As the fourth major salt tide invades Shanghai's water regions, adding more pain to the city's ills from the most severe snowstorm in years, Shanghai authorities insist that they can handle the problem without cutting off water supplies.

The mouth of the Yangtze River tends to be hit by salt tides in winter or early spring, causing chloride levels to rise. The Shanghai water authority said yesterday the salt tide that hit last Friday would last two more days, according to China Daily.

To ensure a steady supply of drinking water, 200,000 tons of fresh water will be transferred from the Baosteel reservoir near the Yangtze estuary, said Ouyang Tiaojun, a spokesman for the water bureau.

A 24-hour monitoring system has also been set up for the upper reaches of the Yangtze. No water use restrictions are in place at the moment as the situation is manageable, Ouyang said.

However, The 21st Century Business Herald reported yesterday that several districts in Shanghai had been widely cut off from water supplies for several days already, since January 25.

The newspaper said that those residents living on upper levels of high rises would have special trouble getting adequate water.

"The water level is as low as it usually is in winter. After the salt tide hit here on January 25, the reservoir at the mouth of the Yangtze River couldn’t get adequate water resources. Now the reservoir is using stored water. But the fact is: the less the amount of water, the lower the hydraulic pressure. So some residents living in the upper levels of high rises building may not be able to get water," The Herald reported, citing an operator employed by the north Shanghai water supply hotline.

This report was totally refuted today by the water bureau; "The water supply has never been stopped. Everything is going well. No such malfunction has occurred due to the salt tide." The bureau added that to ensure adequate water supplies, they had in place an effective emergency plan, which was launched when the first tide arrived.

Shanghai is a frequent victim of salt tide due to the city's position. Back in 1978, the tide not only invaded the mouth of the Yangtze River, but also entered the Huangpu River, trapping Shanghai's Chongming Island for nearly 100 days. When the salt tide came on October 24, 2006, the Pudong New Area had to cut off one fourth of its water supply.

Salt tide is a disastrous phenomenon in which the lower course of a river, with its lower altitude with respect to sea level, becomes salty when the discharge of the river is low during dry season.

In recent years, the salt tide threat for Shanghai has become bigger and bigger. "Because other reservoirs along the Yangtze River are absorbing river waters, the water volume here has hugely declined. Moreover, the time gap between salt tides has also shortened," an anonymous official told The Herald yesterday, adding that the snowstorm also has been responsible for part of the disaster because it caused pipes to freeze, and some transmission pipes burst, but the situation currently remains under control.

As for the blizzard, Shanghai's water authorities have already issued an urgent notice twice on January 28 and January 29, stressing the significance of keeping the water supply safe and sound.

Any security incident, if it happens, must be reported to the authorities as soon as possible – in no more than ninety minutes, said the notice. The repair teams for all drinking water companies in Shanghai are standing by on 24 hour alert, and every emergency will be effectively tackled according to pre-plans, the Shanghai TV reported.

When current disasters are out of the way, a new initiative will start. Shanghai's third reservoir will be built on Chongming Island – the third largest island in China and the largest alluvial island in the world. The project is expected to be completed by 2010. It is expected to somehow ease the salt tide threat for Shanghai in the future.

(China.org.cn by Zhang Rui, February 1, 2008)