THE MEKONG RIVER

THE MEKONG RIVER

The Mekong River and its tributaries are dominant features of the waterways of Cambodia. From its northern source in the Himalayas, the Mekong flows southward, passing through China, Laos, Thailand, and in a south-eastern direction across Cambodia. Finally, the waters of the Mekong discharge into the South China Sea. At Phnom Penh, the Tonle Sap River, a major tributary, joins the Mekong at which an interesting phenomenon occurs. During the rainy season, between May and October, the silted channels of the Mekong River system are insufficient to accommodate the amount of water added to that sent forth by the melting mountain snows, so the river backs up.

The impact of the overflow forces the Tonle Sap River to reverse its course each year between July and October or November and feeds into the Tonle Sap or 'Great Lake'. This action more than doubles the size of the lake, which normally covers an area of approximately 2,600 square kilometres (1,000 square miles), and makes it a natural reservoir. When the flow reverses at the end of the monsoon the Cambodians traditionally hold a celebratory festival, Bon Om Tuk that coincides with the full moon to give thanks to the spirits for bounteous waters. When the waters from the snows drain off, the course of the Tonle Sap River reverses once again to resume its normal flow.

Zhou Daguan, a Chinese envoy of the Mongol Empire who lived at Angkor for a year in the late 13th century, gave the earliest recorded account of this feature: 'From the fourth to the ninth moon there is rain every afternoon, and the level of the Great Lake may rise seven to eight fathoms. Large trees go under water, with only the tops showing. People living at the water side leave for the hills. However, from the tenth moon to the third moon of the following year not a drop of rain falls; the Great Lake is navigable only for the smallest craft, and the depth of the water is only three to five feet'.

The Great Lake was the lifeline of the Khmers. Its pattern of movement provided the structure and rituals of daily life and served as a source of fish and rice to an agrarian society. When the water doubled its volume the lake became an ideal feeding ground for spawning fish and, when it receded, the fish easily fell into the traps laid for them. This movement of the waters enabled the cultivation of floating rice, the earliest known form of Khmer agriculture. It IS fast growing and germinates in deep water. The stems can grow up to 10 centimetres (4 inches) a day and reach a length of 6 metres (20 feet). The rice stays on the surface because its growth parallels the rise of the water level. Zhou Daguan recognised the unusual characteristics of floating rice and described 'a certain kind of land where the rice grows naturally, without sowing. When the water is up one fathom, the rice keeps pace in its growth. This, I think, must be a special variety', he noted 700 years ago.