When asked about his future, Nguyen Van Nghe, a fisherman in Dong Thap Province answered: “No flood, no money. What a trade!” He was referring to the fact that over the last 10 years the construction of high dykes in Dong Thap and the Long Xuyen Quadrangle has blocked the annual replenishment of freshwater, nutrients, and sediment on which fish depend. In turn, this has destroyed the wild fisheries on which the landless, including Nghe, who make up 20% of the Mekong Delta’s population, depend. Wild fish production has declined by 40% over the last 10 years and species that were once used as fertilizer now sell for VND180,000/kg. The predatory snakehead, which once occupied the top of the aquatic food chain, has disappeared. The high dykes have also greatly reduced the annual flushing. This has resulted in the accumulation of pathogens and toxins in the surface water and growing public health problems.
High dykes were built to allow a third, or autumn-winter, rice crop to be grown because of the high prices this off-season crop can fetch on the international market. In 2011, 560,000 hectares of autumn-winter rice were planted, up from 520,000 hectares in 2010. But because of the loss of sediment, rice productivity can only be maintained through the heavy use of fertilizer. Nguyen Huu Thien, a wetland specialist based in Can Tho, questions whether the third rice crop is profitable once you take into account the increased use of fertilizer and pesticide, the cost of dyke maintenance, the loss of wild fish, and, inevitably, the cost of dyke failure: when dykes failed in 2011, 50 people were killed and tens of millions of dollars of houses, roads, and other infrastructure was destroyed. The intensification of rice production has also resulted in the virtual extinction of the traditional long-stem floating rice varieties, which in Brazil sell for $3,500/ton, almost ten times the price of autumn-winter rice.
Dr. Ngo Van Be of the Dong Thap Muoi Institute of Research and Development says that the floods that used to be “mild” are now “fierce” and unpredictable. In hydrological terms, what the high dykes have done is to separate the Mekong River from its 1.5 million-hectare floodplain. According to Dr. Le Anh Tuan of Can Tho University, these dykes have narrowed the floodplain during the peak October-November flood from 150 kilometers to a few tens of kilometers. This has accelerated the water flow and displaced flooding to residential areas downstream. Reduction of the flooded area has also reduced groundwater recharge, reduced river base flows, and increased dry season saline intrusion, which increases the cost of drinking water supplies. The violent floods of 2011 call into question the value of the third rice crop and instead argue for a more natural hydrology that provides multiple benefits, including greater resilience to climate change, which is likely to result in more intense rainfalls and flash flooding.
To learn more about these issues, watch this 30-minute file produced by the Center for Water Resources Conservation and Development (WARECOD) and VTC16.