Vietnam’s two ‘rice bowls’ and Hue’s historic Perfume River

The heartland of Vietnam
The Red River (‘Song Hong’) stretches about 1,200km from its source in China's Yunnan Province. Its two main tributaries, the Song Lo (also called the ‘Lo’, or ‘Clear’ River) and the Song Da (the Black River), swelling its volume to an average 5,000 cubic metres per second, rising to nearly 40,000 cubic metres per second in the summer rainy season.

The Red River Delta, a flat, triangular region of 3,000 square kilomtres, is smaller but more intensely developed and densely populated than the Mekong Delta. Once an inlet of the Gulf of Tonkin, it has been built up by an enormous amount of alluvium deposited over millennia. Currently, the delta advances a further hundred metres into the gulf each year. The ancestral home of the ethnic Vietnamese, the delta accounted for almost 70 percent of the agriculture and 80 percent of the industry of North Vietnam before 1975.

The entire delta region from the coast up to the steep incline of the forested highlands is no more than three metres above sea level, and much of it is a metre or less. Consequently, it floods frequently: at some places, the high-water mark is 14m above ground level. An extensive system of dikes and canals was built to contain the Red River and to irrigate its rich paddy fields. Modelled on that of China, this ancient system has sustained a highly concentrated population and made double-cropping wet-rice cultivation possible throughout about half the region.

The Imperial River
The Perfume River was the chosen location for Vietnam’s imperial capital. The city of Hue straddles the river, and its great Citadel, now a World Heritage Area, overlooks it from the opposite bank. Rising in nearby steep mountains, the river is only 80km long but feeds the largest lagoon in Vietnam. Unfortunately, deforestation and eco-system degradation has limited the retention of water on hill slopes, increasing flooding and thus damaging the buildings and heritage artefacts of Hue. A plan to control the situation is under development.

The mighty Mekong
At 4,220km, the Mekong is one of the world’s longest rivers. Rising in Tibet, it flows through Xizang and Yunnan in China,and constitutes the boundary between Laos and Myanmar (Burma), and that between Laos and Thailand. Below Phnom Penh, it divides into two, flowing through Cambodia and the Mekong basin to drain into the South China Sea through ‘cuu long’ (nine mouths).

Heavy sedimentation means that the river is navigable by shallow-draft seagoing craft only as far as Kompong Cham in Cambodia. A tributary entering the river at Phnom Penh drains the Tonle Sap, a shallow freshwater lake that acts as a natural reservoir to stabilize the flow of water through the Mekong delta. When the delta outlets are unable to carry off the high volume of floodwater, they back up into Tonle Sap, inundating as much as 10,000 square kilometres. When the flood subsides, the flow reverses and excess water drains to the sea, thus alleviating the devastating floods that reach a height of one to two metres. However, climatic change and deforestation in Cambodia has increased the flow and overwhelmed the capacity of the Tonle Sap. In recent years, the floods from August to October have been noticeably higher and lasted longer, sometimes leading to considerable loss of life amongst the Mekong’s residents.

The Mekong Delta is a very large pancake-flat flood plain, no more than three metres above sea level at any point and criss-crossed by a maze of canals and rivers. About a billion cubic metres of silt is deposited annually, almost thirteen times that laid down by the Red River, and advances the delta some sixty to eighty metres further into the sea each year. The level of the water is, therefore, a major concern for visitors to the area. About 10,000 square kilometres of the delta are under rice cultivation, making the area one of the largest rice-growing regions in the world. The southern tip, known as the Ca Mau Peninsula (Mui Bai Bung), is covered by dense jungle and mangrove swamps.