The survey, during which many advanced technological means were employed, provides a lot of fundamental data for water and soil conservation at the river valley, an expert said Wednesday.

The Yellow River, which runs through the Loess Plateau, carries about 1.6 billion tons of mud and silt a year. The second longest river in China and the muddiest in the world has a 37-kg silt content in every cubic meter of water. The figure rises to 300-500kg after heavy rain.

The 5,464-km-long river irrigates 20 million hectares of arable land and feeds more than 100 million people in northwest and north China.

Harnessing the river is of great importance to the country, and the survey was launched in 1999, aimed at making a thorough investigation of soil erosion, collecting accurate data for monitoring the result of efforts for water and soil conservation, and protecting the environment along the river.

More than 130 technical workers were involved in the project. They used remote sensing and GPS (global positioning system) technology to carry out the survey in an area of 790,000 square kilometers covering Qinghai, Sichuan, Gansu, Shaanxi, Shanxi, Henan and Shandong provinces and Ningxia Hui and Inner Mongolia autonomous regions.

The survey has laid a sound foundation for the establishment of a monitoring system for future water and soil conservation along the entire valley of the river, experts said.

They also called on government departments concerned to allocate special fund for this purpose.

Over the past few years, China has launched a series of afforestation projects along the upper and middle reaches of the Yellow River and its major tributaries, in a bid to reduce the amount of sand and mud washed into the river.

Experts predicted that the river's silt could be halved by 2030.

(Xinhua News Agency July 24, 2002)