Author(s): Phan Khanh Linh; Marcel J. F. Stive
Linked Author(s): Marcel Stive
Keywords: Mekong Delta; Mangroves; Erosion
Abstract: This contribution addresses some important issues with regard to the future development of the Mekong Delta Coast and Estuaries in the context of environmental and climate change. After a general review of present and future environmental and morphologic conditions, two highly relevant issues will be discussed in more detail. The first issue concerns the morphological impact of possible construction of discharge sluices in the three main branches of Tien River to prevent salt intrusion. The second issue concerns the impact of sea dike construction on the health of the existing mangrove forests. The Mekong Delta Estuaries play an important role in flood relief, water transportation, water management and land reclamation; however they are also the root of serious problems such as salinity intrusion and tide-induced high water levels. According to possible future development plans, discharge sluices could be constructed in the three main branches of Tien River to prevent salinity intrusion. To evaluate the consequences of these structures to the Mekong Delta Estuaries, an empirical relationship between tidal prism and river cross-section is derived. Based on field observations an important result derived for the Mekong Delta Estuaries is an empirical relationship between the tidal and river discharge prism, P and Q, and the river cross-section, Ac. Using this finding, it is found that the two open branches of Tien River will deepen by more than 10 meters when all three other branches are closed. Thus, mangroves along the river bank of these two branches should be strengthened in order to prevent river bank erosion. Due to the need of land for agriculture and other economic sectors, sea dikes are always built close to or often even in the mangroves forest. Along the Southern Coast of Viet Nam there are many places where mangrove degradation and coastline erosion is observed on a large scale when sea dikes are built too close to or in the mangrove forests. Based on field observations a relationship is derived relating mangroves width and coastline evolution. It is concluded that a critical value of 300 to 400 meters of mangroves width is necessary for the stability of the East Coast of Viet Nam.