Mekong Utility Watch

Salween Dams: a study

(May 23, 1994) This report is an introduction to the impacts of large dams in general, the environmental problems associated with existing large dams in  Asia, and the potential impacts of damming the Salween.



This report is an introduction to the impacts of large dams in general, the environmental problems associated with existing large dams in Asia, and the potential impacts of damming the Salween.

For the purpose of discussion this report deals with damming the Salween — regardless of exact location of dam site — excluding the proposed dams on Salween tributaries and other Thai-Burma border rivers.

The idea of damming the Salween has been studied for many years by dam proponents. The dams are intended to generate hydroelectricity for export to Thailand and possibly also to divert water from the Salween into river basins in Thailand.

The dams to date proposed represent only a theoretical estimate of the hydroelectric power that could be generated by harnessing flows of the Moei and the Salween.

What actually ever gets built will depend not upon the engineers proposals but more upon political decision makers and international financiers who will weigh the political and economic stakes of each dam project separately.

In any case, it is improbable that all of these large dams would ever be built because there are some serious problems and risks associated with damming the Salween or Moei rivers which dam builders would not be able to solve and which will make the dam projects far less economically attractive than originally projected.

Regardless of where exactly the Salween would be dammed, any dam on the Salween is cause for concern for people throughout the Salween river basin who depend upon the forests, land and rivers for their livelihoods and local economies.

1.1  Reservoir Sedimentation Shortens Dam Lifespan

All rivers carry sediment and other organic matter which accumulates in the reservoirs created by dams. Eventually all reservoirs fill with sediment but long before this happens, the buildup of sediment in the reservoir can interfere with the operation of the dam and shorten the dam’s operating lifespan.

The Salween is a Himalayan river with a naturally high sediment load but logging and road building in the upper reaches of the Salween river basin has made the Salween extremely muddy most of the year. Therefore a reservoir on the Salween could be expected to slit up rapidly.

Dam reservoirs on other Himalayan rivers in China and India, for example, have filled with sediment only a few years after completion  even though the dam builders predicted a 50 year operating life.

To date there are no successful measures to keep reservoirs sediment  free and therefore the economic benefits of the dam are often far less  than the dam builders originally estimated.

1.2  Aging and Decommissioning of Dams

Dams are usually designed to have an economic lifespan of anywhere  from 50 to 100 years but their useful lifespans are inevitably  shortened as the reservoirs become clogged with sediment and as the  concrete and other dam materials age. As with nuclear power plants,  careful monitoring and costly maintenance of older dams must  eventually be followed by a difficult decommissioning process, for  which the dam building industry is unprepared.

Dams designed to hold back the force of the standing water can  require expensive new construction in order to withstand the greater  force of a wall of dense sediment.

Over the course of several decades, the structural integrity of dams  not designed to function as artificial waterfalls can be undermined,  threatening to collapse in a catastrophic flood of mud and debris.

In the fifty years of building large dams, no large dam has yet been  decommissioned although it is now being discussed in the USA  where some of the first megadams were built.

1.3  Dams and Earthquakes

The pressure applied to often fragile geological structures by the vast  mass of water impounded by a large dam can — and often does — give  rise to earthquakes.

Although it is difficult to establish the geological conditions under  which induced earthquakes can occur, scientists now conclude that  all large reservoirs can be considered potential sources if induced  seismic activity.

The first hint that dams could cause earthquakes came in the late  1930s, when increased seismic activity was recorded after the Lake  Mead reservoir was impounded by the Boulder Dam in Colorado,  USA.

Since then major earthquakes have occurred at large reservoirs in  China, Africa, Greece and India. The Aswan dam and Akosombo  dams have experienced earthquakes even though the dams are  located in what were classified as low risk areas.

Originally it was thought that earthquakes can only occur when a  reservoir was being filled — or immediately after it reached its  maximum height. But earthquakes can also occur when a reservoir is  emptied and then refilled, as has occurred at dams in France and  Greece.

Despite the risks associated with large dams and reservoirs many  dams are still being built — or planned — in areas of seismic activity.

In the last two decades, the science of seismology has advanced  rapidly, with new research and recognition of reservoir-induced  earthquakes. But many large dams have been designed using earlier  optimistic estimates of fault displacement and ground accelerations.

Dam safety experts now fear there are tens of thousands of existing  dams in the USA, India and former Soviet Union that are unsafe.  Independent researchers in China estimate there might be as many as  85,000 small and medium-sized dams built since the 1950s that are  unsafe.

In August 1993, the Gouhou dam in Qinghai province, northwest  China, collapsed killing hundreds of people and unleashing torrents  of water on town and villages downstream. Dam experts suspect that  the 1990 earthquake weakened the dam leading to its collapse under  this year’s floodwaters.

If the Salween dams are built, millions of people living downstream of  the dams would be forced to bear the burden of risk that someday an  earthquake could cause the dam to crack or burst unleashing a terrible  flood downstream.

1.4  Forced Eviction

The people who are now living near the dam sites and reservoir areas  would be forced to leave their homes and land.

It is unlikely that the dam proponents would make any provision for  these people given that the SLORC [Burma’s ruling State Law and  Order Restoration Council] is waging war against the people living in  the Salween river basin, and that Thai authorities would claim no  responsibility for people affected beyond their border.

Exact location of the dam sites and details of the areas that would be  flooded (towns, army bases, villages, natural/historical points of  interest etc.) by the dams are as yet unrecorded and will depend upon  exact dam location, height and local topography.

1.5  Effects of Dam Construction

Tonnes of explosives would be used to blast through the river gorges  and rocky rapids to prepare the foundation for construction and the  channel downstream of the dam and power station.

There would be a large-scale extraction of building materials — such  as stones, gravel, sand and clay for dam construction.

Forests would be cleared for access roads to the site on either side of  the Thai-Burma border.

Temporary housing for a large labour force of thousands of workers  would have to be constructed for the years that it will take to build  the dam. Wastewater and sewage will be dumped directly into the  river.

This labour force would rely heavily on the forests in the vicinity of  the construction site for their daily fuelwood.

The people evicted to make way for the construction site and worker  camps would then be forced to clear new farm plots in the forest.

Construction and blasting of the river to transform it into straight  intake and outflow channels will scare away animals and aquatic life  as well as destroy their habitat.

1.6  From River to Reservoir

The physical form of a natural river and the ecosystem that depends  on it have evolved together over thousands of years, created by the  natural flows and sediment moved from the river’s watershed.

The construction of a large dam destroys this balance and within  several decades the changes in the river system would be far more  costly than the economic benefits of the dam.

When a river is dammed a body of water is impounded behind the  dam and is known as a reservoir. This impoundment has an immediate  impact on the physical and biological systems within the reservoir.

Physical Changes

Transformation of a free-flowing river into a regulated reservoir  systems would initiate the following changes in the river systems:

The free flowing river would be transformed into a deep, slow moving  or still water system (depending on actual operation), up to several  hundred kilometres or more in length (depending on dam height and  topography).

Migration of fish either upstream or downstream would be blocked by  the dam.

Forests and fertile, low-lying land along the river and in the tributary  valleys would be permanently submerged by the reservoir. These  areas are now used for seasonal cultivation of crops which serve the  needs of local families and communities.

The flooding of the river will disrupt aquatic and land-based animal  habitat along the river banks. In the case of the Lower Salween dam,  the western edge of the Salawin Wildlife Sanctuary in Thailand would  be drowned.

As water velocity is reduced, fine particles of sand and clay, known  as sediment, would settle to the bottom of the reservoir.

Initially, as the water level in the reservoir rose, land would be  inundated and nutrients (and pollutants) would be drawn out from the  flooded soils and decomposing vegetation.

The flooded vegetation would provide new habitat for young fish and  there might be a population boom over the short term for some fish  species.

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