Traffic on the Three Gorges Dam two-way ship lock slowed drastically Friday as a year-long project to raise the beds of the uppermost two tiers began.

Traffic can now only move in one direction, alternating every 24 hours.

Frogmen jumped into the top tier of the southern track to seal off the water flow at 8:00 a.m., while the northern track was left open to allow ships to pass.

The project will raise the beds of the two topmost tiers from 131 to 139 meters, said Pan Dazhong, deputy director of the construction department of the China Yangtze River Three Gorges Project Development Corporation.

The work will ensure safe navigation for ships when the water level behind the dam rises from 135 meters to 156 and finally 175 meters.

Work on the northern track will begin once the southern track has been finished. In the interim, the lock's handling capacity will go down by 60 percent.

Three Gorges Project, the world's largest water control facility, is located on the middle reaches of the Yangtze River, China's longest and one of the most important inland waterways for shipping in the country. It boasts a 185-meter-high dam which was completed on June 20 and a ship lock.

6.4 km in length and costing 6.2 billion yuan (US$775 million), the ship lock, built in mountainous terrain on the northern bank of the Yangtze River, is the only way ships can pass after free navigation stopped in 2002.

Construction of the ship lock began in April 1993. It was trialed ten years later and became fully operational in July 2004. By Dec. 31, 2005, a total of 190,000 ships carrying 89 million tons of cargo and more than 1.88 million passengers had passed through the lock.

Passing through the five-tier ship lock is like going up or down a 40-storey building, said Jin Yihua, director of the Yangtze River Shipping Affairs Bureau with the Chinese Ministry of Communications.

The level of the Three Gorges Reservoir behind the gigantic dam will rise from the current 135 meters to 156 meters by early October.

Cargo ships were hardest hit when one-way traffic was imposed on Friday, said Hu Yang, deputy head of shipping safety with the Yangtze River Three Gorges Navigation Affairs Bureau.

During the one-way traffic period, the ship lock will only be able to handle about 100 ships daily, carrying about 50,000 tons of cargo, and about 130 to 160 ships will have to wait their turn.

To reduce the negative impact of the one-way traffic period on shipping and economic development along the river, the Yangtze River Shipping Affairs Bureau with the Chinese Ministry of Communications has worked out a series of measures to facilitate passage through the ship lock over the next twelve months.

Only 20 passenger ships have been given approval to pass through the ship lock. Passengers who board ships not on the list will have to switch to highway transport in order to cross the Three Gorges Dam.

No special arrangements have been made for cargo shipping apart from coal transport which requires special permits for the lock, according to Jin Yihua, director of the Yangtze River Shipping Affairs Bureau with the Chinese Ministry of Communications.

"It is going to be a difficult period, but when the project is finished, shipping conditions in the Three Gorges Reservoir will be greatly improved," said Jin.

The annual handling capacity of the Three Gorges Project is currently 34 million tons but it will increase to 50 million tons in 2009.

By 2009, the time needed to travel from Yichang to Chongqing will be shortened by six hours and shipping costs will be slashed by 40 percent. A fleet of ships with 10,000 DWT will sail directly from Wuhan, the biggest city on the middle reaches of the Yangtze, to Chongqing, another key city on the upper reaches of the river.

"The Yangtze River will then outstrip other famous world rivers such as the Mississippi to become the world's No.1 waterway in terms of shipping capacity and it will regain its 'golden waterway' reputation," Jin added.

(Xinhua News Agency September 16, 2006)