GEOGRAPHY

Building embankments to defend against flooding in the Yellow River could be counterproductive


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Image credit: LWM/NASA/LANDSAT/ALAMY

A Feb. 22 study published in Science Advances by a team of Chinese and American scientists analyzed flooding in China’s Yellow River and showed that building dikes along the river to protect against flooding could be counterproductive.

More extreme and frequent rainfall due to global warming means that flooding is a growing threat to millions of people around the world. While there is a great deal of research on how climate change affects flood risk, the role of human activity in this is less clear.

To explore this, the U.S. team analyzed the frequency of flooding in the Yellow River. This waterway is the cradle of Chinese civilization.

Using historical records and data from river sediments, the researchers compiled a timeline of the Yellow River’s floods over the past 12,000 years. They found that between 12,000 and 7,000 years ago, floods were rare, averaging only 4 times every 100 years.

They then compared flood timelines to records of human activities, such as agriculture, and found that floods became more common about 4,000 years ago as local human settlements expanded.

Yu Shiyong, a professor at Jiangsu Normal University and one of the paper’s authors, said the analysis showed that the frequency of flooding increased dramatically when people began building mud ridges along rivers as flood barriers about 1,500 years ago.

The researchers found that over the past 1,000 years, the Yellow River floods have occurred 10 times more frequently than before ancient Chinese civilization began. Yu said their analysis showed that human activities, mainly the use of artificial dikes, contributed to about 80 percent of the increase in flood rates, with the rest attributable to natural variability in climate.

Computational models of the river show that mud ridge embankments along the river may cause more sediment to accumulate at the bottom of the river. This raises riverbeds and water levels, making flooding more likely.

James Best, from the University of Illinois at Urbana-Champaign, said: “This work highlights the need to study human activities affecting flooding in the context of climate change. This is important information that we must keep in mind today. ”

Today, artificial dikes are no longer used to curb the flooding of the Yellow River. Since the early 80s of the 20th century, the Chinese government has introduced policies to protect wild vegetation near rivers, which keeps the soil around rivers stable. Yu Shiyong said that this helps prevent the soil from falling into the water and may be a better approach.

Yu Shiyong said that the successful experience of flood prevention and water control through soil and water conservation puts forward a holistic approach to sustainable river governance. However, in many parts of the world, building dikes remains the preferred flood control strategy, and Yu believes that other countries should also abandon artificial dikes. One can learn from studying the history of rivers. (Source: Wang Fang, China Science News)

Related paper information:https://doi.org/10.1126/sciadv.adf8576



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