Research area

The three river basins or sub basins examined in the joint R&D project IWRM Vietnam represent three typical hydrological situations and usage situations in Vietnam. These are

  • the upper Dong Nai river basin
  • the Red River sub basin
  • the Cuu Long sub basin (Mekong Delta)

Upper Dong Nai river basin

The upper Dong Nai river basin largely lies in Lam Dong Province in the southern Central Highlands in Vietnam in the Lang Bian plateau and in the Di Linh-Bao Loc plateau. The highest mountains in the Lang Bian plateau are Bidoup (2,287 m above sea level) and Lang Bian (2,176 m above sea level). Within the plateau the two largest headwaters of the Dong Nai are the Da Dung and the Da Nhim. The La Nga has its source in the Di Linh-Bao Loc plateau. Both the Dong Nai and the La Nga flow into the Tri An reservoir. This lies at approximately 50 m above sea level, to the north of the city Bien Hoa with a reservoir volume of 2,470m m³ and a water surface of approximately 324 km².
The river basin features a large number of rock formations with various hydrological characteristics. The Lang Bian plateau massif and the Di Linh-Bao Loc plateau mountain range essentially consists of intrusive rock. Furthermore, the Di Linh-Bao Loc plateau contains large-scale basalt sheets. To a limited extent, quaternary deposits can be found in the river valleys and the floodplains of the Dong Nai system. These basalts especially are highly aquiferous.
The plateau and the region around the provincial capital Da Lat features heavy forestation. Roughly one quarter of the upper Dong Nai river basin is used agriculturally for perennial crops, such as coffee and tea. Large-scale contiguous producing regions are found in the Di Linh-Bao Loc plateau in the river valleys and tributaries of the Dong Nai as well as on the lower reach of the La Nga.
The most significant water users are agriculture for irrigation purposes and rural and urban population for drinking water. A further significant part of water usage is waterpower energy extraction. Water quality is affected by agricultural fertilization, direct discharge from industrial, commercial and untreated domestic wastewater.

Figure 1: System illustration for the upper Dong Nai river basin

For visualization purposes, a system illustration has been created (Figure 1). It depicts the characteristic features in topography, land use and hydrogeology.

Red River sub basin

The evaluated Red River sub basin is in Nam Dinh Province in the north of Vietnam. It lies in the Red River delta and its topography is fairly flat, only a few meters above sea level. The water management here is characterized by the use of polders. Each polder represents a closed water management unit in itself. Dry season irrigation is carried out under consideration of the salt content in salt-water intrusion from the sea through pumping stations. In the rainy season these pumps are used to drain the polders. Water management problems exist due to salt-water intrusion and due to the discharge of industrial and manufacturing facilities within the polders. The hydrological situation is characterized by ternary and quaternary loose rock (alternating sequences of sands, clays and silts). The sands represent groundwater aquifers. The commonly lie below layers of clays and silts. Below the mentioned loose rocks we find solid rocks (limes, sandstones etc.), some of which also represent groundwater aquifers. Water use here is chiefly characterized by agricultural irrigation, drinking water for urban and rural population and industrial and service water applications.

Cuu Long sub basin (Mekong Delta)

The evaluated Cuu Long sub basin (Mekong Delta) in southern Vietnam lies in the urban area of Can Tho. A tight network of canals and rivers characterizes this sub basin. The waterbody network is k is an open system with a direct connection to the sea.
Quaternary and tertiary sediments (alternating between fine gravels, sands, silts and clays) characterize the hydrogeology. The fine gravels and the sands are groundwater aquifers in several layers, some of which may be up to 120 m thick. Above the uppermost groundwater aquifer we find up to 100 m thick cover layers made out of clays and silts.
The canals and rivers in the sub basin are used for irrigation and as transport routes. The water supply is generally sufficient in the dry season as well. In many areas, however, the water quality fluctuates strongly throughout the year due to salt-water intrusions from the sea.
The main water user is agriculture for irrigation purposes, followed by the industry for service water application and the urban population for drinking water.