By Robert Wu for his family and friends
Yesterday, I read a historical atlas of China that relates historical landmarks against current ones. The maps show that only two thousand years ago, deltas of the Yangtse and Pearl Rivers were still not fully formed. The future City of Shanghai was some 50 miles out to sea, and South China Sea was lapping at the shores of Guangzhou City.
I remember reading about the discovery of an ancient shipyard in a Guangzhou neighborhood and it was attributed to the Qin (pronounced Chin) Dynasty of 2,200 years ago. The shipyard built ships for the First Emperor’s navy and it was set at the seashore. Today, the sea is about 50 miles down river through flat delta lands.
In two thousand years, silts from these major rivers of China settled and created some of the richest farmlands of China. But if the silting were always this severe, delta would have been formed hundreds of miles out to sea in the last million years. The fact that they were formed only recently indicates that severe silting occurred only recently.
I think the recent rapid silting was caused by the explosive population growth and intensive cultivation of the land in the last two millennia. While our ancestors were hunting and gathering, woodlands and forests of China were not disturbed. But as more people lived in China from about 2,000 years ago, forests were cut and farmlands were formed. Topsoil then began to be washed down the rivers to form the deltas.
The impact of human habitation can be devastating to the land. I remember flying over Vietnam once and saw a river with two color streaks. The dark green color streak came from a feeder stream that flowed from a virgin forest. The brown color streak came from a stream that flowed down a denuded hill that had been clear cut of trees. The soil being washed from the bare hill may build a delta at the mouth of the river, if conditions are right. But then it might just flow out to the sea and be lost forever.