.”

There may even be positive aspects of hydropeaking on the Mekong, as it may mitigate the problem of excessive algal bloom. Unfortunately, if China is unwilling to share operational data this, or any other positive impact, is impossible to assess.

“The Chinese government and investors never listen or care about people downstream,” says Teerapong Pomun. “We don’t have good mechanisms for engagement.”

The Third Pole