The lower reaches of the Yellow River, a famous "suspended river" with a riverbed four to six meters higher than the surrounding fields, is symbolized as "a sword hanging above the heads of local residents." Continuous droughts and increasing silt deposits in the riverbed in past 10 years have built up another "suspended river," which, three to five meters higher than the base of the first one, adds greater pressure to the work of flood control.
According to Hong Shangchi, deputy general engineer of the Yellow River Conservancy Commission the river course becomes remarkably broad when the Yellow River flows into the lower reaches. Of the total area of 4,200 square kilometers of the river course, 84 percent is beach land and only the narrow sunken part in the middle serves as riverbed.
In a normal year, 30 percent of the silt brought down by the Yellow River is dumped into the riverbed while 70 percent of it is deposited in the beach land. The river course used to be at a condition of higher beach land and lower riverbed.
However, during the past 10 years, the Yellow River has been short of water for most of the time. As a result, 90 percent of its silt has been deposited in the riverbed. The beach land, then, has had less sedimentation due to less exchange of water and sand. Another "suspended river" higher than the original riverbed has thus been formed in the river course. Currently, a 300-kilometer-long "second-level suspended river" lies on riverbed of the Yellow River's lower reaches.
Some experts from the Yellow River Conservancy Commission pointed out that under the condition of the "second-level suspended river," once big floods occur, it will cause great changes in the river's flow. The main stream of the Yellow River may flow wildly and hit the embankment directly, greatly increasing the risk of flooding and the breaching of dykes. Therefore, the control of the "second-level suspended river" has become an extremely urgent task in harnessing the Yellow River.
A trial project of controlling the "suspended river" in the lower reaches of the Yellow River was started on June 6 in Puyang, central China's Henan Province. Builders will dredge a six-kilometer-long river section ranging from Nanxiaodi to Penglou of Puyang in order to increase the flood discharging capacity of the riverbed. The project will hopefully help accumulate experience for more powerful and effective control of the "second-level suspended river" in the future.
(China.org.cn by Wang Qian, July 24, 2003)
