Introduction to the Mekong Delta

Mekong Delta

The Vietnamese Mekong Delta region is roughly a 40,000 square kilometers triangle stretching from Gò Công in the east to Tân Châu and Hà Tiên in the northwest, down to Cà Mau at the southern tip of Vietnam, and including the islands of Phú Quốc and Côn Đảo.

The Mekong River Basin[1].

The Mekong River is the tenth-largest river in the world. The Mekong River Basin drains a total land area of 795,000 km2 from the eastern watershed of the Tibetan Plateau to the Vietnamese Mekong Delta. The Mekong River flows approximately 4,909 km through China, Myanmar, Lao PDR, Thailand, Cambodia and Vietnam.

The Mekong Delta begins near Phnom Penh in and ends up as a huge fertile flat plain in southern Vietnam where the largest tributary, the Bassac (VN name: Hau) River, branches away from the Mekong (VN name: Tien) River. The Mekong and Bassac Rivers split into a number of smaller distributaries, forming an area known as the “Nine Dragons.”

Upstream flow contributes around 20% of the total flow. Most of the total flow volume is delivered to the Mekong from tributaries in the Lower Mekong Basin.

The Vietnamese Mekong Delta plain can be divided in two parts: an inner delta that is dominated by fluvial processes, and an outer delta that is affected by marine processes. The inner delta is low-lying and close to sea level while the outer delta is built of coastal deposits, is fringed seawards by mangrove swamps, beach ridges, sand dunes, and tidal flats. A diurnal tide is dominant in the Gulf of Thailand, whilst a semi-diurnal tide is dominant in the East Sea. Tidal effects extend throughout the Vietnamese delta region[2]. The delta consists a variety of landscapes, including tidal flats, sand ridges and tidal back swamps in the coastal area, estuaries at river mouths, river flood plains, broad depressions, peat swamps, alluvial levees and terraces further inland. Inland, Melaleuca forest and grassland used to cover most of the acid sulphate soil area but now mainly remains in the protected areas in the U Minh peatland region in Kien Giang and Ca Mau, in Ha Tien grassland in Kien Giang province, and in the Plain of Reeds and the Long Xuyen Quadrangle.

The wetlands of the Vietnamese Mekong Delta are among the richest ecosystems in the Mekong basin. They are important breeding sites for many aquatic species migrating from upper reaches of the Mekong River. They can broadly be categorized into three groups: (i) saline wetlands with coastal mangrove and saltwater lagoons along the east coast and the west coast; (ii) inland wetlands dominated by melaleuca forest and seasonally inundated grassland habitats, and (iii) estuarine seasonally saltwater wetlands, distributed mainly at the mouths of the Mekong River.

The annual flood pulse plays a vital role in agriculture and fisheries. Large areas in the Plain of Reeds and the Long Xuyen Quadrangle are usually inundated in the flood season. The floods flush and dilute stagnant and polluted waters, recharge groundwater tables, maintain river morphology, sustain the productivity of freshwater fisheries, and floodwaters are retained for use in the dry season, particularly for irrigation. Flood-deposited sediments improve soil fertility across the floodplains. The flood season in the Mekong River Basin lasts from June to November and accounts for 80 to 90% of the total annual flow.

In the past decennia, the Vietnamese Mekong Delta has developed into a major food producing area, which plays a central role not only for national food security, but also in the wider regional ASEAN and global context through food-related export revenues and, hence, the foreign trade balance.