The TonLeSap, Mekong and those dams....

Recently, senior officials from countries in the Mekong basin met to commemorate the 15th anniversary of the Mekong River Commission. High on the agenda were the pressures to deal with 2 pressing issues that affected the Mekong River system - the falling waters of the Mekong, and the impact of upriver dam constructions.

The Cambodians living off the Mekong basin, as well as the Tonle Sap flood plains are obviously concerned. The river waters have fallen. And while the presence of hydroelectric dams are not expected to materially affect the total flow of water down the Mekong unless it allows for greater tapping of waters for irrigation upstream, the dams actually reduce the predictable seasonal fluctuations of river water levels. The other serious implications are the effect the loss of seasonality will affect the breeding of river fishes.

Because of our work with the floating village, we are also concerned about how these villages of the Tonle Sap flood plain will be affected by the increasing number of dams of the river systems that feed the Mekong. Clearly the health and livelihood of these communities will be seriously affected.

I reproduce excerpts from two publications for your reading:

a] The Angkorcivilization blog: Hydroelectric dams endanger Cambodia's river people

"The water is also no longer drinkable. The village gets its drinking supply from a well, recently dug by a German non-governmental organization (NGO). "It's very difficult to find food to eat," Teouy says. The main diet consists of rice and salt, with traces of fish, meat and wild vegetables when available.

The villagers are used to seasonal fluctuations of the water table and even to flooding during the wet season, but since the dam construction, the river levels have been changing frequently and erratically. Diurnal fluctuations of the water table have made fishing and farming difficult, if not impossible.

The basin's entire ecosystem is in danger, with many varieties of riverine plants having dwindled because of unnatural flooding, and bird and turtle nests having been swept away."

b] Stimson Report: MEKONG TIPPING POINT: HYDROPOWER DAMS, HUMAN SECURITY AND REGIONAL STABILITY

"China’s eight-dam cascade in Yunnan, already half-completed, will significantly alter the timing and volume of the river’s seasonal flows and hold back a significant amount of the silt that annually provides nutrients for downstream agriculture that are critical to food security. This will severely alter the natural rhythm of the river and jeopardize the annual flooddrought

cycle that makes the Mekong the world’s largest freshwater fishery and one of the most productive regions of wet rice cultivation.

The Lower Mekong mainstream dams in Laos, Thailand, and Cambodia, by one estimate published in a December 2008 issue of the MRC’s journal, Catch and Culture, will block the spawning migration of 70 percent or more of the most commercially important species, imperilling the food security and livelihoods of millions, most of them in Cambodia and the Mekong Delta. A more recent preliminary “technical note” also published by the MRC provisionally estimates that if all eleven Lower Mekong dams are built, the population of the main commercial species, will decline by less than 22 percent in all. However, the study notes that the impact will be disproportionately borne by Cambodia (43 percent decline) and Vietnam, affecting populations that are the poorest and most dependent on fish for their protein needs. The study estimates that Thailand will be little affected while Laos may experience an increase of up to 25 percent, presumably because of the expansion of the currently narrow mainstream wetlands.

The greatest downstream ecological impact will be felt in Cambodia’s Tonle Sap Great Lake that connects to the Mekong mainstream at Phnom Penh, and Vietnam’s Mekong Delta. Upstream dams, including two planned by Cambodia itself, will seriously degrade the Tonle Sap, by far Cambodia’s most important fishery and the seasonal “nursery” of many of the Mekong’s most important fish species. The Mekong Delta of Vietnam will also be severely impacted. The Delta, which produces about 52 percent of Vietnam’s rice and most of its aquaculture fish and shrimp exports, will suffer major consequences from the upstream dams, including the capture of vital silt in dam reservoirs, pollution from mining operations, and a large increase in the use of chemical fertilizers and increased effluents from accelerated urbanization and a decrease in natural soil replenishment."

Tonle Sap flood plains

The TonleSap flood plain. The dark blue areas represent the permanent waters of the Tonle Sap, while the lighter blue regions are the flood plains. I have inserted the approximate location of Baray in the map so you can see where it is relative to the flood plains and the Tonle Sap.

Extracted from the Inventory of Conflict and Environment (ICE) website. For more information about the Mekong flood plain please go there.

Through a unique natural process, the Tonle Sap, which is fairly small and shallow for the most of the year, increases in size and volume almost nine-fold during the monsoon season when the Mekong floods and pushes water into the lake. Due to its rich biodiversity, the Tonle Sap floodplain is one of the most productive inland fisheries in the world, supporting over 3 million people and providing at least 60% of the Cambodians’ protein intake.

The problem is further complicated by the overall decline of the Mekong River, caused by adverse human interference and climate change. While exact origins of the Mekong have not been identified, it is known that its source lies somewhere in the mountains of Tibet. Every spring, when the ice melts the resulting water flows into the river, replenishing it. With Asia becoming hotter and drier as a consequence of climate change, the glaciers that provide Mekong’s water may diminish with time, supplying less and less water with each consequent year. Such decline in water supply at the source, exacerbated by excessive demands imposed on the Mekong’s flow by filling of dam basins, may lead to severe deterioration of the Tonle Sap and its biosphere.


Here are some pictures to show you what the flood plains look like when they are flooded. These pics were taken on the way back from the 'fishing village'. In the dry season, these would just be open land, some being cultivated with padi.