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LMDCZ-AFD

Par ECOLA Dernière modification 06/01/2017 05:44

LMDCZ-AFD project: study of erosion processes and protection measures for the Lower Mekong Delta Coastal Zone (Web page here)

Collaborators: I operate as team leader in this French-Vietnamese project, coordinating with Dinh Cong San (SIWRR), Nguyen Thuy Anh (AFD) and Nguyen Kim Dan (Paris-Est). Other close collaborators are Nguyen Thong (HCMUT/CARE), Nguyen Lan Anh (VNU), Nguyen Nguyet Minh (USTH/CARE),  Nicolas Gratiot (IRD-LTHE/CARE), and Rafael Almar, Rachid Benshila, Elodie Kestenare (LEGOS) ...

River deltas rely on sustained sediment supplies in order to maintain their shoreline position and to balance subsidence and sea level rise. Because of diminishing sediment supplies due to damming and sand mining, coastlines of many of the world’s river deltas are retreating with significant political, economic and environmental consequences. A typical example of such delta systems is given by the Mekong. Here as in other delta systems, coordinated international efforts are needed for appropriate research studies leading to sustainable protection measures. The present project aims in that direction. It is funded by the European Union (EU) and the French Development Agency (AFD) and coordinated by Vietnamese and French institutes (notably the IRD) and under the guidance of about 10 international experts from France, Germany and the Netherlands.

EROSION OF THE MEKONG COASTAL ZONE

The Mekong River basin drains six countries, ending in South Vietnam where the Lower Mekong Delta (LMD) covers 13 provinces and cities. The total area of the LMD is near 4 million ha, accounting for 12% of the country, with a population of 19 millions (21% of the national population). It provides 50%, 90%, and 60% of Vietnam’s food, rice production (the world’s second most important rice exporter), and seafood, respectively. Besides strong activity in agriculture and animal husbandry, the delta has the most concentrated fish biodiversity per unit area of any large river basin in the world and is ranked second only to the Amazon in overall biodiversity.

The coastal area of the Lower Mekong Delta (LMD) is influenced by waves and tides, changing sediment loads from the Mekong and Saigon-Dong Nai river system, and storm surges from the East and West Sea. In addition, human activity has an impact on erosion and deposition processes through dyke construction and drainage, agriculture, aquaculture, and fishery exploitation along the coastal areas. In recent years, the impact of upstream dams, especially on the Mekong main river, has reduced sediment feeding into the LMD and its estuary. All of these impacts have caused shore erosion along approximately two thirds of the total coastline length, and a land loss rate of about 500 ha/year in the past ten years. In the future, the expected sea level rise will make this situation worse.

 

APPROACH

A novel approach for this project is integration from general to specific, regional to local scales. First, the delta as a whole system must be considered in the East and West seas (the seas around Vietnam), about 100km West and East of the Ca Mau peninsula, with its complexe hydrodynamic characteristics: winds, waves, tides, salinity fronts. Second, the response of the coastal system, in terms of sediment dynamics and morphodynamics, to estimated changes of sediment supply will be estimated. Finally, protection measures will be tested.

METHODS

Both experimental and numerical approaches are used here. State-of-the-art numerical models such as ROMS and DELFT3D (3D), TELEMAC-2D and MIKE21 (2D) are used to compute waves, currents, salinity and sediment transports in the LMDCZ. Regional solutions need to be locally refined using various techniques according to the models' approaches (structured or unstructured grids; nesting or grid stretching), focusing in two selected study areas: Go Cong (largely impacted by the Mekong river mouths in the East sea) and U-Minh in the gulf of Thailand off the west coast of the Ca Mau peninsula (southwest of the river mouths in the West sea). The computational domain for will thus cover the whole LMDCZ region, extending offshore across a major part of the continental shelf and inland up to Can Tho (on the Bassac/Hau River, which is the southern branch of the Mekong proper) and Sadec (on the Mekong/Tien River, which is the northern branch).

Shore protection measures for Go Cong and U-Minh should be considered both as “hard” and “soft” measures such as mangrove rehabilitation. The appropriate protection measures need to be assessed, not only on the basis of numerical models but also satellite observation and physical models as well, focusing on their possible long-term impact, under changing conditions for sediment sources and climate.

In order to calibrate and validate the models for flows and sediments, observations are needed in Can Tho and Sadec, at the mouth of the Mekong River, and over the shelf area. No such extensive data sets is available yet and we thus planned 2 measurement campaigns, each lasting 15 days, in the Mekong estuaries and in coastal zones (plus stations in Can Tho and Sadec). The first survey took place in October 2016 and was successful. The second is scheduled for February 2017.

 

Institutes

  • VIETNAM: SIWRR, HCMUT (CARE lab), WRU, ...
  • FRANCE: LEGOS, LTHE, ...

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