Diversion work completed in largest barrier lake

The critical diversion project to drain Tangjiashan barrier lake in quake-hit Sichuan province has been completed. Tangjiashan barrier lake was the largest of its kind. Such quake-lakes were formed when rivers were blocked by landslides triggered by the massive earthquake. Nearly 200,000 residents living downstream in the city of Mianyang have been evacuated to safer areas in case Tianjiashan lake overflows it banks.

By 10 pm on Saturday, about 135,500 cubic meters of mud and rocks had been removed from the Tangjiashan barrier lake. For six consecutive days and nights, soldiers from the armed police and experts have been working here against extremely adverse conditions. Their combined efforts have created a 475-meter-long, 12-meter wide channel - to divert waters from the giant blockage. Originally, the channel was only supposed to be 10 meters wide.

Jiao Yong, vice minister of Ministry of Water Resources, said, "The wider the diversion channel is, the more water it's capable of channeling out. Even if the channel is only one meter wider than the original plan, it will be able to divert 5 to 6 million more cubic meters of water from the lake."

Since the diversion channel was completed in time, authorities decided to abandon a back-up plan to clear an opening in the blockage with explosives. The water level of the lake has been rising about 1.6 meters each day. It is expected that the rising water will run over the blockage and be channeled out through the man-made canal in 2 or 3 days.

By Saturday night, more than 340 soldiers and engineers had been evacuated by helicopters from Tangjiashan Lake. The remaining team is expected to leave later on Sunday. Only a small squadron of 20 soldiers will stay at Tangjiashan to monitor the situation.

Jiao Yong said, "We will keep a constant watch over the lake, mainly from 3 aspects. The first aspect is hydrological monitoring. We are paying close attention to the variations of water level on the lake.

We are also monitoring any signs of change in the water along the diversion channel and the blockage. The Chinese Academy of Sciences is supporting us with high-tech means. Through satellite remote sensing, they can transmit real time data from the site to us."

Experts have set up a monitoring network covering over 3,500 square kilometers of the lake's upstream area. 12 monitoring stations have been put in place to collect information about precipitation, water level variations and meteorological conditions.

Downstream in the city of Mianyang, nearly 200,000 people were evacuated to safer areas as of 8 am on Saturday. The action is designed to deal with any emergency arising from one third of the water volume in Tangjiashan Lake bursting over its banks. Authorities in the city are organizing more drills to deal with even worse scenarios. Some 1.2 million people will have to be relocated if half of the lake volume is released. And 1.3 million people will need to be evacuated if the whole volume of water in the lake bursts it quake-made barrier.

Mount Fule is the highest point in Mianyang City. During normal times, it is a nice resort area for city dwellers. But now, it's home to more than 30,000 evacuees. Life in tents or makeshift cottages is inconvenient. But most people here are dealing with the situation as best as they can.

A Mianyang resident said, "We feel that the government is bearing our safety in mind. We moved here and have done what we can to arrange our daily life. We have brought with us daily essentials like rice, cooking oil, flour and even stoves. Eating should not be a problem here."

Authorities say even if the worst happens residents in the city will have enough time to leave. Experts are monitoring the Tangjiashan barrier lake around-the-clock. And they say they will issue a warning to the city's authorities 24 hours before the lake bursts.

Chen Youxue, deputy general commander of Mianyang Quake Control and Disaster Relief Headquarters, said, "Every district, county and township in the jurisdiction of Mianyang city will receive the warning as soon as possible. We will keep them informed immediately via special hot lines. In the city of Mianyang, 44 mobile or permanent air-raid alarms will be triggered in an emergency."

Provincial authorities in Sichuan say the work to divert all barrier lakes is well underway. And all of the work is expected to conclude no later than June 10th.