I raised the issue of chronic flooding in China that caused the rise and fall of societies.

Around the world, (click here) unruly rivers have long driven a hard bargain. In exchange for rich soil, irrigated land and convenient transportation, they have forced floodplain dwellers to deal with an occasional washout. Engineers have labored for thousands of years to lessen the risk, but their attempts at managing Mother Nature have been mixed—often resulting in as much failure as success.

The Yellow River runs into the Yellow Sea. There is a known history of this area of the Pacific. The Yellow Sea at times has dried up enough to allow people to wade across to Japan. There are similar ancient rice found in both countries by people that migrated. The reason the Yellow Sea would literally become shallow was due to ice ages advancing.

The Yellow Sea is a sea and not an ocean. At it's current shallowest state is 60 meters or 197 feet, but, at it's deepest it is 80 meters or 262 feet. That is not much more than some of the Great Lakes in the USA. So, when the ice ages advanced it pulled waters out of these seas, hence, shallow enough for the Chinese to migrate to Japan. Being the Yellow River is north they would migrate north and not south. The southern ocean would prevent that migration.

China has had a particularly long and terrible history of flooding. In the last 2000 years, the Yangtze River has flooded more than 1000 times. But it is the Hwang Ho or "Yellow River" that has been responsible for China's most catastrophic floods. Three thousand miles long, it begins high above sea level in the northern mountain province of Qinghai and ends at the Yellow Sea. Westerners have dubbed it "China's Sorrow," because over the centuries it has killed more people than any other river in the world. In 1887 flooding killed nearly two million people, in 1931 the death toll was almost four million, and in 1938 it was almost one million.

Much of the problem stems from the high silt content of the river—in some stretches as much as 60% by weight. Millions of tons of yellow mud choke the channel, causing the river to overflow and change course. In its lower reaches, the river bed has actually become higher than the level of the surrounding countryside. Water is held in by dikes of ever increasing height, some reaching 30 feet and more.

Attempts at controlling the Yellow River were begun as early as the third century B.C. An engineer named Yu came up with the idea of dredging the river to encourage the water to flow in its proper channel. Yu was made Emperor of China for his contribution, but managing the river's silt would continue to be an ongoing challenge....