City officials of Shanghai Municipality are considering the construction of a dam on the Huangpu River to prevent potential flooding that the coastal metropolis faces owing to rising sea levels and subsiding land, government and expert sources said.

"The draft scheme is generally set and has been filed to the Ministry of Water Resources for approval," Shen Guoping, director of the Research Center under Shanghai Urban Planning and Design Research Institute, told China Daily. "Its main function is to prevent the downtown areas from being inundated with floods."

The dam, dubbed as Shanghai's "Three Gorges Project," will be located at the lower reaches of the Huangpu River in the northern Baoshan District, according to the draft plan.

"Such a dam will help Shanghai's urban area ultimately avoid any possible flooding," said Shanghai Water Resources Bureau chief engineer Chen Meifa.

To build a dam as a long-term solution is more advantageous compared with the proposal of further building up existing flood walls along the Huangpu River, Chen said in a recent work report.

The project is estimated to cost around 2 billion yuan (US$241.8 million) and take five to seven years to complete, according to Chen's report.

Shanghai has been very cautious about flooding from the Huangpu, which winds its way through the city from south to north with essential functions such as supplying water and transporting goods and services.

The city has completed 318 kilometers of flood walls along the river.

But the height of the flood walls has to increase constantly due to the rising water levels of the waterway, which rose by between 200 and 300 millimeters in the 1990s, according to water authorities.

Higher sea levels on Shanghai's coast and land subsidence are regarded by experts as the main causes for the river's rising water levels.

Shanghai's sea levels rose 20 millimeters between 2000 and 2003, ranking second among major Chinese coastal cities only after Tianjin which witnessed a rise of 25 millimeters, according to the 2003 Bulletin on Sea Levels issued by the State Oceanic Administration earlier this month.

The rise totals over 60 millimeters since the late 1970s, according to the bulletin.

Meanwhile, parts of Shanghai's land have been continuously subsiding.

In 2002, the city sank 10.22 millimeters on average and from 1990 to 2001, Shanghai subsided at an average annual rate of around 16 millimeters.

Today's flood walls along the Huangpu River have been built to 6.9 meters on average, compared with 4.8 meters in the late 1980s, to ensure good resistance against the largest flood in 200 years.

"The flood walls cannot grow any more... they may cause serious damage to the splendid scenery along the Huangpu River," Shen said.

As well, more potential risks may arise in case the water levels of the Huangpu River get any higher, according to Shen.

However, opposition to the dam project does exist.

Some experts believe that too many artificial modifications may have negative effects for the environment along the Huangpu River, and break the ecological balance which has been formed naturally over thousands of years.

Shanghai built a small floodgate on its Suzhou Creek, a branch of the Huangpu River, in the late 1980s as a trial project.

The gate has functioned well over the past decade, successfully holding back a number of major floods in the 1990s.

(China Daily February 9, 2004)