By Francis Markus BBC correspondent in Shanghai

Throughout Chinese history, how to tame the waters of the country's great rivers has been an issue of central concern to people's lives.

Personalities from 2,000 years ago are remembered as clearly as figures of yesterday for their contribution to irrigation and flood control.

One need only look at the grim statistics of lives claimed by the waters to see why.

In the 1930s, floods throughout huge tracts of China killed more than 400,000 people.

The controversial Three Gorges dam is set for completion in 2009

Tens of thousands died in the 1950s, while the most recent large-scale flood disaster was in 1998, when more than 4,000 people died.

Chinese leaders today continue to battle with the problem.

They hope the controversial project to dam up one of the world's longest rivers, the Yangtze, at a site called the Three Gorges, will help, although some engineers worry about what will happen in a generation's time if the level of the lake they are creating gradually rises.

In contrast, large parts of northern China suffer from regular disastrous droughts.

That provides the rationale for a second massive project to channel water from the flood-prone Yangtze northwards to the Yellow River, which is progressively dwindling.

But it is still too early to say what impact these plans will have on the recurring patterns of Chinese history, not least because nobody knows precisely what role new factors, such as climate change, are playing.