Workers work at the permanent ship locks of the Three Gorges Project on the Yangtze River in central China's Hubei Province Monday, June 9, 2003. The ship locks are ready to store water for navigation. [xinhua]

The water level of the huge Three Gorges Reservoir will achieve its target depth of 135 metres tonight, five days ahead of schedule.

Sources with the Three Gorges Project Development Corporation said the filling of the reservoir is progressing well despite the appearance of some debris. Sailing boats have been heavily affected by the debris, such as rubbish and tree branches floating in the reservoir.

"Their speed has been greatly slowed down by the obstacles and sometimes, the safety of the boats and ships are threatened," an official surnamed Cao said.

The debris appeared after a large area of mountains, towns and land was covered by the reservoir. The official said his corporation is preparing a large-scale clear-up of the rubbish.

About 1.3 million rural and urban residents in 12 counties in the Chongqing Municipality and Hubei Province have made way for the gigantic project which costs a total of 180 billion yuan (US$21.6 billion).

Dozens of natural and cultural heritage sites and tourist attractions have been submerged.

Despite the current filling, the water quality has been unaffected by the flooding of the reservoir, and acidity and alkalinity showed little difference from records of the past decades, said local authorities tasked with monitoring the quality of the Yangtze River water.

Zhang Xiaoping, director of water quality monitoring for the Yangtze River valley, said that a two-month-long study showed that by Sunday afternoon, the quality of water in the 150-kilometre area between the Three Gorges dam and Wushan Mountain was as good as before.

Meanwhile, soil erosion is becoming less threatening in the reservoir area, where soil erosion is decreasing at an annual rate of 1 per cent, according to a remote sensing survey.

The survey has shown the area of erosion at the reservoir area has decreased from 38,800 square kilometres in the mid-1980s to 30,000 square kilometres.

It indicated that serious soil erosion had been effectively curbed in the region, said Hu Jiajun, director of the Yangtze River Soil and Water Conservation Bureau.

"But we need to keep alert as the reservoir is growing," said Hu.

The Three Gorges Reservoir area covers 21 counties and cities in Central China's Hubei Province and Chongqing Municipality with a total area of 58,000 square kilometres. Soil erosion is serious in the region because of the hilly landscape, exposed mantle rock and heavy rainfall.

As the ecological environment has a direct impact on the normal operation of the reservoir, the Chinese Government has spent 500 million yuan (US$60 million) in special funds to curb soil erosion in the region since the 1980s.

The central and local authorities have also injected large amount of money into creating a tree belt and converting poor farmland into forest since late 1990s.

As a result, the area covered by forest around the reservoir area expanded by 2.2 million hectares in the past two decades, according to Hu.

The central government will allocate another 2 billion yuan (US$240 million) in the coming years to improve eroded lands, Hu said.