Tonle Sap-- the reversing river

 FT, A Geographer’s Notebook: the reversing river

The Tonlé Sap’s extraordinary change of direction is caused by a remarkable hydrological phenomenon driven by the Mekong.

In the central plains of Cambodia, at the end of a tributary linking it to the mighty river Mekong, lies a lake named Tonlé Sap. It is not a particularly impressive lake during the dry season, little more than a reedy swamp, but when the monsoon rains begin Tonlé Sap is filled by the flow of a unique reversing river.

During the wet season the water level in the lake rises from just a metre to 10 times that depth. At the same time, the surface area more than quadruples to cover 15,000 sq km. The increase in water is caused by a remarkable hydrological phenomenon driven by the Mekong, one of the world’s largest rivers. When the south-west monsoon season begins in June, the Mekong suddenly swells into a raging torrent. Its water level rises so fast that not all of the water can escape to the sea.

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Instead, some of the floodwater runs into the Tonlé Sap river, which joins the Mekong at Phnom Penh.

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The force of water causes the river’s current to be reversed, north towards Tonlé Sap lake. For the next four or five months, the river flows upstream instead of down. Since it is the lake’s only outlet, the water has nowhere else to go, so the lake fills. This is the world’s only naturally reversing river on a regular seasonal basis. Some rivers in cold latitudes may get reverse flow on occasion due to ice damming; surface flow can sometimes reverse on rare occasions and for short periods due to high winds (for example on the Detroit River); and famously, the Chicago River was made to ‘flow backwards’ in a vast civil engineering project at the start of the 20th century.(...)

In full: https://www.ft.com/content/03e8ac3c-0b2d-11e7-ac5a-903b21361b43

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 PPP,Tonle Sap River yet to reverse 

View from Cambodiana Hotel over Mekong-Tonle Sap intersection.

Fishermen and fishery conservationists are concerned about low Mekong River water levels which have prevented the annual reversal of the Tonle Sap River’s water flow, an important event which eventually fills the Tone Sap Lake with water and fish.

Some parts of the lake are drier than they’ve ever been during the rainy season.

Chak Choeun, a fisherman in Stoung district’s Peam Bang commune in Kampong Thom province, has been fishing in the area for years. But now, he is facing a severe lack of fish.

In the past, he used to catch around 6kg of fish per day and sold them for about $7. Now he catches only one or 2kg.

“This year, it is dried up. I cannot catch anything. There was water here last year, but there is nothing now. Some fishermen have left to work in construction and some have gone searching for fish deeper in Tonle Sap Lake.

“We still can catch a little fish and sell it for up to 10,000 riel [$2.50]. It is not enough even to buy rice,” he said.

He said Peam Bang commune used to be filled with fish, and people from Stoung district would often travel to fish there. Although the area is now dry, there are still people along the dock, waiting for their fortunes to change. He said they may disappear soon due to the dry spell. (...)

In full:https://www.phnompenhpost.com/national/tonle-sap-river-yet-reverse-0

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 Ministry of Tourism, Phnom Krom - Tonle Sap Lake

(Photo: Ministry of Tourism)

    Tonle Sap, the largest freshwater lake in Southeast Asia, is itself a natural wonder.This great lake exists as an ecological anomaly.  In early June, at the start of the rainy season, the water level of the Mekong River rises to divert part of its flow off its course to the South China Sea and redirect it into the Tonle Sap. This forces the current to reverse direction, beginning a process that by the end of October will see the great lake increasing its size almost tenfold, making it the largest freshwater body in Southeast Asia.

The Tonle Sap Lake, fed by the mighty Mekong and the Tonle Sap Rivers, is a vast expanse of water that forms the most significant topographical feature in Cambodia.  This ‘Great Lake’ represents a people’s identity and way of life for the thousands of Cambodians who live on the lake and are dependent on the Tonle Sap and its ebbs and flows to maintain life.  

There is a whole community here; besides homes, there is a school, police post, fire station, church and a few restaurants as well.  This self-sufficient community of the great lake, known commonly as the floating village of Cambodia, draws crowds daily to observe life and to share their time in this wonderful neighborhood of the great Tonle Sap Lake.(...)

In full: https://tourismcambodia.org/provinces/search/detail/389/phnom-krom-tonle-sap-lake-1550809011

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