Vietnam’s Mekong quandary: settling the sediment issue

Vietnam’s Mekong Delta has been suffering a lot of land erosion in recent years. Is this linked to upstream developments, including dams?

Richard Cronin: Numerous recent studies based on both current and historical data show that sediment-trapping hydropower dams upstream on the main stem and tributaries of the Mekong River are by far the most important cause of the fast increasing erosion of the coast and deeper penetration of sea water, even into the interior of the delta.

Richard Cronin, a Mekong specialist at the American think-tank Stimson Center.

Most large dams trap between 80-90 percent or more of the historical sediment flow.

Important but lesser causes of land erosion include sand-mining upstream and in the delta and the construction of canals that expose more surface area of the land to erosion.

So what is in store for the Mekong Delta in terms of the sediment it has received, historically?

Coastal erosion and sediment flows are highly connected.

Already, upstream dams in China and on major Lower Mekong Basin (LMB) tributaries in Thailand, Laos, and Vietnam have trapped a major share of the historical sediment flow into the delta.

China's half of the river provides only about 16 percent of the river’s total annual discharge, but is the source of more than half of the river’s total sediment load.

Estimates of sediment trapping by upstream dams is not an exact science, but tracking sediment flows in the LMB is much more difficult because of a lack of meaningful data. The exception to this situation is Chang Saen, Thailand's northernmost river port, where record-keeping on sediment flows has been carried out for a long time. In this case, Chinese dams are estimated to be trapping 83 percent or more of the historical flow of sediment from the Chinese half of the river.

One study that assumes 38 dams with reservoirs that already exist or are highly likely to be built--what MRC modelers call the "Definite Future" scenario - estimates that 51 percent of the historical sediment load that previously reached lower reaches of the LMB, including the Tonle Sap, the Cambodian floodplain and the Mekong Delta, would be trapped in the dam reservoirs.

If the highest development scenario were to come to pass, 96 percent of the sediment would be captured upstream and only 4 percent of the historical flow would reach the delta.

Construction of the controversial Three Gorges Dam, in Yichang, Hubei Province, China. Photo by Reuters

What about Cambodia's Sambor Dam? How would it affect water, fish sources and livelihoods of people in downstream areas?

A report has described the Sambor Dam, as originally designed, as "probably the largest and most destructive dam in the Mekong River Basin." Numerous other studies share the same view, some calling the 18 kilometers-wide dam a "fish killer" and massive sediment trapper. The full proposed dam would largely end the role of the Tonle Sap Lake and flood plains as one of the world's most productive fresh water fisheries and deny nutrient-rich sediment to the downstream Cambodian agricultural flood plains and the Mekong Delta.

The report by the California-based Natural Heritage Institution (NHI) could not be more pointed and concise as to the impact: "The Sambor reach of the Mekong is the corridor that experiences perhaps the largest annual migration of fish biomass on the planet. A large scale dam and impoundment at this site would obstruct this migration, which is vital for the completion of the life cycles of the migratory fish that characterize the most productive freshwater fishery in the world. It would also capture most of the sediments and nutrients that maintain and replenish the morphology of the Mekong Delta and nourish the food web for the fishery."

How should member countries in the Mekong region use recommendations mentioned in this report?

This is the most important question. The two NHI reports, the Sambor Alternatives Assessment and the Sustainable Hydropower Master Plan for Xe Kong Basin in Lao PDR, convincingly establish that both the planned Xe Kong 1 dam and the Sambor dam would have a devastating impact on the most productive part of the river and the Mekong Delta.

The concept of floating solar arrays on dam reservoirs and lakes is no longer novel. A large number of hybrid projects have been built or are under construction in the U.S., the U.K., Australia, Japan and elsewhere. Especially with the rapidly falling cost of solar panels and the generally rising cost and high financial and political risks to large dam projects, Laos and other lower income countries that want to exploit their natural resources can make the leap to a cheaper and more environmentally sustainable energy future.

The NHI studies found that this approach would be considerably less expensive, much faster to deploy and do no more damage to the environment.

This could open up new sources of financing. While the ABD, the World Bank and developed country aid donors have largely declined to finance dams on the Mekong mainstream and major tributaries, it's likely that they would be responsive to this approach, which is both environmentally responsible, cheaper, and hence more "bankable."

Given the risks to the Mekong Delta from the planned dams and the many advantages of the proposed hybrid alternatives the Vietnamese government should have every incentive to seek more information on the hybrid technology, logically from companies and countries that are already deploying it.

Both reports note the high stakes for Vietnam and encourage the government to be more active in engaging with the leaders of Laos and Cambodia and at the ministerial levels.

A man climbs down from his house in Attapeu, Laos, as the area is flooded following a dam collapse in July. Photo by VnExpress/Thanh Nguyen

Regarding the Sambor dam, the fact that the project carries high political and financial risks, and probably technical/engineering risks as well, means that it is still possible for the Vietnamsese government to exercise influence.

Cambodian government officials insist that Sambor dam is a high priority project but the company that was originally picked to build the dam, China Southern Power Grid, pulled out of the project in late 2011 as a result of protests by Cambodian villagers that the dam would decimate the fish population and also because the plan would require relocating 19,000 people.

The Vietnamese government should also have significant leverage regarding the Sambor dam since Vietnam reportedly is to be the off-taker of 70 percent of the power, with another 10 percent going to Thailand.

How can Vietnam complain about the impact of the dam on the delta while buying a major share of its output?

Although the CEO of the Mekong River Commission (MRC) must remain impartial, the fact that the current CEO, Dr. Pham Tuan Phan, is Vietnamese puts him in a position to focus more research on the hybrid concept and engage with the governments about incorporating this attractive alternative into the organization's next 5-year strategic development plan.

Regarding Xe Kong 1 and other planned dams, the report emphasizes that Laos has made good progress with the promulgation and approval by the National Assembly of a new policy on sustainable hydropower development, but notes that the policy guidelines declare goals and procedures but no specific responsibilities and substantive criteria. The report seeks to fill this gap as much as possible.

Given that Vietnam's environmental policies and procedures regarding hydropower dams are more advanced, this is an area where Vietnam could help, especially in conjunction with international expertise and financing.

Moreover, the fact that the national utility, EVN, is a major investor in the Xe Kaman 1 dam should ease the problem of trying to persuade the dam developer-owner to agree to the deployment of floating solar panels on the reservoir and integration of its output with the hydropower house.

Because the politically influential Royal Group is a minor investor in the Lower Sesan 2 (LS2) dam, deploying solar panels on the reservoir in lieu of building the Sambor dam may not be so easy.

In addition to its stake in LS2, the Royal Group currently is the only identified potential investor in the Sambor project and reportedly is in line to carry out the pre-feasibility, feasibility and social and environmental impact studies. Allowing the deployment on the LS2 reservoir would undercut the group's strong interest in the Sambor project.

*Richard Cronin is a Mekong specialist at the American think-tank Stimson Center.