Mekong basin
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The Mekong,
the mother of all rivers
The Mekong
rises in Tibet
and is the fourth
largest river
in Asia in terms
After flowing around the Himalayas,
the river flows through the deep and
narrow valleys of China and Laos.
It continues its journey through Thailand
and Cambodia and finally reaches
the mangrove delta in Vietnam.
and agriculture. Two areas of the basin
are particularly productive: the Tonlé Sap a complex system that combines a tributary
of the Mekong and the largest freshwater
lake in South-East Asia - and the delta,
one of the largest in the world.
The Mekong basin is one of the richest
areas of biodiversity in the world.
It is home to around 70 million people,
85% of whom make their living from fishing
From May to October, the Mekong
drainage basin region is under the influence
of the monsoon season.
DID YOU KNOW?
of discharge
(after the Yangtze,
the GangesBrahmaputra
and the Yenisei).
Almost half of the Mekong’s total length runs through China.
People there call it the «turbulent river» because of its gorges
and precipices. On its 2,000 km journey through China,
the Mekong passes from an altitude of over 4,500 m to 500 m.
Due to the steep gradients in the river
and its tributaries in the Upper Mekong,
four hydroelectric dams have been built
in China and around twenty are being
planned in Thailand, Laos and Cambodia.
IDENTITY CARD
Source: The Himalayas
Mouth: South China Sea
Length: between 4,350 and 4,900 km
Annual average discharge:
15,000 m3/s
Surface of drainage basin:
0.8 million km²
Countries: China, Burma (Myanmar),
Laos, Thailand, Cambodia, Vietnam.
The Mekong Delta.
The Mekong Delta is one
of the largest in the world. It includes
a multitude of channels, waterways
and land routes, rice fields
and marshes. 20 million people
inhabit it.
The delta is the “bread basket” of Vietnam, accounting
for 50% of food production, 95% of rice exports, 65% of fish
production and 70% of food production.
The Tonlé Sap, which normally covers 3000 km², becomes 4 times
larger during the monsoon.
The Mekong grows to the south
of Luang Prabang, where it regularly
floods the area
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Mekong basin
Under surveillance
Already affected by higher than average
water rises in 2011 and 2013 and more
severe droughts in 2010, scientists predict
that the Mekong’s flow will be subject
to bigger changes in the future.
According to recent research, the
annual average temperature will increase
0.7°C throughout the basin by 2050.
The average annual rainfall will increase
10% in the Upper Mekong, both in the dry
season and the monsoon, while remaining
constant in Cambodia and in the delta.
Flow will increase, making water more
available in the dry season and increasing
the risk of flooding during the rainy season.
These predicted changes are affected
or worsened by human action in the basin:
hydroelectric dams and water collection
for irrigation reduce the flow during
the monsoon. On the other hand,
deforestation and intensive land use
exacerbate flooding. However, the combined
effect of all these factors is complicated
and makes forecasts uncertain.
RESEARCH
The Mekong-HYCOS project aims to minimize human losses
and damage by reducing populations’ vulnerability to flooding in
the Mekong basin. This observatory consisting of around 50 remote
transmission stations, as well as a hydrological information system,
covers 800,000 km² of the downstream section of the drainage basin.
This powerful tool allows floods to be monitored in real time
and to be better predicted.
The Mekong,
which is
characterised
by regular
seasonal flows,
with a period
of flooding
and a period
of low waters,
will be affected
by climate
change and
the development
of human
activities.
Variations in water level in the Lower
Mekong. Periods of flooding occur regularly,
reaching a peak in October. However,
its magnitude varies, for example the flood
of 1998 high water level was lower
than average.
The Tonlé Sap, the largest freshwater lake
in South-East Asia, has an unusual
hydrological pattern: during the monsoon,
the overflow from the river fills the lake.
In the dry season, the opposite takes place.
During high water, the Mekong can discharge
up to 60,000 m3/s compared to 1500 m3/s
at times of low water.
A dam regulates a river’s flow, reducing
the intensity of flooding and drought, and creating
a reservoir for irrigation and electricity production.
However, it also modifies the river’s natural
flow patterns, affects fish migration, and blocks
sediments.
In 2011 in Phnom Penh, 75,000 people
were affected by flooding.
In recent years, the summer floods
in the delta, high water levels have been limited.
With no silt to fertilise their rice fields,
farmers had to use more fertilisers.
The discharge of the Mekong
and its tributaries may increase up to
30 times during the monsoon
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Mekong basin
A fishing paradise
The Mekong contributes to the livelihood
of 70% of lower basin inhabitants, including
fishing and fish processing activities.
During the monsoon, the Tonlé Sap Lake
and the delta create flooded areas where
fish come to spawn. In the dry season,
the lake’s fish-rich waters flow into the river.
In the delta, aquaculture is developing
rapidly, with 32 species native to
the Mekong. The Catfish (Pangasianodon
hypophthalmus) farming is most common,
with annual production of over one million
tons per year. Giant tiger and freshwater
prawns are also farmed on a large scale
in salt water basins.
Dozens of dams planned in China
and Laos are endangering fisheries.
Catches will fall by 25% by 2030. The dams
will form barriers to fish migration,
despite the inclusion of fishways.
The existing dams are also blamed
for declining water levels.
But the operators rather blame that the effects
of climate change.
RESEARCH
The Mekong Basin Commission’s Fisheries Programme includes
4 elements: programme management, coordination of fisheries
information and capacity building; understanding the area’s ecology,
assessment of catches and management of environmental impacts;
developing techniques for native species aquaculture; and developing
technical and institutional measures for managing fisheries.
The Mekong
basin, the most
biodiverse
in the world
after the Amazon
basin, is home
to 850 freshwater
fish species.
With 2.6 million
tonnes caught
each year,
it is the world’s
largest inland
fishery.
Tens of thousands of fishermen live
along the banks of the Tonlé Sap or
on floating villages which move depending
on water levels. 60% of the Cambodian
fishing, which is now largely industrial,
comes from this lake.
Fishing in the Mekong Delta.
Catfish farming (Pangasianodon hypophthalmus).
The fish are generally raised for 6-8 months until
they reach 0.6 to 1 kg in weight.
The Irrawaddy dolphin (Orcaella
brevirostris) living in the Mekong
is threatened by fishing. With fewer than
50 adult individuals, this population
is classified as critically endangered.
Catlocarpio siamensis. At least 40% of
the Mekong’s fish species migrate to breed
following the river’s flow. Therefore, Dams
could contribute to the decrease in numbers
or even the extinction of these species.
The Fishways at dams run the risk of being
ineffective if they are not adapted to local species.
It is estimated that 12 million
households earn their livelihood
from fishing in the basin
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Mekong basin
Going with the flow
There are many environmental impacts
of deforestation. The soil is no longer
protected from heavy rain by forest cover
and is eroded. Deforestation for agricultural
purposes, extraction of mineral and forest
resources and the bombardments from
the 1965-1975 conflicts bear the greatest
responsibility.
The loss of forest cover and the consequent
weakening of its regulatory effect,
associated with the strengthening of
the monsoon, lead to more frequent flooding,
particularly in the delta. The impact
of raindrops on bare soil, as well as surface
runoff, transports pathogenic agents from
the surface of the soil into the watercourse.
In addition, researchers have highlighted
that the concentration of sediments
in the river has reduced by 50% to 75%,
mainly caused retention in dams
or sediments extractions upstream.
This in turn leads to a shortage of fertile
material in the agricultural areas of the delta
and coastal regression.
Human activities
and climate
change
have significant
influence on
surface runoff
and soil
RESEARCH
The PASTEK project brings together French and Asian
researchers who are studying the impacts of global change
on water volume and quality in one of the Mekong sub-basins:
the Nam Khan drainage basin (7,400 km²). Their aim is
to understand the link between land usage, rainfall indicators,
hydrological responses and water quality to establish a model
for the period 2010-2050.
conservation
with severe
consequences
for the discharge,
water quality
and the amount
of sediment
carried by
the Mekong and
In Southern Laos, many bombs were
launched between 1965 and 1975
as throughout World War II, destroying
70% of the rainforest. It has been replaced
by herbaceous vegetation which retains
soil less effectively.
In one hectare of sloping terrain,
deforestation for agriculture leads
to 10 tonnes of soil loss per year, compared
to 0.1 tonnes per year in a wooded area.
The impact of raindrops liberates soil particles
which can be rich in faecal matter containing
Escherichia coli bacteria. During the rainy
season and exceptional floods, contamination
can be extremely high.
Sediment-rich water near Khone
Phapheng Falls in Laos. Dams trap some
of the sediment in watercourses. As a result,
sediment density in the river decreases.
The extraction of sediment from the river
bed, typically for building roads and houses,
contributes to reduce levels of solid matter
in the water.
Less and less sediment and therefore
fertile material reaches the Mekong Delta.
As a result, farmers use more fertilizer,
and due to a lack of sediment to compensate
for erosion from the sea, the coastline retreats.
its tributaries.
Erosion reduces
soil fertility on slopes
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