One of Shanghai's two sources of fresh water could be at risk
from sea water flowing into the mouth of the Yangtze River during
the Spring Festival period.
About 30 percent of the city's fresh water comes from the
Yangtze.
Hundreds of thousands of families in northern Shanghai could be
affected in a worst case scenario. But water suppliers said they
have sufficient backup reserves.
A salt tide is expected to take place between January 29, the
first day of the Year of the Dog, and February 12, according to the
Shanghai Municipal Raw Water Co Ltd.
The tide takes place at the mouth of the Yangtze every winter or
early spring when water flowing from the river decreases.
It will last up to five days, forcing water suppliers to stop
pumping fresh water from the Yangtze for a period of time each
day.
A huge reservoir, on the bank of the Yangtze in Baoshan
District, will therefore see its water level decrease. Pumps will
not operate at full capacity and will be shut down when salt levels
are too concentrated.
The reservoir has a capacity of 8.3 million cubic meters. The
fresh water is stored and filtered for impurities before pumped to
tap water plants for further treatment.
Without daily intakes, the reservoir at full capacity can only
ensure water for 7 to 10 days for six water plants in northern
Shanghai.
"That scenario is hardly possible for we have various
contingency plans. It's worth noting the salt tide this year will
not be serious," said an official with the Shanghai Municipal Raw
Water Co. He would only give his surname as Wei.
The company manages the fresh water supply for all plants
downtown. Wei said they have reached an agreement with Baosteel
Corp for a supply of up to 100,000 cubic meters a day from the
steel firm's reservoir, also along the Yangtze River.
In a worst case scenario, officials with the Shanghai Water
Supply Administration said they will ask water utilities that use
the Huangpu River as a source for fresh water to dispatch tap water
to areas that may be affected by the salt tide.
"The tide this year comes later than usual, but it should be
less serious than last year judging from current conditions," said
Yin Rongqiang, an administration official.
A salt tide caused problem in 2004. The reservoir operator asked
Baosteel to help for the first time.
(Shanghai Daily January 20, 2006)