Experts warn that new HCMC drains won’t withstand global warming

Update: 20/05/2009
An unforeseen increase in rainfall and tide levels may reduce the effectiveness of major water drainage projects underway in Ho Chi Minh City, experts warn.The projects are based on old hydrometeorology statistics and will likely fail to handle the actual amount of rain in the city, where flooding remains a major concern, said Ho Long Phi of the HCMC University of Technology.

Three water drainage projects are currently under construction in HCMC with a total investment of nearly US$800 million. The construction of the projects, including around 100 kilometers of street barriers erected for a new sewage system, has caused frequent gridlocks on HCMC roads.

The city’s Department of Transport has maintained that most of the city’s flood problems will be solved when the projects are finished in the next two years.

But Phi said statistics on rainfall and tides, provided by the Japan International Cooperation Agency which helps the city carry out these projects, were based on information prior to 2000 and the zoning of the drainage systems was approved by the government in 2001.

These statistics are outdated, he said, and there have been notable, unexpected changes in the weather since that time.

The anti-flood systems were designed to withstand a maximum level of 93 millimeters of rain per rainfall.

However, rain levels in HCMC have increased by around 0.8 millimeters per year while rainfalls of more than 140 millimeters have become more common.

The projects also fail to recognize the change in tide levels of the Saigon River, which spill over flooding the city’s streets and other drainage systems. These flood tides have also increased in height and are more common now.

Before 2000, there were virtually no tides of more than 1.4 meters in height. But tides surpassed this level twice in 2000 and 12 times in 2007.

Phi also said that flooding could be exacerbated when downpours combine with high tides.

To Van Truong, former head of the Southern Irrigation Planning Institute, said he was “unsure” in regards to a recent media report saying the city would overcome floods in the next four years thanks to a plan laid out by the Ministry of Agriculture and Rural Development.

The plan, which was approved by the government last October, would construct canal systems, lakes and drainage valves over vast areas on the banks of the Saigon River.

Truong said he was doubtful that HCMC could reduce its flooding problem in the next four years and added that it would be difficult to prevent the problem entirely.

Additional projects

Phi said the drainage projects, funded by foreign official development assistance, could not be stopped or changed at this point.

City officials say they have planned more projects to cope with the unexpected increase in rainfall and high tides. The city’s anti-flood project management board has approved the construction of more than 300 drainage valves at areas prone to severe flooding.

One such venture will augment one of the three original projects by installing drainage valves in seven of the city’s districts at a cost of VND220 billion ($12.9 million).

Another VND11.5 trillion ($672.5 million) project is also in the works, according to officials. However, experts are concerned that it may not be enough to cope with the city’s drainage problems.

Phi said there is a need for even more projects, including building lakes to store water from overloaded sewage systems, paving sidewalks to allow rainwater to be absorbed through, and constructing more grassy areas in the city.

Truong also agreed that more research and projects are needed, and suggested construction dams on the Soai Rap and Long Tau tributaries of the Saigon River to reduce the impact of high tides.

Source: VietNamNet/TN