In an effort to head off expected future water shortages in the city, the Shanghai Water Authority announced plans yesterday to build a new reservoir on Changxing Island.

The planned reservoir, which is scheduled for completion in 2010, will be the city's third source of tap water, joining similar facilities at the Songpu Bridge, which draws water from the Huangpu River, and at the town of Chenhang in Baoshan District, which takes water from the Yangtze River.

The new facility, which will draw water from the mouth of the Yangtze River, will be able to store 200 million cubic meters of water and provide 3 million tons of raw water every day.

"Quality of the untreated water, taken from the mouth of Yangtze River, can reach Level One after one day of self-purification," said Chen Meifa, chief engineer of the water authority.

China rates its water supply from Level One - water that is drinkable - to Level Five, the filthiest usable water.

The project is part of a national plan to dredge and develop the Yangtze River mouth, which was under discussion yesterday in Shanghai by experts from the Ministry of Water Resources.

City officials estimate the local project will cost 4 billion yuan (US$482 million) and construction will begin before 2005. The city and national governments are expected to pick up the entire tab, said Chen.

The city's current water supply is capable of providing 7.2 million tons of water a day, with most of it coming from the Huangpu River.

"By 2020, the city is expected to need 2.58 million more tons of water per day," said Chen Yin, director of the water authority. "But the Huangpu River has reached its maximum capacity of water supply. If we draw more water from it, the river will dry up."

He notes that water quality from the city's two current sources hovers between Level Three and Level Four. To improve water quality, the city plans to spend a large amount of money to pretreat raw water from the Huangpu River biologically, which is uncommon for a large city.

"The two factors force us to seek a new water source from the Yangtze River and Shanghai will become more dependent on the river from a long-term view," Chen said.

Obstacles still remain before the facility can be built, including one critical problem - the backflow of seawater into the Yangtze River.

During the dry water season from October to April, seawater flows backward into the Yangtze River along the coast of Chongming Island, contaminating the water with salt.

A study of the problem found that the seawater mainly flows back along the northern coast of the island, and then contaminates water along the southern coast, where the new water pump will be located.

To resolve the problem, experts plan to reclaim land along the north coast to reduce the amount of seawater flowing into the river and then build an anti-seawater gate, which can be closed to stop seawater in the dry water season.

( eastday.com August 10, 2002)