By Li Xiaohua, Dong Chen

The Beijing Bureau for Geology & Mineral Exploration disclosed on May 6 that it had submitted a proposal to build several large underground reservoirs to the Beijing municipal government. The reservoirs would be used to store water transferred to Beijing as part of China's massive south-to-north water diversion project.

The proposal calls for the construction of five underground reservoirs with a total storage capacity of 4.7 billion cubic meters, which would make it the biggest water storage facility in China.

Water expert Xiao Shaoyong said that several cities including Shanghai, Dalian and Shijiazhuang had already started work on underground reservoirs as a method of storing strategic water reserves.

Underground strategic water reserve

The south-to-north water diversion project is scheduled to begin delivering water to Beijing in 2010.

The underground reservoir proposal would ensure Beijing's water security by storing water from the diversion project in rainy years for emergency use in periods of drought.

Underground water is the major source of Beijing's water supply, accounting for 65 percent of consumption. Since the 1970s, Beijing has pumped an average of 2.5 billion cubic meters of underground water annually, and as much as 4 billion cubic meters in peak years.

But the water table is gradually dropping and pollution of underground water sources is an increasing problem.

Beijing recently allocated 100 million yuan to drill 2000 exploratory wells to test the quality of Beijing's water sources. Initial observations indicate that pollution of underground water will become a critical problem if additional measures are not taken to protect and replenish underground water sources.

The Bureau for Geology & Mineral Exploration proposes a comprehensive plan covering the sourcing of water from both mountainous areas and plains, and underground storage of water reserves.

Water conservation will be the priority in mountainous areas with a strong emphasis on protecting headwater quality. In the plains which provide 90 percent of Beijing's underground water supply, the main task will be to replenish and improve the quality of water sources.

The proposal also calls for the two million cubic meters of sewage that Beijing generates everyday to be recycled and reused. This will not only add to useable water resources, but will also help replenish underground water sources.

Will the south-north transfer project solve Beijing's water shortage?

The south to north water diversion project will deliver about 1 billion cubic meters to Beijing in 2010 which will relieve Beijing's current water deficiency. However, some experts say there are many problems with the project.

An official from Beijing Water Bureau pointed out that Beijing residents will have to foot the bill for water transferred from the south. The price per cubic meter is very high and the cost could rise even further if leakage becomes a significant problem.

In case of a drought in both north and south, both areas will suffer from shortages. When both regions have a surplus, water will be wasted because there are no large and medium sized reservoirs downstream from the Danjiangkou Reservoir, the upriver supplier of water to Beijing.

Additionally, there is a risk that water may be contaminated during its long distance transfer.

"Beijing will still be a water deficient region, even after the south to north water diversion project has been put into effect." said Cheng Jing, head of Beijing's Water Bureau.

Underground reservoirs a controversial plan

A Beijing Water Bureau official said it would be better to use high-cost transferred water immediately rather than store it in underground reservoirs. Using transferred water first would relieve the strain on underground water resources, allowing them to be naturally replenished by rainfall and other sources.

Moreover, experts also question the feasibility of constructing the reservoirs. Natural underground reservoirs are complicated geographical phenomena occurring in locations with many underground rivers. Artificially adding transferred water may damage the underground hydrograph and cause further problems when it is subsequently drawn off.

Beijing's topography is high in the west and low in the east, and most of Beijing's buildings were constructed in periods of drought. Adding vast amounts of underground water may destabilize these buildings.

Cheng Jing said that Beijing's long term water supply will continue to come from surface water, underground water and secondary water. The focus of Beijing's water management effort should be on sewage reclamation and recycling. Recycled water already accounts for 15 percent of consumption and this figure will increase in the near future.

"Secondary water cannot replace the local water supply." said Cheng Jing. "Beijing must first reuse its own water and only then consider water transferred from other places. If we continue to develop sewage reclamation, with the aid of secondary water, Beijing will no longer be water deficient and there will be no need for artificial underground reservoirs."

(China.org.cn May 9, 2008)