MEKONG RIVER: ITS ROUTE, FLOW, HYDROLOGY

MEKONG RIVER

View of the sunrise over the mountains and Mekong from Mount Phou in Luang Prabang Laos

The Mekong River is one of the world's great rivers. Originating in Tibet, not far from the source of the Yangtze River, it tumbles down through the Himalayas and southern China into Southeast Asia and flows along the borders of Laos, Burma and Thailand through the heart of the Golden Triangle into Cambodia, where it flows in one direction in the wet season and the opposite direction in the dry season. It finally empties into the South China Sea at the Mekong Delta in Vietnam. Its source in Tibet as not discovered until 1994.

The Mekong River is shared by China, Thailand, Myanmar Laos, Cambodia, and Vietnam and goes by many names. It is known as Lancang Jiang (Turbulent River) in China, the Mae Nam Khong in Thailand, Myanmar and Laos, Tonle Than (Great Waters) in Cambodia and Cuu Long (Nine Dragons) in Vietnam. It is also known as River of Stone, Dragon Running River, Mother River Khong, and Big Water.

The Mekong is the longest river in Southeast Asia, the 12th longest in the world and the 10th largest in terns of volume. With about half of its length in China, it flows for 4,350 kilometers (2,703 miles) and provides food and water for 60 million people and disgorges 475 billion cubic meters of water each year into the South China Sea and the Pacific Ocean. It has a drainage area of 805,604 square kilometers (311,045 square miles).

The Mekong River is one of the wildest rivers in he world and is surprisingly undeveloped for such a large river. There are no large cities or industrial zones along its banks. It is not dammed. Until 1994 there were note even bridges across the lower stretches of it. For the most part the it is brown and muddy and still wild and free. The Upper Mekong features turbulent rapids, steep gorges and long section with no people. Often the only way to cross it is on cables strung between cliffs. The Lower Mekong River is calmer and more placid and incredibly wide in some places.

The Mekong flows through some poorest countries and regions in the world. For many the countries that border it development of the river is vital to the development of the country. China wants to develop the river to help the impoverished Yunnan Province. Around 60 million people depend on the river and its tributaries for food, transport and many other aspects of their daily lives.China has placed three dams across the upper reaches of the Mekong and more are planned. But otherwise the mainstream flows free (some major tributaries have dams). The Mekong River Commission (MBC) is an organization with representatives from Cambodia, Thailand, Laos and Vietnam committed to water utilization, basin development and environmental protection. Myanmar and China are not members just observers.

A good book on the river is “Mekong “ by Edward AA. Gargan (Knopf, 2002) written by a former correspondent for The Times. “Great Mekong Subregion Atlas of the Environment “ by the Asian Development Bank and United Nations Environmental Programme is well written and contains excellent photographs, charts and maps.

Route of the Mekong River

Mekong river basin

The Mekong River is 4,220 kilometers long and is one of the 12 great rivers of the world. From its source in the Tibetan plateau, it flows through the Tibet and Yunnan regions of China, forms the boundary between Laos and Burma as well as between Laos and Thailand, divides into two branches--the Song Han Giang and Song Tien Giang--below Phnom Penh, and continues through Cambodia and the Mekong basin before draining into the South China Sea through nine mouths or cuu long (nine dragons).

The river is heavily silted and is navigable by seagoing craft of shallow draft as far as Kompong Cham in Cambodia. A tributary entering the river at Phnom Penh drains the Tonle Sap, a shallow fresh- water lake that acts as a natural reservoir to stabilize the flow of water through the lower Mekong. When the river is in flood stage, its silted delta outlets are unable to carry off the high volume of water. Floodwaters back up into the Tonle Sap, causing the lake to inundate as much as 10,000 square kilometers. As the flood subsides, the flow of water reverses and proceeds from the lake to the sea. The effect is to reduce significantly the danger of devastating floods in the Mekong Delta, where the river floods the surrounding fields each year to a level of one to two meters. *

The Mekong River flows through a narrow, 200-kilometer-long gorge in southern China and along the Myanmar-Laos. From the tripoint of China, Burma (Myanmar) and Laos the river flows southwest and forms the border of Burma and Laos for about 100 kilometres (62 miles) until it arrives at the tripoint of Burma, Laos, and Thailand. This is also the point of confluence between the Ruak River (which follows the Thai-Burma border) and the Mekong. The area of this tripoint is sometimes termed the Golden Triangle, although the term also refers to the much larger area of those three countries that is notorious as a drug producing region.

As one travels south on the Mekong its become easier to navigate and higher numbers of greater varieties of boats appear. From the Golden Triangle tripoint, the Mekong turns southeast to briefly form the border of Laos with Thailand. It then turns east into the interior of Laos, flowing first east and then south for some 400 kilometres (250 mi) before meeting the border with Thailand again. Once more, it defines the Laos-Thailand border for some 850 kilometres (530 mi) as it flows first east, passing in front of the capital of Laos, Vientiane, then turns south. A second time, the river leaves the border and flows east into Laos soon passing the city of Pakse. Thereafter, it turns and runs more or less directly south, crossing into Cambodia. At Khone Falls the river cascardes over rocks and separates into several branches, divided by forested islands, before it enters Cambodia.

The Mekong River flows through the east-central portion of Cambodia. Over much of its course it occupies an elevated bed paralleled by natural levees. Beyond the levees are huge depressions known as “beng “. The Mekong River is navigable from the sea by small ocean-going vessels as far as Phnom Penh. Shallow draft boats are necessary to further upstream. The northern Mekong River area of Cambodia is fairly undeveloped. There are some stretches where the villages are more than 30 kilometers miles apart. River traffic is light. The main fishing season is after the rainy season ends in September and the fish begin migrating northward. Villages use scoop nets to gather small, silvery fish.

Mekong River Basin

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Mekong river boat The Mekong basin cover an area the size of France and Germany. More than 80 percent of the people that live in the Mekong River basis in rely on the river for agriculture or fishing. More than 41 percent of the land in the heavily populated Lower Mekong basin is used for agriculture, which accounts for 90 percent of all water use. In the forested uplands of the region, with a prime teak tree worth $20,000 or more, it is no surprise that illegal logging is a problem.

Eleanor J. Sterling and Merry D. Camhi wrote in Natural History magazine, The Mekong’s name translates from Lao as “mother of the waters.” It’s no wonder: the river snakes some 3,000 miles from its headwaters on the Tibetan Plateau to its outlet through the Mekong River Delta into the South China Sea. It and the uncountable “feeder” rivers and streams in Cambodia, China, Laos, Myanmar, Thailand, and Vietnam make up the 300,000-square-mile Mekong River Basin. [Source: Eleanor J. Sterling and Merry D. Camhi, Natural History magazine, December 2007]

The five Southeast Asian countries—Thailand, Vietnam, Myanmar, Cambodia and Laos—and one Chinese province—Yunnan—that embrace the Mekong basin are home to about 270 million people, roughly the population of the United States, but it lies on land a forth of the size of the U.S. The vast majority of the people that live on the region depend on the river either directly or indirectly.

Kevin Short wrote in the Yomiuri Shimbun,“A watershed ecosystem, of course, pays no attention to national boundaries. Deforestation high in the uplands, for example , can impact water quality and fish resources far downstream. Recognizing they share a common limited resource base and therefore a common future, the concerned nations and province have fored the Greater Mekong Subregional Plan, a coordinated effort to encourage sustainable resource utilization while preserving biological and cultural diversity throughout the watershed.” [Source: Kevin Short, Daily Yomiuri, February 2005]

Khone Falls and Limits of the Mekong River as a Transport Route

Khone Falls (on the Mekong River along the Laos-Cambodian border) is the widest waterfall in the world according to the Guinness Book of Records. The series of rapids and falls are 6.7 miles wide, with a drop of 70 feet. The falls are most impressive at the end of the rainy season when the flow is 1.5 million cubic meters per second. This is more than any other fall in the world, and twice as much as Niagra Falls.

Known properly as Khônephapheng Falls, Khone is six mile chain of cataracts. There are two main cascades: Phapheng and Somphamit Falls and several smaller sets of rapids. In some places some flimsy bamboo platforms have been set up for fishermen to use. Don’t try to use them yourself. The magic manikhot tree that sits in the middle of the falls is said to have never been touched by human hands. The river cruise to the falls passes by numerous islands and temples with saffron-robed monks.

Li Phi falls (Khone Phapeng), connecting with Khone Falls, Don Khon, Si Phan Don, Southern Laos

The falls are one of the reasons why the Mekong River was one of the last rivers to be explored and developed. Fish amazingly can make their way up the falls but boats can’t. It dashed the hopes of French hoping to use the Mekong River as a transportation link to China.

The French built a 14-kilometers railway so that goods could be moved across two islands to bypass the falls. Cargo at one end of the railway was hoisted from boats and placed on railcars and unloaded back onto to boats at the other end of the line. Sometimes entire boats were lifted and put on railway cars The railroad operated until the end of World War II and was the only railroad built in Laos. After the war the rails were carried away by villagers. All that remains really are two piers, a bridge between the two islands, remains of sleepers and gravel and a rusting steam locomotive. On Khone Island you can hike on part of the old railway bed.

Flow of the Mekong River

The Mekong is the tenth-largest river in the world by volume, but this fluctuates considerably depending on the season. At its widest point in Laos, near Si Phan Don in the south, the river is 15 kilometres (9 miles) wide during the monsoon season, but it can be shallow and difficult to traverse in its upper reaches during the dry season.

Harmony Patricio, a conservation biologist and the conservation director at FISHBIO, told mongabay.com: “One unique thing about the Mekong is that it has the highest range of flows of any river on Earth. The difference in flows between the wet season and the dry season is immense. During the rainy season, the water levels rise and deposit a lot of nutrients and sediments along the banks. [Source: Jeremy Hance, mongabay.com, April 23, 2013 |~|]

During spring melt and the monsoon season from May to October, the Mekong became a raging torrent, sometimes producing a flood wave that is 46 feet high. Annual floods often kill dozens of people. Floods in Cambodia and Vietnam in 2000, killed 500 people and wiped out herds, crops and orchards. At the end of the dry season in March, April and May the river level can drop as much as 40 feet in some places, exposing large rocks and sand bars, and making navigation even in small boats difficult.

Vital Sediment Carried by the Mekong River

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Foot bridge over the Mekong in China The Mekong River carries sediment from the Tibetan Plateau through China, Myanmar, Laos, Thailand, Cambodia, and Vietnam before reaching the South China Sea. This sediment contains nutrients that maintain fertile farmland, strengthen riverbanks, and support fisheries and wetlands. In the late 2000s, the river transported approximately 143 million tonnes of sediment to the Mekong Delta each year. By 2020, however, the Mekong River Commission estimated that only about one-third of that amount was reaching Vietnam's floodplains, and projected that less than 5 million tonnes per year could reach the delta by 2040 if current trends continue. .[Source: Kanupriya Kapoor, Simon Scarr and Phuong Nguyen, Reuters December 15, 2022]

The decline has affected farming throughout the Vietnamese Mekong Delta. Farmers have reported increasing riverbank erosion, saltwater intrusion, and declining crop yields as nutrient-rich sediment becomes scarce. One rice farmer in Soc Trang Province said his harvest had fallen to about half of its previous level, while erosion was gradually washing away his farmland. Many rural residents have sought work elsewhere as agricultural conditions have become more difficult.

Scientists have identified upstream hydropower dams as a major factor reducing sediment transport. A joint analysis by Reuters and the German remote-sensing company EOMAP used satellite imagery to examine sediment levels around four major dams in China and Laos. The study found that the dams reduced downstream sediment loads by an average of about 81 percent.

Three Parallel Rivers in Yunnan, China

The Three Parallel Rivers in Yunnan is a UNESCO World Heritage Site. Here the upper reaches of three of Asia's mightiest rivers — the Yangtze, Mekong, and the Salween — flow parallel to one another within a 55 mile band, divided by high mountain ridges. The Yangtze river, known in this area as the Jinsha, marks the boundary between Tibet and Kham. The Mekong is known as the Lancang. The Salween is called the Nujiang. “Jiang” is the Chinese word for river. The area is stunningly beautiful but rarely visited because the terrain carved by the rivers is so severe and rugged.

Fed by monsoon rains, the Yangtze, Mekong and Salween all sweep east of the Himalayas then drop due south, parallel to one another, before heading off in different directions. The gorges of the upper Yangtze, Mekong and Salween are among the deepest in the world, each twice the depth of the Grand Canyon, and reaching three kilometers in some places. Each gorge is separated from the others by towering mountains with more than a hundred peaks over 5,000 meters.

Described by the United Nations as the “epicenter of Chinese biodiversity,” the Three Parallel Rivers region is home to 6,000 vascular plant species, 30 species of timber trees, and 500 medicinal plants. Among the 173 species of mammal are clouded leopard and red gorel. More than 440 species of birds have been seen here. The 300,000 human inhabitants include more than a dozen ethnic groups. Among these are Tibetans, Naxi, Lisu, Yi and Nu, divided by mountains and uncrushable rivers.

The area was not explored by Westerners until the 1920s and 1930s. The first roads were gouged into the area to exploit the area’s timber in the 1950s. Entire mountainsides of old growth forest were clear cut. By the mid 1990s 80 percent of the regions’ income came from timber. Logging was cut back in the late 1990s partly in response to flooding on the Yangtze — that killed 4,000 and left more than a million homeless — that was blamed on deforestation-caused erosion.

By the late 1990s tourism began making inroads into the region and quickly displaced logging as the main money earner. People also began making money from harvesting medicinal herbs and matsutake mushrooms to export to Japan. Now the biggest issue concerning the region is how extensively to dam to the Jinsha, Lancang and Nu. The Jinsha has four dams under construction as of 2009. The Lancang already has three. Two are under construction and nine more are proposed. There are two on the Nu and a plan put on the table in 2003 calls for 13 more.

There are plans to build 100 dams in Sichuan and Yunnan in the Three Parallel Rivers area, where three great rivers. The plan calls for more than a dozen dams larger than the Grand Coulee dam and one that will be the tallest in the world. Even though the dams are in remote mountainous areas they are set to displace 1 million people.

Mekong River in Laos

The Lao PDR is criss-crossed with a myriad of rivers and streams. The largest is the Mekong River, flowing for 1,898 kilometers from the North to the South, with 919 kilometers of the river forming the major portion of the border with Thailand. It is estimated that some 60 percent of all the water entering the Mekong River system originates in Laos. These rivers and streams provide great potential for hydropower development with 51 percent of the power potential in the lower Mekong basin contained within Laos. Mekong River is navigable much of length but is not navigable between the sea and Laos because of Khone Falls in southern Laos. The Nam Ou, Na That and Nam Ngum are large tributaries of the Mekong River.

The Mekong River and its eastern tributaries drain all of Laos with the exception of Samneua Province in the northeast. The 1,600 kilometers of navigable water of the river that passes through Laos or along its border is the longest transportation and communication route in the country. But rapids in the far north and far south effectively cut Laos off from the sea and cross-border and international commercial possibilities.

Most of the western border of Laos is demarcated by the Mekong River, which is an important artery for transportation. The Khong falls at the southern end of the country prevent access to the sea, but cargo boats travel along the entire length of the Mekong in Laos during most of the year. Smaller power boats and pirogues provide an important means of transportation on many of the tributaries of the Mekong. The Mekong has thus not been an obstacle but a facilitator for communication, and the similarities between Laos and northeast Thai society--same people, same language--reflect the close contact that has existed across the river for centuries.

Mekong River in Cambodia

The Mekong River Cambodia’s largest river, dominates the hydrology of the country. The river originates in mainland China, flows through Myanmar, Laos, Thailand before entering Cambodia. At Phnom Penh, with alternative arms, the Bassak River from the south, and the Tonle Sab River linking with the " Great Lake " itself –Tonle Sap – form northwest. It continues further southeastward to its lower delta in Viet Nam and to the South China Sea.

The Mekong River in Cambodia flows southward from the Cambodia-Laos border to a point below Kracheh city, where it turns west for about 50 kilometers and then turns southwest to Phnom Penh. Extensive rapids run above Kracheh city. From Kampong Cham the gradient slopes very gently, and inundation of areas along the river occurs at flood stage--June through November--through breaks in the natural levees that have built up along its course. At Phnom Penh four major water courses meet at a point called the Chattomukh (Four Faces).

The section of Mekong River passing through Cambodia lies within the topical wet and dry zone. It has a pronounced dry season during the Northern Hemisphere winter, with about 80 percent of the annual rainfall occurring during the southwest monsoon in May-October. The Mekong River average annual flow at Kratié of 441 km3 is estimated as 93 percent of the total Mekong run-off discharge into the sea. The discharge at Kratié ranges from a minimum of 1,250m3/s to the maximum 66,700m3/s.

Tonle Sap and the Mekong River

The Tonle Sap (north of Phnom Penh in Cambodia) is the largest freshwater lake in Southeast Asia at the end of the wet season but is only a large lake in the dry season when it shrinks to a fraction of its wet season size Stretching almost all the way from Phnom Penh to Angkor Wat, it provides water for half of Cambodia's crops, and yields fish that supplies Cambodia’s population with half its protein It is also one of the country’s most important transportation links.

Tonle Sap lake—which is connected to the Mekong by a short river also called Tonle Sap—alternately feeds, and feeds from, the Mekong River. During raining season from June to October, the lake is fills with water flowing from the northward-flowing Mekong River and becomes 14 meters deep in some places and expands it surface area to around 10,000 square kilometers. In dry season from November to May its shrinks in size to 3,000 square kilometers, with an average depth of only two meters as water flows out from the lake when the Mekong changes course and flows south.

In the Angkor era, Tonle Sap was to the Khmers what the Nile was to the Egyptians: a source of abundance that freed labor to produce grand monuments and create a high level of culture. In the dry season, the Khmers captured the lake’s retreating waters and used them to irrigate crops, and thus were able to grow two or three crops a year. In the wet season, they used the waterway’s advancing waters to carry quarried stones to build Angkor’s great temples. In the Khmer language "Sap" means “lake.”

Mekong River Delta

The Mekong Delta (about 3 hours south of Saigon in Vietnam) is huge delta created by massive amounts of silt, some of it originating in the Himalayas, carried downstream by the Mekong River and deposited in southernmost part of Vietnam, where the great river empties into the South China Sea. About 10,000 square kilometers of the delta are under rice cultivation, making the area one of the major rice-growing regions of the world. The southern tip, known as the Ca Mau Peninsula (Mui Bai Bung), is covered by dense jungle and mangrove swamps.

The Mekong Delta is a low-level plain not more than three meters above sea level at any point and crisscrossed by a maze of canals and rivers. So much sediment is carried by the Mekong's various branches and tributaries that the delta advances sixty to eighty meters into the sea every year despite waves, typhoons and tides that gobble it up. An official Vietnamese source estimates the amount of sediment deposited annually to be about 1 billion cubic meters, or nearly 13 times the amount deposited by the Red River.

Flat, hot and green, the Mekong Delta is Vietnam's most important agricultural region. Much of the area is covered by rice paddies that are irrigated by delta water and fertilized by delta silt. Many paddies and farms produce three crops of rice a year, enough to feed the entire country, with some left over to export, Almost half of Vietnam’s exported rices comes from the Mekong Delta. Other products from the region include sugar cane, coconuts, pumpkins, various kinds of fruit, fish and snakes. There also large numbers of catfish and shrimp farms.

Image Sources: Wikimedia Commons

Text Sources: New York Times, Washington Post, Los Angeles Times, Times of London, The Guardian, National Geographic, Smithsonian magazine, The New Yorker, Time, Reuters, Associated Press, AFP, Atlantic Monthly, The Economist, , Wikipedia, BBC, CNN, and various books and other publications.

Last updated August 2026