. . . .At Chu-t'ang a straight cleft yawns:
At Yen-yū islands block the stream.
Long before night the walls are black with dusk;
Without wind white waves rise.
The big rocks are like a flat sword:
The little rocks resemble ivory tusks. . . .
Thus in 518 A.D., the Chinese poet, Po Chui, expressed his alarm at the roaring Yangtze gorges in Central China, the bottleneck through which the waters of the 3,000-mile-Iong river pour out of the Szechwan basin and Tibetan foothills onto the flat paddies of China's rice bowl. Then as now,...