More reservoirs needed to reduce floods

Due to severe rainstorms and heavy downpours, massive floods have swept across southern China almost every year. Since the start of this year, many parts of southern China have experienced frequent, intense rainfall within a short of period of time.

This year the floods, caused by natural climate fluctuations and an increase in extreme weather conditions due to climate change, have been more severe than in previous years.

Completely preventing floods in regions influenced by changing climate patterns may not be humanly possible. Yet by implementing efficient and effective water conservancy programs, the authorities can better control floods and minimize the loss of lives and properties.

China has made remarkable achievements in building reservoirs and dams, which have not only reduced the chances of floods but also provided water and electricity for the people. Statistics show that despite the rainfall this year breaking 80-year-old records in many places, the loss of lives and properties will not be as high owing to effective management of water facilities during floods. But people's lives and properties should be better protected.

Although big dams, in recent years, have sparked huge controversies due to their ecological impact, high costs and the relocation of residents, China still doesn't have enough water conservancy facilities. In particular, the capacity of reservoirs on big rivers and the drainage system in some Chinese cities need to be further improved.

The United States is similar in size to China, but its reservoirs' capacity is 50 percent more compared with China. Specifically, China has the capacity to store 900 billion cubic meters of water, while for the US it is 1.3 trillion cubic meters.

Thus, the amount of rainfall that can overwhelm China's reservoirs and cause floods with huge volumes of freshwater flowing into the sea can be transformed into valuable water resources in the US thanks to its larger water-storing capacity.

Chongqing in Southwest China, for example, is experiencing one of the worst floods in recent history, mainly because of the inadequate storage capacity of the reservoirs in the upper reaches of the Yangtze River. The threat has been further compounded by news that all hydroelectric dams on Jinsha River, a branch of the Yangtze River in the upper stretch, are full to capacity.

During major floods, rumors start doing the rounds that the high water level in the Three Gorges Dam in Yichang, Hubei province－the dividing point of the midstream and upstream of the Yangtze River-caused water levels in Chongqing to rise. But the fact is Chongqing is located in the upper reaches of the river southwest of the dam.

It is clear such rumors are baseless. Compared with the level and volume of water in reservoirs during several massive floods in Cuntan, Chongqing, before and after the Three Gorges Dam－the world's largest hydroelectric power project－gradually expanded operation over the past decade, the change is quite small. That's because despite being part of the Three Gorges reservoir, the water level during floods in Cuntan, a port in the upstream of the Yangtze River, often is 160 meters and－always higher than the maximum level in the reservoir during the rainy season (145 meters according to national rules). It's the torrents that determine the water level at Cuntan. Even if the reservoir allows the water level to rise to prevent floods in the middle and lower reaches of the Yangtze River, the impact on Cuntan's water level would be negligible.

Historical data can clear some misunderstandings about the role of the Yangtze Three Gorges Project in floods, while reminding the government and the public that the best way to prevent floods in Chongqing is to build more water conservancy facilities based on scientific research.

China selectively built some hydroelectric dams in the last century due to shortage of funds, and they were mainly key projects with comprehensive social benefits－generating electricity and minimizing flood risks. As such, the authorities should allocate more resources, including funds, to build more water conservancy facilities in order to improve the flood-control system.

The views don't necessarily represent those of China Daily.

The author is deputy secretary general at China Society for Hydropower Engineering.