|29 June 2014
Humans have been changing Chinese environment for 3,000 years
Research from Washington University in St Louis USA links increasingly deadly flooding along the Yellow River to man-made environmental degradation and related flood-mitigation efforts that began changing the river's natural flow nearly 3,000 years ago.
"Human intervention in the Chinese environment is relatively massive, remarkably early and nowhere more keenly witnessed than in attempts to harness the Yellow River," said Dr TR Kidder, lead author of the study. "In some ways, these findings offer a new benchmark for the beginning of the Anthropocene, the epoch in which humans became the most dominant global force in nature."
The study offers the earliest known archaeological evidence for human construction of large-scale levees and other flood-control systems in China. It also suggests that efforts to tame the Yellow River with levees, dikes and drainage ditches actually made periodic flooding much worse.
"New evidence from China and elsewhere show us that past societies changed environments far more than we've ever suspected," said Kidder.
Kidder's research, co-authored with Liu Haiwang, senior researcher at China's Henan Provincial Institute of Cultural Relics and Archaeology, relies on a sophisticated analysis of sedimentary soils deposited along the Yellow River over thousands of years, including data from the team's ongoing excavations at the sites of two ancient communities in the lower Yellow River flood plain.
The Sanyangzhuang site, known today as "China's Pompeii," was slowly buried beneath five meters of sediment during a massive flood circa 14-17 CE, which likely killed millions and triggered the collapse of the Western Han Dynasty's five-century reign of power.
The Anshang site includes the remains of a levee and three irrigation/drainage ditches dating to the Zhou Dynasty, circa 1046-256 BCE.
Kidder's research suggests the Chinese began building drainage/irrigation canals and bank/levee systems along the lower reaches of the Yellow River about 2,900 to 2,700 years ago. By the beginning of the first millennium CE, the levee system had been extended much farther up river, lining the banks for hundreds of kilometres.
"Our evidence suggests that the first levees were built to be about 6-7 feet (2 metres) high, but within a decade the one at Anshang was doubled in height and width," Kidder said. "It's easy to see the trap they fell into: building levees causes sediments to accumulate in the river bed, raising the river higher, and making it more vulnerable to flooding, which requires you to build the levee higher, which causes the sediments to accumulate, and the process repeats itself. The Yellow River has been an engineered river - entirely unnatural - for quite a long time."
Periodic breaches of the levee system led to devastating floods - some shifting the river's main channel hundreds of kilometres from its initial course.
While the research offers new insight into Chinese history, it also has interesting implications for modern river management policies around the globe.
Edited from Terra Daily (24 June 2014)
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