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| High tide and heavy rain cause flooding in Thoai Ngoc Hau Street, in HCM City"s Tan Binh District. The city will spend US$550 million on building a dyke system to protect it from floods and high tides |
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The dyke system will be built along one side of the Sai Gon River bank (from Ben Suc District in Binh Duong Province), along the Soai Rap River and one bank of the Vam Co Dong River to Duc Hoa Town in Long An Province.
The earthen barriers will be two to three metres high and 7.5 metres wide.
A closed system of 12 culverts will be built at river and canal mouths connecting the Sai Gon, Nha Be, Vam Co and Vam Co Dong rivers. The culverts are aimed at controlling water levels inside the dyke system.
Deputy director of the HCM City Flood Control Centre, Nguyen Ngoc Cong, said the culvert system would reduce but not completely stop floods caused by climate change.
"The area inside the dyke system will be prevented from flooding, but outside the dykes, other measures will be needed to stop rising water," said Cong.
Several irrigation scientists have cast doubts about the long-term usefulness of the dyke, considering the large amount of money being spent.
Director of the Science, Technology and Environment Management Institute, Le Huy Ba, said the city should not be too hurried in building the system.
"We need to take account of the city flood situation over the next 40 to 50 years. The dyke system may be suitable at this moment, but might quickly become out of date," said Ba.
He said water rose quickly during flood-tides and that it would take a long time to drain off the extra water through underground culverts. In addition, the geological structure of HCM City was weak and unstable, so, he said, big underground culverts might sink.
Professor Nguyen Huu Lan from Ton Duc Thang University said the dream to flood-proof could be a dream if the climate change scenario of the Ministry of Natural Resources and Environment eventuated.
This scenario forecasts that the sea level may rise about 30cm by 2050 and 75cm by the end of the century. This would place more than 200sq.km, or 10 per cent of the city area, under water.
Lan said the best measure was to build embankments along rivers, but not a closed dyke system around the city. The city should restore the ecological system of mangrove forests; replant watershed forests; carry out water flow management in all river basins and build up ecological lakes.
Record high tides on the Sai Gon River early this month caused flooding in several residential areas. The tides were the highest in the last 50 years.
(V.N.S, 30/11/2010)