Mekong River Commission

7. Impact of the 2005 flood - Country reports (cont')

7.4 Impact of the 2005 flood in Viet Nam

7.4.1 Background

Covering 8% of the Mekong River Basin and contributing 11% of total flow volume to the main river, the Vietnamese Mekong River Basin stretches from the north to the south of Viet Nam and includes 21 provinces which are home to some 20 million people. These areas include two sub-areas: 5 provinces of the Central Highland and 13 provinces of the Mekong Delta (as well as small areas of Dien Bien, Quang Tri and Thua Thien- Hue provinces). Two typical regions represented by two different topographic features of the mountain and plain landscapes which are characterised by two types of flood events: flash flood and tidal plain flood.

The "Mekong Delta" covers an area of approximately 39,700 km2 and has a population of 17 million people (roughly 400 inhabitants/km2). Some districts have a density close to 1000 inh/km2. The Delta produces 50% of the country's food staples and 60% of its fish. Urbanisation is growing rapidly and industrialisation is increasing. The yearly flood is characterised by extended areas inundated by water, including the Bassac River, the Mekong River and the numerous natural and artificial canals linking these two rivers which flow laterally to tbe low lands. In some years, high water levels in the Bassac/Mekong systems may not drain easily to the sea due to strong tidal effects.

Nine serious flood events occurred in the Mekong Delta in the past 45 years of data recording. The years 1961, 1966, 1978, 1984, 1991, 1996, 2000, 2001 and 2002 were the biggest flood events represented by water level² (in metres) at the main hydrological stations:

Figure 49: Water heights in flood years

People alter their lifestyles during the "high water" period and large areas become similar to "lake villages". Many infrastructure such as roads, small embankments, canals and gates are under water for several weeks. So even "soft" floods may generate damage, mainly by erosion of embankments or by sedimentation of the canal systems. Even in "soft" flood years, casualties happen among the several hundred thousand people living for several weeks "on" water. A large proportion of the victims are children.

The perception of flood, locally called "high water season", is very different in the delta from any other areas of the Mekong Basin. People know that water will rise every year and they are prepared. The second rice crop is tuned for harvesting before the early flood. Water rises slowly and regresses slowly. People in rural areas are mainly affected by the erosion of land and embankments. Every year house and land losses are recorded.

Benefits from floods are widely recognised. The positive effects of flood flows are huge, such as supplying fresh water for irrigation and domestic use, increased fishery resources, improving navigation transport, bringing more.

natural fertiliser, killing insects, flushing acid water caused by sulphate soils, pushing salt water toward the sea, etc. On the other hand, the flat natural conditions of the Delta receive nearly the whole flood volume of the Mekong and this, together with increasing human activities, means that the damage caused by floods is considered the cause of negative effects on economic development and to people's livelihoods.

Prior to 1978, farmers living in the Mekong Delta considered the flood season a time which brought natural resources and they had learned to live with floods. After flood 1978, building of infrastructure to control floods began, with the aim of developing the socio-economy of the Mekong Delta. This rapid growth led to the 2000 flood becoming the most damaging flood in terms of human life and assets. Many lessons were learnt from the 2000 flood and the strategy and response methods for dealing with heavy floods were quickly reviewed. Embankments have been heightened using the 2000 water level as a reference, resettlement areas have been created, and rescue teams are better prepared. In principle, less damage may be expected if a similar flood happens again.

However the rapid pace of development is increasing the risk of potential damage in case of severe floods. Protecting the paddy fields and other crops, and ensuring the security of the population is a legitimate major concern of the decision makers. But it may be to the detriment of the conservation of flood prone lowlands, which not only are recognised as bringing benefits but which also have a key role in limiting the peak water level in the Mekong/Bassac system.;

7.4.2 Availability of Data

In the Mekong Delta, data are collected very precisely, sometimes comparing the evolution of parameters since the “dreadful” flood of 2000, where huge damage was recorded. Many lessons were learnt from that flood, including the need for precise monitoring of the impacts of floods and the measures which should be taken to limit the damage in the event of a similar flood. As infrastructure are very exposed to the annual rising of water, assessment of damage is done not only in order to establish a budget for repairs, but also to consider improvement of the "black" sections. The situation regarding housing is also well monitored, with the policy being to gradually relocate people living in flood risk areas to safer places, where resettlement areas, based on the water levels of 2000, have been built.

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²Warning system for flood events in the Vietnamese Mekong Delta as determined by MRC representing by water levels at Tan Chau and Chau Doc Stations (refer to Ha Tien Datum) as following:

Class		Tan Chau (Mekong River)	Chau Doc (Bassac River)
Class	1	3.0	2.5
Class	2	3.6	3.0
Class	3	4.2	3.5 (alarm level)

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