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Viet Nam

Water resources

The distribution of water resources is highly variable during the year owing to unevenly distributed monsoon rainfall. High variations, combined with limited storage and flood control infrastructure, result in devastating floods in the wet season and extreme low flows in the dry season. About 70-75 percent of the annual runoff is generated in three to four months.

Viet Nam has a dense network of 2 360 rivers with a length of more than 10 km each. There are 16 river basins that are larger than 2 000 km2, eight of which have a catchment area larger than 10 000 km2 (Table 2). Other basins are either have a small area, such as Tien Yen and Muc, or have several small coastal rivers grouped together, such as Giang/Huong, Tra Khuc and Cai-Luy. The eight major basins represent 77 percent of the country’s area. The largest basins are the Mekong and the Red river/Thai Binh, covering 45 percent of the territory.

Almost 60 percent of the total water resources are generated outside the country, making the country susceptible to decisions made about water resources in upstream countries. The total area of all international basins in and outside Viet Nam is to 1.2 million km2.

Viet Nam has abundant surface water resources in terms of total runoff, which accounts for 848 km3/year on average, but the shortage of water is aggravated during the 6-7 months dry season when the runoff is only 15-30 percent of this total. About 323 km3/year (38 percent) of the total runoff are generated within the country.

More than 90 percent of the Mekong river basin and 45 percent of the Red river basin lie outside Viet Nam. The Ma and Ca rivers both have about 40 percent of their basin area outside the country and the Dong Nai 15 percent. The average annual contribution from neighbouring countries to the runoff in Viet Nam is around 524.71 km3, including 470.1 km3 (Mekong) and 1.41 km3 (Dong Nai) from Cambodia, 44.1 km3 (Red) from China, and 9.1 km3 (Ca and Ma) from Lao People’s Democratic Republic.

Internal renewable groundwater resources are abundant, an estimated 71.418 km3/year. Over 50 percent of these resources are in the central part, about 40 percent in the north and 10 percent in the south. A large amount of water is stored in unconsolidated alluvial sand and gravel geological formations found in plains and valleys. An estimated 35 km3/year returns to the rivers as base flow and can be considered to be the overlap between surface water and groundwater. Therefore total Internal Renewable Water Resources (IRWR) are an estimated 359.418 km3/year (=323+71.418-35). By adding together the internal and external water resources, the total renewable water resources are an estimated 884.128 km3/year.

The exploitable groundwater resources are about 6-7 km3/year. In some areas, over-exploitation has caused water tables to fall, which has contributed to further land subsidence and salinity intrusion, especially in the Mekong river delta.

Viet Nam is rich in freshwater and marine wetlands, which are mainly distributed in the Red river and the Mekong river deltas and along the 3 260 km coastline. The Directory of Asian Wetlands lists over 25 wetland sites in Viet Nam that meet the criteria for ‘Wetlands of International Importance’. Despite this the only designated site under the Ramsar Convention is the Xuan Thuy National Park, a 12 000 ha mangrove in the Red river delta region. However, there are plans for additional Ramsar sites, including the Tram Chim National Park in Dong Thap province in the Mekong river delta.

In 2000, Can Gio mangrove forest was designated as ‘Man and Biosphere Reserve’ by the United Nations Educational, Scientific and Cultural Organization (UNESCO), Viet Nam’s first protected area. More wetland sites are being proposed for inclusion in a list of protected areas. Also, to fulfil the government commitments to the Ramsar Convention, the Ministry of Natural Resources and Environment (MONRE) has submitted a government decree on wetland conservation and sustainable utilization to the Prime Minister. A national strategy on wetland management and conservation was approved in 2003.

There are two natural lakes in Viet Nam: Lake Ho-Tay with a surface area of 4.13 km2 and a volume of 8 million m3, and Lake Ba Be with a surface area of 4.5 km2 and a volume of 90 million m3.

Viet Nam has 800 medium and larg dams and reservoirs, and 1 967 reservoirs with a storage capacity of at least 0.2 km3. In 2009, total dam capacity was about 28 km3. Seven dams have a capacity of more than 1 km3: Hoa Binh (9.5 km3), Thac Ba (2.9 km3), Tri An (2.8 km3), Tuyen Quang (2.2 km3), Dau Tieng (1.6 km3), Thac Mo (1.4 km3) and Yaly (1.0 km3). Another four dams of over 1 km3 are under construction: Son La (9.3 km3), Phuoc Hoa (2.5 km3), Ban Ve (1.8 km3) and Cua Dat (1.4 km3). Most reservoirs are multipurpose: hydropower, flood control, navigation, irrigation and fisheries.

Viet Nam has an estimated hydropower potential of about 14 000 to 17 000 MW of which nearly 3 600 MW have been developed, and about 800 MW are under construction. The National Hydropower Plan Study plans a possible installation of an additional 5 045 MW. Hydropower is a non-consumptive use of water, but the need to maintain a certain water level may negatively affect availability downstream. This may cause local drought and water use conflicts between hydropower and agriculture downstream, and sudden releases may cause flooding and river erosion. Therefore, the operation of hydropower plants needs to be coordinated with other water using sectors, mainly agriculture.

In 2003, out of a total of 1 100 million m3 of wastewater produced, about 250 million m3 were treated, of which 70 percent (175 million m3) were reused (Table 3).


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