VietNamNet Bridge - A group of experts from the University of Aix-Marseille (France), the program for sustainable hydropower and river basins of the World Wildlife Fund (WWF) and the Vietnam Academy of Science and Technology recently published the research on relations between rapid erosion in the Mekong Delta and human activities.

Sand mining in the Co Chien River.

Formed nearly a century later than the other large plains in Asia, the Mekong Delta of Vietnam is facing many challenges of sustainability by erosion, sea level rise and flooding as the consequences of construction of hydroelectric dams in the 70s and 80s of the last century.

Based on analysis of satellite images, for nearly a decade, scientists have quantified coastal erosion and land loss on a large scale during the period from 2003 to 2012.

Specifically, over 50% of the 600 km of coastline in the Mekong Delta are strongly eroded.

The most serious erosion occurs in the Eastern coast with an average speed of 50m per year, accounting for nearly 90% of the total length of 183 km of coast in the region.

In the Southwestern coast, Gulf of Thailand, the situation is not as severe but erosion also occurs for over 60% of the total length of 200 km of this stretch of shore. This phenomenon is contrary to the trend of strong expansion due to accretion of the southwest coast in the past three millennia.

The report summarizes the strong encroachment of the sea into the mainland that took away more than 5 km2 of land of the Mekong Delta. In the 2007-2012 period alone, each day the delta lost an area equivalent to 1.5 of a football ground.

The delta in general depends heavily on sediment stability to maintain the coastline and compensate for subsidence. However, the amount of sediment in the river is diminishing as the sediment is kept behind hydropower dams.

Many plains around the world are faced with the phenomenon of subsidence and faster erosion, loss of land and are vulnerable to widespread impact of floods and sea level rise. The Mekong Delta of Vietnam is not an exception.

Depletion of alluvium

This group of experts said the significant deterioration of mud volume for the shore during the flood season was recorded by MERIS satellite image, while the sea encroachment speed at estuaries declinedwith the large scale mining of sand.

Sand is trapped in deep holes and creeks due to sand mining also causes reduced supply of sand for the beaches in the middle of the estuary. The coastal sediment reduction leads to less wave energy being dissipated, consequently causing faster erosion.

The phenomenon of rapid subsidence due to groundwater exploitation has occurredon the eastern coast, where the heaviest erosion was recorded.

The reduction of alluvium in the Mekong Delta will be more serious when 11 dams are built in the downstream Mekong River. In November 2012, the construction of Xayaburi Dam (Laos, with a reservoir of 225 million m3) raised concerns of the international community and opposition from the government of Vietnam and Cambodia as well as scientists and environmental organizations.

If 11 hydropower dams are put into operation, the amount of sediment trapped in reservoirs will increase from 11-12 million tons/year to 70-73 million tons/year.

Another study pointed out more serious results: the reduction of accumulation of sediment for the delta can be up to 51% - 96%, corresponding to the amount of 38 hydropower dams across the mainstream of the Mekong River.

This risk can come before 2020 if sand mining in the plains and the upstream river continues at its current pace.

Food security affected

The Mekong Delta is the third largest delta in the world and the home of nearly 20 million people. It plays a very important role in the food security of Southeast Asia. The Mekong Delta provides 90% of rice exports, 60% of seafood exports of Vietnam, with export turnover worth billions of US dollars a year.

In addition, the Mekong Delta is also dynamically developing areas of agriculture and livestock. The Mekong River Basin is home to great biodiversity of fish with higher density than any other major river basins in the world. In terms of biological diversity in general, the Mekong River is just behind the Amazon.

NLD