|Tidal flooding on Phan Dinh Phung Street in HCM City. A sluice would regulate tidal flow. — VNA/VNS Photo Trang Duong
HCM CITY — Scientists have proposed the construction of a sluice to regulate tidal flow in and out of the Soai Rap estuary in HCM City, in an effort to reduce salination and flooding in the city as well as Dong Nai and Long An provinces.
Prof Nguyen Tat Dac of HCM City University of Industry, who has conducted research on the proposal, said HCM City's topography had 65 per cent of low land, and as a result, the city could easily be hit by tidal flooding, especially now with climate change.
Prof Dac also added that work to prevent salination and flooding was direly needed.
However, any construction must ensure good irrigation towards the sea, smooth waterway traffic and low environmental impact.
The proposed sluice should be built to work well with 12 other small sluices that have either already been built or will be built on several estuaries in Long An Province.
Dac recommended building an 1km wide sluice on the three-km Soai Rap estuary.
The estuary, which is part of the Sai Gon – Dong Nai river system, lies on the border between the city Can Gio mangrove forest and Long An and Tien Giang provinces.
Tidal flow and salination through the estuary, and the nearby Long Tau estuary, could affect the city as well as Dong Nai and Long An provinces.
According to Dac, the sluice would operate with a different mechanism for three different times of the year, depending on the tidal height and water volume from upper rivers.
The sluice would open at a width of 0.4km for water flow from January to May and 0.15km from June to August.
From September to December, it would open 0.1km in one direction and 0.7km in the other direction.
The sluice also should work harmoniously with the Tri An reservoir in Dong Nai Province and the Dau Tieng reservoir in Binh Duong and Tay Ninh provinces when the two release water in the rainy season.
Experts have called the sluice a good option for reducing salination and tidal flooding in HCM City and provinces.
Earlier this year, Dr Dao Xuan Hoc, deputy Minister of Agriculture and Rural Development, proposed building a 23-km sea dyke that would be extend from one point on the coastline near Vung Tau City to another point on the coastline off Long An Province.
The dyke would block the strait, which is created by two emerging land cliffs in Vung Tau and Long An, turning it to a 56,000ha lagoon, with the total volume of water amounting to 3.3 billion cubic metres.
The dyke, which would cost about VND50 trillion (US$2.4 billion), would block the Soai Rap and Long Tau estuaries as well.
Prof Le Huy Ba of the Institute of Science, Technology, and Environment Management opposed the idea, saying the dyke would bring only "tiny economic benefits in agriculture and aquaculture but would create severe losses to the economy and environment."
Ba said it would affect a wide range of seaports in HCM City and Ba Ria – Vung Tau Province as well as the Can Gio Reserve.
The dyke would have a negative environmental impact and would be economically worthless, according to Le Trinh, chairman of the Association of Environmental Impact Assessments.
"The dyke would end up just being a collecting area for waste water from HCM City and Dong Nai Province," he said, urging that the government adopt Prof Dac's sluice recommendation. — VNS