The most significant saltwater tides of the year will hit the shores of Guangdong Province over the coming days, a scientist said yesterday.
Due to a series of recent astronomical factors, costal cities, such as Zhuhai, will encounter huge daily tides from Saturday to Monday.
Li Jianji, director of the Guangdong astronomical society, said that at 6 pm on Saturday, the Earth and the moon will be at the closest they have been all year - 360,815 km apart. This will cause what is known as a perigean tide.
At 8 pm on Sunday, the moon will move into the Tropic of Cancer and will be directly above the Pearl River Delta, he said. This event will cause a tropic tide.
And at 9 am on Monday, the moon, sun and Earth will all align, causing another strong tide known as a spring tide.
"With these three tides occurring consecutively, a huge amount of saltwater will pour on to the land," Li told China Daily yesterday.
Zhuhai, a costal city in the south of Guangdong, has been hit by a number of large saltwater tides recently, he said.
But the three upcoming tides are much more serious and will affect a larger area, he said.
The situation will be worsened by the fact that rainfall in the Pearl River Delta has been much lower than normal this year. The total rainfall in Guangzhou this year is just 60 percent of the amount that fell in 2006, and is the lowest since 2003, Li said.
According to the Guangdong water resource department, if the flow capacity in the upper reaches of the river is less than 1,800 cu m per second, it will be too weak to block a saltwater tide.
In the first half of this month, a hydrologic station in Wuzhou, a city in Jiangxi Province, located in the upper reaches of the Pearl River, recorded the flow capacity at just 1,710 cu m per second.
"All these reasons combine to make the saltwater tide much more serious than before," Li said.
The Guangdong water resource department said a lot of preparatory work had already been done in Zhuhai to combat the saltwater tide.
A large reservoir was opened this year and the fresh water it holds will be sufficient to meet the city's demands for several weeks.
Li said the saltwater tide will weaken from Wednesday, when all three tides have receded. But he warned the threat of the saltwater tide will not completely fade away until the end of spring.
(China Daily December 20, 2007)