Rumors over water project destructive
The South-NorthWater Diversion Project is expected to begin supplying water to Beijing by the end of this week, but rumors are doing the rounds that the capital may have to wait longer for water from South China because the central route canal has frozen.
In a widely circulated blog posting, an “observer” claims to have noticed the “slow flow” in the central route canal, saying this could prevent water from reaching the capital in winter. The “observer” also says silting could damage the canal.
The blogger’s claims are absurd, to say the least. The blog posting says the central canal will transfer water at the rate of 22.4 cubic meters per second, or one-tenth of the designed capacity, because a China Central Television news video shows a Rubber Duck moving 10 centimeters per second in its water.
People with even the basic knowledge of physics know that the velocity of a floating object is not equal to that of water, because the former meets resistance from the latter from below and air from above. Besides, the water velocity varies with depth— a river that is calm might have fierce currents flowing below the surface. A rough calculation shows a speed of 10 cm per second means 8 kilometers in 24 hours. If the canal water indeed travels at such a slow pace, as the blog posting claims, the water should not have crossed South China even today.
The fact, however, is, water in the canal reached Zhengzhou, Henan province, in Central China earlier this month, three days after the project’s central route was opened and flowed intoHebei province inNorth China a fewdays ago. Does the blogger know these facts?
The South-NorthWater Diversion Project’s ultimate aim is to transfer 44.8 billion cubic meters of freshwater northwards from the Yangtze River every year. The eastern route canal will transfer water through Jiangsu, Zhejiang, Hebei and Shandong provinces, the central route to Beijing and Tianjin, and the western route to Shanxi, Shaanxi, Gansu andQinghai provinces and the InnerMongolia and Ningxia Hui autonomous regions.
The blogger’s concern over silt, mainly deposits of mud and sand, appears a little more reasonable, though, because it is unavoidable given the relatively slow flow of water in the Danjiangkou Reservoir inHubei province, a major source of water for the project. But this problem is confined to the Danjiangkou Reservoir, because the flow of water in the central canal will ensure that it is not plagued by silt. Thus, there is no need to worry about the canal being damaged by silt.
Even the silt in the Danjiangkou reservoir is nothing serious. The reservoir, built in 1958, is a multi-purpose facility that serves as a major source of water for the region, generates electricity and controls floods. Since the canal that supplies water to power plants is situated at a lower altitude than the one which supplies water to the south-north project, silt in the reservoir won’t do any harm as long as the hydraulic power plant functions normally.
Silting is a normal phenomenon, typical of all reservoirs. Every reservoir has a balancing point of silt deposits and the volume of water, and the Danjiangkou Reservoir reached that point long ago. The blog posting didn’t consider this most basic principle.
According to project authorities, the climate varies along the canal, which stretches 1,432 km from South to North China, and the section north of Anyang in Henan province could freeze in the winter. It is estimated that the rate of flow in the canal would drop by 40 percent because of the freezing on the surface — but that will not affect the flow of water under the surface.
Concern over the South-North project is welcome, but spreading rumors is rather destructive. Once the water from the south reaches Beijing, rumors will die a natural death. The author is a senior researcher at China Society forHydropower Engineering.