The Misunderstanding of the Function of Three Gorges Dam

Misunderstanding - No Flood Discharge

Some people think that the flood control of three gorges dam is to block the flood in the three gorges reservoir, so they don't understand why the three gorges dam would discharge the flood during the flood period.

Positive Solution

The principle of flood control is to control the flood crest. Generally, the function of the reservoir is to store the flood during the flood period and discharge the water to fulfill the dry during the dry period, like the American Hoover Dam and the Egyptian Aswan Dam. But the condition of our country is different.

On one hand, the amount of water during the flood period takes up more than eighty percent of that of the whole year. By now, we have no such a reservoir with a storage capacity of eighty percent of the flow of the whole year. Taking the three gorges as an example, the water flow of the whole year of Yangtze River is about 1000 billion square meters, seventy to eighty percent of which is centered during the flood period. The storage capacity of three gorges reservoir is 39.2 billion, and the adjustable capacity is just 22.1 billion, so it is nearly impossible for the three gorges reservoir to control the flood with no flood discharge.

On the other hand, the river in our country has a large containment of sand, in order to prevent the sand from drainage in the reservoir, especially during the flood period, when the water is dirty, so we should enlarge the amount of drainage.

With these two reasons, the principle of the flood control of three gorges is not to store the flood for a long time, but to control the flood crest for a short time. That is to say, during the flood crest, when the water level of the downstream is rising and the flood is strong in the upstream, the reservoir should store the flood. While when the flood crest is over, the strength of the flood crest is within the limits and control. We should discharge the flood immediately, to decrease the water level, so as to empty some space for the next flood crest and prevent from the sedimentation of sand.

Misunderstanding - No Flood Disaster

Some other people think that, now that the three gorges dam has been constructed, there should not be flood. But there is still the phenomena of cities been submerged, properties been lost, people get dead.

Positive Solution

Three gorges dam is just an important factor of flood control but not the whole factor. The three gorges project is just like a big hole of the main steam of Yangtze River, providing exist for the water from the upstream, and through the controlling, it may decrease the drainage to the downstream, which is just the direct function of three gorges dam. Apart from the main stream, there are some other tributaries, lakes and mountain flood, which might be influenced by the three gorges project. But the three gorges project has no decisive function on the flooding. Apart from the factor of the amount of water, there is another factor like the dyke breaching. By now, there hasn't been a renovation of large scale of the tributaries and small rivers. High standard flood control system hasn't been formed yet. Three gorges dam is not almighty. We should not doubt the function of three gorges project for the overflowing of flood, serious situation of flood control.