Rivers
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
kilometres, 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.
|
